Radioactivity and Particles Flashcards
what are isotopes
atoms with the same number of protons but a different number of neutrons
what happens if the nuclei of an isoptope is unstable
if the nucleus has an imbalance of protons or neutrons it is more likley to decay into several smaller nuclei until stable nuclei are obtained
when does radiactive decay happen
spontaniously
it is UNaffected by physical conditions like temperature or any sort of chemical bonding
what happens when the nucleus decays
it will emmit one or more types of radiation
- alpha, beta or gamma
examples of background radiation
substances on earth (air, food, soil..)
radiation from space
living things
human activity
how does nuclear radiation cause ionisation
nuclear radiation causes ionisation bu bashing into atoms and knocking electrons off of them
the atoms are turned into ions
what is the machine for detecting ionising radiation
geiger-muller dectector
photographic film
what are alpha particles made of
and they qualities
2 protons
2 neutrons
big, heavy, slow moving
how do alpha aprticles work
they are strongly ionising meaning they bash into a lot of atoms and knock electrons off them which creates a lot of ions
what does emmiting alpha particles cause
decrease the atomic number of the nucleus by 2 and the mass number by 4
what are beta particles
and qualities
an electrons which as been emmited from the nucleus of an atom when a neutron turns into a proton and electron
fast and small
moderately ionising
what happens when a beta particle is emmited
the number of proton in the nucleus increases by 1 the atomic number increases by 1
BUT the mass number stays the same
what are gamma rays
no mass and just energy
they penetrate a long way into materials
no charge
weakly ionising
pass through rather than colliding with atoms
what effect does gamma ray emission have
it has no effect on the atomic or mass number of the isotope
order of more ionising
alpha are more than beta
beta are more than gamma
rule for nulcear equations
the overall charge and mass has to be the same before and after a nucelar reaction has happened
how can alpha be blocked
paper, skin or a few cm of air
how can beta particle be blocked
a few cm of metal
how can gamma rays be blocked
thick lead or very thick concreate
set up for how to investiage penetration of radiation
how to find the penetration of radiation
remove the source and find the background radiation
place the source and measure the count rate
then place different materials between the source and detector
how to know if the material can block the penetration of radiation
of the count rate remains the same when the material is insterted, then the radiation can penetrate the material
if it drops by a large amount then the radiation is being absorbed and blocked by the material
if it drops to zero after the background count if subtracted, the radiation is being completely absorbed
safety for radioactive sources
use in a lead lined box when not in used
on picked up using long-handled tongs or forceps
do not point at anyone
definition of half life
the time taken for half of the radioactive atoms now present to decay
short vs long half lifes
short half life means the activity falls quickly and lots of nuclei decay quickly
long half life means the activity falls slowly because the atoms dont decay for a long time
steps for finding half life
the activity of a radioactive isotope is 640Bq
Two hours later it has fallen to 40 Bq
Find the half life of the sample
initial count - 640
after one half life (/2) - 320
after two half lives (/2) - 160
after three half lives - 80
after 4 half lives - 40
it takes 4 half lives for the activity to fall from 640 to 40
this means 2 hours represents 4 half lives so the half life is (2 hours / 4) = 30 minutes
how can beta and gamma radiation be used
in medical tracers
eg
a source which emmits beta or gamma can be injected or sqalloed and it will penetrate the body tissues to be detected externeally but a source
doctors can use this to make sure organs are working as they should
how can gamma rays be used
for sterilising food equipment
it will skill a microbes and it doesnt involve high temperatures so things such as plastic instruments or fresh fruit can be sterilised without being damaged
how can ionising radiation cause damage to cells and tissues
alpha radiation collides with molecules in your cells and this can either damage or destroy the molecules
low dose will cause minor damage and cause mutations which is cancer
high doses kill cells completely and it causes radiation sickness
irridation
object near a radioactive source causes irridation (they are exposed to it)
it DOES NOT make it radioactive
contamination
if unwanted radioactive atoms get onto or into an object the object will be contamination
these atoms may decay causing you harm
what is nulcear fission
the splitting of an atom which releases energy
it can be spontaneous
what happens in nuclear fission
a slow moving neutron is absorbed by a uranium 235 nucleus the nucleus can split
each time this happens it spits out a small number of neutrons which may go hit other ones causing them to split and so on
it creates daughter nuclei
energy with nuclear fission
each nucleus which spitso ut gives out a lot of energy in the kenetic stores of the fission products
what does a nuclear reactor need
and what needs to be controlled
a chain reaction to keep it runing
when it is producing energy at the required rate 2 things need to be controlled:
the number of free neutons in the reactor
the energy in the free neutrons
what do control rods do
often made of boron they limit the rate of fission by absorbing excess neutrons
what does the moderator do
usually made of prapgie or water it slows down the neutrons
how does a nuclear reactor work
what is nuclear fusion
when 2 light nuclei collide at high speed and join (fuse) to create a larger and heavier nucleus
energy in fusion
it relases a lot of energy
what is the sheilding layer in a reactor for
it prevents any radiation from escaping even neutrons
what is fusion an example for
the energy source for stars
2 points for fusion
it only happens at REALLY high pressure and temperature
this is because the positivley charged nuclei have to get very close to fuse so they have to be moving very fast to overcome the strong force
difference between fission and fusion
fusion: 2 nuclei of lighter elements combine to make a nucleus of a larger element
fission: the nucleus splits into 2 smaller nuclei
