Gamma spectrometry with crystal detectors

Gamma spectrometry with Nal(Tl) crystals or solid state detectors such as Ge/Li or Si/Li systems. 

In an earlier section, I briefly mentioned the collection of the charge carriers produced by interaction of the gamma-ray with the detector crystal. If we are to understand some of the problems in gamma spectrometry, it is necessary to discuss charge collection and the mobility of the charge carriers in more detail. 

In 1947, Robert Hofstadter invented the sodium iodide thalhum-activated scintillation crystal, which made possible gamma energy spectrometry, pioneered by P.R.Bell and Craig Harris at ORINS. Spectrometry greatiy improved the efi dency of detection of radioactive tracers labeled with multiple radionuchdes. Crystal detectors were more sensitive in the measurement of radioactivity both in vivo and in vitro. 

The most common type of detector in current use for gamma-ray spectrometry is the coaxial HPGe detector in an aluminum can. These detectors are available with either a p-type or n-type crystal. The efficiency of a p-type detector typically decreases quickly below 100 keV whereas the n-type detectors can be used at energies as low as 3 keV with a beryllium window. 

---