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Question 1

Gamma irradiation of foods

Answer 1

Uses gamma rays from 60Co or 137Cs to prevent growth of bacteria to increase shelf life

Question 2

Radon gas

Answer 2

Released from naturally occurring U deposits
Breathed in and decays in the lungs into high energy alpha-emitters e.g. 218/214Po, 214Pb, 214Bi which can cause DNA damage

Question 3

Why is neutron emission rare?

Answer 3

Because neutrons are bound by 8 MeV

Proton emission is even more rare

Question 4

Ionisation

Answer 4

The process by which a neutral atom acquires a positive or negative charge

Question 5

Gamma interactions

Answer 5

Cataclysmic
Have 3 possibilities
1. Pass through with no interaction
2. Interact, lose energy, change direction (Compton effect)
3. Transfer all energy and disappear (photoelectric effect)

Question 6

Compton effect

Answer 6

When an incident photon interacts with an orbital electron to produce an ejected electron (recoil electron) and a scattered photon of less energy than the incident photon

Question 7

Why is alpha radiation the least penetrating?

Answer 7

Large nucleus so will interact with matter quickly

Question 8

Alpha particles have…

Answer 8

…“high linear energy transfer”, can cause great biological damage

Question 9

Effect of shielding high energy beta particles with lead

Answer 9

Can generate more radiation than it shields
“Bremsstrahlung X-rays” - a type of secondary radiation produced as a result of slowing/stopping the primary radiation (beta-particles)

Question 10

Metastable nucleus

Answer 10

= can remain in an excited state for a prolonged period of time

Question 11

Photon emission from X-rays

Answer 11

1. An electron from a lower energy level is removed
2. Electrons from higher energy levels then occupy the resulting vacancy by photon emission - a negatively-charged, high speed electron is attracted towards the positively-charged nucleus which causes it to lose some velocity
3. This deceleration means the electron loses some of its kinetic energy, which is given off in the form of a photon
   * Bremmstrahlung = “braking radiation” - the X-rays produced when accelerating electrons are suddenly decelerated upon collision with a metal target

Question 12

Element with most binding energy per nucleon

Answer 12

56Fe

Question 13

4 nuclei with stable odd/odd numbers of p/n

Answer 13

2D, 6Li, 10B, 14N (18F is radioactive)

Question 14

Magic numbers

Answer 14

2, 8, 20, 28, 50 82, 126

Question 15

4 fundamental fores in nature

Answer 15

Strong
Electromagnetic
Weak
Gravity

Question 16

What holds quarks together in protons/neutrons?

Answer 16

The strong force

Question 17

Neutrons

Answer 17

2 down, 1 up
Free neutrons are unstable (t1/2 = 15 mins)
Down quark splits into up quark and W- then e- i.e. n —> p + e + v

Question 18

Protons

Answer 18

2 up, 1 down
Free protons are stable (t1/2 = >10^33 years)
Unstable nuclei with excess energy can convert an up quark and an electron to a down quark i.e. p + e + energy —> n or p+ —> n + beta+ + v

Question 19

Residual strong force

Answer 19

Holds protons and neutrons together, determines the size of nuclei

Question 20

What holds protons and neutrons together?

Answer 20

Residual strong force

Question 21

The strong force is distance-dependent

Answer 21

Repulsive at <0.7 fm
Very strong at 1 fm
Negligible at >2.5 fm

Question 22

Why is 2He (diproton) an extremely unstable He isotope?

Answer 22

2 protons, 0 neutrons
Pauli exclusion principle forces the 2 protons to have anti-aligned spins which gives the diproton a negative binding energy
Would be more stable if the strong force was 2 % greater

Question 23

Forces in the nucleus

Answer 23

Strong force between quarks by exchange of gluons (very short range)
Residual strong force between protons and neutrons (short range)
Electrostatic repulsion between protons (weaker than the strong force, but can become stronger at >2 fm)
Weak force holds the neutron together (very short range, leads to beta- decay)

Question 24

All members of a decay series…

Answer 24

…differ in A by 4.

Question 25

Thorium decay series

Answer 25

4n

232Th —> 208Pb

Question 26

Neptunium decay series

Answer 26

4n + 1

237Np —> 209Bi

Question 27

Uranium

Answer 27

4n + 2

238U —> 206Pb

Question 28

Actinium

Answer 28

4n+3

235U —> 207Pb

Question 29

14C

Answer 29

Created by cosmic radiation in the thermosphere
t1/2 = 5730years
7.5 kg produced per year - incorporated into CO2 and becomes part of the carbon cycle

Question 30

Beta- emission from living plants

Answer 30

13.6 disintegrations min-1 g-1 (14C)

Question 31

238U:206Pb ratio of 1:1

Answer 31

Means 1 half life has passed