Nuclear Physics

Question 1

Atom

Answer 1

Particle made of protons, (neutrons) and electrons.

Question 2

Element

Answer 2

Type of atom with a specific number of protons.

Question 3

Nucleus

Answer 3

Core of an atom, consisting of protons and neutrons held together by the strong force.

Question 4

Nucleon

Answer 4

Particle in the nucleus i.e. protons and neutrons.

Question 5

Proton

Answer 5

Particle with 1 mass and 1 charge.

Question 6

Neutron

Answer 6

Particle with 1 mass and 0 charge.

Question 7

Electron

Answer 7

Particle with approximately 0 mass and -1 charge.

Question 8

Atomic Number

Answer 8

Z, number of protons in the nucleus of a specific atom.

Question 9

Atomic Mass

Answer 9

A, number of nucleons in the nucleus of a specific atom.

Question 10

Isotope

Answer 10

Type of atom, with specific numbers of protons and neutrons. Isotopes of an element have the same chemical properties due to having the same number of protons but have different physical properties due to differing numbers of neutrons.

Question 11

Nuclide

Answer 11

Specific nucleus, with certain numbers of protons and neutrons.

Question 12

Nuclear reaction

Answer 12

Any process causing changes to a nucleus. Mass number and charge must be conserved.

Question 13

Stable Nuclide

Answer 13

Specific nucleus that will remain the same indefinitely. Strong force is enough to overcome electrostatic repulsion between protons. For light elements (Z<21), require 1:1 ratio of protons to neutrons. For medium elements, require slightly more neutrons than protons. Heavy elements (Z>82) cannot be stable – size of nucleus is too great for the very short ranged strong force to hold it together.

Question 14

Stable isotope

Answer 14

Specific atom with a nucleus that will remain the same indefinitely.

Question 15

Unstable nuclide

Answer 15

Specific nucleus that will spontaneously change to become more stable.

Question 16

Radioisotope/unstable isotope

Answer 16

Specific atom with a nucleus that will spontaneously change to become more stable.

Question 17

Radioactive

Answer 17

Material containing unstable nuclei.

Question 18

Nuclear decay

Answer 18

Emission of particles (or energy) from a nucleus to become more stable.

Question 19

Activity

Answer 19

Number of decay events per second for a radioactive substance

Question 20

Half life

Answer 20

Measure of exponential decay rate for a nuclide. Time for half of the remaining particles to decay.

Question 21

Transmutation

Answer 21

Changing of one nuclide into another through nuclear decay.

Question 22

Daughter nuclide/isotope

Answer 22

Product nucleus of nuclear decay.

Question 23

Decay series

Answer 23

A sequence of nuclear decays through multiple unstable nuclides to an eventual stable nuclide.

Question 24

Nuclear radiation

Answer 24

Particle or energy emitted from a nucleus.

Question 25

Alpha decay

Answer 25

Emission of an alpha particle from a nucleus that is too large to be stable.

Question 26

Beta minus decay

Answer 26

Emission of a beta (minus) particle from a nucleus that has too many neutrons as a neutron becomes a proton.

Question 27

Beta plus decay

Answer 27

Emission of a beta plus particle from a nucleus that has too few neutrons as a proton becomes a neutron.

Question 28

Gamma decay

Answer 28

Emission of a gamma ray from a nucleus that has too much energy to be stable. Commonly occurs after an alpha or beta decay.

Question 29

Ionising radiation

Answer 29

Radiation capable of adding electron to or removing electrons from atoms, turning them into ions. Alpha, beta and gamma radiation.

Question 30

Alpha particle/radiation

Answer 30

He-4 nucleus (2 protons, 2 neutrons). 2+ charge, travels at 0.1c, highly ionising, weakly penetrating.

Question 31

Beta minus particle radiation

Answer 31

Electron. -1 charge, travels at 0.9c, moderately ionizing, moderately penetrating.

