Polarized 3He Neutron Spin Filter Research Articles

Micro in situ 3He Polarizer for Dimensional Extreme Magnetic Neutron Diffractometer at the High Flux Isotope Reactor

A new micro in situ polarized 3He neutron spin filter has been custom built for use as a neutron polarizer on the Dimensional Extreme Magnetic Neutron Diffractometer (DEMAND) at the High Flux Isotope Reactor (HFIR). The 3He is polarized via spin-exchange optical pumping with a high-power fiber-coupled laser. The 3He neutron spin filter polarizer is designed to be compact in size with the length along the neutron beam only 30 cm because of the limited space available on the beamline. The polarizer is used for the shorter wavelength neutrons (1.005 Å and 1.546 Å) at DEMAND. A 3 bar 3He cell was filled to provide enough opacity so that good neutron polarization can be attained. At DEMAND the polarizer is mounted on an Automated Polarizer Changeover system (APCS) enabling quick switching between polarized and unpolarized neutron diffraction.

Development of a Spin-Exchange Optical Pumping-Based Polarized 3He System at the China Spallation Neutron Source (CSNS)Supported by the National Key Research and Development Program of China (Grant No. 2020YFA0406000), the National Natural Science Foundation of China (Grant No. 11875265), the Scientific Instrument Developing Project of the Chinese Academy of Sciences (Grant No. 284(2018)), Guangdong Basic and Applied Basic Research Foundation

Polarized 3He neutron spin filters (NSFs) can be used as a vital tool for neutron polarization production and analysis. The China Spallation Neutron Source (CSNS), as one of the major neutron facilities in China, has committed resources to the development of a polarized 3He NSF program to support its growing polarized neutron research. A spin-exchange optical pumping (SEOP)-based polarized 3He system and other necessary hardware for NSF transport has been recently developed. The performance of the system is benchmarked using an in-house developed cell named “Trident”. Neutron beam measurements yield a 3He polarization of 77% with over 200 h of on-beam relaxation time. Combining this newly developed SEOP system with the recently reported cell fabrication station, CSNS is now capable of the fully self-sustained production of 3He NSFs that shall support its future neutron polarization research.

New design of a magnetic device for wide-angle XYZ polarization analysis PASTIS-3, from the concept to first tests with thermal neutrons

We present the new concept and neutron test results of the third generation PASTIS device for XYZ wide-angle polarization analysis for thermal neutrons. PASTIS-3 uses two polarized 3He Neutron Spin filter Cells (NSF) for polarizing and analyzing neutrons spins, flipping the incident neutron beam polarization by reversing the 3He spin state of the polarizing entrance cell. We detail a new coil design for high spatial homogeneity of the magnetic field in any field direction, and the calculation method employed to optimize the geometry and to characterize the field gradients. Various components of the apparatus are described with particular attention to their performance and impact on the relaxation time of the NSF cells. Finally, we present test results of the new device tested on the thermal triple-axis spectrometer IN20 at the ILL.

Development of a polarized 3He neutron spin filter based on spin exchange optical pumping at China Mianyang Research Reactor

Development of a polarized 3He neutron spin filter based on spin exchange optical pumping at China Mianyang Research Reactor

Measurement of the absolute neutron beam polarization from a supermirror polarizer and the absolute efficiency of a neutron spin rotator for the NPDGamma experiment using a polarized 3He neutron spin-filter

Accurately measuring the neutron beam polarization of a high flux, large area neutron beam is necessary for many neutron physics experiments. The Fundamental Neutron Physics Beamline (FnPB) at the Spallation Neutron Source (SNS) is a pulsed neutron beam that was polarized with a supermirror polarizer for the NPDGamma experiment. The polarized neutron beam had a flux of ∼109 neutrons per second per cm2 and a cross sectional area of 10 × 12 cm2. The polarization of this neutron beam and the efficiency of a RF neutron spin rotator installed downstream on this beam were measured by neutron transmission through a polarized 3He neutron spin-filter. The pulsed nature of the SNS enabled us to employ an absolute measurement technique for both quantities which does not depend on accurate knowledge of the phase space of the neutron beam or the 3He polarization in the spin filter and is therefore of interest for any experiments on slow neutron beams from pulsed neutron sources which require knowledge of the absolute value of the neutron polarization. The polarization and spin-reversal efficiency measured in this work were done for the NPDGamma experiment, which measures the parity violating γ-ray angular distribution asymmetry with respect to the neutron spin direction in the capture of polarized neutrons on protons. The experimental technique, results, systematic effects, and applications to neutron capture targets are discussed.

Development of a polarized 3He neutron spin filter for POLANO at J-PARC

We have developed a polarized 3He neutron spin filter (NSF) for a new polarized neutron spectrometer, POLANO, at the Japan Proton Accelerator Research Complex (J-PARC). POLANO aims to utilize high energy neutrons polarized by a 3He NSF and spin analyzed by an array of magnetic supermirrors for inelastic neutron scattering. The 3He gas is continuously polarized in-situ by spin-exchange optical pumping to provide a highly and stably polarized neutron beam. The POLANO 3He NSF is designed to polarize neutrons with energies as high as 200 meV and fit in a restricted space. It is equipped with adiabatic fast passage NMR that enables one to flip the 3He spins, and consequently, the neutron spins.

