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KFN01Sr02_Components, Structure, and Identification of the A.doc r6 6/9/2014 3:21:00 PM

ACADBASIC CURRICULUM

NUCLEAR SCIENCE

CHAPTER 1

COMPONENTS,STRUCTURE,AND IDENTIFICATION OF THE ATOM

STUDENT TEXT

REV 2

TM

2003General Physics Corporation, Elkridge, Maryland

All rights reserved. No part of this book may be reproduced in any form or by

any means, without permission in writing f rom General Physics Corporation.


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TABLE OF CONTENTS

FIGURES AND TABLES ........................................................................................................... ii

OBJECTIVES ............................................................................................................................ iii

ATOMS ........................................................................................................................................ 1

History ...................................................................................................................................... 1

Structure .................................................................................................................................... 1

Atomic Mass Unit ..................................................................................................................... 2

Identification Of Atoms ............................................................................................................ 3

Isotopes ..................................................................................................................................... 4

Chart of the Nuclides ................................................................................................................ 5

SUMMARY ................................................................................................................................. 7

PRACTICE EXERCISES ............................................................................................................ 8

GLOSSARY ................................................................................................................................. 9

EXAMPLE EXERCISE ANSWERS ......................................................................................... 10

PRACTICE EXERCISE ANSWERS ........................................................................................ 11

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FIGURES AND TABLES

Figure 1-1 Structure of Helium Atom ........................................................................................ 2

Figure 1-2 Standard Notation for an Atom ................................................................................ 3Figure 1-3 Isotopes of Oxygen .................................................................................................. 4

Figure 1-4 Portion of the Chart of the Nuclides ........................................................................ 5

Table 1-1 Electrical Properties of Atomic Particles .................................................................. 2

Table 1-2 Atomic Particle Location ........................................................................................... 2

Table 1-3 Atomic Weight of Atomic Particles .......................................................................... 2

Table 1-4 Standard Notation for Selected Atoms ...................................................................... 3

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OBJECTIVES

Upon completion of this chapter, the student will be able to perform the following

objectives at a minimum proficiency level of 80%, unless otherwise stated, on an oral

or written exam.

1. STATEthe characteristics of the following atomic particles, including relative mass, charge,and location within the atom:

a. Protonb. Neutronc. Electron

2. DEFINE the following terms:a. Atomic Mass Unit (AMU)b. Nucleonsc. Nuclided. Isotope

3. STATE the two terms that represent the method by which atoms and subatomic particles aremeasured.

4. Given a sample Chart of the Nuclides, IDENTIFY elements and isotopes.5. Given a standard XA

Znotation for an electrically neutral atom, DETERMINE the following:

a. Number of Protonsb. Number of Neutronsc. Number of Electrons

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ATOMS

HISTORY

Early Greek philosophers speculated that theearth was made up of different combinations of

basic substances, or elements. They consideredthese basic elements to be earth, air, water, and

fire. Modern science shows that the early Greeks

held the correct concept that matter consists of acombination of basic elements, but they

incorrectly identified the elements.

In 1661 the English chemist Robert Boyle

published the modern criterion for an element.

He defined an element to be a basic substancethat cannot be broken down into any simpler

substance after it is isolated from a compound,

but can be combined with other elements to formcompounds. To date, 109 different elements

have been confirmed to exist. Researchers claim

to have discovered nine additional elements. Of

the 109 confirmed elements, 90 exist in natureand the rest are man-made.

Another basic concept of matter that the Greeks

debated was whether matter was continuous or

discrete. That is, whether matter could becontinuously divided and subdivided into ever

smaller particles or whether eventually an

indivisible particle would be encountered.

Democritus in about 450 B.C. argued thatsubstances were ultimately composed of small,

indivisible particles that he labeled atoms. He

further suggested that different substances werecomposed of different atoms or combinations of

atoms, and that one substance could be converted

into another by rearranging the atoms. It was

impossible to conclusively prove or disprove thisproposal for more than 2000 years.

The English chemist John Dalton first proposed

the modern proof for the atomic nature of matter

in 1803. Dalton stated that each chemical

element possesses a particular kind of atom, and

any quantity of the element is made up of

identical atoms of this kind. What distinguishes

one element from another element is the kind ofatom of which it consists, and the basic physical

difference between kinds of atoms is their

weight.

For almost 100 years after Dalton established theatomic nature of atoms, it was considered

impossible to divide the atom into even smaller

parts. All of the results of chemical experiments

during this time indicated that the atom wasindivisible. Eventually, experimentation into

electricity and radioactivity indicated that

particles of matter smaller than the atom didindeed exist. In 1906, J. J. Thompson won the

Nobel Prize in physics for establishing the

existence of electrons. Electronsare negativelycharged particles that have 1/1835 the mass of

the hydrogen atom. Soon after the discovery of

electrons, protons were discovered. Protonsarerelatively large particles that have almost the

same mass as a hydrogen atom and a positive

charge equal in magnitude (but opposite in sign)

to that of the electron. The third subatomicparticle to be discovered, the neutron, was not

found until 1932. The neutron has almost thesame mass as the proton, but it is electrically

neutral.

STRUCTURE

All matter (gas, liquid or solid) is made up ofone or more elements (hydrogen, oxygen, gold,

etc.).

An element is a substance that cannot be

decomposed or broken into more elementary

substances by ordinary chemical means. Atoms

make up all elements. An atom is the smallestamount of matter of an element that retains the

elements properties.

Three fundamental (atomic) particles make up an

atom. The individual numbers of these particles

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within an atom determines the characteristics of

the atom. These particles are as follows:

Table 1-1 Electrical Properties of Atomic

Particles

Particle Charge

Proton +1

Neutron 0

Electron 1

An atom having the same number of electrons in

its shells as protons inside the nucleus is

electrically neutral. Figure 1-1 represents anelectrically neutral atom of helium.

The measurement of energy associated with the

atomic particles is in units termed electron volt(eV). The electron volt is the amount of kinetic

energy gained by an electron when acceleratedthrough an electric potential difference of 1 volt.

One electron volt is equivalent to 1.603 1019

joules, or 1.18 1019

foot pounds (ft lb f). Forlarger values, the units of energy are keV for

thousand electron volts, MeV for million

electron volts, or BeV for billion electron volts.

Figure 1-1 represents the traditionally acceptable

model of a helium atom. It shows neutrons andprotons making up a nucleus of the atom.

Particles within the nucleus are often referred to

as nucleons. The electrons are in concentricorbits (also called shells) around the nucleus.

ELECTRONS

IN VARIOUS

ORBITS P N

N P

Figure 1-1 Structure of Helium Atom

Table 1-2 Atomic Particle Location

Particle Location

Proton Nucleus

Neutron Nucleus

Electron Shell outside nucleus

ATOMIC MASS UNIT

Atoms and their subatomic particles aremeasured on the atomic scale that is based on

mass and energy. Energy measurements are in

units of eV, as discussed previously. The unit ofmeasure for mass is the atomic mass unit

(AMU).

The AMU is based on the mass of the carbon-12atom and is equal to 1/12 of the carbon-12 atom

resulting in a value of 1.66 1024

grams.Table 1-3 displays the properties of the three

particles that make up the atom.

Table 1-3 Atomic Weight of Atomic Particles

Particle Mass (AMU)

Proton 1.00727

Neutron 1.00866

Electron 0.00055

Nuclides do not vary significantly in size. The

radius of the typical atom is approximately

2 108

cm. Significant is that the radius of the

nucleus may vary from approximately1.25 10

-13cm for the smaller nuclides to

8 1013

cm for the largest nuclides. Comparing

this to the typical radius of the entire atom showsthat the entire atom is more than 25,000 times

the size of the largest nucleus.




