How would you perform linear energy calibration for Co60 photopeaks?

[soopo]

Homework Statement

The data obtained in the experiment is in the graph
http://img213.imageshack.us/f/energycalibration.png/

My teacher says that do a linear energy calibration for photopeaks.

The Attempt at a Solution

A photopeak seems to be a peak caused by the emission of photons only.
My attempt is in the image. I assume that the two last peaks are photopeaks.

How would you do the linear energy calibration for the photopeaks of Co60?

 

[NateD]

To do a linear energy calibration for the photopeaks of Co60, you will need to plot the peak energies of the Co60 photopeaks against their corresponding channel numbers. This will form a line and the slope of this line will be used to calculate the energy of any peak in the spectrum. To do this, you will need to determine the two peak energies of the Co60 photopeaks. To do this, you can use the graph above. For the first photopeak (at channel 400), you can determine the energy from the graph as 11.7 keV. For the second photopeak (at channel 700), you can determine the energy as 13.4 keV. You can then plot these two points on a graph with the channel numbers on the x-axis and the energies on the y-axis. This will form a straight line and the slope of the line will give you the linear energy calibration of the Co60 photopeaks. The equation of the line will be in the form of y = mx + c, where m is the slope and c is the intercept. From this equation, you can calculate the energy of any peak in the spectrum.