Ionizing Radiation and Risk

Question 1

What is an alpha particle in terms of mass, constituents and charge?

Answer 1

⁴₂He²⁺= α

Question 2

What is beta-minus, or beta radiation?

Answer 2

A high speed electron (charge -1) - β^-

Question 3

What is beta-plus radiation?

Answer 3

High speed positrons, β⁺

Question 4

What is gamma radiation?

Answer 4

High frequency (high energy) electromagnetic waves of zero mass and charge - γ

Question 5

What are the defining characteristics of alpha radiation?

Answer 5

Alpha radiation is slow, strongly ionising, **easily absorbed by a few cm of paper or air **and is affected by magnetic fields.

Question 6

What are the defining characteristics of beta-minus radiation?

Answer 6

Beta-minus radiation is fast-moving, weakly ionising, **absorbed by ~3cm of aluminium **and is affected by magnetic fields.

Question 7

What are the defining characteristics of gamma radiation?

Answer 7

**Gamma **radiation is very weakly ionizing, travels at the speed of light, **absorbed by many cm of lead **or a few m of concrete and is not affected by magnetic fields.

Question 8

Why is beta-plus radiation not worthy of concern in most situations?

Answer 8

Because it is annihilated almost instantly by an electron.

Question 9

What happens to the intensity of gamma radiation as it passes through concrete?

Answer 9

It decreases exponentially.

Question 10

What is the Gray (Gy) a unit of measurement for?

Answer 10

Absorbed dose of radiation.

Question 11

What is the absorbed dose of radiation?

Answer 11

The energy absorbed per kilo - E/m = Dose [Gy]

E = energy in joules

m = mass in kg

Question 12

What factors is radioactive tissue damage dependent upon?

Answer 12

The type of ionizing radiation and the type of body tissue.

Question 13

Why is a measurement of effective radiation does helpful?

Answer 13

Because it allows comparisons between body tissues.

Question 14

The Sievert [Sv] is a measurement of what?

Answer 14

Effective radiation dose.

Question 15

Effective dose = ?

Answer 15

Absorbed dose x Radiation quality factor

Question 16

Why are alpha particles strongly ionizing and quickly?

Answer 16

Alpha particles are highly positively charged and can easily release an electron from its atom - they transfer energy from themselves to the atom, doing this approximately 10 000 times before losing its energy.

Question 17

Why is β^- radiation weakly ionizing?

Answer 17

β^-’s high speed means it is still able to remove electrons from their atoms, in spite of its low mass and relative charge. It also interacts with fewer atoms than α radiation does before losing all of its energy.

Question 18

What determines a radiation’s quality factor?

Answer 18

How many atoms it ionizes before losing all of its energy - how many ‘interactions’ it has.

Question 19

What is risk equivalent to?

Answer 19

Risk = Probability x Consequence

Probability = how likely it is to happen

Consequence = how severe the effects would be were it to happen

Question 20

What are the uses of radiation?

Answer 20

Power generation by nuclear reactors.

Medicine - treatment and diagnosis.

Food preservation and treatment - radiation can be used to delay ripening and kill harmful microorganisms.

Question 21

What is a risk with great consequence but low likelihood?

Answer 21

A nuclear reactor meltdown.

Question 22

When is it acceptable to take the risk of using radiation to treat cancerous cells?

Answer 22

When the treatment would improve or prolong the patient’s life.

Question 23

Describe binding energy.

Answer 23

Binding energy is the energy which would be required to seperate all the nucleons in a nucleus and it is equivalent to the mass defect. It is also measured in MeV.

Question 24

Why is it that when nucleons join together, they release energy?

Answer 24

Because their total mass decreases - this mass (the ‘mass defect’) is converted into energy and released.

Question 25

How much energy is released when nucleons join together?

Answer 25

The mass defect, converted according to the mass-energy equivalence equation (E=mc²).

Question 26

Binding energy per nucleon = ?

Answer 26

Binding energy ------------------------- Nucleon number

Question 27

Why is it that all unstable nuclei tend towards the formation of Iron (nucleon number 56)?

