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Nuclear Reactions, Radioactivity & Nuclear Energy

1. To learn the types of radioactive decay

2. To learn to write nuclear equations for radioactive decay

3. To learn how one element may be changed to another

by particle bombardment

4. To learn about radiation detection instruments

5. To understand half-life

Objectives

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Nuclear Reactions, Radioactivity & Nuclear Energy

• Nucleons – particles found in the

nucleus of an atom

– neutrons

– protons

• Atomic Number (Z) – number of

protons in the nucleus

• Mass Number (A) – sum of the

number of protons and neutrons

• Isotopes – atoms with identical

atomic numbers but different mass

numbers

• Nuclide – each unique atom

A Review of Atomic Terms

Isotope review activity

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Nuclear Reactions, Radioactivity & Nuclear Energy

A. Radioactive Decay

• Radioactivity – the spontaneous decomposition of a

nucleus forming a different nucleus and producing one or

more additional particles

• Nuclear Equation – shows the radioactive

decomposition of an element

146C → 14

7N + 0-1e

• Nuclear Forces – strong nuclear force holds neutrons

and protons together to form a nucleus (counters

electromagnetic repulsion). Weak nuclear force operates

within individual nucleons and gives rise to some kinds of

radioactivity

Strong and Weak Nuclear Forces

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Nuclear Reactions, Radioactivity & Nuclear Energy

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

Standard Model

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

Discovery of Radioactivity

• Antoine Henri Becquerel (1852-1908)

– Noticed the fogging of photographic plate by uranium

crystals

• Pierre Curie (1859-1906), Marie Curie (1867-1934)

– Further studies of uranium and discovery of polonium

and radium. Marie received two Nobel prizes. She

died from the effects of radiation doses received

during her experiments

• Ernest Rutherford (1871-1937)

– His understanding of atomic structure helped us

understand the role of the nucleus. He defined many

of the terms used to discuss radioactivity today

Discovery

Discovery 2

Discovery 3

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

A. Radioactive Decay

• Alpha-particle production

• Alpha particle – helium nucleus

– Examples

Types of Radioactive Decay

• Net effect is loss of 4 in mass number and loss of 2 in

atomic number.

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

A. Radioactive Decay

• Beta-particle production

Types of Radioactive Decay

• Net effect is to change a neutron to a proton.

• Beta particle – electron

– Examples

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

A. Radioactive Decay

• Gamma ray release

Types of Radioactive Decay

• Net effect is no change in mass number or atomic

number.

• Gamma ray – high energy photon

– Examples

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

A. Radioactive Decay

• Positron production

Types of Radioactive Decay

• Net effect is to change a proton to a neutron.

• Positron – particle with same mass as an electron but with

a positive charge (antimatter version of an electron)

– Examples

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

A. Radioactive Decay

• Electron capture

• Inner orbital electron is captured. New nucleus formed.

Neutrino and gamma ray produced

Types of Radioactive Decay

• Net effect is to change a proton to a neutron

20180Hg + 0-1e → 201

79Au + ν + 00γ

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

A. Radioactive Decay

Conservation of Mass Number and Charge Number

− both are retained in a nuclear reaction

− sum of both from the “reactants and products” are constant

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

Band of Stability

Black squares

indicate stable

nuclei. Decay

occurs to move

isotopes towards

the black line

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

A. Decay Series

Decay

series

activity

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

B. Nuclear Transformations

• Nuclear Transformation – forced change of one

element to another

• Bombard elements with particles

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

• Transuranium elements – elements with atomic

numbers greater than 92 which have been synthesized

UUO

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Nuclear Reactions, Radioactivity & Nuclear Energy

C. Detection of Radioactivity and the Concept of Half-

life

• Geiger-Muller counter – instrument which measures

radioactive decay by registering the ions and electrons

produced as a radioactive particle passes through a gas-

filled chamber

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Nuclear Reactions, Radioactivity & Nuclear Energy

C. Detection of Radioactivity and the Concept of Half-

life

• Scintillation counter

instrument which

measures the rate of

radioactive decay by

sensing flashes of

light that the radiation

produces in the

detector

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

C. Detection of Radioactivity and the Concept of Half-

life

• Half-life – time required for

half of the original sample

of radioactive nuclides to

decay

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

Decay of a Radioactive Element

Half of the

radioactive

parent atoms

decay after one

half-life. Half of

the remainder

decay after

another half-life

and so on……..

Half-life activity

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

Half Life Calculations

• For a radioactive decay, Time passed, Half life, Initial

mass and Final mass can be calculated using the

following formula:

initial mass = final mass x 2 (elapsed time/half life)

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

• To learn about some uses of radioactivity in our lives

Objectives

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

Some Uses Of Radioactivity

• Food Sterilization

• Medical Applications and

Radiotracers

• Smoke detectors

• Radiocarbon Dating

• (Energy Production)

• (Weapons)

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Nuclear Reactions, Radioactivity & Nuclear Energy

Food Sterilization

• Gamma irradiation of foods

often from 60Co source

• Spices, herbs and dehydrated

vegetables. Also pork and

poultry

• FDA approved

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

Medical Applications of Radioactivity

• Radioactive nuclides

can be introduced

into laboratory

reactions or

organisms and traced

for diagnostic

purposes.

