7) Radioactivity and Particles

protons, neutrons and electrons

nucleus - protons and neutrons orbitals - electrons

proton +1 neutron 0 electron -1

proton 1 neutron 1 electron 1/1836

• 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

• 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

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

• sometimes it is due to their large size or

• because the number of protons or neutrons within them are out of balance

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

ionising radiations emitted from unstable nuclei in a random process

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

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

2 protons and 2 neutrons, a helium nucleus

+2

a few centimetres

it is absorbed by paper/card

strongly

an electron

-1

around 1 metre

a few millimetres of aluminium

medium

an EM wave

0

infinite

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

low

• 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

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

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

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

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

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

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

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

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

• photographic film

• Geiger-Muller tubes

• ionisation chambers

• scintillation counters

• spark counters

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

radon gas (underground gases) rocks food humans cosmic rays

building materials medical uses (x-rays) nuclear power

the number of decays occurring in an isotope every second

Becquerels, Bq

it decreases

activity = number of decays/time

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

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

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

0

different isotopes have different half lives

the time for activity to halve in value

• 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

• smoke detectors

• thickness monitoring

• tracers

• radiotherapy

• sterilisation

• 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

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

• 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

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

• 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

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

it is highly penetrating and can be easily detected

• 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

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

• 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

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

when small amounts of the radioactive isotope leaks onto material

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

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

if the material becomes contaminated

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

-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

• can cause mutations in living organisms

• can damage cells and tissue

• problems about disposing radioactive waste

they can be a source of energy

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

2 smaller, daughter nuclei and 2/3 neutrons

it releases energy as kinetic energy of the fission products

Uranium 235 U-235

• one fission occurs, producing 2/3 neutrons

• one of these neutrons could then go on to hit another U-235 nucleus causing another fission

• absorb neutrons, decreasing the number of fissions happening

• so that fissions don't increase over time and cause the reactor to melt

• slow down neutrons preventing them from being absorbed by U-238

• these slowed down neutrons can still go on to create further fissions

carbon and water

• 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

• 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

fission is where large nuclei are split into smaller nuclei

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

• the mass is slightly smaller than the combined mass of the 2 original nuclei

• this mass decreased is caused by a release of energy

stars

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

• 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)