Guide
1
The half-life is constant for the substance.It is not influenced by such external factors as pressure and temperature.However, it should be noted that the isotopes of the same material value of the desired value may be very different.This does not mean that the two half-lives fall apart all the substance.The initial number of atoms will decrease the probability of a given for him in each period by about half.
2
Thus, for example, ten grams of oxygen isotopes 20, whose half-life is 14 seconds, after 28 seconds will be 5 grams, and after 42 - 2.5 grams, and so on.
3
This value can be expres
sed using the following formula (see. Figure).
where τ - the average lifetime of an atom of matter, as λ - the decay constant.Since ln2 = 0,693 ..., it can be concluded that the half-life of approximately 30% shorter than the lifetime of the atom.
4
Example: Suppose that the number of radioactive nuclei that are capable of conversion for some short period of time t2 - t1 (t2 ˃ t1), is N. Then the number of atoms, which are degraded during this time should be denoted by n =KN (t2 - t1), where K - coefficient of proportionality is equal to 0.693 / T ^ 1/2.
According to the law of exponential decay, ie, when the unit time splits the same amount of material for uranium-238 can be calculated that for the year breaks down as follows the amount of substance:
0,693 / (4,498 * 10 ^ 9 * 365 * 24 * 60* 60) * 6.02 * 10 ^ 23/238 = 2 * 10 ^ 6, where 4,498 * 10 ^ 9 - the half-life, and 6.02 * 10 ^ 23 - the amount of each element in grams is numerically equal to the atomic weight.