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half life
the half-life of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve
beta particle
a fast moving electron
isotopes
forms of the same element that have the same nuber of protons and electrons but a different number of neutrons
alpha particle
a particle containing two neutrons and two protons, also known as helium nucleus
gamma rays
electromagnetic radiation of short wave length but high frequency
proton
positively charged particle found in the nucleus
neutron
neutral particle found in the nucleus
electron
negatively charged particle found orbiting the nucleus
ion
formed when atoms gain or lose electrons
atomic number
number of protons or electrons found in an atom
mass number
number of protons and neutrons found in an atom
alpha decay
mass number decreases by 4 and the atomic number decreases by 2
beta decay
mass number stays the same and the atomic number increases by 1
JJ Thomson
Plum pudding model : he proposed that atoms were a general ball of positive charge with discrete electrons stuck in it
Rutherford and Marsden
they took positively charged alpha particles and fired it at a thin sheet of gold
if the positive charge was spread out as Thompson said then the particles should pass straight through as the weak positive charge spread out wouldn't be enough to affect/repel them
instead the alpha particles deflected back proving thompson wrong
what did rutherford conclude from his experiment
- atoms are mostly empty space
- the mass of the atom is concentrated at the centre with a positive nucleus
- the negative charge was in some sort of cloud around the nucleus
what was the fault in rutherford's nuclear model
there was nothing stopping the negative cloud of electrons from rushing towards the positive nucleus which would make the atom collapse
Geiger-Muller
device used to measure radiation counts
aluminium
stops beta and alpha
what stops alpha
Skin/Paper/ a few cm of air stops this type of radiation
what stops gamma radiation
lead or concrete
what stops beta radiation
thin sheet of aluminium
what are some natural sources of background radiation
- radon gas from rocks and buildings
- cosmic rays from space
what are some man made sources of background radiation
- exposure from medical testing
- fallout from nuclear weapons testing and accidents
explain how ionisation occurs in terms of electrons
very occasionally one of the outermost electrons absorb so much energy that it's able to completely leave the atom, this leaves the atom with more protons than electrons so that it's left with a positive charge
When are gamma rays emitted?
after alpha or beta radiation as a way of the nucleus getting rid of extra energy
what happens during beta decay
a neutron in the nucleus turns into a proton; so element changes and a beta particle is emitted
Rank alpha, beta- and gamma in terms of their ionising power (lowest to highest).
gamma
beta
alpha
Rank alpha, beta- and gamma in terms of their penetration power (lowest to highest).
alpha
beta
gamma
what makes alpha particles so ionising
their large size and strong charge
why are gamma rays so penetrative
they have no mass or charge so they pass straight through making them weakly ionising., this means that they can penetrate really far into materials before being stopped
what is the difference between irradiation and contamination
irradiation is the process by which objects are exposed to radiation of any type ( this doesn't mean that the object has been contaminated)
contamination is when radioactive particles get onto other objects ( can't harm others unless you're contaminated)
Why does radioactive decay occur?
Radioactive decays allows the nucleus of an unstable element to spontaneously convert into a more stable element while emitting a radioactive particle
Is radioactive decay random or systematic?
Random - you can't predict which nucleus in a sample will decay next
what is activity and what is it measured in
activity is the rate at which unstable nuclei decay
what are some precautions to avoid exposure to radiation
- keeping the item in a lead lined box
- wearing gloves or overalls
- handling the substance with tools eg. tongs and not habdling directly
why is ionising radiation dangerous
because it can enter our body and damage tissues and cells, in worser cases they can ionise our DNA and cause mutations in them causing them to divide uncontrollably forming a tumour
why does alpha radiation stop being harmful when the source is outside the skin
because alpha radiation can't penetrate skin
what are two uses of radiation in medicine
- medical tracers
- radiotherapy
how do medical tracers work
- we use isotopes with a short half life so that they only emit radiation for a short period
- how it works is we place radioactive material inside the patient's body via injecting them, then we track the movement of the isotope around the body by tracking the radiation they emit
- we can also check is organs are working well by seeing if they absorb the right amount of a substance
eg. giving people iodine-123 which emits gamma radiation we can see if the thyroid glands are absorbing the iodine as they should be
how does radiotherapy work
Cancer cells are destroyed by targeted doses of radiation to stop mitosis, so that they stop dividing and growing.
However sometimes healthy cells are also targeted. It is worth it though as it can save a person's life however it doesn't stop the cancer coming back in other areas.
what is activity and what is it measured in
activity is the rate at which unstable nuclei decay and it's measured in becqurels ( which is one decay per second)
what is half life
the average number of time taken for the count rate and so the number of nuclei in a radioactive isotope to fall by half
