Gamma Spectrum Analysis

Most radioactive sources produce gamma rays of various energies and intensities. These emissions are analyzed with a multichannel analyzer that produces a gamma energy spectrum. A detailed analysis of this spectrum allows the identity and quantity of gamma emitters present in the source to be determined. 

2 Developing Analytical Methods — Thermal Dissociation oe Compounds 

FIGURE 6.22 A HGA used for the atom spectrometric determination of trace elements in solid or dissolved samples. The graphite tube is connected as resistor between two graphite contact cylinders. Quartz window seals are attached to both ends of the primary beam plane, and the entire unit is water cooled. 

The reaction that leads to free atoms is mainly determined by the reductive properties of carbon. The reactions in a graphite tube that finally lead to atomization start in most cases from the oxides. The following mechanisms of atomization are imaginable  

Thermal dissociation in the solid phase takes place if the decomposition point of the product is signihcantly lower than its vaporization point. In the opposite case, thermal dissociation takes place in the gas phase. Halides usually have a significantly lower dissociation temperature than the corresponding oxides that is, dissociation in solid phase is barely possible. The extremely high electron density in a graphite tube at temperatures above 1200°C can lead to a reduction of stable metal oxides of, for instance, iron, chromium, and manganese in solid or liquid phase. This reduction is typically observed at temperatures of around 500°C lower than the dissociation point of the oxides. The last reaction is the dissociation of carbides in the gas phase  

---

Aamio, P.A., Routti, J.T., Sandberg, J.V., and Winberg, M.J., Adapting gamma-spectrum analysis program SAMPO for microcomputers. Nucl. Instrum. Meth., 219 (1984) 173. 

Aarnio, R, Nikkinen, M., and Routti, J., Gamma Spectrum Analysis Including NAA with SAMPO for Windows. J. Radioanal. Nucl. Chem., 193, 179, 1995. 

There are several potential sources of radioactive materials that can contaminate water (see Chapter 4, Section 4.14). Radioactive contamination of water is normally detected by measurements of gross P activity and gross a activity, a procedure that is simpler than detecting individual isotopes. The measurement is made from a sample formed by evaporating water to a very thin layer on a small pan, which is then inserted inside an internal proportional counter. This setup is necessary because P particles can penetrate only very thin detector windows, and a particles have essentially no penetrating power. More detailed information can be obtained for radionuclides that anit y-rays by the use of gamma spectrum analysis. This technique employs solid-state detectors to resolve rather closely spaced y peaks characteristic of specific isotopes in the sample s spectra. In conjunction with multichannel spectrometric data analysis, it is possible to determine a number of radionuclides in the same sample without chemical separation. This method requires minimal sample preparation. 

The sensitivity of analytical methods for trace elements needs to be high, and ideally the reaction or property utilized should be entirely specific. The sensitivity of activation analysis is dependent on the element estimated and in many cases it is extremely high. Specificity is covered by three parameters, half-life of the nuclide produced, its maximum beta energy, and its gamma spectrum. 

The analysis shown that gamma spectrum was compatible only with a hadronic origin(7ro decay)... 

Activation analysis has been proposed to obtain more reliable analytical information.73 The sample is irradiated with neutrons, photons (gamma radiation), or charged particles the radioactivity generated is measured by sensing the entire gamma spectrum with a semiconductor detector. The most reliable variant is neutron activation analysis (NAA).73... 

Note 6. Combining the inequality constraint 0] with known Internal Poisson variance has been used by Guinn for total variance estimation in activation analysis ( 2), by Donahue (88) for the same purpose in accelerator mass spectrometry, by Heydorn (18.89) for the analysis of precision of gamma ray spectrum analysis, and by Currie ( ) for optimal weighting in counting experiments. The variance weighted t approximation derives from work by Cochran (90). Cochran s work, however, applied to a somewhat different model than used here. The statistical properties of this extension of his technique have not been studied. 

Medhat ME, Abdel-Hafiez A, Awaad Z and Ali MA (2005) A routine package for gamma-ray spectrum analysis and routine activation analysis ... 

The uranium content in soil samples collected in the Lesser Himalaya area was determined by gamma spectrometry (Ramola et al. 2011). The samples were collected from a depth of 60 cm and after removal of vegetation and stones were dried at 110°C for about a day. The samples were crushed to a fine powder and sieved and the <150 pm fraction was selected for analysis. Samples were placed in Marinelli beakers and stored for 1 month to establish secular equilibrium prior to measurement for 24 h of the gamma spectrum with liquid nitrogen-cooled HPGe detector. Here too, the and " Pb photopeaks were used to estimate the content in the samples. 

Investigation of the Phenomenon of Controlled Gamma Decay by Analysis of Deformation of Mossbauer Gamma Spectrum... 

The object of energy calibration is to derive a relationship between peak position in the spectrum and the corresponding gamma-ray energy. This is normally performed before measurement, if only in a preliminary manner, but it is usual for spectrum analysis programs to include more sophisticated calibration options. 

More often than not, spectrum analysis software is purchased with the hardware, if only to be certain of compatibility between them, and the market is dominated by software produced by the major gamma spectrometry equipment manufacturers. There are, however, a small number of software providers, independent of the manufacturers, providing reputable programs at a much lower cost these are worthy of consideration. Such companies may be more amenable than the major players to rapid bug-fixes when problems in their programs are identified and may be prepared to customize the program to suit a particular buyer. 

In most branches of analytical science, methods are checked and monitored using reference materials. When purchased, these are accompanied by a certificate that specifies the concentration, with an associated uncertainty, for a number of chemical entities. These will have been analysed by at least two different analytical methods and provide benchmarks against which methods and laboratories can be assessed. Indeed, gamma-ray spectrometrists plying their trade in the service of neutron activation analysis would utilize such reference materials routinely. The corollary for testing gamma-ray spectra would be to have available reference spectra that contained peaks at known positions containing known numbers of counts. It would be unrealistic, perhaps, to expect one spectrum to test aU aspects of spectrum analysis but a small number of... 

Blaauw, M., Fernandez, V.O. and Westmeier, W. (1997). IAEA gamma-ray spectra for testing of spectrum analysis software, Nucl. Instr. Meth. Phys. Res., A, 387, 410-415. 

---