In situ measurement of neutron temperature for the extended k 0 NAA at FRM II
- PDF / 800,017 Bytes
- 7 Pages / 595.276 x 790.866 pts Page_size
- 26 Downloads / 194 Views
In situ measurement of neutron temperature for the extended k0 NAA at FRM II Xiaosong Li1 Received: 31 July 2020 / Accepted: 10 September 2020 © The Author(s) 2020
Abstract The neutron temperature at different irradiation positions in the research reactor FRM II was measured using thermometer labels together with lutetium standards. This was the first time to measure the local temperature at the irradiation positions with this combination. The simplified Westcott formalism was used to calculate the neutron temperature using Lu and g(Tn) factors from different data sources. The results showed agreement between neutron temperature according to the Lu method and the temperature showed on the labels. They can be used as a reliable alternative to determine the neutron temperature instead of using Lu standards in the extended k0 NAA. Keywords k0 method · g factors · Non-1/v nuclides · Westcott convention · Neutron temperature · Temperature monitor
Introduction k0 NAA was introduced in 1980s based on the Høgdahl convention [1, 2]. This is a convenient idea for multi element NAA because only one comparator is enough to calculate the local neutron flux. Later, in the 1990s, this method was modified by using the Westcott convention with consideration of the influence of the neutron temperature, so that the analysis of some non-1/v nuclides with the k0 NAA approach became possible [3, 4]. To unify the two conventions, at least for the non-1/v isotopes, an extended Høgdahl formalism retaining flux parameters f and α and adding the neutron temperature effected by means of g(Tn) was developed a few years ago [5]. However, the determination of the local neutron temperature at the irradiation position becomes unavoidable. Lutetium is usually used as a temperature monitor, because the thermal neutron-capture cross section of the reaction 176Lu(n,γ)177Lu varies with the neutron temperature very strongly. In most cases, the activity of 177Lu is measured and the local neutron temperature Tn is determined from the g factor originally introduced to correct the neutron cross section σ * Xiaosong Li [email protected] 1
MLZ, Forschungs‑Neutronenquelle Heinz‑Maier‑Leibnitz FRM II, Technische Universität München, Lichtenbergstraße 1, 85747 Garching, Germany
for different temperatures. Then, the neutron temperature determined in this way is used for the calculation of the g factor and thus the concentration of other non-1/v nuclides. The g(Tn) factors available in the literature were calculated from the σ(E) values and can be dated back to the 1960s and 1970s [3, 6]. The last updates using the evaluated neutron data libraries ENDF/B-VI, VII were published in 1999 and 2015 [7, 8]. Because the σ(E) values were calculated using different sources, e.g. ENDF or experimental data from technical reports, significant differences in g(Tn) values can be found for Lu and also for other non-1/v nuclides over the last 50 years. These lead to different neutron temperatures determined by using Lu standards. Attempts to measure the temperature were
Data Loading...
