Evaluation of tungsten isotopes in the fast neutron range including cross section covariance estimation

Abstract

Abstract. New evaluations for the tungsten isotopes 180,182,183,184,186 W in the neutron energy range up to 60 MeV were produced. In the resonance range only minor adjustments to the resonance parameters were made due to a lack of adequate experimental data. Evaluations in the fast energy region were based on nuclear model calculations using the EMPIRE-2.19 code. Recently derived dispersive coupled-channel optical model potentials for W and Ta isotopes were instrumental to achieve a very good description of the available microscopic cross section database. Model covariance data were generated with the Monte Carlo technique to produce a prior estimate for the covariance matrix. Experimental data were introduced through the GANDR system. The evaluated files were tested on selected fusion neutronics benchmarks and showed marked improvement compared to other existing evaluations.

EMPIRE: Nuclear Reaction Model Code System for Data Evaluation

“…The excellent agreement of the isomeric calculation validates the γ-emission treatment in the EMPIRE code. [133]. The isomeric contribution is also shown.…”

“…Recently, a new evaluation of neutron-induced reactions on tungsten isotopes up to 60 MeV has been presented [133]. Accurate nuclear data for tungsten isotopes are required because tungsten is a candidate material for first-wall components in fusion devices, a target material in systems based on high-current accelerators and because of the importance of the 186 W(n,γ) reaction for neutron dosimetry.…”

“…In spite of several recent attempts to improve the evaluated cross section data for tungsten [134], the status of the data is unsatisfactory. The reported evaluation in the fast energy range [133] was fully based on nuclear model calculations using the EMPIRE code. A crucial point was the selection of the coupledchannels optical model potential.…”

Evaluation of stable tungsten isotopes in the resolved resonance region

“…Despite the importance of neutron induced cross sections of W, the status of the data is not yet completely satisfactory. Several benchmark experiments in the last decade have pointed out deficiencies and discrepancies in evaluated data files; a rather recent evaluation in the fast neutron range, performed by Capote et al (2007), underlined that no significant improvement in quality seems to be possible without new measurements [ 2]. Also preliminary results obtained at the GELINA facility have highlighted problems in the resolved resonance region databases [ 3,4].…”

The Global Assessment of Nuclear Data, GANDR

“…For example, the GANDR system was employed in recent evaluations of nuclear data and covariances of neutron-induced reactions up to 60 MeV on thorium [2], protoactinium [3] and tungsten isotopes [4]. For these applications, the standard GANDR initialization of the data covariances with a non-informative prior was replaced with Monte Carlo calculated model covariances [5] reflecting nuclide-specific constraints imposed by nuclear physics.…”