Flashcards in physics paper 2 radioactivity Deck (27):
why is an atom radioactive?
its got an unstable nucleus, so it decays and emits radiation- carbon-14 is an unstable isotope of carbon
what is nuclei decay unaffected by?
physical conditions like temp or chemical bonding it's all spontaneous. the nuclei of unstable isotopes break down randomly
4 sources of background radiation
1- substances on Earth-air, food, building materials, ROCKS
2- radiation from space- cosmic rays from the Sun
3- living things
4- human activity -nuclear explosions or waste
what does the nucleus decay into?
spits out one or more of alpha beta gamma in the process the nucleus often changes into a new element
what is ionisation?
bashing into atoms and knocking electrons off them- atoms turn into ions which are charged
the more penetrating the source the less..
ionising it will be
how can you detect ionising radiation?
with photographic film which becomes exposed or used a Geirger-Muller detector
what are alpha particles?
helium nuclei- 2 protons and neutrons- they're big, heavy and slow-moving so don't penetrate for into materials and stopped quickly.
This makes them strongly ionising, bash into a lot of atoms and knock off electrons before they slow down, which creates lots of ions.
they are electrically charged to deflected by electric and magnetic fields
what are beta particles?
electrons- emitted from the nucleus of an atom when a neutron turns into a proton and electron.
They are quite fast ad quite small.
They penetrate moderately before colliding and are moderately ionising.
Charged so deflected by electric and magnetic fields
what are gamma rays?
very short wavelength EM waves
-they have no mass and are just energy
-penetrate a long way into materials without being stopped
-weakly ionising because tend to pass through rather than collide with atoms- but eventually hit something and cause damage
-no charge so not deflected by fields
-gamma emission always happens after beta or alpha decay
what was the gold foil experiment?
gieger and marsden fired alpha particles at thin gold foil. most went through, some were detected by the sinc sulfide screen, some fired straight back
how did rutherford come up with the nuclear model of the atom?
Rutherford- Geiger and Marsden's boss
1) if plum-pudding model was right then alpha particles would just pass straight though the gold foil
2) some bounced back which meant that inside the atoms there must be small positively charged nuclei, which repel the passing the +ve alpha particles
- most of the mass must be concentrated at the centre and most of the atom is empty space
- the nucleus must be small since very few alpha particles are deflected by march
-it must be positive to repel the +ve charged alpha particles
3) the faster the alpha travelling the less it will be deflected
4) the more positively charged a nucleus the more an alpha particle will be deflected
5) the closer an alpha particle passes to the nucleus the more it will be deflected
what is the half -life?
the time is takes for level of radioactivity to halve
what does a short half-life mean?
the activity falls quickly because lots of the nuclei decay quickly
a long half-life means?
the activity falls more slowly because most of the nuclei don't decay for a long time
what is radioactivity measured in?
how do medical tracers work?
source of beta or gamma radiation is injected into the patient or swallowed. it penetrates the body tissues so can be detected externally- as it moves around the body a radiographer uses a detector to monitor its progress.a computer converts the reading to an on-screen display showing where the radiation is coming from- check whether the organs are working as they should
the radioactive source has to have a short half-life so you can use less of the source but still get a reading on your detector
why are beta and gamma more hazardous than alpha outside the body?
can penetrate the skin and soft tissues to reach the delicate organs inside the body- inside the body mostly passes straight out so doesn't do much damage
why is alpha dangerous?
does all damage in localised area- it collides with molecules in your cells causing ionisation which damages or destroys the molecules
what do lower doses of radiation tend to do?
cause minor damage without killing the cell-causes mutations which then divide uncontrollably= cancer
what do higher doses of radiation do?
kill cells completely, causing radiation sickness if a large part of your body i affected at the same time
why is radioactive waste hard to dispose of?
-lower-level can buried in secure landfill sites
-high-level is really dangerous as stays highly radioactive for thousands of years so sealed in glass blocks which are sealed in metal canisters- then buried deep underground
-hard to find suitable places to bury waste as the site has to be geologically stable, as big movements in the rock could distub the canisters and allow radioactive material to leak out-get into ground water and contaminate the soil, plants, rivers and drinking water
what protection to take using radioactive sources?
1) never allow skin contact and always hold with tongs as arm's length
2) keep source pointed away from the body and avoid looking directly at it
3) keep sealed in lead box whenever to being used
what precautions should people take who regularly work with radioactivity?
1- wear lead aprons and stand behind lead screens
2-wear protective full suits to prevent inhalation or lodging on the skin or under fingernails
3- use remote-controlled robot arms
what is nuclear fission?
the splitting of an atom, which releases energy
how does nuclear fission work?
a slow-moving neutron gets absorbed by a uranium-235 nucleus , the nucleus splits into some neutrons, which go onto hit other nuclei repeatedly=chain reaction, and two daughter nuclei=lighter elements- radioactive because wrong number of neutrons in them
each nucleus splitting gives out a lot of energy in the form of KE which can be converted to heat energy in the reactor by collision with other atoms