7) Radioactivity and Particles

What is an atom made of

protons, neutrons and electrons

Which particles are found in the nucleus of the atom and what particle is found in the orbitals

nucleus - protons and neutrons
orbitals - electrons

What is the charge of a proton, neutron and electron

proton +1
neutron 0
electron -1

What is the mass of a proton, neutron and electron

proton 1
neutron 1
electron 1/1836

What is the atomic/proton number

- the number of protons in an atom
- there are the same number of electrons
- the atomic number is found at the bottom of the atomic symbol

What is the mass/nucleon number

- the number of protons and neutrons in an atom
- the number of neutrons can be found by taking away the atomic number from the mass number
- the mass number is found at the top of the atomic symbol

What are isotopes

atoms of the same element which have the same number of protons but a different number of neutrons
(same atomic number, different mass number)

Why are some nuclei unstable

- sometimes it is due to their large size
or
- because the number of protons or neutrons within them are out of balance

Why does an isotope decay

due to the unstable nuclei the isotope decays emitting radiation in order to reduce the size or bring them back to balance

What are alpha, beta and gamma

ionising radiations emitted from unstable nuclei in a random process

what does ionising mean

if the radiation hits other particles, it can knock out electrons

Why is ionisation bad

it can cause chemical changes such as mutations in materials and damage/kill cells and cause cells to become cancerous

What is an alpha particle

2 protons and 2 neutrons, a helium nucleus

What charge does an alpha particle have

+2

What is the range of an alpha particle

a few centimetres

What is alpha absorbed by

it is absorbed by paper/card

How ionising is alpha radiation

strongly

What is a beta particle

an electron

What is the charge of a beta particle

-1

What is the range of a beta particle

around 1 metre

What is beta absorbed by

a few millimetres of aluminium

How ionising is a beta particle

medium

What is gamma

an EM wave

What charge do gamma waves have

0

What is the range of a gamma ray

infinite

What is gamma absorbed by

it is not absorbed by anything but instead reduced by metres concrete or a few millimetres of lead

How ionising is gamma

low

How do you investigate the relative penetration of different types of radiation

- connect a Geiger-Muller tube to a counter
- measure the background radiation over a one minute period
- repeat 3 times and take an average
- place a radioactive source a fixed distance away from the tube
- take a reading over a 1 minute period
- place different absorbers between the source and tube
- take a reading over 1 minute period for each absorber
- if the count over an interval falls to background levels (allow random variation) then the radiation has been absorbed
- repeat this for the other radioactive sources

What is an absorber

a material that absorbs radiation such as paper, aluminium and lead

What are safety points when handling radioactive isotopes

when a source is not in use, keep it in a lead lined container
when a source is in use, keep it a good distance away from yourself
use tongs when handling the source
point the source away from you

What are the conclusions to the experiment

stopped by paper = alpha radiation
stopped by aluminium = beta radiation
reduced by lead = gamma radiation

What effect does alpha emission have on its atom

the nucleus loses 2 protons and 2 neutrons
the atomic number is decreased by 2 and so is the mass number

What effect does beta emission have on its atom

the nucleus gains a proton
the atomic number increases by 1
the mass number stays the same

What effect does gamma emission have on its atom

it has no effect on the atom as gamma is a wave
the atomic and mass numbers stay the same

What effect does neutron emission have on its atom

the nucleus loses 1 neutron
the mass number decreases by 1
the atomic number stays the same

How do radiation detectors work

they detect atoms which have been ionised due to radiation or the chemical changes that they produce

What are examples of radiation detectors

- photographic film
- Geiger-Muller tubes
- ionisation chambers
- scintillation counters
- spark counters

What is background radiation

it is the radiation that is always present everywhere in the environment

What are natural sources of background information

radon gas (underground gases)
rocks
food
humans
cosmic rays

What are man-made sources of radiation

building materials
medical uses (x-rays)
nuclear power

What is activity

the number of decays occurring in an isotope every second

What is activity measure in

Becquerels, Bq

What happens to activity over time

it decreases

What is the formula for activity

activity = number of decays/time

What is the half-life of an isotope

it is the time taken for the activity of that isotope to drop to half of its initial value

In what way can decay be predicted

the probability of the decay is known however it can never be predicted when it will happen

Why does the activity of an isotope decrease over time

because although there is a fixed probability that an isotope will decay per unit of time
the number of nuclei available drops over time as previous nuclei have decayed meaning there are less remaining to decay

What will the activity and number of nuclei never drop to

0

Do all isotopes have the same half-life

different isotopes have different half lives

What is a constant in exponential graphs

the time for activity to halve in value

How can you find half-life from a graph

- look at the value of activity the isotope starts with
- half the value and find it on the y-axis
- draw a line from that number across until you reach the activity curve
- draw a line from that point down to the x-axis to find the half life time

What are the different uses of radioactivity in industry and medicine

- smoke detectors
- thickness monitoring
- tracers
- radiotherapy
- sterilisation

How do smoke alarms work

- use alpha radiation
- alpha particles ionise the air inside the detector, allowing a small current to flow within it
- when smoke enters the detector, the alpha particles are absorbed and the current no longer flows
- the alarm is the triggered

