Explain the following statement: In a windowless proportional counter, the output pulse height from an alpha particle source will increase with increasing alpha energy whereas for beta particles the opposite is true.

Regarding α and β Particles in Windowless Counter, the range of α particles is lower than β particles. Alpha particles typically have range less than the dimensions of the gas chamber so that proportional counters are able to easily record. Hence, with almost 100% efficiency, each particle which enters the so called active volume.

Then, since the pulse height spectra depends on the number of ion pairs which have formed, an aplha particle with higher energy creates more ion pairs in the chamber. However, beta particle range usually exceeds the dimensions of the chamber and therefore most of the betas hit the walls where they deposit energy. Then, fewer ion pairs are formed because very few β’s give their energy to the bulk gas.