Question 32

Beta plus particle radiation

Answer 32

Antielectron/positron. +1 charge, travels at 0.9c, moderately ionising, moderately penetrating. If it collides with an electron they will mutually annihilate emitting gamma radiation.

Question 33

Gamma ray/radiation

Answer 33

High energy photon of light. 0 charge, travels at c, weakly ionising, highly penetrating.

Question 34

Neutron radiation

Answer 34

Neutron. Not ionizing but can be absorbed by a nucleus, potentially transforming it into an unstable nuclide.

Question 35

Mass defect

Answer 35

The difference in mass between a number of free nucleons and that many nucleons as a nucleus. Mass of the binding energy.

Question 36

Binding energy

Answer 36

The energy lost by free nucleons in order to bond together as a nucleus. The energy required to separate all the nucleons in a nucleus into free particles.

Question 37

Binding energy per nucleon

Answer 37

The average energy lost by each nucleon in a nucleus. Measure of stability of the nucleus. Higher binding energy per nucleon – more stable nuclide. Peaks at Fe-56.

Question 38

Nuclear fusion

Answer 38

Joining of light nuclei to form heavier nuclei. Releases energy if the binding energy per nucleon increases, i.e. if moving towards Fe-56.

Question 39

Fusion reactor

Answer 39

Machine maintain stable fusion reaction to generate heat to generate electricity. Requires enormous temperatures and pressures to cause collisions between nuclei, overcoming the electrostatic repulsion. Currently consumes more energy than is produced – developing technology.

Question 40

Nuclear fission

Answer 40

Splitting of heavy nuclei into multiple lighter nuclei (and free neutrons). Releases energy if the binding energy per nucleon increases, i.e. if moving towards Fe-56. Can be spontaneous or triggered by absorption of free neutron.

Question 41

Fissile

Answer 41

Nuclides that will readily undergo fission reactions.

Question 42

Fission reactor

Answer 42

Machine maintaining stable fission reaction, typically to generate heat to generate electricity. Relies on stable chain reaction, fission can be triggered by neutrons and it emits neutrons.

Question 43

Fuel rods

Answer 43

Fuel must be enriched to contain a higher proportion of fissile material.

Question 44

Control rods

Answer 44

Material that absorbs free neutrons to control reaction rate in reactor. Control rods inserted if reaction rate too high.

Question 45

Moderator

Answer 45

Slows neutrons so that they can be more easily absorbed by nuclei to trigger further fission reactions.

Question 46

Shielding

Answer 46

Fission reaction and radioactive fission products emit radiation dangerous to workers. Reaction chamber must be shielded by metres of lead and concrete to absorb radiation, protecting plant workers.

Question 47

Nuclear waste

Answer 47

Fuel lasts a long time but produces waste that remains radioactive for extremely long timespans – must be stored safely.

Question 48

Critical mass

Answer 48

The minimum mass of fuel required to sustain a fission chain reaction. Shape dependent, sphere is most efficient.

Question 49

Absorbed dose

Answer 49

Measure of amount of radiation exposure, based on energy of radiation and mass of target. d=e/m

Question 50

Dose equivalent

Answer 50

Measure of amount of radiation exposure, based on absorbed dose and type of radiation.

Question 51

Electrostatic Force

Answer 51

The long-range force of attraction between unlike charges and repulsion between like charges
The electrostatic and strong nuclear forces are responsible for holding atoms together
The electrostatic attraction between protons and electrons prevents electrons from leaving

Question 52

Strong Nuclear Force

Answer 52

Short range attractive force between nucleons in a nucleus
The strong nuclear force between nucleons balances the electrostatic repulsion between protons and holds the nucleus together
Keeps an atom from falling apart

Question 53

Neutron bombardment

Answer 53

Where neutrons are fired at nuclei until a neutron is absorbed by the nucleus

Question 54

Charge

Answer 54

A property of matter causing electric effects
Charged particles can be deflected by electric and magnetic fields and can be repelled by like charges, reducing their penetrating ability

Question 55

Ionising Ability

Answer 55

The ability of particles or radiation to ionise matter, generally by removing electrons in collisions
Ionising ability increases with increasing charge and decreasing speed

