Radioactivity

Question 1

What are the main 3 decay modes?

Answer 1

1) Alpha
2) Beta
3) Gamma

Question 2

Describe the chart of nuclides

Answer 2

Question 3

Radioactive decay is a __________ process.

Answer 3

Statistical

Question 4

What is the decay law?

Answer 4

The rate at which nuclei decay is proportional to the number of nuclei, N. λ represents the decay constant.

Question 5

Give the equation for the number of decaying nuclei at a given time

Answer 5

N = number of decaying nuclei
N_0 = initial number of nuclei
λ = decay constant
t = time

Question 6

Give the equation for activity

Answer 6

A = activity
λ = decay constant
A_0 = initial activity
t = time

Question 7

Give the equation for half life

Answer 7

T_1/2 = 0.5 half life
λ = decay constant
τ = mean lifetime

Question 8

Describe a graph of radioactive decay

Answer 8

Question 9

What is a Becquerel (Bq)?

Answer 9

One Becquerel is the amount of radioactive matierial in which there is an average of one disintegration per second.

Question 10

What is a Curie?

Answer 10

Question 11

What happens to activity if multiple radioactive species are mixed together?

Answer 11

The activity of the species is added.

Question 12

What is a decay chain?

Answer 12

The sequence when a radioactive parent nuclide decays into a daughter nuclide and so on.

Question 13

Give the equation for the rate of change of a daughter nuclei within a decay chain

Answer 13

Term 1 = rate of change in number of nuclei
Term 2 = - rate of decay of parent nuclei (= rate of formation of daughter nuclei)
Term 3 = rate of decay of daughter nuclei

Question 14

Define equilibrium

Answer 14

The point when products decay at the rame rate thay they are produced.

Question 15

Give the equation for the rate of a nuclear reaction

Answer 15

N = number of nuclei
t = time
R = reaction rate

Question 16

Give the equation for activity in terms of reaction rate

Answer 16

A = activity
λ = decay constant
N = number of nuclei
R = reaction rate
[term] = saturation factor

Question 17

_________ is the opposite of decay.

Answer 17

Activation

Question 18

Define absorbed dose (D)

Answer 18

The energy absorbed per unit mass of material from any kind of ionising radiation, measured in Gray (1 Gy = 1 J/kg).

Question 19

Define equivalent dose (H)

Answer 19

The dose delivered, considering the biological effects of different forms of radiation on living tissue. It is measured in sieverts (1 Sv = 1 J/kg).

Question 20

Give the equation for equivalent dose

Answer 20

H = equivalent dose
w_R = radiation weighting factor
D = absorbed dose

Question 21

Define effective dose (E)

Answer 21

The dose delivered, considering the differences of response from different tissues to an equivalent dose of radiation. It is measured in sieverts (1 Sv = 1 J/kg).

Question 22

Give the equation for effective dose

Answer 22

E = effective dose
∑w_T = summ of tissue weighting factors
H = equivalent dose

Question 23

What are tissue weighting factors based on?

Answer 23

Radiative late effects.

Question 24

State 2 natural sources of radioactivity

Answer 24

• Extraterrestrial sources (cosmic rays)
• Radioactive elements in the Earth’s crust

Question 25

What are the three chains of radioactive elements found in the Earth's crust?

Answer 25

1) The Uranium series 2) The Thorium series 3) The Actinium series

Question 26

State 3 man made sources of radioactivity

Answer 26

- Neutron induced fission (e.g. nuclear reactors) - Neutron activation (neutron capture) - Beams of charged particles from accelerators

Question 27

Give the equation for the rate of a nuclear reaction

Answer 27

R = reaction rate σ = cross section Φ = flux of incident particles N = number of irradiated nuclei

Question 28

Define nuclear fission

Answer 28

The process in which a heavy nucleus (e.g. uranium) is caused to split into two lighter nuclei plus several neutrons. This process emits lots of energy and produces several radioactive products.

Question 29

All fission fragments are _______ ____ and ________.

Answer 29

Neutron rich Unstable

Question 30

What happens to fission products following the reaction?

Answer 30

They decay via a series of beta minus decay until a stable nucleus is reached.

Question 31

What is neutron activation?

Answer 31

When a stable nuclide absorbs a neutron to produce a radioactive isotope of the same element. The product normally decays via beta- emission.