Nuclear Radiation Flashcards
what is background radiation
- low level radiation from environmental sources
- always present around us
what are the units of the geiger-muller counter and counter
becquerels (Bq)
what makes 50% of background radiation
radon gas
what 4 other things make the big chunks
- ground and building (14%)
- medical (14%)
- food and drink (11.5%)
- cosmic rays (10%)
how is the radon gas produced
from the decay of uranium ore present in certain rocks
how would you properly measure the background radiation of your environment using a gm tube and counter
- leave the gm tube and counter to count the background radiation over a recorded long period of time (30 mins)
- divide the total counts, shown by the counter, by the number of seconds the counter was counting for
- giving you the number of counts per second (Bq)
why do you record the background radiation over a long period of time
- so a good average is calculate
- as the count rate would be temporarily higher or lower than normal at times
what is the usual reading youd get from this kind of experiment
- 0.5Bq
- anywhere between 0.2 and 0.5 is common in the UK
is you were measuring the radioactivity of a specific substance using a gm tube and counter, how would you calculate the corrected count
- measure the count rate of the background radiation around you
- measure the count rate of the substance
- subtracting the BGR from the count rate of the substance
what is radioactive / nuclear decay
- the process of a nucleus’ structure being changed
- usually accompanied by the emission of a particle
what does the emitted particle have when it leaves the nucleus
kinetic energy
what do these radiation particles usually do
- it will ionise particles in its path as it moves
- losing a small amount of KE at each ionisation
- when all the KE has been transferred, the particle stops moving
- then is absorbed by the substance it is in at that moment
what are the three main types of nuclear radiation
- alpha (a)
- beta (b)
- gamma (Y)
what material does alpha radiation find hard to penetrate
- paper
- a centimeters of air
what material does beta radiation find hard to penetrate
- 5mm thick aluminium
- a few meters of air
what material does gamma radiation find hard to penetrate
- 5cm thick lead
- several meters of concrete
what is an alpha particle, what is its charge and what its ionisation like
- an alpha particle is a helium nucleus (2p 2n)
- it has a charge of 2+
- and it is highly ionising
how many ionisations does an alpha particle cause in the air per millimetre
about 10k
putting two and two together, why do alpha particles get absorbed so easily
- because their high amount of ionisations means they lose their KE very quickly
- therefore they get absorbed very quickly
what is a beta particle, what is its charge and what its ionisation like
- a beta particle is a high speed electron
- it has a charge of 1- or 1+
- and its moderately ionising
how is a b- particle formed
- when a neutron decays into a proton
- and emits an electron (its negative charge)
how is a b+ particle formed
- when a proton decays into a neutron
- and it emits a position (its positive charge)
why are b particle less ionising than a particles
- because they are much smaller
- so they collide with and ionise particles less frequently
what is gamma radiation, what is its charge and what is its ionisation like
- gamma radiation is a type of high energy and frequency EM radiation
- it has no charge
- they are the least ionising of the three
why are gamma rays the least ionising
- because they have no charge or mass
- so they rarely interact with particles in their path
if gamma rays have no mass or charge, what do they do to the nucleus when they are emitted
- they transfer energy out of the nucleus
- causing the nucleus’ energy level to drop
when does gamma ray emission usually occur from a nucleus and why
- after beta or gamma decay
- because they usually leave the nucleus in an excited state
in the experiment where we explore how much lead is needed to reduce the intensity of gamma radiation by a certain amount, a source that emits gamma and alpha radiation is used. what is the main setup point you need to remember
the distance between the source and counter must remain constant through out
what else do you need to do in order to gain accurate results
- place a sheet of paper in front of the source
- to absorb the alpha radiation
- as we only care about gamma
what is done during this practical
- place varying thicknesses of the lead plates in between the counter and source
- for each thickness, record the count over a fixed period of time and work out the count rate
what graph would be plotted
intensity of radiation (count rate) against thickness of lead
what is the mathematical relationship between intensity and thickness of lead
- I dpt e^(ux)
- I = intensity
- u = mu (i really dont know lol)
- x - thickness of lead (m?)
how dangerous is alpha radiation outside and inside the body
- inside its very dangerous, causing radiation poisoning and cancer
- outside its harmless, being absorbed by the surface layer of dead skin
how dangerous is beta radiation outside and inside the body
- inside its moderately dangerous, causing ionisation
- outside is the same story
- basically close exposure should be minimised
how dangerous is gamma radiation outside and inside the body
- inside its not too bad, long term exposure will cause cancer
- outside its the same story
- basically it causes minimal ionisation so dont stay around for long periods
