Neutronic design and measured performance of the Low Energy Neutron Source (LENS) target moderator reflector assembly

Abstract

The Low Energy Neutron Source (LENS) is an accelerator-based pulsed cold neutron facility under construction at the Indiana University Cyclotron Facility (IUCF). The idea behind LENS is to produce pulsed cold neutron beams starting with ∼MeV neutrons from (p,n) reactions in Be which are moderated to meV energies and extracted from a small solid angle for use in neutron instruments which can operate efficiently with relatively broad (∼1 msec) neutron pulse widths. Although the combination of the features and operating parameters of this source is unique at present, the neutronic design possesses several features similar to those envisioned for future neutron facilities such as long-pulsed spallation sources (LPSS) and very cold neutron (VCN) sources. We describe the underlying ideas and design details of the target/moderator/reflector system (TMR) and compare measurements of its brightness, energy spectrum, and emission time distribution under different moderator configurations with MCNP simulations. Brightness measurements using an ambient temperature water moderator agree with MCNP simulations within the 20% accuracy of the measurement. The measured neutron emission time distribution from a solid methane moderator is in agreement with simulation and the cold neutron flux is sufficient for neutron scattering studies of materials. We describe some possible modifications to the existing design which would increase the cold neutron brightness with negligible effect on the emission time distribution. 1

Research opportunities with compact accelerator-driven neutron sources

“…[49,50] The facility offers unique capabilities for research on neutron moderators and rapid testing of novel instrumentation ideas. The neutron scattering instruments are fed by a cryogenic methane moderator, and two of these are devoted to studies of large-scale structure through SANS and SESAME (spin-echo scattering angle measurement).…”

Compact spherical neutron polarimeter using high-Tc YBCO films

“…The prototype device was tested at the SESAME beamline on the Low Energy Neutron Source (LENS) 32,23 at Indiana University, and at the HB-2D beamline on the High Flux Isotope Reactor (HFIR), Oak Ridge National Laboratory. The SESAME beamline 33 provides a pulsed, polarized neutron beam with wavelengths in the range from 2 to 10 Å and polarization up to 92%.…”

“…More recently a SNP device has also been used to study chiral systems in both elastic 7 and inelastic scattering. 20 The application extends to broad fields including multiferroics, 21,22 heavy fermions, 23 and superconductors. 24 Currently most SNP measurements have focused on diffraction; however, the technique can also be used for 3D neutron depolarization 25 and inelastic scattering.…”

Spin echo small angle neutron scattering using a continuously pumped 3He neutron polarisation analyser

“…The SESAME beamline at the Low Energy Neutron Source (LENS) [11,12] is first and foremost a time-offlight polarised neutron instrument with usable wavelength neutrons from 2.5Å to 11Å. The instrument is used for SESANS and also the development of polarised neutron instrumentation [17][18][19][20].…”

“…In transmission, the technique is referred to as Spin Echo Small Angle Neutron Scattering (SESANS) [2,8] while in reflection it is called Spin Echo Reflection Grazing Incidence Scattering (SERGIS) [9,10]. The SESAME beamline has been installed at the pulsed 13 MeV Low Energy Neutron Source at Indiana University [11,12]. This paper focuses purely on the SESANS technique, however with additional motor control this instrument can be used in reflection geometry for SERGIS or diffraction geometry for Larmor diffraction.…”