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Complete the table for the properties of anatom.

Particle Charge Mass

(AMU)

Location

Proton

0

0.00055

Example 1-1

The mass of an electron is:

a. equal to a protonb. equal to a neutronc. greater than a protond. less than a neutron

Example 1-2

IDENTIFICATION OF ATOMS

The number of protons within the nucleusdetermines the atomic number of an element. It

is represented by the symbol Z. This is thereference number used in the periodic table of

elements (Hydrogen with 1 proton, Helium with

2, Oxygen with 8, Uranium with 92, etc.) forelement identification.

The total number of nucleons (neutrons andprotons) in the nucleus is called the mass

number. It is given the symbol A. The number of

neutrons can be calculated by (A Z = N)

Figure 1-2 shows the standard notation for

identification of an atom:

XA

Z

Where:

A = atomic mass number (protons andneutrons)

X = element symbol

Z = atomic number (protons)

Figure 1-2 Standard Notation for an Atom

Table 1-4 provides examples of standard

notation for several elements.

Table 1-4 Standard Notation for Selected Atoms

Helium He4

2

Boron B105

Carbon C126

Oxygen O168

Uranium U23892

Plutonium Pu23994

There are many different possible combinations

of protons and neutrons within the nucleus. Eachunique combination is referred to as a nuclide.

Each one of the atoms shown inTable 1-4 is a

nuclide.




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ISOTOPES

The number of neutrons in an atom of a

particular element may vary. Atoms of the same

element (those with same number of protons)with different numbers of neutrons are called

isotopes of the element. It is common to identify

isotopes by including the atomic number withthe symbol or the name of the element.

Figure 1-3 represents three isotopes of oxygen:

O-16, O-17, and O-18.

ISOTOPES OF OXYGEN

16 17 18

8 8 8O O O

8 PROTONS

8 NEUTRONS

8 PROTONS

9 NEUTRONS

8 PROTONS

10 NEUTRONS

NATURAL ABUNDANCE - ATOM PERCENT

99.758% 0.038% 0.204%

Figure 1-3 Isotopes of Oxygen

Additionally, there are at least eight moreunstable or artificially made isotopes of oxygen.

The Chart of the Nuclides provides a visualrepresentation of stable and unstable isotopes of

all elements.

Because each isotope represents a unique

combination of neutrons and protons in the

nucleus, they are also nuclides.

Important to note here is that isotopes of thesame element all behave the same in chemical

reactions (because they have the same number of

protons and electrons). Isotopes can behavesignificantly different from each other in nuclear

reactions (because they have different numbers

of neutrons).

Define the following Nuclear Science terms:

a. Nucleon

b. Isotope

Example 1-3

How many neutrons are in an atom of U23892 ?

Example 1-4

State the name of the element and the number of

protons, electrons, and neutrons in the nuclides

listed below.

Symbol Name Neutron Proton Electron

H11

B10

5

N147

Co6027

Pu242

94

Example 1-5




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CHART OF THE NUCLIDES

A tabulated chart called the Chart of the

Nuclides lists the stable and unstable nuclides in

addition to pertinent information about each one.Figure 1-4 shows a small portion of a chart. This

chart plots a box for each individual nuclide,

with the number of protons (Z) on the verticalaxis and the number of neutrons (N = A Z) on

the horizontal axis.

Located in the box on the far left of each

horizontal row is general information about the

element. The box contains the chemical symbolof the element, the average atomic weight of the

naturally occurring substance, and the name of

the chemical. The known isotopes (elements

with the same atomic number Z but differentmass number A) of each element are listed to the

right.

Complete charts contain much more details than

shown in the example here. This chart shows the

isotopes, and either the percentage of naturally

occurring atoms or the half-life of radioactiveisotopes. By consulting a complete chart, other

types of isotopes can be found, such as naturally

occurring radioactive types. Complete charts arecommonly color coded to show similar half-lives

and neutron cross section for absorption.

Notice there are three isotopes of Hydrogen;

H11 , hydrogen; H2

1 , deuterium; and H3

1 , tritium.

H11 , hydrogen and H2

1 , deuterium are in gray

boxes, they are stable. Hydrogen occurs

99.985% of the time in nature. Deuterium

occurs 0.015% of the time in nature. Tritium isunstable; it has a half life of 12.3 years.

43

2

6

0 1

1

2

0

3

4

5

N

B 1019.9

B 98E-19 s

B 8770 ms

B 74E-22 s

Be 9100

Li 80.84 s

Be 8~7E-17 s

Li 792.5

Be 753.28 d

Li 67.5

Be 65.0E-21 s

Li 5~3E-22 s

He 73E-21 s

He 6807 ms

He 57.5E-22 s

He 499.999862

B 1220.20 ms

B 1180.1

Be 1113.8 s

Li 9177 ms

He 9Extremely

short

He 8199 ms

He 30.00138

H 20.015

H 199.985

H1.0079

Hydrogen

He4.002602

Helium

Li6.941

Lithium

Be9.012182

Beryllium

B10.811

Boron

Z

H 312.3 a

Be 101.6E6 a

Figure 1-4 Portion of the Chart of the Nuclides




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Using Figure 1-4 Portion of the Chart of the

Nuclides

a. How many elements are identified?

b. How many isotopes of Lithium are

identified?

Example 1-6




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SUMMARY

Atoms consist of three basic subatomic particles.

Protons are particles that have a positivecharge, have about the same mass as ahydrogen atom, and exist in the nucleus ofan atom.

Neutrons are particles that have noelectrical charge, have about the samemass as a hydrogen atom, and exist in the

nucleus of an atom.

Electrons are particles that have a negativecharge, have a mass about eighteen

hundred times smaller than the mass of ahydrogen atom, and exist in orbital shells

around the nucleus of an atom.

The model of the atom consists of a dense nucleus

of protons and neutrons (nucleons) surrounded by

electrons traveling in discrete orbits at fixeddistances from the nucleus.

Nuclides are atoms that contain a particular

number of protons and neutrons.

Isotopes are nuclides that have the same atomic

number and are therefore the same element, but

differ in the number of neutrons.

The atomic number of an atom is the number ofprotons in the nucleus.

The mass number of an atom is the total numberof nucleons (protons and neutrons) in the nucleus.

XAZ represents a specific nuclide.

A represents the mass number, which isequal to the number of nucleons (protons

and neutrons).

X represents the chemical symbol of theelement.

Z represents the atomic number, whichis equal to the number of protons (andelectrons).

Number of neutrons N = A Z




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PRACTICE EXERCISES

1. Use the figure below of an atom to completethe exercises below:

a.

Assuming the same number of each ofthe particles that make up this atom,

give a label to each particle.

b. What would need to be changed in thefigure to make it represent another

isotope?

c. Label each of the particles in the figurewith the appropriate electrical charge.

d. List the atomic number and atomicmass number for this atom.

2. The two primary means used formeasurement of atoms are: (select one)

a. size and shapeb. mass and energyc. shape and massd. energy and size

3. Complete the following table by inserting thecorrect number for each part of the associated

atom.

