Lecture 7

Question 1

What does Ionising mean

Answer 1

Ionizing is the process by which atoms gain or lose one or more electrons, resulting in the formation of ions with a net electrical charge

Question 2

What is alpha radiation and is it penetrating or ionising

Answer 2

a Helium nucleus (some gamma is also released)
not penetrating
ionising

Question 3

What is beta radiation and is it penetrating or ionising

Answer 3

an electron/positron (antielectron)
moderately penetrating
moderately ionising

Question 4

What is gamma radiation and is it penetrating or ionising

Answer 4

electromagnetic waves (short wavelength) emitted by an excited nucleus
very penetrating
not very ionising

Question 5

What is neutron radiation and is it penetrating or ionising

Answer 5

free neutrons
very penetrating
not very ionising

Question 6

Absorbed dose

Answer 6

measure of the energy deposited in joules/kg by radiation which is incident on a material that absorbs it.

Question 7

what is attenuation and what is the use of the term

Answer 7

different materials will adsorb radiation with different efficacy
describes the best materials to shield from radiation

Question 8

What is specific activity

Answer 8

amount of radioactivity found in a gram of material

Question 9

Do radioactive materials with long or short half lives have low specific activity
and why

Answer 9

Long half lives
because the activity is very low because the decay is slow and the radiation emitted at a slower rate

Question 10

What is the unit of radioactivity

Answer 10

Bequerel (1 disintegration peer second)

Question 11

What is the unit of equivalent dose

Answer 11

Sievert (8 = death)

Question 12

What is used to detect radiation

Answer 12

Friction

Question 13

In terms of detection what does more charge mean

Answer 13

More friction

Question 14

In terms of detection what does more massive mean

Answer 14

More friction

Question 15

In terms of detection what does more friction mean

Answer 15

A shorter range

Question 16

In terms of collisions what causes the biggest damage to lattices (think cricket explaination)

Answer 16

Bigger and more charged particles will cause more damage (meaning alpha does lots of damage and gamma does not a lot)

Question 17

How far can you detect alpha vs gamma

Answer 17

Alpha not far at all
Gamma very very far

Question 18

What are good shielding materials

Answer 18

Lead, concrete, polyethalyne

Question 19

What are good shielding materials for neutrons

Answer 19

Something hydrous like concrete and water

Question 20

Describe the attenuation mechanism - photoelectric effect

Answer 20

low energy gamma radiation, kicks out an electron, electron from higher shell drops down, this emits a characteristic energy which can be detected
all gamma is absorbed creating peak

Question 21

Describe the attenuation mechanism - compton scattering

Answer 21

medium energy gamma, more energy than photoelectric effect, (like billiards), gamma hits an electron in a higher shell which becomes a scattered electron, the gamma becomes a lower energy scattered gamma ray, the energy gained by the electron is equal to the energy lost by the gamma ray
not all gamma is absorbed so can continue to hit other electrons and so the signal released is not as simple

Question 22

Describe the attenuation mechanism - pair production

Answer 22

A very high energy photon (gamma) interacts with the nucleus to create an electron/positron pair. The positron then hits another electron and causes an anihilation creating a distinct peak

Question 23

Types of detectors

Answer 23

Gas and Solid state

Question 24

Example of gas detectors
Postives

Answer 24

geiger counter
clicks to tell you if there is radiation but not what type
Electric field induces ionisation which causes a cascade and therefore it clicks

Question 25

Example of solid state detectors
Postives

Answer 25

Scintillator - flash of light when something interacts with it

Question 26

What are the three regions on the gas aplification curve

Answer 26

1) Recombination regaion
2) Ionisation region
3) Proportional region
4) Limited proportional region
5) Geiger-Mueller region
6) Continuous discharge region

Question 27

What are the advantages and disadvantages of the Geiger-Muller Gas-Filled detectors

Answer 27

ADV
highly sensitive
less insulation required to decrease noise interferance

DISADV
no single detector setup can discriminate between alpha, beta and gamma
no energy discrimination
entire gas volume ionises
limited use in extreme intensity radiation fields