Determination of the cross section for (n,p) reaction with producing short-lived nuclei on the 162,163Dy isotopes at 13.5 and 14.8 MeV

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Highlights

  • The cross sections for the 162Dy(n,p)162Tb and 163Dy(n,p)163Tb have been measured.

  • 93Nb(n,2n)92mNb was used as a monitor for neutron fluence.

  • Codes TALYS-1.6 and EMPIRE-3.2 Malta were used to model the reactions.

  • The results were compared with previous data.

  • Inconsistency with previous data and with model calculations are noted.

Abstract

Activation cross-sections for the 162Dy(n,p)162Tb and 163Dy(n,p)163Tb reactions have been measured by means of the activation technique and a coaxial HPGe γ-ray detector at 13.5 and 14.8 MeV. The fast neutrons were produced via the 3H(d,n)4He reaction on Pd-300 neutron generator. The natural high-purity Dy2O3 powder was used as target material. Theoretical excitation functions were calculated using the nuclear-reaction codes EMPIRE-3.2 Malta and TALYS-1.6 with default parameters, at neutron energies varying from the reaction threshold to 20 MeV. The results were also discussed and compared with some corresponding values found in the literature, with the comprehensive evaluation data in ENDF/B-VII.1 and JENDF-4.0 libraries, and with the estimates obtained from a published empirical formula based on the statistical model with Q-value dependence and odd–even effects taken into consideration.

Introduction

Neutron activation cross-section data around 14 MeV have become important from the viewpoint of fusion reactor technology, especially for calculations of radiation damage, gas production, nuclear transmutation and induced radionuclides (Kawade et al., 2003). A lot of experimental data on neutron induced cross sections for nuclear reactor technology applications have been reported and great efforts have been devoted to compilations and evaluations (CINDA-A, 2000, Mclane et al., 1988). The variations in the cross-sections with the neutron energy are also of great interest for studying the excitation of nuclei to different energy levels and subsequent decay to ground state, either directly or through different energy levels including metastable states (Nesaraja et al., 2003). Dysprosium (Dy) is one of the rare-earth elements. The neutron total cross-section of dysprosium (Dy) is of great importance not only for the design and development of nuclear reactors but also for the basic study of neutron interaction with nuclei (Dzysiuk et al., 2012). Dy is a useful absorbing material for the control rods of thermal reactors due to its large neutron cross-sections in the thermal neutron energy region (Emsley, 2001, Amit and Sharma, 2005).

The reaction cross sections for the 162Dy(n,p)162Tb and 163Dy(n,p)163Tb reactions at around 14 MeV were previously reported by six workers (for 162Dy(n,p)162Tb reaction (Antov et al., 1983; Dzysiuk et al., 2012; Kong et al., 1998; Oms et al., 1968; Qaim, 1976; Sakane et al., 1997; for 163Dy(n,p)163Tb reaction, Dzysiuk et al., 2012; Kong et al., 1998; Oms et al., 1968; Qaim, 1976; Sakane et al., 1997; Wille and Fink, 1960), respectively, but these measurements differ by as much as a factor of 1.5–2.5 and five of them obtained data at only one energy. Therefore, it is necessary to make further measurements to resolve some of the discrepancies and to cover a slightly broader range of energies for the cross sections of the 162Dy(n,p)162Tb and 163Dy(n,p)163Tb reactions. Concerning the cross sections of 158Dy(n,p)158Tb, 156Dy(n,α)153Gd, 160Dy(n,p)160Tb, 162Dy(n,α)159Gd, 164Dy(n,α)161Gd, 156Dy(n,2n)155Dy and 158Dy(n,2n)157Dy reactions of the dysprosium isotopes in neutron energies 13.5–14.8 MeV have been reported by several authors (Bari, 1982, Coleman et al., 1959, Dzysiuk et al., 2012, Jaskola et al., 1968, Khurana and Govil, 1965, Khurana and Hans, 1959, Khurana and Hans, 1960, Kong et al., 1998, Luo et al., 2009, Qaim, 1974, Qaim, 1976, Sakane et al., 1996, Weigel et al., 1975, Wille and Fink, 1960;).

In this work, the cross-sections for the 162Dy(n,p)162Tb and 163Dy(n,p)163Tb reactions were measured using 13.5 and 14.8 MeV neutrons, (n,p) reactions were measured through the photons produced during activation that were measured with 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 (Herman et al., 2013) and TALYS-1.6 (Koning et al., 2013), and compared with experimental data found in the literature and evaluation data in ENDF/B-VII.1 (Kim et al., 2011) and JENDF-4.0 (Iwamoto and Chiba, 2010) libraries.

Section snippets

Samples and irradiations

About 10 g of Dy2O3 (99.995% 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 Nb foils (99.999% pure, 0.5 mm thick) of the same diameter utilized to monitor the neutron fluence via the 93Nb(n,2n)92mNb reaction.

Irradiation of the samples was carried out at the Pd-300 Neutron Generator at the Chinese Academy of Engineering Physics (CAEP), and lasted about 60 min with a yield ~3 to 4×10

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

Calculations of the cross-section systematics

A large number of experimental data have been published on the (n,p) reaction cross sections induced by around 14 MeV neutron. It has been known for a long time that these cross sections vary rather smoothly with the mass number A, neutron number N, and proton number Z of the target nucleus. The experimental cross section of (n,p) reaction induced by fast neutrons can be approximated byσ(n,p)=Cσneexp(as)where σne is the neutron nonelastic cross section, and C and a are fitting parameters for

Results and discussion

The cross sections measured in this work are given in Table 3. The total uncertainty amounts to between 16% and 19%. For the 162Dy(n,p)162Tb and 163Dy(n,p)163Tb reactions, in the neutron energy range of 13–5 MeV, the cross section increases with the increasing neutron energy. We compared our experimental results with estimations obtained from semi-empirical formulae presented in some of relatively recent Refs. (Ait-Tahar, 1987, Broeders and Konobeyev, 2006, Doczi et al., 1997, Forrest, 1986,

Conclusions

We have measured the activation cross-sections for 162Dy(n,p)162Tb and 163Dy(n,p)163Tb reactions induced by 13.5 and 14.8 MeV neutrons using the latest decay data. The present results were compared with those measured previously, with results of TALYS-1.6 and EMPIRE-3.2 Malta nuclear model calculations with default parameters, and with results of systematics. A systematic study and careful comparison of previously reported measured cross sections with the newly measured data reveals that the

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), by the Key Project of Chinese Ministry of Education (No. 211184).

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