Y-ray spectrum

The y-energies are characteristic of the nuclear energy levels and transitions. Figure 10.12 shows the appearance of a y-ray spectrum. Such spectra are of immense value in the identification and determination of radionuclides in a radioactive mixture. 

For example, a) in (radioactivity) counting experiments a non-Poisson random error component, equal in magnitude (variance) to the Poisson component, will not be detected until there are 46 degrees of freedom ( ), and b) it was necessary for a minor component in a mixed Y-ray spectrum to exceed its detection limit by -50 , before its absence was detected by lack-of-fit (x, model error) (7). 

We conclude this chapter by presenting several examples of deconvolution of real data. Most of these examples represent deconvolutions of data that were used as part of a spectral analysis rather than generated as deconvolution examples or tests. The examples include high-resolution grating spectra, tunable-diode-laser (TDL) spectra, a Fourier transform infrared spectrum (FTIR), laser Raman spectra, and a high-resolution y-ray spectrum. 

Several major differences existed between this scheme and one compatible with the PBR facilities. The PBR did not have an operating pneumatic transfer irradiation facility, nor was there a sophisticated y-ray spectrum analysis and data reduction computer program available. Irradiation facilities at PBR were hydraulic. Aluminum capsules (rabbits) were used to contain and transfer samples to and from the core. 

A number of special techniques have evolved to increase the detection sensitivity in y-ray counting. One of the most important is the suppression of the Compton scattering events in the y-ray spectrum by the use of anticoincidence annulus around the central y-ray detector. The idea behind a Compton suppression spectrometer is that most events in which the incident photon undergoes one or more Compton scattering events in the central detector will result in partial energy deposition in the detector with a low-energy photon escaping the detector. 

Fig. 1. (Top) y-Ray energy spectrum of the reaction 19F(p,ay)160 measured by a 3-inch Nal detector. Proton energy is 2.7 MeV, sample material is fluorapatite. (Middle) y-Ray energy spectrum for the same reaction acquired by a high purity germanium detector. The sample is meteoritic material. Low energy lines from several other nuclear reactions can be identified. (Bottom) Low-energy y-ray spectrum from 19F(p,p y)19F inelastic scattering recorded with a thin Ge(Li) detector. Reproduced with permission from Grambole and Noll [59],...

Figure 10.18. y-Ray spectrum of a soil sample from Belarus showing the identification of 4Cs and 1 J7Cs fallout from the Chernobyl accident... 

A typical y-ray spectrum taken with a Ge(Li) detector is shown in Fig. 7.15. Because of the different mechanisms of y-ray absorption (section 6.4) y-ray spectra... 

Quantitative y-ray spectrum analysis of environmental samples such as soil, water or ash of food requires the peak efficiency for volume sample. A Marinelli beaker is often used as a container for a large quantity of sample such as water or soil. As the volume of sample to be measured is usually fixed, the absolute peak efficiency is dependent on energy only, but affected by self-absorption which depends on density of matrix and the elemental composition. The method to be used for determination of the peak efficiency is based on experimental procedures involving the following steps ... 

Filter paper impregnated activated carbon Gaseous (volatile material) " 1,3 S, 2 Hg Gross P-and y-ray measurement y-ray spectrum analysis... 

More often, these occur in multiple steps with the releaseof y-Ray photons of multiple energy. Thus, the resulting y-Ray spectrum is unique to the decaying radionuclide this uniqueness, therefore, is used to identify the unknown nuclide. y-Rays with no mass and charge can penetrate into matter and bring about other chemical reactions in the system. y-Rays are widely used in nuclear medicine. 

For every radionuclide, the deexcitation steps and the corresponding y-ray energies provide a unique y-ray spectrum, which can be used to identify unknown nuclides. Because y-rays are high-energy photons, they interact with matter much less strongly than do a- and P-particles and consequently their penetrating power is very high and more difficult to shield. 

Irradiation Facility. The swimming pool type irradiator includes an irradiation chamber (4 X 4 X 2.3 m) connected to a 4-m-deep pool where the Co panel source is stored (Figure 1). The source activity at present is 7.4 X 10 Bq (2 x 10 Ci), with a permissible maximum of 3.7 X 10 Bq (10 Ci) for this facility. Co gives a very simple y-ray spectrum, two sharp lines of equal intensity at 1.17 and 1.33 MeV. 

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