Radioactivity

proton - relative mass

1

proton - relative charge

1

neutron - relative mass

1

neutron - relative charge

0

electron - relative mass

0.0005

electron - relative charge

-1

what are alpha, beta, and gamma particles?

ionising radiations emitted from unstable nuclei in a random process.

alpha radiation

• very ionising

• not very penetrating (can be stopped by paper/few mm of air.)

• helium nucleus, 2 neutrons, 2 protons, no electrons.

• mass 4

• +2 charge

beta radiation

• a little ionising

• stopped by 3-4mm aluminium

• a fast moving electron

gamma radiation

• not very ionising

• stopped by lead

• an electromagnetic wave

• 0 charge and mass

ionising

how good radiation is at removing electrons from an atom.

ionising radiation

radiation with enough energy to remove tightly bound electrons from the orbit of an atom, causing the atom to become ionisde/charged.

atomic number

number of protons

mass number

protons and neutrons

what happens to the atomic mass and mass number of an alpha nucleus when it emmits radiation?

mass number -4

atomic number -2

what happens to the atomic mass and mass number of a beta particle when it emits radiation?

mass number - no change

atomic number +1

what happens to the atomic and mass number of a gamma particle when it emits radiation?

mass number - no change

atomic number - no change

what happens to the atomic number and mass number when a neutron particle emits radiation?

• decays due to loss of neutrons.

• mass number -1

• atomic number - no change

mass number

• protons and neutrons

• top number

atomic number

• protons or electrons

• bottom number

radioactive decay

• the spontaneous transformation of an unstable nucleus into a more stable nucleus by the release of radiation.

• random process so don’t know if/when a nucleus will decay.

alpha decay proces

1. the heavy nucleus emits and alpha particle.

2. the nucleus changes to a different element (helium?)

beta decay process

1. neutron turns into a proton and emits a beta particle (electron)

2. nucleus changes to a different element.

gamma decay process

1. after a previous decay, a nucleus with excess energy emmits a gamma particle.

neutron decay process

1. in neutron rich nuclides, one or more neutrons are ejected. they are also emitted during nuclear fission.

2. the nucleus becomes an isotope of the original elements.

how to detect radiation using photographic film

• the more radiation absorbed by the film, the darker it gets. (film initially white.)

• worn as badges for people to check how much exposure they’ve had.

how to detect radiation using a Geiger-Muller tube

• a tube which detects radiation.

• each time it absorbs radiation, it transmits and electrical pulse to the machine.

• the machine produces a clicking sounds.

• the greater the frequency of clicks, the more radiation present.

background radiation

weak radiation that can be detected from external sources.

background radiation from space

cosmic rays contain high energy charged particles that penetrate the atmosphere.

background radiation from earth

• radioactive rocks emit radioactive radon gas.

• food and drink.

• nuclear weapons testing.

• x-rays and MRI

• nuclear power plants → radioactive waste

investigate the penetration powers of different types of radiation

• detect using a Geiger Muller tube, which is attached to a counter.

• absorbers: paper, aluminum, lead

• count rate will significantly decrease if radiation is stopped.

SAFETY -

• use tongs when handling the source

• repeat 3 times and find mean average.

• when not using source, store in lead-lined container.

the activity of a radioactive source…

• decreases over a period of time.

• measured in Becquerels.

what is the activity of a radioactive source?

the number of decays which occur per unit time.

1 Bq = 1 decay per second

the half life of an isotope

the time taken for half the nuclei to decay/the time taken for the activity to halve.

half life varies with different radioactive isotopes.

uses of radioactivity in industry: smoke detectors

• smoke detectors.

• long half-life alpha emitters used as smoke detectors.

• if some enters the detector, some of the alpha particles are absorbed, the current drops, triggering the alarm.

uses of radioactivity in industry: thickness monitoring

• long half-life beta emitters can monitor the thickness of metal sheets.

• source and receiver placed on either side of the sheet.

• drop/rise in number of beta particles detected = thickness of sheet has changed.

uses of radioactivity in medicine: sterilisation

• gamma emitters kill bacteria

uses of radioactivity in medicine: diagnosis and treatment

• short half life emitters used a tracers.

• they concentrate in certain parts of the body.

• half life must be long enough for diagnostic procedures, but short enough to not remain radioactive for too long.

• can destroy tumors with high radiation.

contamination

occurs when a radioactive source has been introduced into/onto an object.

the object will be contaminated for as long as the source is in/on it.

irradiation

occurs when an object is exposed to a radioactive source which is outside the object.

the irradiated object does not become radioactive.

how should radioactive waste be disposed of?

• bury in sealed drums deep underground.

• remotely handle it after it has been thoroughly cooled.