Question 56

Penetrating Ability

Answer 56

A measure of how easily radiation passes through matter
Penetrating ability is greatest for radiation with a low ionising ability, e.g. faster moving, uncharged radiation that does not readily interact with matter

Question 57

Natural transmutation

Answer 57

Alpha and beta decay are examples of spontaneous transmutation, where one element is transformed into another in a natural process

Question 58

Artificial transmutation

Answer 58

Transmutations can also occur when a nucleus is deliberately struck by another nucleus or a subatomic particle, such as an α particle
This is known as artificial transmutation
Artificial transmutations include the nuclear reactions that occur in nuclear reactors and nuclear weapons

Question 59

Nuclear fission and fusion

Answer 59

In these reactions, larger nuclei can split into smaller nuclei (fission) or smaller nuclei can join together into larger nuclei (fusion), releasing huge amounts of energy

Question 60

Fission

Answer 60

In fission reactions, a target nucleus absorbs a neutron before splitting into two or more pieces, often releasing additional neutrons

Question 61

Fission Absorption

Answer 61

A nuclide that can undergo fission is said to be fissile
All fissile nuclides have high atomic numbers (e.g. 235U, 239Pu) and most do not occur naturally
Nuclides that need to absorb a very high energy neutron to undergo fission are said to be fissionable, but non-fissile
Most fission products radioactive

Question 62

Energy release in nuclear reactions

Answer 62

The mass of a nucleus is always less than the mass of its individual nucleons
He showed that mass can be converted into energy (and vice versa) under some circumstances
E = mc^2

Question 63

Binding energy

Answer 63

The energy required to split a nucleus into its individual nucleons (e.g. to split a helium nucleus into two protons and two neutrons)

Question 64

Chain Reaction

Answer 64

For a chain reaction to be sustained, enough of these neutrons must be absorbed by other fissile nuclei
If each fission can induce the fission of two other nuclei, the amount of fission reactions occurring and the energy released will grow exponentially
Whether this occurs depends on the proportion of fissile atoms present in the nuclear fuel

Question 65

Nuclear Fuel

Answer 65

A sufficient percentage of neutrons released must be absorbed by fissile nuclei
Naturally occurring uranium, consists of about 99.7 % non-fissile 238U and 0.7% fissile 235U (too low to sustain chain reaction)
To be used as nuclear fuel, the uranium ore must be enriched to ~4% 235U for nuclear reactors or ~90% for nuclear weapons

Question 66

Enrichment

Answer 66

Enrichment generally occurs by ultracentrifuge or electromagnetic separation or gaseous diffusion separation

Question 67

Critical Mass

Answer 67

The minimum spherical mass of enriched material required for sustained fission

Question 68

Nuclear Reactors

Answer 68

Fuel rods: long thin rods of fissile material
Moderator: material that slows the neutrons so they can be more readily captured
Control rods: material that absorbs neutrons to slow the chain reaction
Coolant: absorbs heat energy released in fission and transfers it to water to produce steam

Question 69

Fuel Rods

Answer 69

Fuel rods typically consist of ~96% 238U and 4% 235U. The 235U undergoes fission, releasing energy and neutrons
While 238¬U is not fissile, it can absorb a neutron and form the fissile isotope 239Pu which can undergo fission, releasing more energy and neutrons
“Fast breeder reactors” take advantage of this reaction to produce more fissionable fuel (in the form of 239Pu)

Question 70

Moderator

Answer 70

The fast moving neutrons released in fission of 235U can be more readily captured by fissile nuclei if they are slowed down
A moderator is a material with small nuclei that is able to slow (moderate) these neutrons when they collide
Heavy water, graphite, H2, CO2

Question 71

Control Rods

Answer 71

If the nuclear chain reaction is able to continue in an uncontrolled manner, it will grow exponentially releasing more and more energy any neutrons
Control rods act to control the rate of fission by absorbing neutrons into their nuclei, preventing those neutrons from causing addition fission reactions
Boron

