Radioactivity

Question 1

what is an isotope ?

Answer 1

atoms with the same number of protons but different number of neutrons

Question 2

explain what an unstable / stable isotope is

Answer 2

each element only has one or two stable isotopes with a stable nucleus, the others tend to be radioactive due to the unstable nucleus so decays and emits radiation

Question 3

what is radioactive decay ?

Answer 3

a random and spontaneous process where the nuclei decays, often becoming a new element and spitting out radiation (alpha/beta/gamma)

Question 4

where does background radiation come from?

Answer 4

substances on earth
space
living things
human activity (explosions)

Question 5

what is ionisation ?

Answer 5

electrons being knocked off by nuclear radiation, turning the atoms into ions
the further the radiation penetrates before hitting the atom and getting stopped, the less damage/ionising it will do

Question 6

how can we detect ionising radiation ?

Answer 6

photographic film or Geiger-Muller detector

Question 7

Describe alpha particles (He²⁺)

Answer 7

Helium nuclei made up of 2 protons and 2 neutrons
(big, heavy, slow moving)
so don’t penetrate far (skin or paper)
size makes them very ionising
electrically charged means they are deflected by electric and magnetic fields
POSITIVE CHARGE

Question 8

Describe beta particles (e-)

Answer 8

an electron which has been emitted from nucleus of an atom when a neutron turns into a proton and an electron
move fast and are quite small
moderately penetrating (aluminium) and ionising
deflected by electric and magnetic fields
NEGATIVE CHARGE

Question 9

Describe gamma rays (γ)

Answer 9

have no mass as they are just energy (EM waves)
can penetrate far (thick lead)
weak ionising as they pass through instead of colliding with atoms, but do eventually and do damage
gamma comes after beta and alpha decay
if nucleus has excess energy, it is lost by emitting gamma

Question 10

what blocks alpha

Answer 10

paper, skin or a few centimetres of air

Question 11

what blocks beta

Answer 11

thin metal (aluminium)

Question 12

what blocks gamma

Answer 12

thick lead or very thick concrete

Question 13

state the 3 points of alpha scattering

Answer 13

the faster a alpha particle goes, the less likely it will be deflected by a nucleus 
the more (+ve) charged a nucleus is (high atomic number) the more alpha will be deflected 
the closer an alpha particle pass to the nucleus, the more it will be deflected

Question 14

define half life

Answer 14

time taken for half of the radioactive atoms now present to decay

Question 15

what is a short half-life ?

Answer 15

activity falls quickly because lots of nuclei decay quickly

Question 16

what is a long half-life ?

Answer 16

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

Question 17

how do medical tracers work?

Answer 17

source of beta/gamma (short-life) radiation is put into patient
radiation penetrates skin so can be detected
radiographer uses detector to monitor progress
computer converts reading into screen display, showing where radiation is coming from
used to check whether organs are fine

Question 18

How to use gamma in pipes?

Answer 18

squirt gamma source (short-life) into pipe, let it flow and go along with detector
if there’s a crack, detector will show extra high radioactivity

Question 19

when can alpha particles be dangerous ?

Answer 19

when they get inside your body as they are very ionising and won’t be able to get out

Question 20

how does radiation damage the body?

Answer 20

collides with molecules, causing ionisation, which causes mutations which then divide uncontrollably or even kills cells, causing radiation sickness

Question 21

what is radiotherapy ?

Answer 21

using high does of gamma rays carefully zapped onto the tumour cells to kill them

Question 22

describe the disposal of radioactive waste

Answer 22

very difficult as high-level waste can take tens of thousands of years to go so is often sealed in glass blocks, which are sealed in metal canisters and buried deep in the ground
the site must be geologically stable (no earthquakes) so it doesn’t leak and get into ground water

Question 23

how to keep safe with radioactive materials?

Answer 23

never allow skin contact so use tongs at arms length
keep source pointed away from body and don’t look directly at it
store in sealed lead box

Question 24

what do regular radioactive workers do?

Answer 24

medical workers wear lead aprons behind lead screens
nuclear workers wear full protective suits
they can also use remote controlled robot arms

Question 25

what is nuclear fission?

Answer 25

splitting of an atom, which releases energy

is used in nuclear reactors in a controlled chain reaction

Question 26

what is the normal ‘fuel’ for nuclear fission?

Answer 26

uranium - 235

Question 27

describe the process of nuclear fission

Answer 27

slow-moving neutron gets absorbed by U-235 and nucleus splits
small no. of neutrons spit out, which go hit another U-235 nuclei, causing a chain reaction
when U-235 splits, it forms 2 new daughter nuclei (which are lighter)
energy comes from kinetic energy of fission products and are converted to heat by collisions with other atoms

Question 28

what is the big problem with nuclear power ?

Answer 28

the new nuclei are radioactive as they have the ‘wrong’ number of neutrons, which produces a huge amount of radioactive waste that is difficult/expensive to dispose of

Question 29

what does a moderator do in a nuclear reactor?

Answer 29

(usually graphite or water) slows neutrons so that they can collide with uranium nuclei and sustain the chain reaction

Question 30

what do the control rods do in a nuclear reactor?

Answer 30

(usually boron) limit the rate of fission by absorbing excess neutrons

Question 31

what does the gas do in a nuclear reactor?

Answer 31

(usually carbon dioxide) pumped through the reactor to carry away heat generated
then passes through a heat exchanger, which gives the energy to the water, which heats and turns a turbine