Physics Lecture 8

Front 1

From whence do things things radioactive come from?

Back 1

Accelerators
Fission reactors/Power Reactors=outside the country, Canada, Sweden
Naturally Occurring
Radionuclide Generators

Front 2

Particle Accelerators

Linear Accelerator =

Back 2

Moves particles in a straight path.
Radiation therapy, high energy X-Ray/electrons

Front 3

Cyclotron

Back 3

Moves particles in a circular path.

Front 4

Linear accelerator are usually large.

Back 4

Cyclotron can be kept in a relatively small room.

Front 5

Cyclotrons can produce

Back 5

carrier free material; all useful product.

Front 6

Particles in an accelerator

Back 6

gain energy, can reach one billion volts.

Front 7

Particles must be charged to be accelerated. Use of attractive and repulsive forces

Back 7

are used in an accelerator to speed up the particle.

Front 8

Particles accelerated can be protons, or

Back 8

2H,3H,4H.

Front 9

Energy gained must be sufficient to overcome repulsive attraction

Back 9

of the positive particle and the positive nucleus. There is a threshold energy for these reactions.

Front 10

Accelerating a positive charge particle

Back 10

Enough speed will overcome repulsive forces and create nuclear reactions

Front 11

Isotopes produced by cyclotron used in NM

Back 11

TI-201
I-123
Ga- 67

Front 12

PET isotopes

Back 12

N-13
0-15 = short half life, more for research
F-18

Front 13

Direct reaction
Study

Back 13

Indirect Reaction Study

Front 14

Conseil europeen pour la recherche Nucleaire

Back 14

CERN

Front 15

The largest particle physics laboratory in the world, located at Geneva.

Back 15

Very large accelerators are used to smash particles into each other

Front 16

The fragments of the collisions are detected

Back 16

and studied

Front 17

Experiments have found new short lived fundamental particles. One of the first to be discovered was a third charge particle like the electron and the muon. This new particle called the

Back 17

tau, lives for only one third of a millionth of a millionth of a second (0.3 x 10^-12s)

Front 18

Fissions Reactions
- Largest source

Back 18

All the radionuclides used in nuclear medicine are man made, They are either created in a reactor, or made in a particle accelerator by bombarding a target with charged particles.

Front 19

Study the diagram of

Back 19

the nuclear reactor

Front 20

Spontaneous fission is an extremely unlikely event.

Back 20

Naturally occurring isotopes which meet this condition are very stable against spontaneous fission. Fission mist be initiated by neutrons.

Front 21

235U + n ---->

Back 21

236U fission fragments + neutrons + energy
- binding energy

Front 22

Energy released from one atom of U-235 fissioning is about 200 MeV

Back 22

1.125 g fissioned/MW-d

Front 23

Fission fragments range from Z = 30- 64.

Back 23

The two fragments are usually split in weight in a 60:40 ratio.

Front 24

Criticality (mass)

Back 24

Neutrons produced by a fission reaction lead to more fission reactions.

Front 25

Fission reactions are important for 2 reasons in NM

1.

Back 25

Fission fragments are usually radioactive, if they are separable, they can be used as medical tracers.
I-131 and Mo-99 are fission fragments

Front 26

2.

Back 26

Neutrons are produced in reactors, these neutrons can be used to produce radioactive material through "neutron activation"
- Neutrons enter an atom very easily

Front 27

Fission of U235 usually splits into the atom of about

Back 27

60/40 ratio
235 x 0.6 = 94

235 x 0.6 = 141

Front 28

Nuclear Reactors

a. fuel elements

Back 28

typically U235 or a combination of U235 & U238

Front 29

Natural Uranium is only 0.7% U-235

Back 29

It must be enriched 3-5 % U-235 for use as fuel in a light water reactor
- Weapons grade uranium is 85% U-235

Front 30

Nuclear Reactors
b. moderators

Back 30

low Z material, used to slow neutrons, graphite and water

Front 31

c. control rods

Back 31

control fission reaction rate, composed of material which absorbs neutrons, like boron & cadmium = grab onto neutrons a lot!, neutron affinity

Front 32

Neutron Activation

Back 32

Involves the capture of a neutron by a stable nucleus transforming it into a radioactive substance.

