Recommended standards for γ-ray energy calibration (1999)

https://doi.org/10.1016/S0168-9002(00)00252-7Get rights and content

Abstract

A consistent set of γ-ray energies, generally with uncertainties of less than 10 ppm, is recommended for use in the energy calibration of γ-ray spectra. The energy scale used for the previously recommended standards (1979) has been modified to take into account subsequent adjustments in the fundamental constants (−7.71 ppm) and in the γ-ray wavelengths deduced from a revised estimate of the lattice spacing of Si crystals (+1.91 ppm). On this revised energy scale, the strong line from 198Au, the “gold standard”, has an energy of 411 802.05±0.17 eV, which is 2.4 eV (or 5.80 ppm) lower than the 1979 value. A significant improvement has come from the reduction in the uncertainty in the wavelength-to-keV conversion factor from 2.6 to 0.3 ppm. The criteria for the selection of γ rays to include are described. The list of γ-ray energies recommended for calibration, especially for Ge semiconductor detectors, has values for about 260 γ-rays from 50 radionuclides ranging from 24 to 4806 keV. Also, γ-ray energies are also given for about 70 additional lines, including 5 other radionuclides.

Introduction

During the 4th International Conference on Atomic Masses and Fundamental Constants in 1971, it became clear that progress in precision γ-ray spectroscopy, in particular the study of (n,γ) and (p,γ) reactions, was hampered by a lack of uniformity and precision in the γ-ray energy standards used. In May 1972 the IUPAP Commission on Atomic Masses and Fundamental Constants established a task group, including the authors of the present article, to produce, recommend, and publish a consistent set of calibrations standards for use in γ-ray spectroscopy.

In response to that charge, the authors produced such a list which was published in 1979 [1]. The energy scale for these γ-ray energies was based on a set of γ-ray wavelength measurements made at the US National Institute of Standards and Technology, NIST (then known as the National Bureau of Standards, NBS). Subsidiary measurements allowed these wavelength results to be quoted relative to the optical wavelengths that define the meter.

A revision of the 1979 list is desirable for three reasons. First, there is a revised value for the lattice parameter for the Si crystals used in the NIST γ-ray wavelength measurements; second, there is a new set of adjusted fundamental constants; and third, new high-precision measurements have been published. The first two changes result in a downward shift of the γ-ray energies by 5.8 ppm from the values given in 1979. The new adjustment of the fundamental constants has resulted in a significant reduction in the uncertainty in the wavelength-to-keV conversion factor, which in our 1979 results was often the dominant uncertainty on the keV scale. In the 1979 paper this uncertainty was quoted as 2.6 ppm, now it has been reduced to 0.3 ppm.

The γ-ray energies recommended in 1979 have not been simply scaled down by 5.8 ppm, since only a complete analysis can treat the many new data on an equal basis. Moreover, the set of γ-ray wavelength values, on which this energy scale is based, was revised by the NIST group in 1980 because of a re-analysis of the raw data. Therefore, we have chosen to carry out a completely new analysis.

All of the data used in this analysis are explicitly listed to make it clear which data have been used. We separate the various measurements into groups to show what was actually measured: absolute wavelengths, wavelength ratios, energy differences, or γ-ray energies.

We have taken the energy of the 412-keV γ ray from the decay of 198Au as the reference for the energy scale. The NIST absolute wavelength measurements do not convey this special status to this line and, in fact, all of their wavelengths have equal status. However, the majority of the relative wavelengths for γ rays from radioactive decay have been measured relative to this 198Au line. Therefore, it is convenient to use this line, the so-called “gold standard”, as the standard for this data evaluation.

In our 1979 paper [1], we discussed the mass-based scale on which the γ-ray energies could be given. As in that case, we have not made any use of this scale; see Wapstra et al. [2], [3] for discussions of the mass-based data.

We have divided this paper as follows: the definition of the energy scale (Section 2), the criteria for the selection of data (Section 3), the wavelength data and their treatment (Section 4.1), the Ge semiconductor data (4.2 γ-Ray energy differences from Ge detectors, 4.3 γ-Ray energies from Ge detectors), the recommended γ-ray energies (Section 5), and summary and comments (Section 6).

Section snippets

The γ-ray energy scale

The basis of the γ-ray energies that are reported herein is a set of measurements that relate the wavelengths of several γ rays to the optical wavelength standards. First, the wavelength of the photons from a 129I2(B)-stabilized HeNe laser was linked to the Cs oscillator frequency, yielding an uncertainty in this optical wavelength of 0.004 ppm. The measurements of γ-ray wavelengths require synthetic Ge and Si single crystals with high geometric perfection. The lattice spacing of a particular

Criteria for the selection of data

The current criteria for the selection of the sources and γ-ray lines to be included started from the criteria used in Ref. [1] and were then slightly relaxed in order to extend the list of recommended calibration lines, especially to include some short-lived nuclides.

