0000000000025112
AUTHOR
H. Humblot
The3He neutron spin filter at ILL
Abstract Neutron Spin-Filters (NSF) using gaseous polarized 3He have long been recognized as having enormous potential value in many polarized neutron scattering applications and, accordingly, ILL started a development program some years ago. This report gives an account of the present status of the project. Let us first briefly recall the reasons why the 3He-NSF is desirable as a generic polarization tool: Being a pure transmission device, NSF naturally decouples the neutron spin selection from other optical functions. Designing polarized instruments will be simplified having no geometrical constraints due to Bragg optics or beam deviation in the polarizer. Angular acceptance and energy ba…
Interdisciplinary experiments with polarized 3He
Abstract Optical pumping of metastable 3 He atoms is a very efficient method to produce large quantities of nuclear spin-polarized 3 He. Recent developments in mechanical compression of the gas, its storage and transport allow for its flexible use in different fields of physics and applied science. Among these are (1) scattering experiments of polarized beams from polarized 3 He-targets, (2) 3 He as neutron spin filter to polarize neutron beams at research reactors, and (3) polarized 3 He gas inhaled into the lungs to perform magnetic resonance imaging. The paper discusses the different topics along with results obtained in a first round of experiments.
3He neutron spin filter at ILL
Abstract The strongly spin-dependent absorption of neutrons in nuclear spin polarized 3He opens the possibility to polarize neutrons over the full-spectrum of cold, thermal and epithermal neutrons. At ILL a neutron spin filter (NSF) development started which uses the direct optical pumping of metastable 3He atoms in a 3He plasma at 1 mbar. At present 0.5 bar 1 of gaseous 3He can be polarized within 1 h. Subsequent polarization-preserving compression by a two-stage compressor system enables one to prepare NSF cells of about 300 cm3 volume in the required pressure range of several bars. A remote type of operation based on relaxation times of up to 100 h has been demonstrated in a first survey…
Neutron optics P-violation effects near p-wave resonance
Abstract The observations of large enhancement of parity-violation at p-wave compound resonance encourage prompt active discussion of TRI test in neutron optics. One of the most attractive objects for investigation is the p-wave resonance of 139 La at energy 0.734 eV for which the strongest P-odd effect of spin dichroism has been observed. A new technique of neutron spin analysis based on optically pumped 3 He spin filter has been applied successfully to measure the complementary effect of P-odd spin rotation near the same p-wave resonance of 139 La . The results obtained are consistent with theory predictions.
Realization of a broad band neutron spin filter with compressed, polarized 3He gas
The strongly spin dependent absorption of neutrons in nuclear spin polarized 3He opens the possibility to polarize beams of thermal and epithermal neutrons. An effective 3He neutron spin filter (NSF) requires high 3He nuclear polarization as well as a filter thickness corresponding to a gas amount of the order of 1 barl. We realized such a filter using direct optical pumping of metastable 3He∗ atoms in a 3He plasma at 1 mbar. Metastable exchange scattering transfers the angular momentum to the whole ensemble of 3He atoms. At present 3 × 1018 3He-atoms/s are polarized up to 64%. Subsequent polarization preserving compression by a two stage compressor system enables to prepare NSF cells of ab…
Realization of a broad-band neutron spin filter with compressed, polarized 3He gas
The strongly spin-dependent absorption of neutrons in nuclear spin polarized 3He opens the possibility to polarize beams of thermal and epithermal neutrons. An effective 3He neutron spin filter (NSF) requires high 3He nuclear polarization as well as a filter thickness corresponding to amount of gas in the order of 1 bar 1. We realized such a filter using direct optical pumping of metastable 3He∗ atoms in a 3He plasma at 1 mb. Metastable exchange scattering transfers the angular momentum to the whole ensemble of 3He atoms. At present 3.6 × 1018 3He-atoms s−1 are polarized up to 68%. Subsequent polarization preserving compression by a two-stage compressor system enables to prepare NSF cells o…
Large solid-angle polarisation analysis at thermal neutron wavelengths using a 3He spin filter
Abstract The strongly spin-dependent absorption of neutrons in nuclear spin-polarised 3 He opens up the possibility of polarising neutrons from reactors and spallation sources over the full kinematical range of cold, thermal and hot neutrons. In this paper we describe the first large solid-angle polarisation analysis measurement using a 3 He neutron spin filter at thermal neutron wavelengths ( λ =2.5 A). This experiment was performed on the two-axis diffractometer D1B at the Institut Laue-Langevin using a banana-shaped filter cell (530 cm 3 ) filled with 3 He gas with a polarisation of P =52% at a pressure of 2.7 bar. A comparison is made with a previous measurement on D7 using a cold neutr…