6.1 Radioactive Emissions And 6.2.1 Flashcards
Stable and unstable atoms
- most atoms are stable - they do not break down or decay
- atoms with an unstable nuclei will emit radiation as they decay
- materials that emit radiation are radioactive
Alpha, beta, gamma and neutron - type, symbol, what is it, equation symbol
Alpha - particle - a - nucleus of a helium atom - 42 He
Beta - particle - B - fast moving electron - 0-1 e
Gamma - EM wave - Y - wave of EM spectrum - none
Neutron - particle - n - a particle in the nucleus - 10 n
Top number - mass relative to a proton, bottom number - charge
A nucleus does not contain electrons, so where does the beta particle come from?
Neutrons are not stable. They can decay to make a proton and an electron.
Geiger counter - how does it work?
- you can detect radiation with a Geiger counter. This is the device that ‘clicks’ when radiation enters it. Each click is a tiny current produced when the radiation ionises atoms of the gas inside the tube.
How do you stop alpha, beta and gamma?
- alpha, beta and gamma have different penetrating powers
- you can stop alpha with a few sheers of paper or your skin
- beta is stopped by a few mm of aluminium
- gamma is the most penetrating. It is stopped by a few cm of lead or m of concrete, but some can still get through
Explain ionising radiation
- the radiation emitted by radioactive material is ionising radiation. This means that the radiation can remove electrons from atoms to produce positively charged ions.
Alpha, beta and gamma have different- relative mass, charge, ionising power, range
Alpha - large - +2 - high - short
Beta - small - -1 - medium - medium
Gamma - none - none - low- long
To ionise an atom, energy has to be transferred to it. Alpha particles transfer more energy to the material they travel through hence, their shorter range
What happens in alpha decay?
In alpha decay, an alpha particle is emitted which is made of two protons and two neutrons (helium nucleus).
240,94 Pu —> 236,92 U + 4,2 He
What happens in beta decay
In beta decay, a neutron decays into a proton and an electron.
Mass does not change as the total number of protons and neutrons in the nucleus remains the sake. (1 neutron is lost but 1 proton is gained).
14,6 C —> 14,7 N + 0,-1 e
What happens in gamma decay?
Gamma rays have no mass or charge as they are EM waves. There is no change to the mass or atomic number.
What happens in neutron emission?
The decay of some nuclei leads to the production of large numbers of neutrons. These neutrons are then emitted to make it stable.
5,2 He —> 4,2 He + 1.0 n
Explain acitivity
Radiation is emitted at random. A Geiger counter can measure the activity, which is the radiation emitted per second. It is measured in becquerels (Bq)
Explain what half-life is
Half-life refers to the time it takes for the activity to halve. It is also the time it takes for half the unstable nuclei to decay. The half-life of a material. May be long or short.
Backround radiation, contamination, irradiation
Backround radiation is made up of sources of radiation that we are exposed to all the time.
Contamination - occurs when radioactive material is taken inside the body or on the skin. Internal contamination cannot be removed.
Irradiation - occurs when radioactive material is outside tour body. The radiation can travel into the body.
Uses of radiation in medical tracers
- radioactive isotope is injected, inhaled or swallowed.
- gamma camera is used to detect the radiation to shops problems in the body.
- radiographers have to choose the isotope carefully to ensure the half-life is not too short or too long and that it emits the right type of radiation.
- for example technicium - 99 is absorbed by a range of organs and has a half-life of around 6 hours
Uses of radiation in medicine
- doctors use a moveable source of gamma radiation to focus gamma rays onto a cancer tumor.
- this reduces the dose healthy cells receive preventing their death but gives a high enough dose to the tumour to kill those cells.