The wavelength data and their treatment

The wavelength data used have been divided into two groups that are based on the type of measurement, namely, absolute wavelengths and relative wavelengths. The data in the first group come only from the NIST measurements with double-flat-crystal spectrometers, while those in the second group come from curved-crystal spectrometers and are measured relative to the wavelength of the 412-keV line from the decay of 198Au.

The results of the NIST wavelength measurements, which are given in Table 3,

Processing the data

The computations of the γ-ray energies are given in Table 7. This is a very complex set of data due to the many interrelationships between the energies of the various radionuclides. However, the usage of each piece of data from Table 3, Table 4, Table 5, Table 6 is given explicitly in this table, so the routes used are clear. For example, the 661(137Cs)–657(110mAg) energy difference could have been used in either direction, that is, to determine the 661 keV energy from the 657 keV value, or vice

Summary and comments

This article contains an up-date of the set of γ-ray calibration energies published in 1979 [1] by adjusting the earlier data for a revised value of the lattice spacing of Si crystals and for new fundamental constants. New measurements have also been added. This has resulted in a set of about 260 recommended γ-ray energies from about 50 radionuclides.

As noted in Section 4.2, some measured γ-ray energy differences are between two lines whose energies are known from the wavelength measurements in

Acknowledgements

We wish to acknowledge the assistance of E.G. Kessler, Jr., NIST, for his support over years in the interpretation of the NIST measurements and of C. Alderliesten, Utrech University, for his help in checking the many numbers in the tables. The death of Cor van der Leun in June 1998 was a great loss to the nuclear physics community and he will be missed by the surviving author and many others. The work of RGH was supported by the U.S. Department of Energy through the DOE Idaho Operations Office

References (55)

  • R.G. Helmer et al.

    Atomic Data and Nuclear Data Tables

    (1979)
  • E.R. Cohen et al.

    Nucl. Instr. and Meth.

    (1983)
  • R.D. Deslattes et al.

    Ann. of Phys.

    (1980)
  • E.R. Cohen

    Atomic Data Nucl. Data Tables

    (1976)
  • O. Helene et al.

    Nucl. Instr. and Meth.

    (1993)
  • Y. Lee et al.

    Appl. Radiat. Isot.

    (1992)
  • E.G. Kessler et al.

    Nucl. Instr. and Meth.

    (1979)
  • M.A. Ludington et al.

    Nucl. Phys.

    (1968)
  • B. Jeckelmann et al.

    Nucl. Inst. and Meth.

    (1985)
  • W. Beer et al.

    Nucl. Instr. and Meth.

    (1974)
  • O. Piller et al.

    Nucl. Instr. and Meth.

    (1973)
  • G.L. Borchert et al.

    Nucl. Instr. and Meth.

    (1975)
  • J. Kern et al.

    Nucl. Instr. and Meth.

    (1978)
  • R. Gunnink et al.

    Nucl. Instr. Meth.

    (1968)
  • R.G. Helmer et al.

    Nucl. Instr. and Meth.

    (1975)
  • R.C. Greenwood et al.

    Nucl. Instr. and Meth.

    (1970)
  • R.G. Helmer et al.

    Nucl. Instr. and Meth.

    (1971)
  • R.C. Greenwood et al.

    Nucl. Instr. and Meth.

    (1979)
  • E.K. Warburton et al.

    Nucl. Instr. and Meth.

    (1986)
  • G. Wang et al.

    Nucl. Instr. and Meth.

    (1988)
  • R.G. Helmer et al.

    Nucl. Instr. and Meth.

    (1981)
  • C. Wesselborg et al.

    Nucl. Instr. and Meth.

    (1991)
  • R.G. Helmer

    Nucl. Instr. and Meth.

    (1993)
  • R.G. Helmer

    Appl. Radiat. Isot.

    (1990)
  • R.G. Helmer et al.

    Nucl. Instr. and Meth.

    (1979)
  • C. Alderliesten et al.

    Nucl. Instr. and Meth.

    (1993)
  • H. Kumahora

    Nucl. Instr. and Meth.

    (1985)
  • Cited by (174)

    • Nuclear Data Sheets for A=141

      2023, Nuclear Data Sheets
    • Nuclear Data Sheets for A=242

      2022, Nuclear Data Sheets
    • Nuclear Data Sheets for A=147

      2022, Nuclear Data Sheets
    • Nuclear Data Sheets for A=203

      2021, Nuclear Data Sheets
    View all citing articles on Scopus
    1

    Deceased 17 June 1998.

    View full text