Front 33

(n.y) reaction

Back 33

32P + n --> 33P + y

This is a neutron = gamma reaction

Front 34

Product is always an isotope of the parent, Atomic mass increases by

Back 34

1

Front 35

The parent is never completely activated resulting

Back 35

in the product have a carrier, which is 32 P, never a carrier free.

Front 36

Transmutation

Back 36

the process by which one element is converted into another

Front 37

(n,p) reaction

Back 37

32S + n ----> 32 + p

Front 38

Target and product are

Back 38

isobars!

Front 39

They have different elements so they can be separated chemically resulting in a

Back 39

carrier free product

Front 40

There are no radioisotopes which are neuron emitters for practical purposes.

Back 40

no natural element

Front 41

Radioactivity from these series contributes to a environmental background radiation.

Back 41

Naturally occurring radioactivity does not come only from these series. Other isotopes also naturally occur, the most important for these for human exposure is Potassium - 40

Front 42

Carbon -14 is also an important isotope because it is incorporated in plants. The isotope is continually produced in the

Back 42

atmosphere from Nitrogen-14.

Front 43

Radionuclide Generators

Back 43

box with radioactive in it = it decays into something useful that we need/use

Front 44

Special Cases for Radioactivity

Back 44

Isotopes which decay to other radioisotopes are known as serial transformations.

Front 45

Serial transformations pose an interesting situation which they are in a

Back 45

sealed system

Front 46

Three situations will be considered:

Back 46

1. Secular Equilibrium
2. Transient Equilibrium
3. A No Equilibrium situation.

Front 47

Secular Equilibrium

Back 47

This occurs when the half life of the parent is much greater than the half life of the daughter

Front 48

Secular Equilibrium 2

Back 48

Tp>> td

Front 49

Secular Equilibrium 3
In this situation, the parent decays so slowly it is as if the activity of the parent is constant.

Back 49

As the parent slowly decays, the activity of the daughter increases.

Front 50

It requires about 4 daughter half life's for the activity of the parent and the daughter to reach equilibrium.

Back 50

Equilibrium in this case is when the activity of the parent and the daughter are about constant.

25 days v 75 seconds.

Front 51

Three situations will be considered:

Back 51

1. Secular Equilibrium
2. Transient Equilibrium
3. A No Equilibrium situation.

Front 52

Secular Equilibrium

Back 52

This occurs when the half life of the parent is much greater than the half life of the daughter

Front 53

Secular Equilibrium 2

Back 53

Tp>> td

Front 54

Secular Equilibrium 3
In this situation, the parent decays so slowly it is as if the activity of the parent is constant.

Back 54

As the parent slowly decays, the activity of the daughter increases.

Front 55

It requires about 4 daughter half life's for the activity of the parent and the daughter to reach equilibrium.

Back 55

Equilibrium in this case is when the activity of the parent and the daughter are about constant.

25 days v 75 seconds.

Front 56

The Cardio-Gen 82 is commercially available for

Back 56

Rubidium-82
- PET + nuclear cardiology & Positron emitter

Front 57

Sr-82 with a half life of 25 days, decays to Rb-82 with a half life of

Back 57

75 seconds.
- generator hooked up to patient

Front 58

What can we expect of these isotopes in a closed system?

Back 58

Answer

Front 59

Transient Equilibrium

Back 59

This occurs when the half life of the parent is longer then the half life of the daughter, but not extremely longer.

Front 60

This occurs when the half life of the parent is longer then the half life of the daughter

Back 60

but not extremely longer.

Front 61

Tp > Td
- In this case, as the parent isotope decays, the daughter builds up from zero until

Back 61

it surpasses the parent activity.

Front 62

When the daughter activity reaches its maximum value, the decay of the daughter

Back 62

follows the decay of the parent.

Front 63

When this state of parallel decay is reached, the parent and daughter activates decreases

Back 63

but the ratio of the parent and daughter activities remains constant.
6 days vs 6 hours

Front 64

With transient equilibrium the equilibrium activity of the daughter changes with time because

Back 64

the parent activity is changing. After the condition of equilibrium is reached, the daughter appears to decay with the half life of the parent.

Front 65

No Equilibrium

Back 65

This occurs when the half life of the parent is shorter than the half life of the daughter.