Question 72

How a Nuclear Reactor works

Answer 72

A nuclear reactor core consists of the fuel and control rods inserted into the moderator
The control rods are raised or lowered into the core to control the rate of fission
The heat produced by fission heats the coolant which is piped to a heat exchanger/boiler
Heat from the coolant is used to boil water to produce steam which drives the turbines that power the generator

Question 73

Nuclear Waste

Answer 73

While nuclear power is one of the safest power sources in terms of deaths per GW of electricity generated, it does produce waste that remains radioactive for thousands of years
This waste mostly consists of fission fragments produced in the decay of uranium and plutonium

Question 74

Nuclear Fusion

Answer 74

2 small nuclei fuse to make bigger one
Fusion releases more energy per nucleon than fission and does not produce radioactive waste (e.g. fission fragments)
Very difficult to achieve, electrostatic force of repulsion must be overcome to force nuclei close enough so strong nuclear force can take over

Question 75

Nuclear Fusion must overcome repulsion

Answer 75

To overcome this repulsion, the reactants must have extremely high kinetic energies (e.g. hundreds of millions of degrees, as found in stars)
In our sun, huge temperatures and gravitational pressure forces hydrogen and helium isotopes to fuse in the following reactions

Question 76

Higher binding energy

Answer 76

Nuclei with a higher binding energy are more stable as they take more energy to break apart

Question 77

Iron 56

Answer 77

Iron-56 has the highest binding energy per nucleon (e.g. is the most stable nucleus) with binding energy decreasing as mass number decreases or increases

Question 78

Very stable nuclei, what mass number?

Answer 78

Nuclei with a mass number between 40 and 80 are very stable due to their high binding energy

Question 79

Nuclei larger than iron

Answer 79

Nuclei larger than iron can undergo fission, releasing the extra binding energy as a lighter, more stable nuclei are formed resulting in a mass defect

Question 80

Nuclei smaller than iron

Answer 80

Nuclei smaller than iron can undergo fusion, releasing the extra binding energy as a larger more stable nucleus (that has a lower mass than the combined mass of the reactants) is formed

Question 81

Applications of fusion

Answer 81

Hydrogen bombs
The extreme temperatures required for fusion make it very difficult to design these reactors and commercial fusion reactors have not yet been developed
Fusion reactors have been a target of research, due to their potential to generate electricity without producing large amounts of harmful nuclear waste or greenhouse gases

Question 82

Pest control

Answer 82

Small pests (e.g. aphids, as seen in the diagram to the right) can be sprayed with radioactive materials. Sometime later, a range of predators in the area are captured. The main predator of the pest can easily be identified as it will be the one that has the largest quantity of the radioactive isotope inside it. This knowledge is then used when releasing natural predators to provide biological control of pests.

Question 83

Sterile Insect Technique

Answer 83

Male insects can be sterilised using gamma radiation and then released into the wild. They mate with females which then lay eggs that are infertile. Over time, this reduces the population of that insect.

Question 84

Tracers in Plants

Answer 84

Phosphorus 32 injected into root of plant. Geiger counter used to detect movement and concentration of element through plant, helping biologist find how plant grows and reproduces.

Question 85

Thickness Gauges

Answer 85

Beta radiation used because it can be stopped by thicker metal but passes through thinner metal. If material is too thick, reading decreases and rollers adjusted to make material thinner. Opposite if reading too high.

Question 86

Leaks in Underground Pipes

Answer 86

Leaks detected by adding small amount of gamma emitting radioisotope to fluid. Area above ground where high concentration of radiation is detected corresponds to leak in pipe.

Question 87

Gaps in welds

Answer 87

Penetrating radiation passed through weld on radiographic film resulting in image of objects internal structure being formed on film. Energy absorbed by object is proportional to its thickness and energy. Energy not absorbed = exposure of the radiographic film. These areas will be dark on film. Areas of film exposed to less energy remain lighter. Areas of object where thickness has been changed by porosity and cracks appear darker.

