Fast neutron damage to HPGe Detector

A decrease in the energy resolution of a large HPGe was first seen after the irradiation of 5*10^7 n/cm^2<ref>P. H. Stelson, J. K. Dickens, S. Raman, and R. C. Trammell, “Deterioration of Large Ge(Li) Diodes Caused by Fast Neutrons,” Nuclear Instruments and Methods 98,481 (1972).</ref>, so 5*10^6 n/cm^2 is a safe number to stay under.

The maximum flux occurs right at the center of the detector, where the expression for flux simplifies to [math]n_{rate}\frac{1}{4\pi d^2}[/math]. The number of days it would take to reach an integral flux of [math]5\times 10^6 n/cm^2 [/math] as a function of the CF-252 source distance HPGe face is shown below. The graph assumes the activity of the Cf252 source on 01/2017, which is 19066 n/s.

References

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