Evaluation of the results

Now everything is measured, the values are stored in the computer and you need to calculate the results - weight/activity dependency (self-attenuation) and half-life of the present radionuclide.

The general formula for acquiring the half-life looks like this:

First of all lets plot the values of CPM per gram, one can see the self-attenuation gradually diminishing the effect or added weight.

The computation works as follows:

• Compute log(activity) for all samples
• Compute linear regression for the log(activity)/weight, remember the linear part (y-intercept) of the equation
• Compute antilog of the y-intercept

• Compute the lambda by dividing the antilog by number of 40-K atoms in each gram of KCl (9.69*10¹⁸)
• Compute the half-life by dividing ln(2)/lambda, giving total time in seconds if you started with CPS, or in minutes if you started with CPM. Divide by hours, days and years to get the half-time.