Chapter 7:Chapter 7:

NUCLEARNUCLEARPHYSICSPHYSICS

SCOPE OF STUDYSCOPE OF STUDY 11 main sub topics students should learn and understand in this

chapter are :

Structure and Properties of the Nucleus

Discovery of Neutrons

The Nuclear Forces

Atomic Number and Mass Number

Atomic Mass Unit

SCOPE OF STUDYSCOPE OF STUDY Mass Defect

Binding Energy per Nucleon

Mass-Energy Equation

Isotopes of an Element

Mass Spectrometer

Detection of Presence of Isotopes

STRUCTURE & STRUCTURE & PROPERTIES OF PROPERTIES OF NUCLEUSNUCLEUS Nucleus consists of protons and neutrons.

A proton is the nucleus of the simplest atom hydrogen.

Proton has positive charge.

Neutron carries no electric charge and has mass slightly larger than a proton.

The number of neutrons in the nucleus is N. 

STRUCTURE & STRUCTURE & PROPERTIES OF PROPERTIES OF NUCLEUSNUCLEUS

STRUCTURE & STRUCTURE & PROPERTIES OF PROPERTIES OF NUCLEUSNUCLEUS

STRUCTURE & STRUCTURE & PROPERTIES OF PROPERTIES OF NUCLEUSNUCLEUS Neutrons and protons are collectively called nucleons.

Although hydrogen nucleus consists of a single proton alone, the nuclei of all

other elements consist of both neutrons and protons.

Nuclei is a plural of nucleus.

The different nuclei are often referred to as nuclides.

The radius, r of nucleus depends on atomic mass number, A

3115 m102.1 Ar

DISCOVERY OF DISCOVERY OF NEUTRONSNEUTRONS

James Chadwick (1891-1974) James Chadwick (1891-1974) 

DISCOVERY OF DISCOVERY OF NEUTRONSNEUTRONS In 1932, Chadwick proved the existence of neutrons - elementary particles

devoid of any electrical charge.

In contrast with the helium nuclei (alpha rays) which are charged, and therefore

repelled by the considerable electrical forces present in the nuclei of heavy atoms,

this new tool in atomic disintegration need not overcome any electric barrier and is

capable of penetrating and splitting the nuclei of even the heaviest elements.

DISCOVERY OF DISCOVERY OF NEUTRONSNEUTRONSEXPERIMENT OF NEUTRON

DISCOVERY OF DISCOVERY OF NEUTRONSNEUTRONSChadwick smashed alpha particles into beryllium, a rare metallic element,

and allowed the radiation that was released to hit another target: paraffin

wax. When the beryllium radiation hit hydrogen atoms in the wax, the atoms

were sent into a detecting chamber. In physics it is known that only a particle

having almost the same mass as a hydrogen atom could effect hydrogen in

that manner. The experiment results showed a collision with beryllium atoms

would release massive neutral particles, which Chadwick named neutrons.

NUCLEAR FORCESNUCLEAR FORCES Two types : Strong nuclear forces and weak nuclear forces.

Strong nuclear force is an attractive force that acts between all nucleons

(protons and neutrons alike).

Protons attract each other via strong nuclear force at the same time they repel

each other via electric force.

Strong nuclear force > electric force.

Neutrons (electrically neutral) only attract other neutron or protons via strong

nuclear force.

NUCLEAR FORCESNUCLEAR FORCES Strong nuclear force is a short-range force. It acts only over a very short

distance.

It is very strong between 2 nucleons if they are < 10-15 m apart.

It is 0 if they are separated by a distance > 10-15 m apart.

Electric and gravitational forces are long-range forces.

If the nuclide contains too fewer or too many neutrons relative to the number of

protons, the binding of nucleons reduce (nuclide unstable).

NUCLEAR FORCESNUCLEAR FORCES Nuclei stable – have the same number of protons as neutrons (N=Z) up to about

A = 30.

Beyond this, stable nuclei contain more neutrons and protons.

As Z increase, electric repulsion increase, greater number of neutrons require to

maintain stability.

For very large Z, no number of neutrons can overcome the greatly increased

electric repulsion. (Above Z = 82, no completely stable nuclide).

Weak nuclear force – second type of nuclear force that is much weaker than

strong nuclear force.

NUCLEAR FORCESNUCLEAR FORCES

ATOMIC NUMBER, ATOMIC NUMBER, ZZDEFINITION DEFINITION

Number of protons in the nucleus

To establish the chemical identity of the atom.

Each atomic number corresponds to a different chemical element.

It symbols by Z.

MASS NUMBER, AMASS NUMBER, ADEFINITION DEFINITION

Total number of protons and neutrons

(nucleons) in the nucleus

Neutron number : N = A - Z

MASS NUMBER, AMASS NUMBER, A It symbols by A.

A and Z sufficient to specify a nuclide.

Nuclide are symbolized by symbol :

X is the chemical symbol for the element.

It contains the same information of Z but in the more easily in the

recognizable form.

ATOMIC MASS ATOMIC MASS UNITUNIT It is symbolized by amu or u.

It is a unit to specify the nuclear masses because the very small size of protons it

is not convenient to express the mass of nuclei and atomic particles in the

conventional unit of kilograms.

Masses of atoms are measured with reference to the carbon-12 atom, which is

assigned a mass of exactly 12 u.

ATOMIC MASS ATOMIC MASS UNITUNIT The relationship between the atomic mass unit and kilogram is :

where c : speed of light = 3.0 x 108 m/s

ATOMIC MASS ATOMIC MASS UNITUNIT

MASS DEFECT, ∆mMASS DEFECT, ∆mDEFINITIONDEFINITION

The amount by which the sum of the individual masses

of the protons and neutrons exceeds the mass of intact

nucleus

The amount by which the sum of the individual masses

of the protons and neutrons exceeds the mass of intact

nucleus

It is also known as the difference in mass of the nucleus.