Why is alpha radiation used for smoke alarms

because it is easily absorbed by smoke which then triggers the alarm
it has a short rage and cant penetrate through the casing and damage humans

How does thickness monitoring work

- use beta radiation
- they can be used to measure the thickness of thin materials such as paper
- the material moves above the beta source
- the beta particles are partly absorbed by the material
- the thickness is monitored by the count of beta particles the detector counts
- if the material gets thinner, less beta particles are absorbed meaning more pass through and the count rises
- if the material gets thicker, more beta particles are absorbed meaning less get through and the count goes down
- this allows the machine to make adjustments to keep the thickness the same

Why is beta used for thickness monitoring

it is partly absorbed meaning some still pass through the material
if alpha was used all of the particles would be absorbed
if gamma was used all of the particles would get through
therefore not detecting change in thickness

How do tracers work

- use gamma radiation
- radioactive isotopes are added to fluids so the flow of the fluid can be monitored
- the amount of the isotope used is kept to a minimum
- isotopes which are chosen have short half lives of around a few hours, which is long enough to carry out the procedure but not so long that they cause long term harm

What are the uses of tracers

can be added to blood to check the blood flow and search for blockages such as blood clots
can be added to an oil pipeline in order to check for any leaks

Why is gamma used for tracers

it is highly penetrating and can be easily detected

How does radiotherapy work

- uses gamma radiation
- it is the treatment of cancer using radiation
- gamma is highly effective at treating cancer even though it causes it
- bacteria and cancer cells are more susceptible to radiation than other cells
- beams of gamma are directed at the cancerous tumour
- the beams are moved around to minimise harm to healthy tissue whilst still being aimed at the tumour

Why is gamma used for radiotherapy

highly penetrating and can kill bacteria and cancer cells
it can also reach the tumour by penetrating through the body

How does sterilisation work

- uses gamma radiation
- medical instruments are sterilised by exposing them to gamma radiation
- gamma kills the bacteria and viruses
- penetrates the instrument, reaching areas that may otherwise not be properly sterilised

Why is gamma used in sterilisation

highly penetrating and can kill bacteria and viruses
can also penetrate the instrument

What is contamination

when small amounts of the radioactive isotope leaks onto material

What happens because of contamination

small amounts of the isotope in the contaminated areas will give off radiation

What is irradiation

the process of exposing a material to alpha, beta or gamma radiation

How can a material become radioactive

if the material becomes contaminated

Does irradiating a material make it radioactive

no, it will not make a material radioactive regardless of the strength of the radiation or how long the material has been exposed to radiation for

What factors need to be taken into consideration when disposing nuclear waste

-some waste is highly reactive = thick shielding requires
-some waste have very long half lives = need to be stored for long periods of time
-containers holding the waste must not corrode or degrade over time = no nuclear waste leaks
- must be stored in geologically safe areas, away from dangers of earthquakes
- must be stored away from water sources so they wouldn't get contaminated if there was a leak
- storage areas should be clearly marked using meaningful pictures = future societies can understand the nature of what is stored

What are the dangers of ionising radiation

- can cause mutations in living organisms
- can damage cells and tissue
- problems about disposing radioactive waste

What can fission, fusion and radioactive decay be a source of

they can be a source of energy

What is required for nuclear fission to happen

the nucleus requires energy, this can be given by hitting the nucleus with a neutron

What does nuclear fission produce

2 smaller, daughter nuclei and 2/3 neutrons

What does nuclear fission release

it releases energy as kinetic energy of the fission products

What isotope is usually used for nuclear fission

Uranium 235
U-235

How can a chain reaction be set up for fission

- one fission occurs, producing 2/3 neutrons
- one of these neutrons could then go on to hit another U-235 nucleus causing another fission

What is the purpose of control rods

- absorb neutrons, decreasing the number of fissions happening
- so that fissions don't increase over time and cause the reactor to melt

What is the purpose of the moderator

- slow down neutrons preventing them from being absorbed by U-238
- these slowed down neutrons can still go on to create further fissions

Which substances can be used as moderators

carbon and water

What does U-238 do

- nuclear reactors contain a large amount of U-238 as well as U-235
- U-238 absorbs high energy neutrons released by fission
- this prevents the rector from exploding
- however it can stop chain reactions from occurring

What is the purpose of shielding in a reactor

- fission releases lots of radiation (neutrons and beta particles)
- if left unshielded, the radiation given off would be extremely hazardous to anyone nearby
- the shielding absorbs the radiation preventing it from leaving the reactor

What is the difference between fission and fusion

fission is where large nuclei are split into smaller nuclei

fusion is where small nuclei are brought together to form a larger nucleus

What is the mass of the nucleus like after fusion

- the mass is slightly smaller than the combined mass of the 2 original nuclei
- this mass decreased is caused by a release of energy

What is fusion the energy source for

stars
- hydrogen nuclei are fused together to form helium nuclei at the centre of stars, releasing energy

Why does nuclear fusion not happen at low temperatures and pressures

- due to electrostatic repulsion of protons
- in order for protons to overcome the repulsion, they have to travel at high speed (high temp)
- there also needs to be lots of successful collisions (high pressure and density)