Question 88

Why are fission fragments radioactive?

Answer 88

Heavy isotopes require more neutrons to keep them stable. When fission occurs, there’s an excessive ratio of neutrons to protons. Therefore, the fragments undergo beta decay to try and become stable.

Question 89

Explain whether an alpha emitter would be a more suitable radiation source to be used in the thickness detector.

Answer 89

No, Alpha particles have low penetrating ability and will be stopped by the plastic sheet

Question 90

Would it be reasonable to use tritium as a radioisotope in medical treatment or diagnosis? Explain your reasoning.

Answer 90

No, it would be hard for the body to absorb a form of hydrogen gas for diagnostic purposes. The half life of the tritium is also too long for a radioactive isotope to be in the body emitting Beta negative particles.

Question 91

Describe how the neutrons released in this reaction differ from those that took part in the initial fission reaction.

Answer 91

Uranium-235 can only absorb slow neutrons but the neutrons produced will have much greater speed when the nucleus splits

Question 92

State and explain two precautions that workers at customs would employ to prevent any unwanted personal health issues.

Answer 92

Shielding from device: gamma rays require ~2m of concrete or many cm of lead to absorb the ionising radiation and prevent the workers from receiving an absorbed dose
Distance: workers would distance themselves from the device when in operation as the intensity is
inversely proportional to distance squared

Question 93

Why is iodine-123 selected for different procedures?

Answer 93

Gamma has a lower ability to ionise hence less destructive to other cells. Gamma has greater penetrating ability than alpha or beta. Short half-life to reduce exposure time. Ability to concentrate at thyroid (if for thyroid cancer)

Question 94

State the major obstacle needed to overcome in order to create a fusion reactor.

Answer 94

To create a fusion reaction, a large amount of energy is needed. The hydrogen particles must have sufficient kinetic energy to collide and fuse.

Question 95

State and explain two benefits of a fusion reactor compared to a fission reactor.

Answer 95

No dangerous nuclear waste. Fusion is typically creating elements with low mass numbers that are stable.
Greater energy released per fusion number of nucleons/mass. About 10 times greater energy released

Question 96

State and explain two ways the medical team can reduce or eliminate the effects of radiation on their own body:

Answer 96

Shielding from radiation. Staff can wear lead aprons or stand behind dense walls (concrete). These
materials stop the radiation.
Increase distance from source. Radiation can only travel a set distance in air.

Question 97

Are fast neutrons or slow neutrons more damaging to humans? Explain why.

Answer 97

The effect of radiation on humans is measured in terms of the quality factor. The quality factor for fast neutrons is 10 compared to 3 for slow neutrons. This is because of the higher energy of the fast neutrons and they will therefore be more harmful.

Question 98

Explain in detail how you could determine the type of radiation emitted.

Answer 98

Use the Geiger counter to measure the background radiation and then the activity of the sample at a certain distance. Measure activity at the same distance with some paper in the way. Measure activity at the same distance with aluminium foil in the way. Subtract background radiation from all measurements. If the activity didn’t change, it’s gamma radiation, if the activity decreased a lot with paper, it’s alpha radiation, and otherwise beta radiation.

Question 99

Gamma knife

Answer 99

Many sources of gamma rays are placed around the head, all aimed at cancer in the brain.
Each individual beam of gamma rays is too weak to cause significant damage.
* The individual beams intersect at the cancer, so it receives a much higher dose of radiation.

Question 100

Why are fission fragments radioactive?

Answer 100

Heavy isotopes need more neutrons to keep stable so when fission occurs, the fragments have an excessive ratio of neutrons to protons, so they undergo beta decay in an attempt to be stable.

Question 101

SPECT

Answer 101

Single photon emission computerised tomography. Detected by gamma camera.

Question 102

PET

Answer 102

Positron Emission Tomography
Position emitting radionuclide injected and accumulates in target tissue. As it decays it emits a positron which combines with a nearby electron resulting in 2 gamma rays in different directions. Detected by PET camera. Most used in oncology. Fluorine 18 tracer.

