Determination of the cross section for (n,p) and (n,α) reactions on 165Ho at 13.5 and 14.8 MeV
Introduction
Holmium can absorb nuclear fission neutrons, and is used as a burnable poison to regulate nuclear reactors (Emsley, 2001). However, the cross sections for the 165Ho(n,p)165Dy and 165Ho(n,α)162Tb reactions have not been so far reported in major nuclear data libraries, such as ENDF/B-VII.1 (ENDF, 2011), JEFF-3.2 (ENDF, 2014), and JENDL-4.0 (ENDF, 2010). The reaction cross sections for 165Ho(n,p)165Dy at around 14 MeV was only previously reported by two workers (Fukuzawa, 1961, Ryves et al., 1990), with large discrepancies in their data. The result of Fukuzawa (1961), using a tritiated zirconium target, a plastic scintillator and associated alpha particle counting, was about 10 times higher than that of Ryves et al. (1990), who utilized a T-Ti target, a Ge–In detector and 56Fe(n,p)56Mn monitor reaction. Therefore, it is necessary to make further measurements to resolve some of the discrepancies for the cross sections of the 165Ho(n,p)165Dy and 165Ho(n,α)162Tb reactions.
In this work, the cross-sections for the 165Ho(n,p)165Dy and 165Ho(n,α)162Tb reactions were measured at neutron energies of 13.5 and 14.8 MeV, and a gamma-ray counting technique was applied using a high-resolution gamma-ray spectrometer. Measurements were corrected for gamma-ray attenuation, random coincidence, deadtime and fluctuation of neutron flux. The neutron energies in this measurement were determined by the method of Luo et al. (2013). The cross sections were also estimated with the nuclear-reaction codes EMPIRE-3.2 Malta and TALYS-1.6, and compared with experimental data found in the literature.
Section snippets
Experiments
About 6 g of Ho2O3 (99.99% pure) powder was pressed at 980 MPa, and thin 20 mm diameter samples were obtained. The samples were irradiated in contact with the target, sandwiched between standard Al foils (99.999% pure, 0.04 mm thick) of the same diameter utilized to monitor the neutron fluence via the 27Al(n,α)24Na reaction.
Irradiation of the samples was carried out at the K-400 Neutron Generator at the Chinese Academy of Engineering Physics (CAEP), and lasted about 60 min with a yield ~3–4×1010 n/(4
Nuclear model calculations
The measured cross sections were compared with theoretical cross sections obtained from two state-of-the-art nuclear reaction codes: EMPIRE-3.2 Malta (Herman et al., 2013) and TALYS-1.6 (Koning et al., 2013).
The calculations performed with the nuclear-reaction code EMPIRE-3.2 Malta (Herman et al., 2013) included contributions from direct (DI) reactions, pre-equilibrium (PE), and compound nucleus (CN) reactions. Direct reactions to the low-lying collective states of the deformed nuclei were
Results and discussion
The cross sections measured in this work are given in Table 3. The total uncertainty amounts to between 15% and 45%. For the 165Ho(n,p)165Dy and 165Ho(n,α)162Tb reactions, in the neutron energy range of 13–15 MeV, the cross section increases with the increasing neutron energy.
For the 165Ho(n,p)165Dy reaction, there are only two earlier measurements obtained by Fukuzawa (1961) and Ryves et al. (1990) at 14.2 MeV. At neutron energy 13.5 and 14.8 MeV, the cross sections are reported here for the
Conclusions
We have measured the activation cross-sections for 165Ho(n,p)165Dy and 165Ho(n,α)162Tb reactions induced by 13.5 and 14.8 MeV neutrons using the latest decay data. The present results were compared with those measured previously and with results of TALYS-1.6 and EMPIRE-3.2 Malta nuclear model calculations with default parameters. Discrepancies with previously reported measured data are attributed to measuring methods and experimental conditions.
Acknowledgments
We would like to thank the Intense Neutron Generator group at Chinese Academy of Engineering Physics for performing the irradiations.
This work was supported by the National Natural Science Foundation of China (Grant no. 11165007) and by the Key Project of Chinese Ministry of Education (No. 211184).
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