Nuclear

Question 1

What is the ionising and penetrating power of alpha particles?

Answer 1

Strongly ionising, low penetrating.

Question 2

What is the ionising and penetrating power of Beta radiation?

Answer 2

Weakly ionising, can penetrate several cm of aluminium, or a few meters of air.

Question 3

What is the ionising and penetrating power of Gamma radiation?

Answer 3

Very low ionising, Highly penetrating and can go through several mm of lead and through several meters of concrete.

Question 4

Structure and charge of alpha particle?

Answer 4

2 protons and 2 neutrons, 2+

Question 5

What is beta- decay

Answer 5

When a neutron turns into a proton and releases an electron

Question 6

What is beta+ decay?

Answer 6

When a proton turns into a neutron

Question 7

Explain gamma decay

Answer 7

A way of unstable nuclei releasing extra energy in the form of a electromagnetic wave from a spontaneous process.

Question 8

Explain the effects of ionising radiation:

Answer 8

If it hits an atom it can knock of electrons/ ionise them. These can cause chemical changes, which in the body can damage or kill living cells.

Question 9

How would you investigate the absorption of different types of ionising radiation?

Answer 9

Set up Geiger counter aimed at an absorber (made of aluminium for example). Place counter close to absorber so air particles affect on alpha radiation is minimised. Measure background radiation for a set amount of time. Then place radioactive sample on other side of absorber. Measure activity for set time, then repeat with increasing thicknesses of absorber. Then repeat with each different radioactive source.

Question 10

What is Half thickness?

Answer 10

The thickness of absorbing material needed to half, on average, the number of photons that get through.

Question 11

Define Absorbed Dose and what is it’s units?

Answer 11

The number of Joules per Kilo absorbed by a tissue. Measured in Gray (Gy)

Question 12

Define Effective Dose and what is it’s units?

Answer 12

The Absorbed Dose multiplied by various quality factors that takes into account the type of radiation absorbed and the tissue that has been exposed to it. Measured in Sieverts, Sv.

Question 13

What are the two equations for radioactive risk?

Answer 13

(equivalent dose) * (incidence per Sievert)
and
(probability of event occurring) * (consequence)

Question 14

What is the allowed dose per year for a person?

Answer 14

1000 micro Sieverts per year.

Question 15

Explain the trend of stability for stable isotopes as mass number increases:

Answer 15

Smaller nuclei have equal numbers of protons and neutrons. As mass increases, heavier stable nuclei have more neutrons than protons too overcome electronic propulsion which is negated by the strong nuclear force.

Question 16

What is the strong nuclear force?

Answer 16

A fundamental force which holds nuclei together and opposes the electronic repulsion of protons.

Question 17

What is binding energy?

Answer 17

The amount by which the rest energy of a nucleus is less than the rest energy of the protons and neutrons completely seperated.

Question 18

What is the equation for rest energy?

Answer 18

E[rest] = mc^2

Question 19

What is the name for the difference in mass between a nucleus and the sum of the masses of all of its protons and neutrons completely separated?

Answer 19

Mass defect

Question 20

Equation for binding energy per nucleon?

Answer 20

(Binding energy)/ (no. of nucleon)

Question 21

Explain the trend between the tightness of the bind of a nucleus and the mass of its nucleons:

Answer 21

The tighter the nucleus is bound, the smaller the mass of the nucleons.

Question 22

Explain the Nuclear valley:

Answer 22

Between Hydrogen and Iron (which is the strongest nuclear bonded element) binding energy per nucleon becomes more negative. Atoms “fall down” the valley via nuclear fusion. Elements heavier than iron tend to fall down the valley via alpha decay.

Question 23

Explain why unstable nuclei have less negative binding energies per nucleon:

Answer 23

The nucleons are less tightly bound. Therefore they have a greater mass. This means the difference in mass between these nucleons and nucleons which are completely unbound is less neagtive.

Question 24

What is the definition of an atomic mass unit (u)?

Answer 24

the weighted mean mass of approximately one proton or neutron compared to 1/12th of the mass of a carbon-12 atom.

Question 25

Define nuclear fission:

Answer 25

The splitting of heavy nucleus into smaller nuclei, fast moving neutrons, and energy.

Question 26

Define a chain reaction:

Answer 26

The process in which the products of one nuclear fission go on to start one or more further reactions.

Question 27

What is a nuclear moderator?

Answer 27

A material (usually water) which is used to slow down the speed of neutrons in a reactor, so that they are more likely to be absorbed/ captured into the nuclei instead of being deflected.

Question 28

Why does the use of a moderator and thereby increasing the Volume to Surface area ratio increase the rate of fission?

Answer 28

Fewer neutrons will escape from the large mass of fuel without being absorbed.

Question 29

Define when a reaction “goes critical”.

Answer 29

When the products from each fission are self sustaining and go on to trigger on average one other event.

Question 30

What is the use of control rods in a reactor?

Answer 30

To be able to be lowered and raised into a reactor to moderate the number of neutrons being absorbed, so that the rate of fission can be increased or decreased.

Question 31

Define activity (A) and state its units

Answer 31

The number of nuclei decaying per second. Becquerel, Bq

Question 32

Define half life

Answer 32

The time taken for the number of nuclei in a radioactive source to fall to half the original value. Alternatively, it is the time taken for the activity of a sample to fall to half the original value.

Question 33

Explain how you would determine the half life of a radioactive source:

Answer 33

Measure background count. Place the radioactive source in front of the detector. Record the count of activity every 10 seconds for about 3 mins. Count rate is found by dividing the number of counts in each period by 10. The corrected count rate is found by subtracting the total count rate by the background count rate.

Question 34

How do you determine half life from a graph of count rate against time?

Answer 34

…

Question 35

What is the decay constant, λ, and measure its units.

Answer 35

The probability that a nucleus will decay in a given time.

Question 36

Equation to model radioactive decay?

Answer 36

ΔN/Δ t = -λN

Question 37

Equation linking half life and decay constant?

Answer 37

T[1/2] = (ln2)/λ