radioactivity and particles Flashcards
atomic (proton) number
the number of protons in the nucleus of an atom
mass (nucleon) number
the total number of protons and neutrons in the nucleus of an atom
isotope
atoms of the same element that have the same number of protons but a different number of neutrons
what are alpha, beta, and gamma particles/rays
alpha particles, beta particles, and gamma rays, are ionising radiations emitted from unstable nuclei in a random process
alpha particles
- 2 protons
- 2 neutrons
- overall 2+ charge
- strongly ionising due to large size and strong charge
- short range in air (5-8cm)
- stopped by single sheet of paper
beta particles
- (electrons) so overall 1- charge
- moderately ionising
- moderate range in air (a couple meters)
- stopped by thin sheet of aluminium
gamma rays
- electromagnetic waves, not particles
- weakly ionising
- highly penetrating
- stopped by thick layer of lead or concrete
- happens usually after alpha or beta decay as a way for the nucleus to get rid of extra energy
sources of background radiation in earth and space
- radon gas in the air
- cosmic rays
- food e.g bananas
- medical (e.g gamma rays for sterilisation)
- ground and buildings (the rocks)
the activity of a radioactive source
the activity of a radioactive source decreases over time and is measured in becquerels
half-life
the average time taken for the activity of that isotope to drop half of its initial value
- different for every different radioactive isotope
uses of radioactivity in industry and medicine
- radiotherapy: kills cancer cells and stops them dividing, involves high dose of gamma rays which are directed to kill the cells in the tumour
- sterilising food and equipment: food and medical equipment can be irradiated with a high dose of gamma rays, kill all microbes
- medical tracers: source that emits beta or gamma radiation is injected into the patient, radiation can be detected externally, detector is used to monitor its progress.
dangers of ionising radiation
- can cause mutations in living organisms (cancer)
- can damage cells and tissue
- high level radioactive waste is difficult to dispose of safely, sealed in glass blocks which are sealed into metal canisters but difficult to find a suitable place to bury them. site has to be geologically stable.
contamination vs. irradiation
irradiation: exposure to radiation, does not make the source radioactive
contamination: radioactive particles getting onto objects, contaminating atoms might decay and release radiation causing you harm
nuclear fission
slow moving neutron is fired at and absorbed by a U-235 nucleus which is unstable, making it even less stable. This causes it to split into two smaller radioactive daughter nuclei while releasing a small number of neutrons and a lot of kinetic energy. These fast- moving neutrons strike other U-235 nuclei triggering a chain reaction.
the role of control rods, moderators, and shielding in nuclear reactors
control rods: absorb neutrons by being lowered into the reactor which slows the rate of fission
moderator: material surrounding the fuel and control rods in the reactor which slows down the neutrons. the fast moving neutrons collide with the molecules in the reactor which causes them to lose momentum, slowing the rate of fission
shielding: absorbs hazardous radiation, made of thick layers of steel and concrete