Proton Neutron Electron Nucleons

Hydrogen H1

1

Tritium H31

Silver Ag10747

Uranium U23592

Uranium U23892

4. Using the figure below,

U2362.34E7 a

U2357.04E8 a

U2342.46E5 a

U2331.59E5 a

U23923.5 m

U23270. a

U2376.75 d

U2384.47E9 a

Pu23887.7 a

Pu23745.2 d

Pu2362.87 a

Pu23525.3 m

Pu24114.4 a

Pu2392.41E4 a

Pu2348.8 h

Pu2406.56E3 a

Th23322.3m

Th23424.10d

Th2357.2m

Th2321.40E10a

Th2307.54E4a

Th2311.063d

Th23637.5m

Pa23524.4 m

Pa2346.69 h

Pa23327.0 d

Pa2321.31 d

Pa2382.3 m

Pa2369.1 m

Pa2313.28E4a

Pa2378.7 m

Np2361.55E5 a

Np2372.14E6 a

Np2351.085 a

Np2344.4 d

Np2401.032 h

Np23336.2 m

Np2382.117 d

Np2392.355 d

a. Identify each nuclide.

b. Determine the number of isotopes ofuranium.




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GLOSSARY

Atomic Mass Unit

(AMU)

A unit of measurement equal to 1/12 the mass of a Carbon 12 atom

(1.6605402 x 1024

grams).

Electron Sub-atomic particle that makes up an atom, has a mass of 0.00055 AMU, anegative charge, and is located outside the nucleus in probability shells

(orbits).

Electron Volt (eV) Amount of kinetic energy (eV) gained by an electron when accelerated

through an electric potential difference of 1 volt. It is equivalent to

1.603 1019

joule. It is a unit of energy or work, not of voltage, and is

the common measure of a neutrons energy. Larger multiple units of the

electron volt are frequently used: keV for thousand or kilo electron volts,MeV for million electron volts, and BeV for billion electron volts.

Element A basic substance that cannot be broken down into any simpler substanceafter it is isolated from a compound, but can be combined with other

elements to form compounds.

Isotopes A nucleus of the same element (same number of protons) with a different

number of neutrons.

Neutron Sub-atomic particle that makes up an atom, has a mass of 1.00866 AMU, a

neutral charge, and is located in the nucleus.

Nucleon Any particle that is part of the nucleus of an atom, neutrons and protons.

Nuclide Any atom containing a unique combination of neutrons and protons in the

nucleus.

Proton Sub-atomic particle that makes up an atom, has a mass of 1.00727 AMU, a

positive charge, and is located in the nucleus.




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EXAMPLE EXERCISE

ANSWERS

Complete the table for the properties of an

atom.

Particle Charge Mass

(AMU)

Location

Proton +1 1.00727 Nucleus

Neutron 0 1.00866 Nucleus

Electron 1 0.00055 Shell

Example 1-1

The mass of an electron is:

a. equal to a protonb. equal to a neutronc. greater than a protond. less than a neutron

ANSWER: "dless than a neutron

Example 1-2

Define the following Nuclear Science terms:

a. Nucleon

Any particle that is part of the

nucleus of an atom; neutrons and

protons.

b. Isotope

A nucleus of the same element (same

number of protons) with a different

number of neutrons.

Example 1-3

How many neutrons are in an atom of U23892 ?

AZ = N

238 92 = 146 neutrons

Example 1-4

State the name of the element and the number of

protons, electrons, and neutrons in the nuclides

listed below.

Symbol Name Neutron Proton Electron

H11 Hydrogen 0 1 1

B105 Boron 5 5 5

N147 Nitrogen 7 7 7

Co6027 Cobalt 33 27 27

Pu24294 Plutonium 138 94 94

Example 1-5

Using Figure 1-4 Portion of the Chart of the

Nuclides

a. How many elements are identified?

a. Five; hydrogen, helium, lithium,

beryllium, and boron

b. How many isotopes of Lithium are

identified?

b. Five; Li-5, Li-6, Li-7, Li-8, and Li-9

Example 1-6




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PRACTICE EXERCISE

ANSWERS

1. Use the figure below of an atom to completethe exercises below:

a. Assuming the same number of each of

the particles that make up this atom,give a label to each particle.

b. What would need to be changed in thefigure to make it represent another

isotope?

Change number of neutrons in the

nucleus.

c. Label each of the particles in the figure

with the appropriate electrical charge.

Electrons labeled with negative

charge, neutrons no charge, protons

positive charge.

d. List 1) the atomic number and 2) atomicmass number for this atom.

Atomic mass number of 4 and atomic

number of 2

2. The two primary means used formeasurement of atoms are: (select one)

b. mass and energy

3. Complete the following table by insertingthe correct number for each part of the

associated atom.

Proton Neutron Electron Nucleon

Hydrogen

H

1

1

1 0 1 1

Tritium H31 1 2 1 3

Silver Ag10747 47 60 47 107

Uranium U23592 92 143 92 235

Uranium U23892 92 146 92 238

4. Using the figure below,

U2362.34E7 a

U2357.04E8 a

U2342.46E5 a

U2331.59E5 a

U23923.5 m

U23270. a

U2376.75 d

U2384.47E9 a

Pu23887.7 a

Pu23745.2 d

Pu2362.87 a

Pu23525.3 m

Pu24114.4 a

Pu2392.41E4 a

Pu2348.8 h

Pu2406.56E3 a

Th233

22.3m

Th234

24.10d

Th235

7.2m

Th232

1.40E10a

Th230

7.54E4a

Th231

1.063d

Th236

37.5m

Pa23524.4 m

Pa2346.69 h

Pa23327.0 d

Pa2321.31 d

Pa2382.3 m

Pa2369.1 m

Pa2313.28E4a

Pa2378.7 m

Np2361.55E5 a

Np2372.14E6 a

Np2351.085 a

Np2344.4 d

Np2401.032 h

Np23336.2 m

Np2382.117 d

Np2392.355 d

c. Identify each nuclide.5, thorium, protactinium, uranium,

neptunium, plutonium,

electrons

two neutrons and two protons




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d. Determine the number of isotopes ofuranium.

8, U-232, U-233, U-234, U-235, U-236, U-

237, U-238, U239




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KFN02Sr02_Mass Defect and Binding Energy.doc r8 6/9/2014 3:22:00 PM


NUCLEAR SCIENCE

CHAPTER 2

MASS DEFECT AND BINDING ENERGY

MASS DEFECT

Mass of all of the individual particles isgreater than the mass of the combinednucleus. The difference is called the

Mass Defect.

INDIVIDUAL

PARTICLES

COMBINED

NUCLEUS

p

p

p

p

p

n n n

n

n

e

e e

STUDENT TEXT

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TABLE OF CONTENTS

FIGURES AND TABLES ........................................................................................................... ii

OBJECTIVES ............................................................................................................................ iii

FORCES WITHIN THE ATOM.................................................................................................. 1

Electrostatic and Nuclear Force ................................................................................................ 1

Nuclear Force And Nuclear Stability ........................................................................................ 2

Neutron Contribution To Nuclear Stability .............................................................................. 2

TYPES OF RADIATION ............................................................................................................ 3

Alpha Particles .......................................................................................................................... 3

Beta Particles ............................................................................................................................ 4

Gamma Rays ............................................................................................................................. 4

Neutrons .................................................................................................................................... 4

MASS DEFECT AND BINDING ENERGY .............................................................................. 5

Mass Defect .............................................................................................................................. 5

Binding Energy ......................................................................................................................... 7

Binding Energy Per Nucleon .................................................................................................... 8

Binding Energy Per Neutron ................................................................................................... 10

Energy Released by Fission .................................................................................................... 11

SUMMARY ............................................................................................................................... 13

PRACTICE EXERCISES .......................................................................................................... 14

GLOSSARY ............................................................................................................................... 16




MASS DEFECT AND BINDING ENERGY REV 2


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FIGURES AND TABLESFigure 2-1 Electrostatic and Nuclear Forces .............................................................................. 1

Figure 2-2 Nuclear Force Boundary .......................................................................................... 2

Figure 2-3 Neutron to Proton Ratio ........................................................................................... 2

Figure 2-4 Radiation Types ....................................................................................................... 5

Figure 2-5 Mass Defect .............................................................................................................. 5

Figure 2-6 Mass Energy Equivalence ........................................................................................ 7

Figure 2-7 Mass Defect .............................................................................................................. 7

Figure 2-8 Binding Per Nucleon vs. Mass Number ................................................................... 8

Figure 2-9 Binding Energy of a Neutron ................................................................................. 10

No Tables




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OBJECTIVES



or written exam.

