p7//2 Flashcards
what is the activity of a radioactive source
the number of unstable atoms in the source that decay per second
what is the unit of activity
Bq
how can we measure the radiocactivity of a sample
measuring the count rate which is number of counts per second
what is half life
is the aveerage time it takes for a radioactive isotopes nuclei to halve
draw the graph for half life
what is the count rate equation
initial count rate / 2^n
what is the number of unstable nuclei after n half lives equation
initial number of unstable nuclei/ 2^n
how is the flow of a substance through an organ measured
radioactive tracers
the patient is injected with a radioactive isotope that emits gamma radiation inside the organ
a gamma camera picks this up and builds an image of the organ
what must the half life be like for radioactive tracers
must be long enough to give a useful image but must decay shortly after image has been taken
what nuclear radiation destroys cancerous tumours
gamma radiation
how is gamma radiation used to destroy cancerous tumours
radioactive implants in the form of small seeds or rods are placed into cancerous tumours
the implants contain gamma or beta isotopes
what is nuclear fission
the splitting of an atom nucleus into two smaller nuclei
what does the fission process result In
two or three high speed neutrons
energy in the form of gamma radiation and kinetic energy
what substance is used mostly for nuclear fission
enriched uranium that contains 2-3% uranium 235
how can fission occur
if the uranium 235 or plutonium 239 absorbs a neutron
what occurs after a neutron collides with uranium 235 or plutonium 239
a chain reaction occurs
how is fission controlled in a nuclear reactor
one fission neutron per fission on average goes on to produce further fission
control rods in the reactor core absorb surplus neutrons
fast neutrons dont cause further fission so a moderator slows them down
what is nuclear fusion
process of forcing two nuclei close enough together so that they form a single large nucleus
how is nuclear fusion bought about
making two light nuclei collide at high speed
why is nuclear fusion hard
nuclei approaching each other will repel due to charge so they must be heated to give them enough energy to overcome repulsion