Recent on-beam tests of wide angle neutron polarization analysis with a 3He spin filter: Magic PASTIS on V20 at HZB

A complete XYZ polarization analysis solution is under development for the new thermal time of flight spectrometer TOPAS [1], to be operated in the coming east neutron guide hall at the MLZ. Polarization Analysis Studies on a Thermal Inelastic Spectrometer, commonly called PASTIS [2], is based on polarized 3He neutron spin filters and an XYZ field configuration for the sample environment and a polarization-preserving neutron guide field. The complete system was designed to provide adiabatic transport of the neutron polarization to the sample position while maintaining the homogeneity of the XYZ field. This system has now been tested on the polarized time-of-flight ESS test beam line V20 at HZB [3]. Down to the minimum wavelength of 1.6 Å on the instrument, the magnetic configuration worked ideally for neutron spin transport while giving full experimental freedom to change between the X, Y or Z field configuration. The 3He cell used was polarized at the 3He lab of the JCNS at the MLZ in Garching and transported to HZB in Berlin via car showing that such a transport is indeed feasible for such experiments. We present results of this test and the next steps forward.

Conceptual design of a polarized 3He neutron spin filter for polarized neutron spectrometer POLANO at J-PARC

A 3He neutron spin filter (NSF) has been designed for a new polarized neutron chopper spectrometer called the Polarization Analysis Neutron Spectrometer with Correlation Method (POLANO) at the Materials and Life Science Experimental Facility of the Japan Proton Accelerator Research Complex. It is designed to fit in a limited space on the spectrometer as an initial neutron beam polarizer and is polarized in situ by spin exchange optical pumping. This will be the first generation 3He NSF on POLANO, and a polarized neutron beam up to 100 meV with a diameter of 50 mm will be available for research on magnetism, hydrogen materials, and strongly correlated electron systems.

SEOP polarized 3He Neutron Spin Filters for the JCNS user program

Over the past several years the JCNS has been developing in-house applications for neutron polarization analysis (PA). These methods include PA for separation of incoherent from coherent scattering in soft matter studies (SANS), and online polarization for analysis for neutron reflectometry, SANS, GISANS and eventually spectroscopy. This paper will present an overview of the user activities at the JCNS at the MLZ and gives an overview of the polarization 3He methods and devices used. Additionally we will summarise current projects which will further support the user activities using polarised 3He spin filters.

Polarized 3He Neutron Spin Filters for Neutron Scattering at Oak Ridge National Laboratory

Polarized neutron scattering is a very useful method of determining spin densities and magnetic structures. It can also be used to separate nuclear coherent scattering from spin-incoherent scattering. When compared to other neutron polarizing techniques like Heusler crystals and polarizing supermirrors, polarized 3He neutron spin filters provide several unique advantages: First, polarized 3He can effectively polarize neutrons over a broad range of energies. Second, it has a large acceptance angle for incoming neutron beams. Third, it does not change direction of, or add divergence to, neutron beams. At Oak Ridge National Laboratory (ORNL), a polarized 3He program has been established to meet the increasing needs from various neutron beamlines. 3He is polarized through spin-exchange optical pumping at ORNL. Both ex situ and in situ systems have been developed to accommodate the requirements of different instruments. We report the current status of our development and present test results on several neutron beamlines at ORNL. Future application in small angle neutron scattering will also be discussed.

Development of portable polarized 3He neutron spin filter and its application to magnetic field imaging at J-PARC

In order to expand the measurable neutron energy range up to the energy of epithermal neutrons in polarized neutron experiments, a portable polarized 3He neutron spin filter (NSF) was developed in the Materials and Life science experimental Facility (MLF) at J- PARC. After the generation of 3He polarization through a spin exchange optical pumping method, the NSF was used as a neutron spin polarizer and flipper in a beam line. We constructed a simple neutron spin analysis apparatus with two 3He NSFs and made a preliminary attempt to visualize magnetic fields generated by a coil. The results represented that our apparatus could function for neutron wavelengths between approximately 0.5-5 Å through the use of a neutron time-of-flight method.

Measurement of polarization of 3He with mobile polarized 3He neutron spin filter

A mobile polarized 3He neutron spin filter was developed for both optical pumping and transportation, and the polarization of 3He was measured with cold neutrons of HANARO in KAERI. The progress of polarization build-up during the optical pumping of the 3He cell was observed by adiabatic fast-passage NMR system. The 3He cell was made of an alumino-silicate glass GE-180 with a cylindrical shape of 40mm in diameter and 60mm in length from KEK. A cell contained 5.74bar⋅cm of 3He gas. The whole installation after 8h pumping was transported to the general-purpose test station of the HANARO research reactor and the polarization of 3He was measured with cold neutrons. The measured polarization of 3He was 0.18±0.01 by measuring the neutron transmission through the 3He cell.