Question 103

PET-CT

Answer 103

PET with computed X ray tomography (CT)

Question 104

PET-MRI

Answer 104

Good for brain imaging, enables diffusion weighted imaging in soft tissue with dynamic contrast and magnetic resonance imaging

Question 105

Nuclear imaging and other techniques (X rays)

Answer 105

Difference is the positioning of radiation source. Inside (nuclear), outside (xray).

Question 106

Gamma imaging

Answer 106

Provides a view of the position and concentration of the radioisotope within body.
Organ malfunction indicated if isotope is partially taken up in organ (cold spot) or excess (hot spot).

Question 107

Advantage of Nuclear Imaging over X ray

Answer 107

Both bone and soft tissue can be imaged successfully

Question 108

Diagnostic Pharmaceuticals

Answer 108

Some chemical are absorbed by specific organs. You can attach various radioisotopes to biologically active substances. Once a radioactive form of these substances enters body, its incorporated into normal biological processes and excreted in usual ways.

Question 109

What do diagnostic pharmaceuticals do?

Answer 109

Theyre used to examine blood flow to brain, funcitoning of liver, lungs, heart, to asses bone growth. It can predict the effects of surgery and assess changes since treatment

Question 110

Radiation dose

Answer 110

Amount of pharmaceutical given is just sufficient to obtain required info before decay. Its medically insignificant. Paitent experiences no discomfort. Radioisotope must emit gamma rays of sufficient energy to escape from body and short enough half life to decay as soon as imaging finished

Question 111

Technetium 99 - in 80% of nuclear medicine procedures, isotope of artificially produced technetium

Answer 111

Half life 6 hours long enough to examine metabolic processes, short enough to minimise radiation dose
Decays by isomeric process (emitting gamma, low energy electrons so no high energy beta emission, radiation dose to patient low)
Low energy gamma escape body easily, accurately detected
It can form tracers by being in biologically active substances

Question 112

Technetium Generators

Answer 112

Lead pot in glass tube containing radioisotope
Contain Molybdenum 99, half life 66hrs, decays to Tc99
Tc 99 washed out of pot when required

Question 113

Flurodeoxyglucose (FDG) F-18

Answer 113

Main radiopharmaceutical
Half life under 2 hours as a tracer
Readily incorporated into cell without being broken down, good indicator of cell metabolism

Question 114

Radiosurgery

Answer 114

Cancerous growths are sensitive to damage by radiation. Some cancerous growths are controlled or eliminated by radiation by irradiating area containing growth, this is radio surgery.

Question 115

Tele-therapy (external irradiation)

Answer 115

Using gamma bean from radioactive Co-60 source. External radiation procedure known as gamma knife radiosurgery involves focusing gamma radiation from 201 sources of Co-60 on precise area of brain with cancerous tumour.

Question 116

Internal radionuclide therapy (brachytherapy)

Answer 116

Planting small radiation source, gamma or beta emitter in target area. Short rage radiotherapy known as brachytherapy. Iodine 131 mainly used for thyroid cancer. Gives less overall radiation to body and more localised to target tumour, cost effective.

Question 117

TAT Targeted Alpha Therapy

Answer 117

Short range of every energetic alpha emissions in tissue means alot of radioactive energy goes to cancer cells.

Question 118

NCEPT Neutron Capture Enhanced Particle Therapy

Answer 118

Inject the paitent with neutron capture agent before irradiation with protons or heavy ions
This boosts target dose without increasing dose to healthy tissue and delivers significant dose

Question 119

Therapeutic Radiopharmaceutical

Answer 119

For some medical conditions its useful to destroy or weaken malfunctioning cells using radiation. Beta radiation causes destruction of damaged cells. This is radionuclide therapy (RNT) or radiotherapy. Short range radiotherapy is brachytherapy.

Question 120

Ideal therapeutic radioisotope is a strong beta emitter with just enough gamma to enable imaging

Answer 120

Lutetium-177 and Yttrium-90