1. DESCRIBE the characteristics of the following, including relative effective distance, changewith distance, and nucleons involved with each:

a. Electrostatic Forceb. Nuclear Force

2. STATE the role that neutrons have regarding the stability of a nucleus.3. DEFINE the following terms:

a. Binding energyb. Binding energy per nucleonc. Fissiond. Mass defecte. Mass-energy equivalencef. Nuclear Stability

4. STATE the purpose of radioactive decay.5. IDENTIFY the four basic types of radiation.6. For each of the four basic types of radiation, DISCUSS the following:

a. Relative ability to penetrate substances when compared to the other three types ofradiation.

b. Size or mass.c. Electrical charge.




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OBJECTIVES

7. Given a Chart Of Nuclides, or equivalent information, CALCULATE the binding energy andbinding energy per nucleon of a given nucleus.

8. Given a plot of binding energy per nucleon, EXPLAIN the changing slope of the curve.

NUCLEAR SCIENCE - CHAPTER 2 - iv 2003 GENERAL PHYSICS CORPORATION



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FORCES WITHIN THE

ATOM

ELECTROSTATIC AND NUCLEAR

FORCE

One basic law of electricity is that objects withthe same electrical charge repel each other and

objects with opposite charges attract. This is

termed electrostatic force (also called coulombforce). The force acts over relatively long

distances and is cumulative.

Because the nucleus is composed of positively

charged protons and neutrally charged neutrons,

an attractive force of some kind must exist in astable nucleus to overcome the repulsive

electrostatic force associated with the protons.This attractive force is termed nuclear force.

Nuclear forces are much stronger than

electrostatic forces when acting over very short

distances, but decrease dramatically withincreasing distance.

The nuclear forces act upon any adjacent

nucleons: proton to proton, neutron to proton,

and neutron to neutron. Figure 2-1 shows asimplified diagram of the concept of electrostatic

and nuclear force.

Like charged particles slightly

separated will experience a

coulomb force of repulsion:

Nuclear forces of attraction

are produced when adjacent

nucleons are involved:

ELECTRONS

- -

PROTONS

+ +

PROTONS

+ +

PROTON AND NEUTRON

+ n

NEUTRONS

n n

Figure 2-1 Electrostatic and Nuclear Forces

Nuclear force is strong over ________(long/short) distances and is _________

(stronger/weaker) than electrostatic forces

at that distance.

Example 2-1




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NUCLEAR FORCE AND NUCLEAR

STABILITY

Nuclear stability is the inherent ability of anatom to resist changing its atomic structure or

energy.

Stability of the nucleus depends upon the

balance between the repulsion of the electrostatic

forces and the attraction by the nuclear force. Asshown in the simplified illustration ofFigure 2-2,

there is a short boundary surrounding a proton

within which it is attracted to its nearest protonsor neutrons. Outside this boundary, it repels all

other protons within the nucleus by electrostatic

force.

Proton

NuclearForce

Boundary

Figure 2-2 Nuclear Force Boundary

The limited range of effectiveness of the nuclearforce has a major role in the stability of the

nucleus.

Define nuclear stability.

Example 2-2

NEUTRON CONTRIBUTION TO

NUCLEAR STABILITY

Because there is no electrostatic repulsion

between protons and neutrons or between

neutrons and neutrons, the effective boundary for

nuclear force is larger between these nucleons.To put it another way, the nuclear force is more

effective between a neutron and proton, and most

effective between two neutrons. This mightsuggest that a nucleus having a greater number

of neutrons than protons would be more stable

(tightly bound) than one that does not. Thefollowing discussion shows this to be true to a

point.

Figure 2-3 is a graph that has two plots. The

dashed line is a reference plot showing what the

graph would look like if all nuclides had thesame number of neutrons as protons (N=Z). The

line of random dots represents the plot of

naturally occurring stable nuclides.

LINE OF

STABILITY

NUMBER OF NEUTRONS (N = A - Z)

NUMBE

R

OFPROTONS(Z)

100

80

60

40

20

0

0 20 40 60 80 100 120 140

NZ = 1

Figure 2-3 Neutron to Proton Ratio

The plot shows that for small nuclei the ratio of

neutrons to protons is nearly equal to one. In

progressively larger nuclei the neutron to proton

ratio

Z

ZA becomes larger. This

phenomenon is mainly due to the neutrons

contributing a strong but very short nuclear force

and no repulsive electrostatic force. With




26/191


increasingly larger nuclei the ratio of neutrons to

protons increases to add enough nuclear force to

overcome the sum of the electrostatic repulsive

forces and maintain a stable nucleus.

As the size of the nuclei increases there is a pointwhere increasing the population of neutrons no

longer results in the balance of the repulsive andattractive forces within the nucleus. At thispoint, the addition of neutrons will result in an

unstable nucleus.

There is no known stable nucleus with an atomic

number larger than bismuth ( Bi20983 ). Nuclei with

more than 83 protons are unstable and

spontaneously undergo radioactive decay and

emit various types of energy in the process.

Describe the plots shown in Figure 2-3

Neutron to Proton Ratio

Z

N=1

Line of Stability

Example 2-3

TYPES OF RADIATION

Radioactive decay is the process by which anunstable nucleus spontaneously transmutes from

one form (element) to another to reach a more

stable state. Radioactive decay is discussed ingreater detail in Chapter 3. The term is

introduced here because it is the birthplace of

most of the radiation occurring in a nuclear

power plant.

The radioactive decay process is normallyaccompanied by the emission of one or more

types of radiation. The radiation is in the form

of either particles or electromagnetic energy(gamma rays or photons).

In general, the following statements are trueregarding radiation interactions:

The larger the mass, the greater the ability tointeract with a target substance, resulting in

lesser ability to penetrate the substance

The greater the electric charge, the greaterthe ability to interact with a target substance,

and lesser ability to penetrate the substance.

The greater the velocity, the greater theability to penetrate a target substance.

There are four basic types of radiation: alpha

particles, beta particles, gamma rays, and

neutrons.

ALPHA PARTICLES

An alpha particle () is a charged particle

consisting of two protons and two neutrons.Another way to look at it is as a Helium nucleus

with a double positive charge and a relatively

large mass. The large mass and the double

positive charge cause it to interact easily withany substance it contacts. The large mass and

charge results in a very short range of travel,




27/191


because it interacts so much. A piece of paper

stops most alpha particles. Typically alpha

decay occurs at the upper end of the line of

stability.

BETA PARTICLESA beta particle () is a positively (+) ornegatively () charged particle emitted from thenucleus with a mass equal to that of an electron.

