Long term variations in background due to recoil effect in a silicon detector based alpha spectrometer

Detection limits (DL) play an important role in the assessment of radionuclides exposure due to actinides incorporated in the human body. DLs primarily depend on the background count rates of the detection system and the need is also to maintain a steady and constant background over a long period of its use. Generally users are particularly concerned of detector contamination with recoil nuclei while counting the standards and/or samples. During the decay of alpha sources, the recoil atoms which generally are also radioactive, hit the surface of the detector or the vacuum chamber walls and may lead to the contamination. This paper gives the variations observed in background of four detectors, operational over four years and suggest corrective measures for eliminating/minimizing the recoil contamination. For low level counting applications, the recoil contamination is not as serious a problem generally associated with high level counting. The simple ways of addressing the contamination are: Gentle cleaning of chamber and later the detector with damp cotton, operating the chamber at slightly higher pressure than specified 50 mT and replacing the detector is also not an expensive option