Gamma energy spectrometry

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 recent general availability of solid state Ge(Li) gamma-ray detectors has made possible new applications of activation analysis to multielement trace analysis. A simplified schematic representation of a Ge(Li) detector is given in Fig. 6. The principal advantage of these detectors is their excellent energy resolution for gamma-ray spectrometry 52>. While a typical 3 X 3" NaI(Tl) scintillation crystal may have a photopeak resolution of 50 KeV fwhm (/ull width at Aalf maximum) for the 137Cs... 

Nielson, J. M., and H. A. Kornberg Multidimensional Gamma-Ray Spectrometry and its Use in Biology. Radioisotope Sample Measurement Techniques in Medicine and Biology, pp. 3—15. Vienna International Atomic Energy Agency 1965. 

H. L. Beck, et al, In Situ Ge(Li) and Nal(Tl) Gamma-Ray Spectrometry, U.S. Department of Energy, Environmental Measurements Laboratory, HASL-258, September 1972. 

The Working Level (WL) is equal to any combination of the short-lived decay products of Rn in I L of air resulting in the ultimate emission by them of 1.3 x 10 MeV of alpha-particle energy (obtained from 9800 Rn atoms or about 0.5 pCi/L). Equivalent uranium (eU) is U concentration estimated from the Bi concentration (usually determined by gamma-ray spectrometry) assuming secular equilibrium. 

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. 

Standard Test Method for Determination of Impurities in Uranium Dioxide by Inductively Coupled Plasma Mass Spectrometry Standard Test Method for Gamma Energy Emission from Fission Products in Uranium Hexafluoride... 

Water quality Determination of the activity concentration of radionuclides by high resolution gamma-ray spectrometry Nuclear energy Chemical separation and purification of uranium and plutonium in nitric acid solutions for isotopic and dilution analysis by solvent chromatography... 

In gamma-ray spectrometry the pulse height scale has to be calibrated in terms of absolute energy in keV to identify unknown gamma-ray emitters. For this purpose the channel position of the maximum of each... 

See also Radiochemical Methods Gamma-Ray Spectrometry. Surface Analysis X-Ray Photoelectron Spectroscopy. X-Ray Absorption and Diffraction X-Ray Diffraction - Singie Crystal. X-Ray Fluorescence and Emission X-Ray Fluorescence Theory Wavelength Dispersive X-Ray Fluorescence Energy Dispersive X-Ray Fluorescence Total Reflection X-Ray Fluorescence Particle-Induced X-Ray Emission Synchrotron X-Ray Fluorescence. 

Gamma spectrometry is performed mainly by using MCAs, and the relation between the obtained pulse height or corresponding channel number and gamma energy must be established. When an absolute method of standardization is applied, the peak detection efficiency p of the detector with surrounding material must also be measured. 

We have already seen that gamma emissions are the result of transitions between the excited states of nuclei. As the whole technique of gamma spectrometry rests on (a) the uniqueness of gamma energies in the characterization of radioactive species, and (b) the high precision with which such energies can be measured, it is of interest to consider briefly some relevant properties of the excited states. 

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