New instrumentation for precise (n,γ) measurements at ILL Grenoble

Abstract

An array of eight Ge detectors for coincidence measurements of γ rays from neutroncapture reactions has been constructed at the PF1B cold-neutron facility of the Institut Laue-Langevin. The detectors arranged in one plane every 45 • can be used for angular correlation measurements. The neutron collimation line of the setup provides a neutron beam of 12 mm in diameter and the capture flux of about 10 8 /(s×cm 2 ) at the target position, with a negligible neutron halo. With the setup up to 10 9 γγ and up to 10 8 triple-γ coincidence events have been collected in a day measurement. Precise energy and efficiency calibrations up to 10 MeV are easily performed with 27 Al(n, γ) 28 Al and 35 Cl(n, γ) 36 Cl reactions. Test measurements have shown that neutron binding energies can be determined with an accuracy down to a few eV and angular correlation coefficients measured with a precision down to a percent level. The triggerless data collected with a digital electronics and acquisition allows to determine half-lives of excited levels in the nano-to microsecond range. The high resolving power of double-and triple-γ time coincidences allows significant improvements of excitation schemes reported in previous (n, γ) works and complements high-resolution γ-energy measurements at the double-crystal Bragg spectrometer GAMS of ILL.

Abrupt shape transition at neutron number N=60 : B(E2) values in SrRégis1, Jolie2, Saed-Samii3 et al. 2017Phys. Rev. C342270View full textAdd to dashboardCite

“…The mixed array was installed at the exit of the collimation line of the cold-neutron guide PF1B [14,15] of the ILL reactor. The collimated cold-neutron beam 12 mm in diameter provided a flux of 10 8 neutrons per second and cm 2 at the target position to induce fission in 235 U.…”

The (n,γ) campaigns at EXILL

“…The collimator described in Ref [3] provided, at the target position, a 12-mm diameter cold neutron beam of ~10 8 n/(s.cm 2 ). Perpendicular to the beam, 8 EXOGAM Clover detectors, with their BGO shields, were mounted in a ring while the additional detectors were mounted in the forward and backward directions at 45° (see figure 2).…”

“…EXILL is partially a follow-up of a previous campaign using 8 EUROBALL capsule Ge detectors and a highly collimated cold neutron beam for (n,J) measurements [3]. The EXILL campaigns, which took two reactor cycles of 49 days each, used beside the (n,J) also the (n,fission) reaction on 235 U and 241 Pu targets.…”

High precisionγspectroscopy of69,71Zn from (n, γ) reactions using EXILL

“…It is well established that the neutron capture reactions serve as an excellent tool for such type of "complete" spectroscopy. With the development of very efficient arrays of γ spectrometers, the measurements of γ radiation following the neutron capture reactions offer now new, rich and complete information on nuclear structure [7].…”