Paper 1 - Radioactivity Flashcards
what is an isotope
a different form of an atom of the same element with the same number of protons but different number of neutrons, therefore having a different mass number
what are the three types of ionising radiation
alpha, beta, gamma
why is an atom unstable sometimes
isotopes are sometimes unstable because they have too many neutrons
when would an atom stop being radioactive
when it has formed into a stable new element
what is background radiation and where does it come form
radiation that is always present everywhere, coming from... cosmic rays from space living things buildings/air/food/soil/rock human activity eg nukes or nuclear waste
what is ionisation
when radiation emits a particle which knocks into a neutral atom and knocks off electrons from it, making it an ion
what is the relationship between penetrating power and ionising power
the more penetrating, the less ionising
features of alpha particles
they are helium nuclei mass number 4, atomic number 2 2 protons and 2 neutrons very heavy and slow strongly ionising electrically charged - therefore are deflected by electric and magnetic fields
features of beta particles
they are electrons
created when a neutron turns into a proton and an electron
relatively fast and small - moderately ionising
negatively charged so are deflected by electric and magnetic fields
features of gamma rays
no mass - just energy emitted only after the emission of a beta or alpha particle - never alone weakly ionising penetrate very well no charge, no deflection emitted when a nucleus has excess energy
effect of alpha particle emission on nucleus
mass number decreases by 4
atomic number decreases by 2
effect of beta particle emission on nucleus
mass number stays the same
atomic number increases by 1
effect of gamma emission on nucleus
everything stays the same
how to balance nuclear equations
the total atomic and mass number has to be the same on both sides of the equation
what is half-life
the time taken for half of the radioactive atoms now present to decay
how to find half life
divide total time by how many half lives in that time
how to find half life on graph
halve vertical axis and time corresponding time
penetrating power of alpha particles
blocked by paper, skin and even a few cm of air
penetrating power of beta particles
blocked by thin metal
penetrating power of gamma radiation
thick lead or thick concrete
uses of alpha radiation and how it works
fire alarms
Some smoke detectors use a piece of radioactive Americium, and α emitter. The α particles are sent into two chambers — one is a reference one, the other is open to air. Since the air is ionized in the process, a voltage difference between the two cells is measured. If smoke enters the chamber open to air, it affects the voltage difference between the smoke filled and reference chambers, and if this difference reaches a threshold, the alarm goes off.
uses of beta radiation and how it works
thickness gauges
beta radiation directed at piece of paper or metal being thinned
detector on the other side
detector senses changes in radiation, which causes it to adjust thickness
beta is used as it can penetrate paper/metal when thin, but not too well when thick
uses of gamma radiation and how it works
medical tracers
- radioactive source which emits gamma or beta is injected into body
- detected externally, allowing doctor to monitor progress
- checks if organs are working properly
- must have short half life so it is high enough to be detected but also doesn’t stay in body too long
tracers to check pipe leaks
-same concept, can detect where leak are in pipes
how is radiation used to treat cancer
radiotherapy which kills tumor
radiation for sterilisation
medical equipment / food - kills microbes
what is irradiation
exposure to radiation
what is contamination
when radioactive atoms get onto or into an object
what is nuclear fission
the splitting of a nucleus
what is nuclear fusion
the joining of two nuclei
describe the process of nuclear fission and chain reactions
slow moving neutron absorbed by a uranium -235 nucleus, causing nucleus to split which releases more neutrons which will collide with more nuclei and so on
what is formed when uranium is split (excluding neutrons)
two daughter nuclei form which are usually radioactive - this is nuclear waste
how is energy generated from nuclear fission
co2 pumped round the reactor which transfers the energy by heating to the water , which becomes steam and spins a turbine
how is overheating in a reactor prevented
boron control rods which absorb neutrons
what is the purpose of the moderator and what is it
graphite, water or heavy water which slows down neutrons so they can be absorbed by uranium nuclei
what happens in fusion
two lighter nuclei collide and fuse together to form a larger, heavier nucleus
the larger heavier nucleus doesn’t have as much mass as the two small ones combined as a lot is lost as it is converted to energy
problems of fusion
requires too high temperature and pressure in order to overcome electrostatic repulsion between nuclei that cannot be recreated on earth (yet)