It is a high-energy particle of small mass, but theelectrical charge causes an immediate interaction

with the atoms of any material it comes in

contact with. A thin sheet of metal and mostsafety glasses stops beta particles.

There are two types of beta particles: electron

and positron.

An electron (beta minus ) is a negative betaparticle. It is typically emitted from unstablenuclei decaying below the line of stability. It is

commonly found with fission products created

from the fission of fuel in commercial reactors.

A positron (beta plus +) is a positive betaparticle that is typically emitted from unstable

nuclei decaying above the line of stability. It is

not commonly seen in commercial nuclear powerplants.

GAMMA RAYS

A Gamma ray () is an electromagnetic energythat possesses neither mass nor charge. It is in a

class of energy known as photons. Photons are

discrete bundles of energy that have

characteristics of waves and particles. Withessentially no mass and with generally high

energy (velocity), it penetrates materials easilyand does not interact electrically with a

materials atoms. The distance a gamma ray

travels relies greatly on the density of thematerial it interacts with. It often requires

several inches of metal or a couple of feet of

concrete to stop.

NEUTRONS

A Neutron ( n10

) is a particle with no electrical

charge originating in the center (nucleus) of anatom. Energy level can vary greatly. It has a

relatively large mass when compared to Beta

particles, but small in comparison to an alphaparticle. It has no electrical charge, so it easily

penetrates substances. The only way for a

neutron to interact is through collisions with thematerials atoms. It continues to travel until it

gives up all its energy and is absorbed by the

nucleus of an atom terminating its travel. Itusually requires about a foot of water to stop a

neutron.

Figure 2-4 shows these radiation types.




28/191


GAMMAELECTROMAGNETIC

RADIATION

CHARGE: 0

MASS: 0

NEUTRON10

n

CHARGE: 0

MASS: 1 AMU

n

BETA MINUS

0

-1e

ELECTRON

CHARGE: -1

MASS: 1/1800 AMU

-

BETA PLUS

+0

+1e

POSITRON

CHARGE: +1

MASS: 1/1800 AMU

+

ALPHA

42

He++

HELIUM

NUCLEUS

CHARGE: +2

MASS: 4 AMU

+

+

Figure 2-4 Radiation Types

Of the four radiation types, which one is leastpenetrating and why?

Of the four radiation types, which carry no

electrical charge?

Example 2-4

MASS DEFECT AND

BINDING ENERGY

MASS DEFECT

Whena nucleus is assembled from its component

parts (protons and neutrons and electrons), thetotal mass of the nuclide is less than the total

mass of the individual particles (Figure 2-5).

This mass difference is called the mass defect

(m).

MASS DEFECT

Mass of all of the individual particles isgreater than the mass of the combinednuclide. The difference is called the MassDefect.

INDIVIDUALPARTICLES

COMBINEDNUCLEUS

p

pp

p

pn n n

n

n

e

ee

Figure 2-5 Mass Defect




29/191


The mass defect is measured in atomic mass

units (AMU). One AMU is equal to

1.66 10-24

grams. It is possible to calculate the

mass defect for each nucleus usingEquation 2-1.

MmZ)-A(Zmm nH +=

Where:

m = mass defect (AMU)

Z = atomic number (number of

protons)

mH = mass of H11 atom

(1.0078 AMU)

A = atomic mass number (number

of nucleons)

mn = mass of a neutron(1.0087 AMU)

M = mass of the atom

Equation 2-1

The values for the variables in the aboveequation can be found in the Chart of the

Nuclides. To account for the mass of an atoms

electrons, we use the mass of a hydrogen atomvice the mass of a proton. The mass of the

hydrogen atom has been experimentally

determined and includes the mass of theelectrons.

Calculate the mass defect of the U-235

atom. Uranium-235 has a mass of235.0439 AMU.

M = 235.0439 AMU

MmZ)-A(Zmm nH +=

0439.235

)92)(1.0087-235(1.0078)(92m

+=

0439.2352441.1447176.92m +=

AMU9178.1m=

Example 2-5

Calculate the mass defect of the U-238

atom. Uranium has a mass of

238.0508 AMU.

MmZ)-A(Zmm nH +=

=m

Example 2-6




30/191


BINDING ENERGY

Equation 2-2 is derived from Einsteins Theory

of Relativity. Initially postulated, it was later

experimentally proven to be:

2mcE=

Where:

E = energy released (MeV)

m = mass (AMU)

c = speed of light

sec

m

Equation 2-2

Figure 2-6 shows a simplified sketch of this

mass-energy equivalence.

MASS-ENERGY EQUIVALENCE

E = mc2

TWO FORMS OF THE SAME THING

MASS ENERGY

Figure 2-6 Mass Energy Equivalence

Incorporating various conversion factors, a

simplified equation for the mass defect to energyequivalence results:

( ) ( )

=AMU

MeV5.931AMUmMeVE

Equation 2-3

The energy term, as related to mass defect, is

known as binding energy (BE). Binding energy

is defined as the energy equivalent of the massdefect and has units of MeV (mega electron

volts). Binding energy represents the amount of

energy released when protons, neutrons, and

electrons combined to form an atom, as shown in

Figure 2-7.

MASS DEFECT

Mass of all of the individual particles isgreater than the mass of the combinednuclide. The difference is called the MassDefect.

INDIVIDUALPARTICLES

COMBINEDNUCLEUS

p

pp

p

pn n n

n

n

e

e e

Figure 2-7 Mass Defect

Binding energy also represents the amount of

energy that must be supplied to the atom to

separate the atom into its individual protons,

neutrons, and electrons. The more tightly boundthe atom, the greater the binding energy required

to dismantle the atom.

In a previous example, it was determined that a

mass defect occurred when forming a U-235

atom from its component parts. The missingmass was converted into binding energy that

holds the atom together. It is possible to relate

the mass defect to a certain amount of energy.




31/191


Consider the following examples:

Determine the energy equivalence of themass defect of a U-235 atom.

The mass defect for a U-238 atom was1.9178 AMU.

( )

=AMU

MeV5.931AMUmE

E = (1.9178)(931.5)

E = 1786.4307 MeV

Example 2-7

Determine the energy equivalence of the massdefect of a U-238 atom. Recall that the massdefect for a U-238 atom was 1.937 AMU.

Example 2-8

BINDING ENERGY PER NUCLEON

The binding energy of an individual member of

the nucleus, or the binding energy per nucleon

A

BE, is another important concept. This term

represents the average energy required to remove

a nucleon from a given nucleus. Dividing the

total binding energy by the number of nucleonsequals the binding energy per nucleon.

Plotting binding energy as a function of atomicmass number results in a curve similar to the one

inFigure 2-8. Note that the binding energy pernucleon increases to a maximum of 8.6 MeV at a

mass number of 60. Binding energy per nucleon

slowly decreases as the mass number increasesbeyond 60. For A > 209, no stable nuclei exist.

B

INDINGE

NERGYPER

NUCLEON

(MeV)

MASS NUMBER

Figure 2-8 Binding Per Nucleon vs. Mass

Number

The area of interest in this curve is the region of

decreasing binding energy per nucleon with an

increasing mass number.

This occurs because the proton-to-protonrepulsive force increases faster than the nuclear

attractive forces. In this region, there is a net

gain of energy (energy is released) in a fissionreaction. The total binding energy of the system

after a fission reaction is greater than the total

binding energy of the system before the fission




32/191


reaction. The increase in binding energy results

in the release of energy from the system. In

other words, some amount of mass is lost after

the fission reaction. This missing mass convertsinto energy and radiates from the system.

