Question

Explain the nature of escape peaks in gamma spectroscopy with a HP Ge detector. How does their efficiency depend on the geometry of the detector?

Answer 1

Answer:

In Gamma Spectrum with HP Ge detector, there are two kinds of escape peaks:

1. Single Escape Peak

2. Double Escape Peak

So, the Single Escape Peak appears due to the escape of one of the 511KeV gamma ray produced in the pair production and it appears at (E-511) KeV as shown in figure below in red mark.

The double Escape Peak appears due to escape of both of the 511KeV gamma ray produced in the pair production and it appears at (E-511) KeV as shown in figure below in red mark:

The peak shape is Gaussian in nature, which when differentiated two times i.e. when its second derivative is taken, gives a central large negative peak flanked by two smaller positive peaks. Whereas a smooth background gives, a constant first derivative and hence a zero second derivative and a Compton edge gives only one positive peak instead of two peaks as in a Gaussian peak. This behavior of the second derivative is considered as the signature of the peak and it is located at the center of the negative lobe. If there are two or more close by peaks than the behavior will be still different from a single peak.

Part B:

It depends by a factor of 4 pi.