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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.
Use the computer to start calculations
Locate the computer and make sure all values on the Weight Values and Calculate Counts tabs are filled correctly.
Switch to the third tab called Half-life Calculation and press the Evaluate button. Three plots will populate using the measured data and half-life is calculated. Discuss and verify the results with acknowledged books, teacher or supervisor.