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

Abstract

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 $).