E.3.3 Half Life

Actvity

number of decays per second measured in Bq

graoh for actvity vs time will be exponential, since rate of decay is directly proportional to number of nuclei

same as the rate of rate of emission

count rate

number of alpha, beta, or gamma detected by a Geiger counter every second (decays per second)

the higher the activity of a source, the higher the count rate

half life

the amount of time it takes for half the nuclei to decay.

short half-life = rapid decay

also teh same as rate fo emission, as for each decay a radioactiv particle is emitted

background radiation

there is radioactive isotopes in almost everything , this a shield is needed in experiments so that the Geiger-Muller count pick up on background radiation

• but some come through causing systematic error

examples:

• rocks, the air may contain radon gas from rocks, and the sun

foam decay curve

the foam height halves in equal times, irrespective of the chosen height

decay constant

the probability of decay per unit time. constant for a given isotope, regardless of how many nuclei are present or how long decay has been going on for

the higher the probability the faster the decay

examples of application of radioactive isotopes

• the americium in smoke detectors because of its alpha decay has a large half-life, thus does not have to be replaced

• beta emitters an be used in automated control of paper mills, because the count rate is reduced when paper is too thick