Calculate the mass defect of the Nickel 58atom. Ni-58 has a mass of 57.9353 AMU.

M = 57.9353 AMU

m = ZmH+ (A Z) mn M

m = 28(1.0078) + (58 28)(1.0087)

57.9353

m = 28.2184 + 30.261 57.9353

m = 0.5441 AMU

Example 2-9

Calculate the binding energy for Ni-58.

Example 2-10

Calculate the binding energy per nucleon for

Ni-58.

nucleonperMeV74.858

8.506

A

BE==

Example 2-11

Given the binding energy for U-238 is

1804.3, calculate the binding energy pernucleon for U-238.

Example 2-12




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BINDING ENERGY PER NEUTRON

Binding energy is similar in terms of neutron

binding energy. As shown in Figure 2-9, this

represents the minimum amount of energy that aneutron imparts to a target nucleus when

absorbed. This is an important concept; it

determines the feasibility of a fission eventoccurring. When the neutron is absorbed by the

target nucleus, the nucleus becomes excited by

an amount equal to the neutron binding energy

and the kinetic energy of the neutron. If thisexcitation energy is of sufficient magnitude to

overcome the nuclear forces holding the nucleus

together, the target nucleus splits (fissions). Ifthe excitation energy is not of sufficient

magnitude, fission does not occur and the atom

reaches stability by radioactive decay.

Figure 2-9 Binding Energy of a Neutron

How much energy does a neutron add whenit is absorbed into a nucleus of a U-235

atom?

mass

defect=

mass oforiginal

nucleus andneutron

mass of

final

nuclei

*236

92

1

0

235

92UnU +

Given:

mass of U-235 = 235.0439 AMU

mass of n10 = 1.0087 AMU

mass of U-236 = 236.0456 AMU

Substituting into the mass defect equation:

236.0456-1.0087)(235.0439m +=

Calculating the mass loss from the system:

( ) ( )0456.2360526.236m =

AMU007.0m=

Now using the mass to energy equivalence,convert the missing mass into the energy

added into the nucleus.

( )

=

AMU

MeV5.931AMUmE

E = (0.0070)(931.5)

E = 6.5205

Neutron absorption into a U-235 nucleus

adds 6.5 MeV of energy.

Example 2-13




34/191


Calculate the amount of energy added whena neutron is absorbed into a nucleus of a U-

238 atom.

*239

92

1

0

238

92UnU +

Given:mass of U-238 = 238.0508 AMU


mass of U-239 = 239.0543 AMU

Example 2-14

ENERGY RELEASED BY FISSION

With an understanding of the energy required to

hold the nucleus together, it is easy to see that if

the nucleus is broken apart energy can bereleased from the nucleus. The amount of

energy released can be calculated using the same

formulas used to determine the mass defect andthe mass-to-energy conversion. The concept

remains the same to determine the difference

between the mass of the reactants and the mass

of the products. If there is additional mass fromthe reactants that is not accounted for in the mass

of the products then energy has been released.




35/191


How much energy is released from thefollowing fission event?

++++ n2PdTenPu 10108

46

130

52

1

0

239

94

Given:mass of Pu-239 = 239.0522 AMUmass of n = 1.0087 AMU

mass of Te-130 = 129.9062 AMU

mass of Pd-108 = 107.9039 AMU.


mass

defect=

mass oforiginal

nucleus and

neutron

mass of

final

products


( )[ ]0087.129039.1079062.129-1.0087)(239.0522m

++

+=

( ) ( )8275.2390609.240m =

AMU2334.0m=


released from the system.

( )AMUmAMU

MeV5.931E

=

2334)(931.5)(0.E=

MeV4.217E=

There are 217.4 MeV released from thisfission event.

Example 2-15


++++ n3XeSrnU 10139

54

94

38

1

0

235

92

Given:

mass of U-235 = 235.0439 AMUmass of n = 1.0087 AMUmass of Sr-94 = 93.9154 AMU

mass of Xe-139 = 138.9178 AMU.

Example 2-16




36/191


SUMMARY

Mass defect is the difference between the massof the atom and the sum of the masses of its

constituent parts.

Binding energy is the amount of energy that

must be supplied to a nucleus to completely

separate its nuclear particles. Binding energy isthe energy equivalent of the mass defect.

Mass defect can be calculated by using the

equation below.

m = [Z(m H11 ) + (AZ)mn ] matom

Binding energy can be calculated by multiplyingthe mass defect by the factor of 931.5 MeV per

AMU.

( ) ( )

=AMU

MeV5.931AMUmMeVE




37/191


PRACTICE EXERCISES

1. Define the term nuclear stability.2. For each of the following statements,

determine if the statement is applicable to a.nuclear force or b. electrostatic force.

a. Of the two nuclei, it exists only betweenthe protons. ___

b. Effective over relatively long distancewithin the nucleus.___

c. Very strong for short distances. ___d. To a point, adding more neutrons to the

nucleus makes the force less effective.___

e. Exists between both particles in thenucleus. ___

3. Generally, the ratio of __________ to___________ is __________ for___________ nuclei. (Select the correct one

below)

a. protons, neutrons, larger, smallerb. neutrons, protons, larger, smallerc. protons, neutrons, smaller, smallerd. neutrons, protons, smaller, larger

4. For the four types of radiation introduced inthis chapter fill in each column in the table

below, to make the column true

Has

Electrical

Charge

Order Of

Penetrating

Ability(High-Med-

Low)

Has

Mass?

Is a

Photon

5. Describe the relationship between the termsmass defect and binding energy.

6. State the condition that determines whetherfission does or does not occur when a

nucleus absorbs a neutron.

7. Calculate the mass defect of the H-1 atom.Hydrogen-1 has a mass of 1.00782503 AMU.

8. Determine the energy equivalence of themass defect of a H-1 atom.

9. Calculate the binding energy per nucleon forH-1.

10.Calculate the mass defect of the Plutonium-240 atom. Pu-240 has a mass of 240.053808

AMU.




38/191


11.Determine the energy equivalence of themass defect of a Pu-240 atom.

12.Calculate the binding energy per nucleon forPu-240.




39/191


GLOSSARY

Binding Energy (BE) The energy equivalent of the mass defect (MeV). Represents the amount of

energy that is released when an atom is formed from its component protonsand neutrons. Also, represents the amount of energy that must be supplied

to the atom to completely separate it into its individual protons and neutrons.

Binding Energy (BE)

Per Nucleon

Average energy required to remove a nucleon from the nucleus.

Electrostatic Force The attractive or repulsive force that exist between two objects due to their

electrical charge.

Fission The splitting of an atoms nucleus resulting from an energy input (excitationenergy) into the nucleus greater than the nuclear forces holding the nucleus

together.

Mass Defect (m) The difference in mass between a nucleus and the sum of the masses of theindividual protons and neutrons in the nucleus (AMU).

Mass-Energy

EquivalenceThe conversion factor equating mass to energy (931.5

AMU

MeV).

Nuclear Force The strong attractive force in a nucleus between to adjacent nucleons.

Nuclear Stability The inherent ability of an atom to resist changing its atomic structure orenergy level.

Radioactive Decay The process by which an unstable nucleus spontaneously transmutes from

one form to another to reach a more stable state.




40/191


EXAMPLE EXERCISE

ANSWERS

Nuclear force is strong over ________

(long/short) distances and is _________(stronger/weaker) than electrostatic forcesat that distance.

Example 2-1

Define nuclear stability.

The inherent ability of an atom to resist

changing its atomic structure or energy.

