It is accepted to understand some period for which a half of kernels of this amount of substance manages to break up as a half-life period (particles, kernels, atoms, power levels, etc.). This size is the easiest to use as full disintegration of substance never happens. The broken-up atoms can form some intermediate states (isotopes) or enter interactions with other elements.
Instruction
1. The half-life period is constant for the corresponding substance. It is not influenced by such external factors as pressure and temperature. However, it should be noted that at isotopes of the same substance the value of required size can differ very strongly. At the same time does not mean at all that for two half-life periods all this substance will break up. The initial amount of atoms will decrease with the probability set for it during every period approximately half.
2. Thus, for example, from ten grams of isotopes of oxygen-20 which half-life period is equal to 14 seconds in 28 seconds there will be 5 grams, and through 42 - 2.5 grams and so on.
3. This size can be expressed, using the following formula (see the drawing). Here τ – the average time of life of atom of substance, and λ – a disintegration constant. As ln2 = 0.693..., it is possible to make the conclusion that the half-life period is about 30% shorter, than atom life time.
4. Example: let the number of the radioactive kernels capable to transformation for some short period of t2 - t1 (t2 ˃ t1), makes N. Then the number of atoms which decay during this time follows will designate through n=KN (t2 - t1) where To – proportionality coefficient equal 0.693/Т^1/2. Under the law of exponential disintegration that is when the same amount of substance in unit of time breaks up, for uranium-238 it is possible to calculate that in a year the following amount of substance breaks up: 0.693/(4.498*10^9*365*24*60*60) *6.02*10^23/238=2*10^6, where 4.498*10^9 – a half-life period, and 6.02*10^23 - quantity of any element in grams, in number equal to atomic weight.