Determination of photon emission probabilities of Zn-65 decay and other decay parameters
Project Description
The Zn-65 was the object of an ongoing CCRI(II) Key Comparison. The activity determination using the gamma spectrometry technique is correlated to the decay data uncertainties. The aim of this proposed project is to improve the accuracy of the Zn-65 decay data.
The decay data measurements which have been carried out in the past, from 1959 to nowadays concern the 1115 keV gamma-ray mainly and its recommended emission probability value (0.5060) is affected by an uncertainty of 0.4%. The 344- and 770-keV gamma rays were measured only once. For the 511-keV gamma ray four measurements are available given emission probabilities values from 0.0170(10) to 0.0142 (2). New determinations could precise this value and then the accuracy on the electron capture transition probabilities could be reduced, leading to a better decay scheme evaluation. There is one X-rays measurement available only, for the Kα and Kβ rays.
So, an intensive exercise giving several others results could improve the accuracy on these values and then, from the comparison with the theoretical values calculated from the decay scheme, the consistency of this decay scheme could be checked.
The participants would send their data to BNM-LNHB for decay data evaluation.
BNM-LNHB proposes to provide NMIs with Zn-65 ampoules solution, if required. NMIs from other RMOs could be interested to take part in this exercice.
Final Report 2005-06-17
Over the last twenty years, a number of laboratories have participated to the Système International de Référence (SIR - BIPM) and it appeared that the mass activitiy of 65Zn determined by the gamma-ray spectrometry was less by about 2% than the one determined by using 4πβ-γ coincidence counting.
An international exercise EUROMET, action 721, was organised with the objective of improving the knowledge of decay data in the 65Zn disintegration. Nine laboratories (CMI, IFIN, IRMM, IRD-LNMRI, KRISS, NMIJ, NPL, PTB and LNE-LNHB) participated, sending results for the activity measurement and the 115-keV gamma emission intensity. For the activity measurement, the participants used the 4πβ-γ coincidence method mainly, but two participants have used an ionisation chamber and the Liquid Scintillation Counting method respectively. A CEA report was published (Rapport-CEA-R-6081, 2005), this report describe the methods used, the investigation about the influence of half-live values and the final results obtained by the participants. The uncertainty budgets were reported using the rules express in "Guide to expression of uncertainty in measurements".
From the new gamma emission intensities measured in this exercise and, taking into account previous published values, the intensity of the 1115-keV gamma emission has been determined being equal to: 50.22 (11) %. This new value must lead to derivate activity values higher than those previously obtained, reducing the difference, with other techniques of measurement, to 1%. Moreover, the uncertainty on the emission intensity value has been divided by a factor of two.
A summary report of the decay data will be presented at ICRM2005 conference (Authors: M.-M. Bé and all participants to the EUROMET action 721: M.-N. Amiot, C. Bobin, M.-C. Lépy, J. Plagnard, J.M. Lee, K.B. Lee, T.S. Park, A. Luca, M. Sahagia, A.-M. Razdolescu, L. Grigorescu, Y. Sato, Y. Hino, K. Kossert, R. Klein, M.K.H. Schneider, H. Schrader, P. Dryak, J. Sochorovà, P. Kovar, P. Auerbach, M. Havelka, T. Altsitzoglou, A. Iwahara, M.A.L da Silva, J.U. Delgado, C.J. da Silva, L. Johansson, S. Collins, A. Stroak).
Progress report
As planned, Zn-65 ampoules were sent to NMis in January 2004. In the next step, participants should send their measurement results at the end of June 2004.