Pulse Shape Discrimination

Pulse shape discrimination:

When studying the two waves above (Gamma and Neutron), one can notice that they look very similar. The peak height is about the same and the beginning of the wave is quite similar as well. The tails of the waves, however, differ in the fact that the gamma wave approaches zero at a faster rate than the neutron wave.

NASA takes measurements by looking at the ratio between the area under the peak and the area under the tail of the curve. This ratio is called the pulse shape.

Then they graph the pulse shape vs. pulse height shown in the top center of the phot above. This allows one to see the differences between gamma rays and a neutron.

Note:

When studying gamma rays, one must observe the movement of the electrons because gamma rays cannot be directly observed. As shown in the top right corner of the photo above, the gamma rays will come in and “bump” an electron. By studying the paths of these electrons, one can easily tell where the gamma rays are coming in from.

Similar to the gamma rays, one cannot directly observe the path of a neutron. One could observe the path of a proton that has been “bumped” by a neutron instead. As shown by the diagram on the right center of the photo above, there can be more than one detector to find the path of the neutron by observing the different paths of the protons.