Answer 27

Because Iron has the largest binding energy, and is thereby the most stable nucleus.

Question 28

What type of nuclear reaction do nuclei with a nucleon number less than 56 favour?

Answer 28

Fusion

Question 29

What is nuclear fusion?

Answer 29

The combining of nuclei to form larger, more stable nuclei of a higher binding energy per nucleon. Lots of energy is released by nuclear fusion, and that energy is equivalent to the mass defect between the reactants and the product.

Question 30

Describe nuclear fission.

Answer 30

The splitting of nuclei to form small nuclei and emit neutrons and gamma ray photons; these smaller nuclei have a higher binding energy per nucleon and are therefore more stable.

Question 31

What is the change in binding energy for the nuclei of a fusion or fission reaction equal to?

Answer 31

The energy released by that fusion or fission reaction.

Question 32

What nuclei size, by proton number, is classed as the smallest that will fission?

Answer 32

Nuclei with at least 83 protons are prone to fission because they are unstable.

Question 33

What does the likelihood of spontaneous fission increase with?

Answer 33

Nuclear size.

Question 34

Why is there a limit to the number of possible elements?

Answer 34

Because as the mass of a nucleus increases, so too does its likelihood of spontaneous fission. Spontaneous fission limits nucleon number, thereby limiting the number of possible elements.

Question 35

Why does fission release energy?

Answer 35

Because smaller nuclei have a larger binding energy per nucleon.

Question 36

How is fission induced?

Answer 36

By firing a neutron at a massive nucleus, such as ²³⁵U, causing it to become more unstable and fission.

Question 37

What is fuel is used in nuclear fission reactors?

Answer 37

²³⁵U

Question 38

Describe nuclear fission in a nuclear reactor.

Answer 38

A neutron is fired at a ²³⁵U nucleus, causing it to become unstable and fission. This further produces more neutrons which collide with other ²³⁵U nuclei and cause further fissioning. A moderator (such as water) must be used to slow the emitted neutrons (thermal neutrons) down to allow them to induce fission in other nuclei.

Question 39

What is critical-mass?

Answer 39

The amount of fuel in a nuclear reactor at which there is a steady rate of fission and thereby energy production; 1 fission induces 1 more, and so on.

Question 40

What is super-critical mass for a reactor?

Answer 40

When more than one fission is induced by one fission - i.e. there is enough fuel that, if left unmoderated, the energy production of the reactor would increase exponentially.

Question 41

What mass amount do nuclear reactors use? How do they control this?

Answer 41

Nuclear reactors use a super-critical amount of mass, and moderate their reactions using boron control rods, which absorb neutrons, preventing them from causing further nuclei to fission.

Question 42

How does a nuclear reactor produce energy?

Answer 42

Coolant is passed through the reactor chamber to absorb the energy released from nuclear fission of ²³⁵U; this reactant then heats a tank of water, which turns to steam and runs a turbine.

Question 43

What is the best type of moderator to have for a nuclear reactor?

Answer 43

A moderator which absorbs more neutrons as the reactor heeats up - this type of moderator reduces the likelihood of meltdown.

Question 44

What should be done, then what can be done with the waste products of nuclear fission for power production?

Answer 44

The waste should first be cooled by placing it in cooling ponds, then it can be used as either a tracer in medicine or buried underground in sealed containers.

Question 45

What force must be overcome in order for two nuclei to fuse?

Answer 45

The electrostatic repulsion force between the nuclei - once the two nuclei are close enough, they interact via the strong force and fuse.

Question 46

How much energy is required to fuse two nuclei?

Answer 46

Approximately 1MeV.

Question 47

Describe hydrogen fusion.

Answer 47

Hydrogen fusion is the combining of two hydrogen nuclei (deuterium and tritium) to produce a ⁴He nuclueus and lots of energy.

Question 48

Where does fusion occur naturally? Why is it able to occur there?

Answer 48

In stars - it is able to occur in them because they are hot and strip all their atoms of their electrons, forming a hot plasma (ionic gas). These nuclei then fuse to produce a larger nuclei of a higher binding energy, producing more energy within the star.