Measurements of activation cross sections of (n, p) and (n, α) reactions with d-D neutrons in the energy range of 2.1–3.1 MeV

Abstract

Activation cross sections for (n, p) and (n, α) reactions were measured by the activation method in the energy range of 2.1–3.1 MeV. The irradiated target isotopes were ²⁷Al, ⁴¹K, ⁴⁷Ti, ⁵¹V, ⁵⁴Fe, ⁵⁹Co, ^58,61Ni, ⁶⁵Cu, ⁶⁷Zn, ⁶⁹Ga, ⁷⁹Br, ⁹²Mo, ⁹³Nb, and ⁹⁶Ru. The cross sections for ⁴¹K (n, p) ⁴¹Ar, ⁶¹Ni (n, p) ⁶¹Co, ⁶⁵Cu (n, p) ⁶⁵Ni, ⁶⁷Zn (n, p) ⁶⁷Cu, ⁷⁹Br (n, p) ^79mSe, ⁹⁶Ru (n, p) ^96m+gTc, and ⁶⁹Ga (n, α) ⁶⁶Cu reactions were obtained for the first time. Irradiation was from the d-D neutron source of the Fusion Neutronics Source at the Japan Atomic Energy Research Institute. All cross section values were determined relative to those of the ¹¹⁵In (n, n′) ^115mIn reaction. To obtain reliable activation cross sections, careful attention was paid to correct neutron irradiation and to correct the measurement of induced activity as well as to determine the mean neutron energy at the irradiation positions. To measure weak activity levels, a highly efficient measuring technique with a well-type High Purity Germanium detector was applied to the activities. The present results were compared against the comprehensive evaluated data in JENDL-3.3,-3.2, and-Activation File 96 as well as in ENDF/B-VI, and FENDL/A-2.0. We concluded that the evaluated data for ⁴¹K (n, p) ⁴¹Ar, ⁵¹V (n, p) ⁵¹Ti, ⁶¹Ni (n, p) ⁶¹Co, ⁷⁹Br (n, p) ^79mSe, ⁹⁶Ru (n, p) ^96m+gTc, ⁶⁹Ga (n, α) ⁶⁶Cu, and ⁹³Nb (n, α) ^90mY reactions were overestimated or underestimated by more than 30%.

Introduction

A database of activation cross sections for neutron energy up to 20 MeV is required for the design of a D-T fusion reactor, for neutron dosimetry and neutron shielding in an accelerator facility, and to confirm predictions based on nuclear reaction calculations. A number of cross section data have been reported in energy around 14 MeV with d-T neutrons (IAEA, 2002). These data have been compiled in several evaluated-data libraries, such as JENDL-3.3 (Shibata et al., 2002) and ENDF/B-VI (Rose, 1991). The data in those libraries are evaluated mainly on the basis of theoretical calculations. Experimental data, if available, are used to normalize the calculated excitation functions and to improve the accuracy and reliability of those functions. In case no measurements have been made, the systematics for the majority of reactions are used to predict unmeasured cross sections. Systematics of (n, p), (n, α), (n, 2n), and (n, np) have been proposed on the basis of experimental data (Kasugai et al., 1996, Kasugai et al., 1998, Sakane et al., 2000). At present, the prediction ability of the systematics is estimated to be ±(20–30)%. As far as data at energy below 13 MeV are concerned, not enough experimental data have been reported, owing to the lack of available neutron sources that have intense neutron fluence rates. The systematics has not been studied in this neutron energy range.

In order to propose the systematics around 3 MeV, we have planned to systematically measure activation cross sections. In the present work we measured 14 (n, p) and 2 (n, α) reaction cross sections in the energy range of 2.1–3.1 MeV by using an intense d-D neutron source and the highly efficient well-type High Purity Germanium (HPGe) detector. The irradiated target isotopes were ²⁷Al, ⁴¹K, ⁴⁷Ti, ⁵¹V, ⁵⁴Fe, ⁵⁹Co, ^58,61Ni, ⁶⁵Cu, ⁶⁷Zn, ⁶⁹Ga, ⁷⁹Br, ⁹²Mo, ⁹³Nb, and ⁹⁶Ru.