Half Life

Question 1

Why do we measure radioactive decay in half life

Answer 1

Radioactive decay never reaches zero
It just gets slower after each decay happens and an alpha, beta or gamma radiation is given out
The more unstable nuclei disappear first and the more stable nuclei remain longer
So we use half life to measure how quickly the activity drops off

Question 2

Definition of half life

Answer 2

Average time it takes for the number of nuclei in a radioactive isotope sample to halve
OR
The time for the count rate from a sample containing the isotope to fall to half it’s starting level

Question 3

How do calculate and show on a graph

Answer 3

Graph will always have a shallowing curve

Equation will always be dividing by 2

Question 4

What is used to detect radiation

Answer 4

Geiger counter

Question 5

Radiation can be particles or waves

Answer 5

Yes it can be both

Question 6

Natural radiation around is known as …..

Answer 6

Background radiation

Question 7

Is it possible to say when a nucleus will decay

Answer 7

No the process is random

Question 8

What is the activity of a radiation source

Answer 8

How many particles it emits each second

Question 9

Where is nuclear radiation always emitted from

Answer 9

The nucleus of the atom

Question 10

What is net decline

Answer 10

Overall amount that the activity of a source has fallen over a period of time

Question 11

What units are Becquerel

Answer 11

Particles decayed per second

Bq means one nucleus decaying per second

Question 12

What are the medical uses of radiation - tracers

Answer 12

Short half life beta or gamma emitters
Certain isotopes injected or swallowed and their progress round body using external detector- computer display
Eg iodine -131 absorbed thyroid gland giving out radiation so we can measure if thyroid taking in iodine as it should

Always beta or gamma so pass out of body quickly - short half life

Question 13

Medical uses - radiotherapy

Answer 13

Treatment of cancers using gamma rays
High doses kill living cells
Must be directed carefully at right dose to kill cancer cells without damage to many other cells
Damage is inevitable so patient is ill but it may still kill the cancer

Question 14

Other uses - for sterilisation

Answer 14

Sterilisation of food - gamma rays will kill microbes and keep food fresh for longer
Medical instruments sterilised same way rather then boiling them
Advantage is that it doesn’t involve high temperatures so fresh food and plastics not destroyed
Food is not radioactive
Isotope must be strong gamma emitter with long enough half life so not replaced too often

Question 15

Other uses smoke detectors

Answer 15

Alpha radiation- weak emitter needed
Close to electrodes
Cause ionisation and current flows between electrodes
Fire smoke absorbs radiation so current stops and alarm sounds

Question 16

Explain radiation damage and reasons

Answer 16

The higher the radiation dose the more at risk of developing cancer
Dose depends on location and occupation
1. Underground rocks eg granite can be higher and radon traps in houses
2. Nuclear workers and miners 10x more likely - protective clothing, masks, special radiation badges monitors and check ups
3. Radiographers in hospitals - lead aprons, lead screens
4 high altitudes background radiation increases (cosmic) so pilot risk
5 underground increases due to rocks - risk to miners

Question 17

Explain deflection of alpha and beta particles

Answer 17

Alpha = + charge
Beta = - charge
Deflected by magnetic or electric field both are deflected in opposite direction
Alpha deflected less because have greater mass
Gamma radiation is electromagnetic wave - no charge so no deflection

Question 18

Safety - how does it harm the body

Answer 18

Alpha beta and gamma enter cells and collide with molecules causing ionisation and destroys molecules
Low dose = minor damage and not kill cell but can cause mutant cells which divide uncontrollable- this is cancer
High dose = kill cells = radiation sickness
Extent of harm depends on how much exposure and energy penetration

Question 19

Which rays are most Dangerous

Answer 19

Outside body - beta and gamma can penetrate to organs but alpha can’t penetrate skin
Inside body - alpha most dangerous in localised area but beta and gamma mostly pass straight out