Example 2-2

Describe the plots shown in Figure 2-3

Neutron to Proton Ratio

Z

N=1

The dashed line is a reference plot ofN = Z.

Line of Stability

A plot of naturally occurring stable

nuclides.

Example 2-3

Of the four radiation types, which one is least

penetrating and why?

Alpha - very large mass and very large

electrical charge causing it to interact

with material on contact.

Of the four radiation types, which carry no

electrical charge?

Gamma and neutron.

Example 2-4

Calculate the mass defect of the U-238atom. Uranium has a mass of

238.0508 AMU.

AMU0508.238M=

MmZ)-A(Zmm nH +=

0508.238

)92)(1.0087-238(1.0078)(92m

+=

0508.2382702.1477176.92m +=

AMU937.1m=

Example 2-6

Determine the energy equivalence of the massdefect of a U-238 atom. Recall that the mass

defect for a U-238 atom was 1.937 AMU.

( )

=AMU

MeV5.931AMUmE

E = (1.937)(931.5)

E = 1804.3155 MeV

Example 2-8




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Calculate the binding energy for Ni-58.

( )AMUmAMU

MeV5.931E

=

E = (931.5)(0.5441)

MeV506.8E=

Example 2-10

Calculate the binding energy per nucleon for

Ni-58.

MeV7.858

8.506

A

BE==

Example 2-11

Given the binding energy for U-238 is

1804.3, calculate the binding energy pernucleon for U-238.

Me58.7238

3.1804

A

BE== V

Example 2-12

Calculate the amount of energy added whena neutron is absorbed into a nucleus of a U-

238 atom.

mass

defect=

mass oforiginal

nucleus andneutron

mass of

final

nuclei

*239

92

1

0

238

92UnU +

Given:

mass of U-238 = 238.0508 AMU


mass of U-239 = 239.0543 AMU


239.0543-1.0087)(238.0508m +=


( ) ( )0543.2390595.239m =

AMU0052.0m=


added into the nucleus.

( )

=

AMU

MeV5.931AMUmE

E = (0.0052)(931.5)

E = 4.8438

Neutron absorption into a U-238 nucleusadds 4.84 MeV of energy.

Example 2-14




42/191



++++ n3XeSrnU 10139

54

94

38

1

0

235

92

Given:

mass of U-235 = 235.0439 AMUmass of n = 1.0087 AMUmass of Sr-94 = 93.9154 AMU

mass of Xe-139 = 138.9178 AMU.


( )[ ]0087.139178.1389154.93-1.0087)(235.0439m

++

+=

( ) ( )8593.2350526.236m = AMU1933.0m=


released from the system.

( )AMUmAMU

MeV5.931E

=

1933)(931.5)(0.E=

MeV1.180E=

There are 180.1 MeV released from this

fission event.

Example 2-16




43/191


PRACTICE EXERCISE

ANSWERS

1. Define the term nuclear stability.The inherent ability of an atom to resist

changing its atomic structure or energy.

2. For each of the following statements,determine if the statement is applicable to A.

nuclear force or B. electrostatic force.

a. Of the two nuclei, it exists onlybetween the protons. B

b. Effective over relatively long distance

within the nucleus. B

c. Very strong for short distances. A

d. To a point, adding more neutrons to the

nucleus makes the force less effective.

B

e. f. Exists between both particles in

the nucleus. A

3. Generally, the ratio of __________ to___________ is __________ for

___________ nuclei. (Select the correct one

below)

a. protons, neutrons, larger, smaller

4. For the four types of radiation introduced inthis chapter fill in each column in the table

below, to make the column true.

Has

Electrical

Charge

Order Of

Penetrating

Ability

(H-L)

Has

Mass?

Is a

Photon

Alpha Gamma Alpha Gamma

Beta Neutron Beta

Beta Neutron

Alpha

5. Describe the relationship between the termsmass defect and binding energy.

Binding energy is equal to the energy

released by the mass defect associated

with the nucleus of any specific atom.

6. State the condition that determines whetherfission may or may not occur when a

nucleus absorbs a neutron.

The target nucleus must receive enoughexcitation energy to overcome the

nuclear forces holding the nucleus

together before fission is possible.

7. Calculate the mass defect of the H-1 atom.Hydrogen-1 has a mass of 1.007825032

AMU.

M = 1.007825032 AMU

m = Z(mp+ me) +(A Z)mn M

m = 1(1.007276470 + 0.0005485) + (1 1)(1.0086649) 1.00782503

m = 1.00782497 + 0.0 + 1.007825032

m = 0.000000062 AMU

8. Determine the energy equivalence of themass defect of a H-1 atom.

( )AMUmAMU

MeV5.931E

=

E = (931.5)(0.000000062)

E = 5.78 x 105

MeV




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9. Calculate the binding energy per nucleon forH-1.

MeV1078.51

1078.5

A

BE 55

=

=

10.Calculate the mass defect of the Plutonium-240 atom. Pu-240 has a mass of 240.053808AMU.

M = 240.053808 AMU

m = Z(mH) +(A Z)mn M

m = 94(1.00782503) + (240 94)(1.0086649) 240.053808

m = 94.73555 + 1.47.26508 + 240.053808

m = 1.9468 AMU

11.Determine the energy equivalence of themass defect of a Pu-240 atom.

( )AMUmAMU

MeV5.931E

=

E = (931.5)(1.9468)

E = 1813.4679 MeV

12.Calculate the binding energy per nucleon forPu-240.

MeV56.7240

4679.1813

A

BE==




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KFN03Sr02_Radioactive Decay and Interactions.doc 6/9/14 3:22 PM R11


NUCLEAR

SCIENCE

CHAPTER 3

RADIOACTIVE DECAY AND INTERACTIONS

n

n

X

-ray

X* X

STUDENT TEXT

REV 2

TM

2003 General Physics Corporation, Elkridge, Maryland




46/191



47/191


TABLE OF CONTENTS

FIGURES AND TABLES ......................................................................................................... iii

OBJECTIVES ............................................................................................................................. iv

RADIOACTIVE DECAY PROCESSES ..................................................................................... 1

Unstable Nuclides ..................................................................................................................... 1

Alpha Decay.............................................................................................................................. 2

Beta Decay ................................................................................................................................ 4

Electron Capture ....................................................................................................................... 6

Photon (Gamma Ray or X-Ray) Decay .................................................................................... 7

Decay By Neutron Emission ..................................................................................................... 7

ELECTRON RADIATION INTERACTIONS ............................................................................ 9

Energy Levels And Location .................................................................................................... 9

Excitation and Radiation ........................................................................................................... 9

RADIATION INTERACTIONS ................................................................................................ 11

Alpha Particle.......................................................................................................................... 11

Beta Particle ............................................................................................................................ 11

Gamma Ray ............................................................................................................................ 12

Photoelectric effect ................................................................................................................. 12

Compton Scattering ................................................................................................................ 12

Pair Production ....................................................................................................................... 13

NUCLEUS RADIATION INTERACTIONS ............................................................................ 15

Excitation And Radiation ........................................................................................................ 15

NEUTRON INTERACTIONS ................................................................................................... 15

Types Of Reactions ................................................................................................................. 15

Scattering Reactions................................................................................................................ 15

Absorption Reactions .............................................................................................................. 16

Radiative Capture ................................................................................................................... 16

Fission ..................................................................................................................................... 17

HALF-LIFE DETERMINATION.............................................................................................. 18

Decay Rates ............................................................................................................................ 18

HALF-LIFE ................................................................................................................................ 19


