Example Spectra

Home Page | QCYK Reference | Long Background | 200 ksLT Background | IAEA RGU | IAEA RGTh

These spectra are presented to illustrate points made in the book. Each is split into four energy ranges and displayed, together with an analysis on separate pages.

The spectra are available for download, so that you can analyse them yourself. The spectra are in ORTEC .spc format, saved as a .an1 file containing all the analysis parameters.

QCYK Reference Material

QCYK is one of the reference materials routinely used for spectrometer calibration. It contains the a number of nuclides covering the energy range 60 keV to 1936 keV. In the order of their lowest energy gamma-ray used for calibration, the nuclides are:

241Am (a), 109Cd (UC), 57Co (EC), 139Ce (EC), 203Hg (b-), 113Sn (EC), 137Cs (b-), 54Mn (EC), 88Y (EC), 65Zn (EC) and 60Co (b-).

The spectrum represents 10.3 kBq, total activity, of QCYK absorbed on a 5 cm diameter filter paper and measured on the cap of a 45% n-type HPGe detector of resolution about 1.8 keV at 1332.5 keV. Several of the nuclides decay by electron capture and their gamma-rays are accommpanied by electron capture X-rays. These factors mean that there is considerable true coincidence summing. Analysis of this spectrum reveals a many of the spectral features discussed in Chapters 2 and 8 - sum peaks (coincidence and random), single and double escape peaks, germanium escape, for example.

The low energy part of the spectrum is dominated by X-rays arising from electron capture. There are many overlaps and, because of the relatively poor resolution (about 1 keV) at low energy, precise identification is difficult. The attributions given in the figure should be taken with a pinch of salt.

The efficiency calibration derived from this spectrum is also described.

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A Very Long Background

This spectrum was sent to me by Peter Bossew of the University of Salzburg. It is a collation of a large number of spectra measured over a number of years. This particular spectrum represents a count period of 15,240,200 seconds live time (176 days). Peter has also reported the analysis of a collated spectrum representing 3.3 years-worth of counting over 16 years of operation. (Applied Radiation and Isotopes 62 (2005) 635644)
The analyses presented illustrate some of the more esoteric effects explained in Chapter 13, where detector background is discussed. The decay schemes of 214Bi and 228Ac, in particular are very complex and there is always potential for coincidence summing. Some minor peaks for which identification is, at best, tentative could be sum peaks.

This spectrum is available in ORTEC's spc and chn formats and Canberra's MCA format. I don't guarantee that the translation to other formats is perfect.

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Download MCA
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A Typical Background Spectrum

This spectrum was a routine background measured over a weekend using a 45% n-type detector, about 1.8 keV at 1332.5 keV, mounted in a standard 10 cm thick graded lead shield located in an unremarkable counting room in a location with no special geological or altitude considerations. (Count period 200,000 seconds live time.) This is presented merely to show what to expect under more typical circumstances than those relevant to Peter Bossew's spectrum. Note the comments above on the possibility of sum peaks.

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IAEA RGU-1 Reference Material

This is a reference material prepared by the AQCS (Analytical Quality Control Service) of the IAEA by mixing CCRMP Uranium ore BL-5 with grain size matched silica sand. The certified concentration of uranium is 400 2 mg/g, which translates to 4.938 0.025 Bq/g of 238U and 0.2303 0.0012 Bq/g of 235U.

Sample geometry was 158.61 g (120 cm3) of RGU-1 in a cylindrical polystyrene tub placed at the centre of the detector cap. Sample height was 41 mm and the thickness of the tub base 2mm. Because the sample is directly on the detector face, there is a likelihood that some minor peaks will be sum peaks or have an enhanced peak area because of summing.

Full details of RGU-1 can be found at http://www.iaea.org/programmes/aqcs/pdf/rl_148.pdf

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IAEA RGTh Reference Material

This is a reference material prepared by the AQCS (Analytical Quality Control Service) of the IAEA by mixing CCRMP thorium ore OKA-2 with grain size matched silica sand. The certified concentration of thorium is 800 16 mg/g, which translates to 3.246 0.065 Bq/g of 232Th. The material also contains 6.3 mg/g of uranium.

The sample measured was 163.85 g (120 cm3) of RGTh-1 in a cylindrical polystyrene tub placed at the centre of the detector cap. Sample height was 41 mm and the thickness of the tub base 2mm. Because the sample is directly on the detector face, there is a likelihood that some minor peaks will be sum peaks or have an enhanced peak area because of summing.

Full details of RGTh-1 can be found at http://www.iaea.org/programmes/aqcs/pdf/rl_148.pdf

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