A re-examination of coincidence and gamma-peak doublet handling in Kayzero-based NAA

Abstract

In order to further strengthen at DSM Research the key analytical technique "neutron activation analysis" based on the KAYZERO/SOLCOI 9 software package, a project was recently started aiming at, among others, improvements in the correction for true-coincidence and in the automatic handling of peak multiplets. Problems could be identified in the calculation of true-coincidence correction factors for a number of analytically important cascade gamma lines of about 20 radionuclides including those formed from the elements Fe, As, Zr, Mo, Ag, Sb, some rare earth elements, Ta, W and U. As an example, in the present paper an outline is given of sources of error -caused by computer programming, decay scheme analysis or selection of relevant decay data -that are related to the measurement of 76As, 124Sb, 149Nd, 182Ta and 187W. For some radionuclides, k0-factors of analytically relevant gamma lines present in multiplets (in most cases doublets) were formerly not available. Hence, problems existed with the automatic computer-assisted conversion of input peak areas to output analytical results. Therefore, remeasurement of the individual k0-factors was carried out by using a high-performance Ge-detector and a gamma-spectrum analysis program with proven accuracy. This study involved a number of gamma lines of radionuclides for the determination of some 10 elements among which Mo, Pd, Ag, Eu and U were included. This now leads to the elimination of important data processing errors. IntroductionAt DSM Research, ko-NAA -supported by the home-designed (and commercially available) KAYZERO/SOLCOI 9 PC-software package [1] -is one of the key analytical techniques [2], complementary to XRF, ICP-MS, ICP-OES and AAS. In order to further increase its manageability and performance capability, a project was recently initiated comprising the following topics: correction for true coincidence, the automatic handling of gamma-peak multiplets, the extension of the nuclear data library with remeasured ko and Qo values, the generalisation of the implemented mother-daughter relations and the correction for fission and threshold reactions. In the present contribution, results are reported on the first two of these topics.A recent comparison of coincidence correction (COI) factors for all gamma-lines in the KAYZERO/SOLCOI ~ database, calculated with SOLCOI 9 and with two other computer codes, revealed that -although in the majority of the cases the results were consistent -sometimes significant discrepancies occurred. This initiated -for the analytically important gamma-lines among these cases -a detailed examination of possible sources of error, either caused by computer programming, decay scheme analysis or selection of relevant decay data. In the present work, examples are given for 7SAs, 124Sb, 149Nd, lS2Ta and lS7W. KAYZERO/SOLCOI 9 is unable to automatically

Compilation of k0 and related data for NAA in the form of electronic database (IUPAC Technical Report)

“…The developed data- A few compilations of the k 0 data can be found in the literature [1,17]. Some data were published stepwise in a number of consecutive compilations, with several extensions and updates over the course of several years [8][9][10][11][12][13][14][15][16]. These partial and fragmentary datasets were assembled [17] and inserted into the tables of the present database.…”