RADIOACTIVE DECAY AND INTERACTIONS REV 2


48/191


TABLE OF CONTENTS

SUMMARY ............................................................................................................................... 22

PRACTICE EXERCISES .......................................................................................................... 24

GLOSSARY ............................................................................................................................... 25






49/191


FIGURES AND TABLESFigure 3-1 Alpha Decay of U-235 ............................................................................................. 2

Figure 3-2 Alpha Decay Using Chart of Nuclides ..................................................................... 3

Figure 3-3 Beta Minus Decay on a Chart of Nuclides ............................................................... 4Figure 3-4 Beta Plus Decay on a Chart of Nuclides .................................................................. 5

Figure 3-5 Electron Capture Decay using Chart of Nuclides .................................................... 6

Figure 3-6 Orbital Electron Capture by the Nucleus ................................................................. 6

Figure 3-7 Neutron Emission from First Excited Daughter of Decay Chain ............................ 8

Figure 3-8 Neutron Decay using Chart of Nuclides .................................................................. 8

Figure 3-9 Simplified Nucleus and Electron Shells ................................................................... 9

Figure 3-10 Alpha Particle Specific Ionization versus Distance Traveled in Air ...................... 11

Figure 3-11 Photoelectric Effect .............................................................................................. 12

Figure 3-12 Compton Scattering .............................................................................................. 13

Figure 3-13 Pair Production ..................................................................................................... 13Figure 3-14 Attenuation of Electromagnetic Radiation (in Lead) ........................................... 14

Figure 3-15Elastic Scattering ................................................................................................. 15Figure 3-16Inelastic Scattering ............................................................................................... 16

Figure 3-17 Radiative Capture ................................................................................................. 17

Figure 3-18Fission of U-235 ................................................................................................... 17

Figure 3-19 Half-Life ............................................................................................................... 19

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OBJECTIVES



or written exam.

1. Given an atom with multiple electron shells:a. COMPARE allowed number of electrons in the outer shell to the allowed number of

the inner shell.

b. COMPARE the energy carried by an electron in an outer shell to the energy carriedby and electron in an inner shell.

c. DESCRIBE the response of electrons in the outer shells to the ejection of an electronin an inner shell.

2. DEFINE the following terms:a. Ground state energyb. Excited state energyc. Iond. Ionizatione. Gamma rayf. X-rayg. Radioactive decayh. Decay chaini. Spontaneous fissionj. Half-life

3. EXPLAIN how each of the following forms of radiation interact with the surroundingenvironment and lose energy.a. Alpha

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OBJECTIVESb. Betac.

Gamma (Photoelectric effect, Compton Scattering, and Pair Production)

4. EXPLAIN how each of the following radioactive decay processes occur:a. Alphab. Betac. Electron Captured. Photon Decaye. Neutron Emission

5. EXPLAIN the radioactive decay processes, including the following:a. Difference in atomic and mass numbers between the parent and daughter nuclidesb. Disposition of energy associated with the process

6. COMPARE elastic and inelastic scattering processes.7. COMPARE radiative capture and fission processes.8. Given a sample of a radioactive element, EXPLAIN the relationship between the number ofatoms contained in the sample and the activity of the sample.9. EXPLAIN the half-life method of determining radioactive decay.

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RADIOACTIVE DECAYPROCESSES

UNSTABLE NUCLIDES

Radioactive decay (or radioactivity) is theprocess by which an unstable nucleus

spontaneously transmutes (changes) from one

form (nuclide) to another to reach a more stablestate. It is termed radioactive decay because one

or more forms of radiation, as discussed inChapter 2, accompany it. Two terms that will be

used extensively in the discussion of radioactive

decay are:

Parent Nuclide, the original nucleuswhich decays.

Daughter Nuclide, the new nucleuspresent after the decay event.

Unstable isotopes will emit particles, energy, or

both particles and energy in an attempt to reach a

stable condition. However, not all isotopes

contain the same amount of excitation energy. Infact, some isotopes have too few neutrons and

others have too many nucleons. An unstablenuclide will attempt to reach a stable conditionby any one, or combination of several decay

mechanisms. In general, unstable nuclides decay

by six (6) basic decay mechanisms:

Alpha decay Beta decay [beta minus or beta plus (also

known as positron)]

Electron Capture (k-capture) Neutron emission Photon (gamma or x-ray) Decay

Internal ConversionEquation 3-1 shows a formula symbolizingradioactive decay.

ERYX AZA

Z ++

Where:

XAZ = parent nuclide

YAZ = daughter nuclide

R = radiation type

E = energy

Equation 3-1

The energy term here includes the kinetic energycarried by the daughter nucleus, and the primary

and any secondary radiation particles. It is thebinding energy represented by the mass

difference (m) between the parent nuclide, andthe sum of the masses of the daughter nuclide

and the radiation particles.

A substantial number of radioactive (unstable)

nuclides (also called radionuclides) exist innature. These naturally occurring elements have

atomic numbers above 83, and are commonlyreferred to as heavy nuclides. Each goes through

a radioactive decay process at a definite rate,depending upon the nature of the nuclide, to

reach stability.

The daughter nuclide resulting from radioactive

decay is itself often unstable, resulting inadditional radioactive decay. Given that most of

the nuclides contained within a nuclear plant fuel

bundle are heavy nuclides, a significant number

of radioactive decay events are occurring fromthis source.

Each fission event within the nuclear reactor

results in two radioactive nuclides, in addition toone or more neutrons and other types of

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radiation. These nuclides are commonly referred

to as fission fragments. Each fission fragmentstarts a radioactive decay chain resulting in

several stages of radioactive nuclides before

reaching a stable element. This may bedemonstrated as follows:

( ) ( )

( ) .)etc(ERSW

ERWYERYX

3A

Z

A

Z

2A

Z

A

Z

1A

Z

A

Z

++

++++

Equation 3-2 Fission Fragment Decay Chain

The decay chains of the fission products are

significant because after the reactor is shutdown,the decay of the fission fragments continues. A

very high percentage of the kinetic energy from

the decay process is absorbed in the system andresults in production of heat energy. Nuclear

plant design must consider methods of core

cooling after reactor shutdown. More detail on

this process will be covered in later chapters.

The radioactive decay of a parent nuclide

always results in a stable daughter nuclide(true/false).

Example 3-1

ALPHA DECAY

Alpha decay involves heavy nuclei, generallythose having mass numbers greater than 210.

These nuclides decay through the emission of an

alpha particle. Equation 3-3 symbolizes alphadecay of a nuclide.

EYX4

2

4A

2Z

A

Z ++

Where:

XA

Z = parent nuclide

Y4A 2Z = daughter nuclide

42 = alpha particle

E = Energy

Equation 3-3 Alpha Decay

The daughter nucleus of alpha decay has two

neutrons and two protons less than the parent

nucleus.Figure 3-1 is an example of alpha decayfor uranium-235.

42

X4A

2Z

-ray

n++nALPHA ()

XA

Z

4

2

KINETIC

ENERGY

+ + KE +

+++ KEThU 42231

90

235

92

Figure 3-1 Alpha Decay of U-235

The U-235 nucleus emits an alpha particle

resulting in a daughter nucleus of thorium-231.The energy released in this decay scheme is thecombined kinetic energy (KE) of the alpha

particle and the daughter nucleus, and the energy

possessed by the gamma radiation. Most of the

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energy (well over 95%) associated with alpha

decay is possessed by the alpha particle.

Explain the radioactive decay process as

represented by the following:

EYX4

2

A

Z

A

Z ++

Example 3-2

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