P7 Atomic Structure/Radioactivity

Question 1

describe alpha radiation

Answer 1

• 2 protons and 2 neutrons - helium nucleus
• mass of 4
• charge of +2
• range in air around 5cm
• stopped by paper/skin
• low penetrating power
• high ionising power
• represented as (He) (α)

Question 2

describe beta radiation

Answer 2

• fast moving electron
• mass of 0 (very small)
• charge of -1
• range in air around 1m
• stopped by thin metal (aluminium)/plastic
• medium penetrating power
• medium ionising power
• represented as (e) (β)

Question 3

describe gamma radiation

Answer 3

• high frequency electromagnetic wave
• mass of 0
• charge of 0
• range in air infinite (in theory)
• stopped by thick lead/concrete
• high penetrating power
• low ionising power
• represented as (γ)

Question 4

describe neutron radiation

Answer 4

• when the nucleus emits a neutron
• mass of 1
• charge of 0
• represented as (n)

Question 5

describe rutherford’s observations and conclusions in the alpha particle scattering experiment

Answer 5

(fired a beam of alpha particles at thin gold foil and measured where they scattered to)
* most went straight through - atom is mostly empty space
* very few were reflected straight back - nucleus of atom is very small but contains most of the mass
* some were deflected/scattered - positive nucleus

Question 6

describe alpha decay

Answer 6

• an unstable nucleus emits an alpha particle (2 protons and 2 neutrons)
• mass number decreases by 4 and atomic number decreases by 2

Question 6

describe beta decay

Answer 6

• a neutron from the nucleus turns into a proton and an electron, then an electron is released

Question 6

describe radioactive contamination

Answer 6

• when an object has a radioactive source in or on it
• if the type of radiation emitted by the decay of the source’s nuclei is highly ionising, it will be a greater hazard
• the hazard lasts as long as the radioactive material is on the object but reduces over time

Question 6

describe irradiation

Answer 6

• when an object is exposed to radiation from an external source
• the object doesn’t become radioactive - objects are safe after irradiation has stopped so is used for sterilising

Question 7

describe the precautions for irradiation (6)

Answer 7

• wear protective clothing e.g. lead apron
• wear a film badge - monitors dose levels
• carry out procedures remotely (e.g. robots)
• keep your distance/ maximise distance away from source
• limit exposure time
• source held with tongs

Question 8

describe peer review

Answer 8

• where independent scientists check a scientific report before it is published - to see if the method is valid and calculations correct

Question 9

describe the number of half-lives elapsed in correlation to the fraction of unstable nuclei remaining

Answer 9

half-lives elapsed –> fraction of unstable nuclei
0 –> 1/1
1 –> 1/2
2 –> 1/4
3 –> 1/8
4 –> 1/16
5 –> 1/32

Question 10

(uses of nuclear radiation) describe industrial tracers and radiation used

Answer 10

• radioactive source is added to e.g. water sup[ply and GM counter is above the ground detecting radiation - to locate blocked/leaking pipe
• use gamma with short half-life - most penetrating to get through ground above, don’t want the source to be radioactive for too long

Question 10

(uses of nuclear radiation) describe medical tracers and radiation used

Answer 10

• patient swallows/injects radioactive isotope and is detected outside body to trace its path - identify blockages
• use gamma with short half-life - most penetrating to get through body, limit patient’s exposure time

Question 10

(uses of nuclear radiation) describe radiotherapy and radiation used

Answer 10

• source is moved around patient directed at the tumour - to kill cancerous cells
• use gamma with long half-life - most penetrating to get through body, don’t want to have to replace the source often

Question 11

(uses of nuclear radiation) describe sterlising and radiation used

Answer 11

• kills bacteria on food/medical equipment
• use gamma with long half-life - most penetrating to kill all bacteria and least ionising when swallowed, don’t want to have to replace the source often

Question 12

(uses of nuclear radiation) describe smoke alarms and radiation used

Answer 12

• use alpha with long half-life - low penetrating power so it cannot pass through smoke, don’t want to have to replace the source

Question 13

(uses of nuclear radiation) describe thickness control and radiation used

Answer 13

• use beta with long half-life - medium penetrating power so is stopped by thick paper but can pass through thin paper, don’t want to have to replace the source

Question 14

define an isotope

Answer 14

different atoms of an element with different numbers of neutrons (but same number of protons)

Question 15

describe the Geiger Muller tube (G-M) and count rate

Answer 15

• detects nuclear radiation particles
• count-rate - number of decays recorded each second

Question 16

describe radioactive decay

Answer 16

• it is random and impossible to predict (can be estimated)
• activity - the rate at which a nuclei in a source decay, measured in Becquerels (Bq)

Question 17

describe how nuclear radiation/ radioactive materials are hazardous

Answer 17

ionising effects - ionisation of an atom in a cell’s DNA can lead to a copying error (mutation) and cancer

Question 18

define half-life

Answer 18

• average time for the number of nuclei to halve
• time for count rate to halve