Calculate decay constant and rate.
The decay constant is the probability per unit time that any single nucleus decays, and it is fixed by the half-life through lambda equals ln 2 over the half-life. Activity — the number of decays per second, measured in becquerels — is that constant multiplied by however many atoms are present, which is why activity falls as a sample ages even though the decay constant never changes. The mean lifetime is the reciprocal of lambda and is always longer than the half-life by a factor of about 1.44.
Decay constant and activity
lambda = ln 2 / half-life; mean lifetime = 1 / lambda; activity A = lambda x N; decays over t = N x (1 - e^(-lambda t))
Educational calculation. Handling radioactive material and assessing radiation dose require qualified health physics oversight and compliance with local regulations.
Because the distribution of individual lifetimes is exponential and has a long tail. The mean is 1/lambda while the median — the half-life — is ln 2 divided by lambda, making the mean about 1.44 times longer.
One becquerel is one decay per second. One curie is 3.7 x 10^10 becquerel, originally defined as the activity of one gram of radium-226.
For practical purposes no. Nuclear decay is insensitive to chemical environment and ordinary conditions; only exotic cases such as electron-capture isotopes under extreme ionisation show measurable shifts.