High-resolution Gamma-ray Spectrometer Research Articles

Gamma-ray energies of radionuclides formed by uranium fission and photon activation

The knowledge of the precise gamma-ray energies of the nuclides is very important for various applications in applied gamma-ray spectrometry such as qualitative activation analysis and the purity study of tracers. The gamma-ray energies cannot always be found with the required precision of better than 0.2 keV in the literature because up to now the decay scheme of a considerable fraction of the isotopes have not been restudied with high resolution gamma-ray spectrometers. Moreover for those isotopes that have be restudied with high resolution detectors, the precision of the gamma radiation is sometimes insufficient for identification purposes. The gamma radiation energies of radioisotopes formed through neutron capture in a nuclear reactor were therefore carefully reevaluated with a high resolution Ge(Li) gamma-ray spectrometer. These data were compiled in tables to assist in the identification of unknown isotopes and were published previously 1'2. Besides they were used as the basis for a computer assisted automatic identification routine? Unfortunately, these tabulations did not take into account isotopes formed solely through uranium fission with the result that the identification is not always possible when uranium is present in the neutron activated sample. It was hence decided to supplement the tabulation with the most abundantly formed fission isotopes. A number of these are already present in the previous tables because they are also formed through (n, ~) or threshold reactions. Other isotopes were measured in a similar manner as explained in a previous article. 1 As a rule all gamma-ray emitters with a cumulative fission yield of more than 0.1, were included. Omissions are 91y, aOTRh ' ~2Ag ' mLa ' ~43La ' 145pr ' j46pr and all antimony fission nuclides except 125Sb" Precise energy calibration was achieved with a number of calibration lines whose gamma energies are sufficiently well known. As a rule these were taken from the table provided by LEDERER. a The following calibration energies were used: 7Be (477.57 keV), 22Na (1274.53 keV, 511.006 keV), 46Sc (889.18, 1120.41 keV), 24Na (1368.53, 2753.6 keV), 54Mn (834.84 keV), 57Co (121.97 keV, 136.33 keV), * Reprints can be ordered from the Co-ordinating Editor (Price: 2 US $).

System Requirements for High-Resolution Gamma-Ray Spectrometry at High Counting Rates

The full potential of high-resolution gamma-ray spectrometers has been severely hampered by degradation in the quality of the pulse-height spectrum at high input data rates. Over the past year or two considerable effort has been expended in the examination of this problem. This paper will briefly review the nature of these instrumental difficulties, define realistic experimental requirements, and illustrate state-of-the-art solutions to these problems. A DC-coupled system which has been developed in our laboratory for high-rate applications will be described and performance presented.

A pair and escape-suppressed spectrometer using Ge(Li) and NaI(Tl) detectors designed for accelerator experiments

A high resolution gamma-ray spectrometer consisting of a 40 cm 3 Ge(Li) detector located at the common centre of two semi-annular NaI(Tl) detectors has been assembled for use in particle accelerator experiments. The three detectors are operated in a triple coincidence and an anti-coincidence mode, simultaneously yielding pair and escape-suppressed spectra in which background and the multiplicity of gamma-ray peaks are reduced. In the pair spectrometer mode the background is reduced considerably relative to the double escape peak e.g. a factor of 20 for a 3.85 MeV gamma ray, and in the escape-suppressed mode by a factor of three to four. The performance of the spectrometer is demonstrated using a Pu- 10B gamma-ray source.

A High-Resolution Gamma-Ray Spectrometer for Use in Outer Space

Preliminary tests indicate that a suitable electronics subsystem for a large-area, high-resolution gamma-ray spectrometer is well within the present state-of-the-art. This subsystem can be made to operate with sufficient precision within the temperature, power, weight and volume constraints typical for space instruments.

Investigation of the96Nb disintegration scheme by means of a high-resolution lithium-ion drift germanium gamma-ray spectrometer

The decay of the 24 h96Nb has been the subject of an extensive investigation in order to obtain more detailed information about the level structure of the even-even nucleus96Mo. For such a purpose, a high-resolution lithium-ion drift germanium γ-ray spectrometer has been used. The higher resolution of this γ-ray detector compared to the NaI scintilation spectrometers used in the previous investigations revealed the existence of several previously unreported γ-rays and allowed to measure their energies and intensities with high accuracy. For instance, the composite peak at about 800 keV in the spectrum of the96Nb decay was very well resolved in its 779, 811 and 851 keV components. Moreover, from the precision energy measurements of the transitions appearing in the decay of96Nb, it could be established that the 459.5, 569.3 and 811 keV γ-rays do not de-excite a single level of the even-even96Mo as previously reported, but the 459.5 keV transition de-excites a level at 2438.5 keV, whereas the 569.3 and 811 keV transitions de-excite a 2440.5 keV level. Furthermore, the existence of the second 2+ vibrational level at 1499 keV in96Mo, excited in the96Nb decay, has been shown and the value of the radio cascade/crossover has been measured and found equal to 2.27±0.55. From the measured value of the cascade/crossover ratio and from the knownɛB(E2)exp quantity, found by means of Coulomb excitation experiments, theB(E2, 2+′→0+)d andB(E2, 2+′→2+)d reduced electromagnetic transition rates for the second two plus state have been determined together with the ratioR=(B(E2, 2+′→2+)d)/(B(E2, 2+′→0+)d). The results areB(E2, 2+′→0+)d==(0.32±0.08)·10−50,B(E2, 2+′→2+)d=(3±0.95)·10−49 andR=0.97±0.30. These results support a collective model interpretation for the two 2+ levels in question.

Semiconductor Lithium-Ion Drift Diodes as High-Resolution Gamma-Ray Pair Spectrometers

Germanium and silicon p-i-n diodes with active volumes up to 2 cm3 have been fabricated using the lithium-ion drift technique. p-type germanium doped with either gallium or zinc (5-10 ohm-cm) and boron-doped silicon (1100 ohm-cm) were the base materials. Diodes were operated at 77°K in conjunction with a low noise amplifier system (270 RMS electron-holes). They have been used as gamma-ray pair spectrometers, germanium diodes giving a resolution of 7 keV (FWHM) at 2.75 MeV gamma-ray energy increasing to 10 keV at 7.64 MeV; resolution from a silicon device was slightly inferior. A germanium diode has been used as the central detector in a triple-crystal pair spectrometer incorporating two NaI scintillators. This arrangement improved the ratio of the height of the pair peak to the background below the peak from 7:1 to 150:1 for 2.75 MeV gamma-rays from a Na24 source.