Radiotracers

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

Medical Applications of Radioactivity - Scanners

• Medical Scanners utilize many types of radiations

X X-Rays – Bone structures opaque to rays

X X-ray computed tomography (CT Scan – X-rays)

X Magnetic Resonance Imaging (MRI – Nuclear magnetism)

X Ultrasound (high frequency sound waves)

√ Positron Emission Tomography (PET Scan)

• Positron emitting tracer into body, concentrates

in organ of interest

• Positrons annihilate with electron giving off pairs

of gamma rays

• Detector maps pair to show image of organ

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

Smoke Detectors

• Americium-241 emits alpha particles and ionizes air in a

space in the detector

• Ions allow a current to flow

• Smoke absorbs alpha particles, interferes with ion

formation and electric current. An alarm sounds

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

Dating by Radioactivity

• Originated in 1940s by Willard Libby

– Based on the radioactivity of carbon-14

Radiocarbon dating

• Used to date wood and artifacts

up to about 50,000 years old

Radiocarbon dating activity

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

1. To introduce fusion and fission as sources of energy

2. To learn about nuclear fission

3. To understand how a nuclear reactor works

4. To learn about nuclear fusion

5. To understand nuclear weapons

6. To see how radiation damages human tissue

Objectives

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

A. Nuclear Energy

• Two types of nuclear processes can produce energy

– Combining 2 light nuclei to form a heavier nucleus -

fusion

– Splitting a heavy nucleus into 2 nuclei with smaller

mass numbers - fission

– Energy produced by conversion of mass, E = mc2

• Sun converts 4 million tonnes per second

Fusion and Fission POGIL

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Nuclear Reactions, Radioactivity & Nuclear Energy

B. Nuclear Fission

• Each atomic fission produces 3 neutrons

• Releases 2.1 1013 J/mol uranium-235

• (Burning methane produces 8.90 x 105 J/mol)

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Nuclear Reactions, Radioactivity & Nuclear Energy

B. Nuclear Fission

• Chain reaction – self sustaining fission process caused

by the production of neutrons that proceed to split other

nuclei Chain Reaction Alternative CR

• Critical mass – mass of fissionable material required to

produce a chain reaction

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Nuclear Reactions, Radioactivity & Nuclear Energy

C. Nuclear Reactors

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

C. Nuclear Reactors

Reactor core

Nuclear Power

Plants

Operation Of Nuclear

Power Plant

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

B. Nuclear Fission

Nuclear Energy in the US?

Chernobyl 1

Chernobyl 2

Chernobyl 3

The Battle Of Chernobyl

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

Nuclear Power Plants in the NJ Area

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

E. Effects of Radiation

• Energy of the radiation

• Penetrating ability of the radiation

• Ionizing ability of the radiation

• Cell repair, death (high dose / acute

damage), incorrect repair (low dose /

cancer)

Factors Determining Biological Effects of Radiation

• Chemical properties of the radiation source

− Strontium-90 and Radium-226 behave similarly to

calcium so tend to accumulate in bones. Radioactive

Iodine concentrates in the thyroid

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Nuclear Reactions, Radioactivity & Nuclear Energy

Penetrating Ability of Radiation

Alpha radiation consists of

helium nuclei and is readily

stopped by a sheet of

paper.

Beta radiation, consisting of

electrons or positrons, is

halted by an aluminum

plate.

Gamma radiation is

dampened by lead

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Nuclear Reactions, Radioactivity & Nuclear Energy

E. Effects of Radiation

Rem: the quantity of ionizing radiation whose biological effect

is equal to that produced by one roentgen of x-rays. Roentgen

is a defined amount of ionization of dry air

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

U.S.Nuclear

Regulatory

Commission

limit of 5,000

mrem/year

above

background

for nuclear

industry

workers

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Nuclear Reactions, Radioactivity & Nuclear Energy

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

D. Nuclear Fusion

• Process of combining two light nuclei

• Produces more energy per mole than fusion

• Powers the stars and sun

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

D. Nuclear Fusion

• Atoms lighter than Fe. Deuterium used

• Requires extremely high temperatures > 100 million K

• Currently not technically possible for use as a power

source – issues with confinement

• Used as “Hydrogen bomb”

• Sun’s energy captured for our use

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

Nuclear Binding Energy

Binding

Energy

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Nuclear Reactions, Radioactivity & Nuclear Energy

Nuclear Weapons

Fission Weapons (“Atomic Bombs”)

− Enriched uranium or plutonium

− Supercritical mass produced in bomb

− Limited up to 500 kilotons of TNT

− Twice used in warfare (Hiroshima and Nagasaki)

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Nuclear Reactions, Radioactivity & Nuclear Energy

Nuclear Weapons

Radioactive fallout can be regulated – salted, neutron bomb

Fusion Weapons (“Thermonuclear

/ Hydrogen Bombs”)

− deuterium and tritium

− fission bomb compresses and

heats hydrogen fuel

− further stages of fission

reactions (depleted uranium)

− largest so far is 57 megatons (“Tsar Bomba” - USSR)

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Nuclear Reactions, Radioactivity & Nuclear Energy

Nuclear Weapons

Delivery

− Gravity bombs

− Missiles (land or submarine launch)

− Multiple Independent Re-entry Vehicles

− “Tactical” weapons: shells, torpedoes

Strategy

− “Cold War, Arms Race”

− “Mutually Assured

Destruction”

− Missile Defense

− Terrorist Threat WWII 1 2 3 4

“Now I am become Death,

the destroyer of worlds”

CHAPTER 19

Nuclear Reactions, Radioactivity & Nuclear Energy

Nuclear Weapons

Regulation

− UN, International Atomic Energy Agency

− Test Ban and Nuclear Non-Proliferation Treaties

− SALT’s and START’s (limitation and reduction)

− Still enough to destroy most human life on Earth (23,000

bombs equivalent to 150,000 Hiroshima bombs)

− US, Russia, China, UK, France, India, Pakistan, North

Korea, Israel (?), South Africa (X)

− Obama (“World without nuclear weapons”)