BINDING ENERGY BINDING ENERGY PER NUCLEONPER NUCLEONBINDING ENERGY

The energy needed to break the nucleus into its

constituent protons and neutrons ( nucleons).

The energy needed to break the nucleus into its

constituent protons and neutrons ( nucleons).

BINDING ENERGY BINDING ENERGY PER NUCLEONPER NUCLEON Because of the strong nuclear force, the nucleons in a stable nucleus are held

tightly together.

Thus, energy is required to separate a stable nucleus into its constituent

nucleons.

The more stable the nucleus is, the greater is the amount of energy needed to

break it apart.

Each of the separated nucleons is at rest and out of range of the forces of the

other nucleons.

BINDING ENERGY BINDING ENERGY PER NUCLEONPER NUCLEON

22defect Massenergy Binding cmc

BINDING ENERGY BINDING ENERGY PER NUCLEONPER NUCLEONBINDING ENERGY PER NUCLEON

The total binding energy of a nucleus divided by

mass number, A

The total binding energy of a nucleus divided by

mass number, A

BINDING ENERGY BINDING ENERGY PER NUCLEONPER NUCLEON

BINDING ENERGY BINDING ENERGY PER NUCLEONPER NUCLEONExample: Binding energy for iron.

Calculate the total binding energy and the binding energy per nucleon for

, the most common stable isotope of iron.

Solution:

Calculate the mass of the iron nucleus, the mass of 26 protons, and the

mass of 30 neutrons. The total binding energy is the difference, 492

MeV, and the binding energy per nucleon is 8.79 MeV.

MASS-ENERGY MASS-ENERGY EQUATIONEQUATION The energy change in a nuclear reaction is considerably greater than that of a

normal chemical reaction.

This change can be calculated using Einstein's equation:

where ΔE is the change in energy,

Δm is the change in mass,

c is the speed of light (3.00 x 108 m/s).

ΔE = Δmc2ΔE = Δmc2

ISOTOPES OF ISOTOPES OF ELEMENTELEMENTDEFINITIONDEFINITION

Nuclei that contain the same number of protons but

different numbers of neutrons

ISOTOPES OF ISOTOPES OF ELEMENTELEMENT

ISOTOPES OF ISOTOPES OF ELEMENTELEMENT Every nuclide is an isotope of some other nuclide.

Most elements have several isotopes.

In most cases some of the isotopes of a given element are stable (not

radioactive), and some are radioactive.

For example, iodine has 23 known isotopes with mass numbers ranging from

117 to 139.

Two of these, I-127 and I-131, are shown below.

ISOTOPES OF ISOTOPES OF ELEMENTELEMENT

ISOTOPES OF ISOTOPES OF ELEMENTELEMENT The relationship between the two nuclides is that they are isotopes.

I-131 is an isotope of I-127, and I-127 is also an isotope of I-131.

For most elements the most common or most abundant form is the stable

isotope.

The radioactive forms are therefore isotopes of the more common forms,

explaining the strong association isotopes have developed with radioactivity.

MASS MASS SPECTROMETERSPECTROMETER

MASS MASS SPECTROMETERSPECTROMETERDEFINITIONDEFINITION

An instrument which can measure the masses and

relative concentrations of atoms and molecules. It

makes use of the basic magnetic force on a moving

charged particle.

An instrument which can measure the masses and

relative concentrations of atoms and molecules. It

makes use of the basic magnetic force on a moving

charged particle.

MASS MASS SPECTROMETERSPECTROMETER

DETECTION OF DETECTION OF PRESENCE OF PRESENCE OF ISOTOPESISOTOPESTwo radioactive isotopes of sodium—sodium-22 and sodium-24—are used

in medicine and other applications. They can be used as tracers to follow

sodium in a person's body. A tracer is a radioactive isotope whose presence

in a system can easily be detected. The isotope is injected into the system at

some point. Inside the system, the isotope gives off radiation. That radiation

can be followed by means of detectors placed around the system.

Two radioactive isotopes of sodium—sodium-22 and sodium-24—are used

in medicine and other applications. They can be used as tracers to follow

sodium in a person's body. A tracer is a radioactive isotope whose presence

in a system can easily be detected. The isotope is injected into the system at

some point. Inside the system, the isotope gives off radiation. That radiation

can be followed by means of detectors placed around the system.

EXAMPLE

DETECTION OF DETECTION OF PRESENCE OF PRESENCE OF ISOTOPESISOTOPESSodium-24 also has non-medical applications. For example, it is used to test

for leaks in oil pipe lines. These pipe lines are usually buried underground.

It may be difficult to tell when a pipe begins to leak. One way to locate a

leak is to add some sodium-24 to the oil. If oil leaks out of the pipe, so does

the sodium-24. The leaking oil may not be visible, but the leaking sodium-

24 is easily detected. It is located by instruments that are designed to detect

radiation.

Sodium-24 also has non-medical applications. For example, it is used to test

for leaks in oil pipe lines. These pipe lines are usually buried underground.

It may be difficult to tell when a pipe begins to leak. One way to locate a

leak is to add some sodium-24 to the oil. If oil leaks out of the pipe, so does

the sodium-24. The leaking oil may not be visible, but the leaking sodium-

24 is easily detected. It is located by instruments that are designed to detect

radiation.

~~ THE END ~~~~ THE END ~~

“ Write it on ur heart that every

day is the best day in the year”

~Ralph Wardo

Emerson~