physics paper 2 radioactivity

Question 1

why is an atom radioactive?

Answer 1

its got an unstable nucleus, so it decays and emits radiation- carbon-14 is an unstable isotope of carbon

Question 2

what is nuclei decay unaffected by?

Answer 2

physical conditions like temp or chemical bonding it’s all spontaneous. the nuclei of unstable isotopes break down randomly

Question 3

4 sources of background radiation

Answer 3

1- substances on Earth-air, food, building materials, ROCKS
2- radiation from space- cosmic rays from the Sun
3- living things
4- human activity -nuclear explosions or waste

Question 4

what does the nucleus decay into?

Answer 4

spits out one or more of alpha beta gamma in the process the nucleus often changes into a new element

Question 5

what is ionisation?

Answer 5

bashing into atoms and knocking electrons off them- atoms turn into ions which are charged

Question 6

the more penetrating the source the less..

Answer 6

ionising it will be

Question 7

how can you detect ionising radiation?

Answer 7

with photographic film which becomes exposed or used a Geirger-Muller detector

Question 8

what are alpha particles?

Answer 8

helium nuclei- 2 protons and neutrons- they’re big, heavy and slow-moving so don’t penetrate for into materials and stopped quickly.
This makes them strongly ionising, bash into a lot of atoms and knock off electrons before they slow down, which creates lots of ions.
they are electrically charged to deflected by electric and magnetic fields

Question 9

what are beta particles?

Answer 9

electrons- emitted from the nucleus of an atom when a neutron turns into a proton and electron.
They are quite fast ad quite small.
They penetrate moderately before colliding and are moderately ionising.
Charged so deflected by electric and magnetic fields

Question 10

what are gamma rays?

Answer 10

very short wavelength EM waves

• they have no mass and are just energy
• penetrate a long way into materials without being stopped
• weakly ionising because tend to pass through rather than collide with atoms- but eventually hit something and cause damage
• no charge so not deflected by fields
• gamma emission always happens after beta or alpha decay

Question 11

what was the gold foil experiment?

Answer 11

gieger and marsden fired alpha particles at thin gold foil. most went through, some were detected by the sinc sulfide screen, some fired straight back

Question 12

how did rutherford come up with the nuclear model of the atom?

Answer 12

Rutherford- Geiger and Marsden’s boss

1) if plum-pudding model was right then alpha particles would just pass straight though the gold foil
2) some bounced back which meant that inside the atoms there must be small positively charged nuclei, which repel the passing the +ve alpha particles
- most of the mass must be concentrated at the centre and most of the atom is empty space
- the nucleus must be small since very few alpha particles are deflected by march
- it must be positive to repel the +ve charged alpha particles
3) the faster the alpha travelling the less it will be deflected
4) the more positively charged a nucleus the more an alpha particle will be deflected
5) the closer an alpha particle passes to the nucleus the more it will be deflected

Question 13

what is the half -life?

Answer 13

the time is takes for level of radioactivity to halve

Question 14

what does a short half-life mean?

Answer 14

the activity falls quickly because lots of the nuclei decay quickly

Question 15

a long half-life means?

Answer 15

the activity falls more slowly because most of the nuclei don’t decay for a long time

Question 16

what is radioactivity measured in?

Answer 16

becquerels (Bq)

Question 17

how do medical tracers work?

Answer 17

source of beta or gamma radiation is injected into the patient or swallowed. it penetrates the body tissues so can be detected externally- as it moves around the body a radiographer uses a detector to monitor its progress.a computer converts the reading to an on-screen display showing where the radiation is coming from- check whether the organs are working as they should
the radioactive source has to have a short half-life so you can use less of the source but still get a reading on your detector

Question 18

why are beta and gamma more hazardous than alpha outside the body?

Answer 18

can penetrate the skin and soft tissues to reach the delicate organs inside the body- inside the body mostly passes straight out so doesn’t do much damage

Question 19

why is alpha dangerous?

Answer 19

does all damage in localised area- it collides with molecules in your cells causing ionisation which damages or destroys the molecules

Question 20

what do lower doses of radiation tend to do?

Answer 20

cause minor damage without killing the cell-causes mutations which then divide uncontrollably= cancer

Question 21

what do higher doses of radiation do?

Answer 21

kill cells completely, causing radiation sickness if a large part of your body i affected at the same time

Question 22

why is radioactive waste hard to dispose of?

Answer 22

• lower-level can buried in secure landfill sites
• high-level is really dangerous as stays highly radioactive for thousands of years so sealed in glass blocks which are sealed in metal canisters- then buried deep underground
• hard to find suitable places to bury waste as the site has to be geologically stable, as big movements in the rock could distub the canisters and allow radioactive material to leak out-get into ground water and contaminate the soil, plants, rivers and drinking water

Question 23

what protection to take using radioactive sources?

Answer 23

1) never allow skin contact and always hold with tongs as arm’s length
2) keep source pointed away from the body and avoid looking directly at it
3) keep sealed in lead box whenever to being used

Question 24

what precautions should people take who regularly work with radioactivity?

Answer 24

1- wear lead aprons and stand behind lead screens
2-wear protective full suits to prevent inhalation or lodging on the skin or under fingernails
3- use remote-controlled robot arms

Question 25

what is nuclear fission?

Answer 25

the splitting of an atom, which releases energy

Question 26

how does nuclear fission work?

Answer 26

a slow-moving neutron gets absorbed by a uranium-235 nucleus , the nucleus splits into some neutrons, which go onto hit other nuclei repeatedly=chain reaction, and two daughter nuclei=lighter elements- radioactive because wrong number of neutrons in them
each nucleus splitting gives out a lot of energy in the form of KE which can be converted to heat energy in the reactor by collision with other atoms

Question 27

how does a nuclear reactor work?

Answer 27

1- free neutrons in the reactor start the fission process

2) atoms produced then collide with other atoms, causing the temperature to rise
3) the moderator, usually graphite or water, slows neutrons so that they can successfully collide with uranium nuclei and sustain the chain reaction
4) the control rods, made of boron, limit the rate of fission by absorbing excess neutrons
5) a gas- co2- is pumped through the reactor to carry away the heat generated
6) this gas then passed through a heat exchanger where it gives its energy to water= heated and turned to steam which turns a turbine which turns a generator, generating electricity.