Developments of In-Situ SEOP Polarized 3He Neutron Spin Filter in Japan

We launched the polarized 3He neutron spin filters (NSF) project in order to provide neutron polarization for the pulsed neutron beams in Japan. We adopted the in-situ spin exchange optical pumping (SEOP) technique to polarize the nuclear spin of 3He atoms because it has some advantages for our applications. The overall system size is compact and it avoids the problem of the time decay of nuclear spin of 3He thus suppressing the costs of maintenance and providing other advantages [1, 2] with respect to data analysis and quality. In this paper, we performed pulsed neutron beam tests of our compact in-situ SEOP NSF system at the BL10 beamline in the Materials and Life Science Experimental Facility of the Japan Proton Accelerator Research Complex (J-PARC). The polarization of the 3He gas reached was 73 % and a pump-up time constant of 9.5 h was observed. This paper is a status report about the development of in-situ SEOP NSF system for the pulsed beam at J-PARC.

Wide-angle polarization analysis with 3He for neutron scattering instrumentation at the JCNS

Polarization analysis is an important technique for polarized neutron scattering as it allows one to obtain the full information about the vector magnetization in the sample that is critically important for detailed understanding of physical properties of molecular magnets, new superconductors, spin electronic and magnetic nanostructures, as well as the self-organization of magnetic nanostructures. In the simplified 1-dimensional version polarization analysis allows for the separation of coherent and incoherent scattering, making it a potentially important technique for studies of non-deuterated biological objects that themselves produce unavoidable background. We compare some of the major considerations between two different methods for the polarization analysis – supermirror based analyzers and polarized 3He neutron spin filters and point out when the latter is beneficial from the point of view of our neutron experiments and instrumentation. We will also discuss some specific requirements to such neutron spin filters and summarize the classes of instrumentation where they will be applied at the JCNS. Finally we will describe a successful application for small-angle neutron scattering from a biological sample.

Applications of 3He neutron spin filters on the small-angle neutron scattering spectrometer SANS-J-II

A polarized 3He neutron spin filter has been applied to polarization analysis on the small-angle neutron scattering spectrometer SANS-J-II at JRR-3. Measurements were taken on silver behenate, which has several coherent peaks in the small-angle region with a background of spin incoherent hydrogen scattering. Here we demonstrate that the coherent and spin incoherent scattering were successfully separated by the polarization analysis using the 3He spin filter on the instrument.

Research on glass cells for 3He neutron spin filters

Glass cells play an important role in polarized 3He neutron spin filters. To evaluate the scattering and absorption contribution from glass cells during neutron scattering experiments, we measured small-angle scattering and neutron transmission in GE180 and other glasses. The small-angle neutron scattering measurements revealed that the glasses used for 3He spin filters have acceptably lower scattering: dΣ(Q)/dΩ=4–7×10−4cm−1 at Q=0.03–0.12Å−1. The transmission measurement was performed at J-PARC. Neutron transmission of about 92% through empty GE180 cells was observed over a wide wavelength range 0.014–7.0Å. To pursue the possibility of being a structural influence on 3He spin relaxation in GE180 glass cells, we performed precise X-ray diffraction measurement using synchrotron radiation at SPring-8. From these measurements, a structural difference was observed among GE180 glasses with different thermal treatments.

Optimised adiabatic fast passage spin flipping for 3He neutron spin filters

We describe here a method of performing adiabatic fast passage (AFP) spin flipping of polarized 3He used as a neutron spin filter (NSF) to polarize neutron beams. By reversing the spin states of the 3He nuclei the polarization of a neutron beam can be efficiently reversed allowing for the transmission of a neutron beam polarized in either spin state. Using an amplitude modulated frequency sweep lasting 500ms we can spin flip a polarized 3He neutron spin filter with only 1.8×10−5 loss in 3He polarization. The small magnetic fields (10–15G) used to house neutron spin filters mean the 3He resonant frequencies are low enough to be generated using a computer with a digital I/O card. The versatility of this systems allows AFP to be performed on any beamline or in any laboratory using 3He neutron spin filters and polarization losses can be minimised by adjusting sweep parameters.

Polarized 3He neutron spin filter program at the JCNS

Polarized neutron instruments will occupy about 80% of the Jülich Centre for Neutron Science (JCNS) instrument park. A successful polarized 3He program will be integral to many of these instruments. We have been focusing the developments on spin-exchange optical pumping (SEOP) to polarize the 3He gas in situ. Where possible, in situ polarization using the SEOP method will provide higher time averaged performance of the instruments. Further this allows a custom-built and independent source of polarized 3He to be developed optimized for each instruments demands. In this paper we will: present an argument for the advantages of in situ polarization; describe an in situ polarizer we have constructed, and initial tests of its performance; describe testing of polarization analysis for small angle neutron scattering on biological samples, and our plans for an in situ polarizer for this application.

A wide angle neutron spin filter system using polarized 3He

Polarized 3He neutron spin filters can operate over a wide neutron energy range and provide a large angular acceptance. A compact 3He neutron spin filter system has been developed for the Multi-Axis Crystal Spectrometer at the National Institute of Standards and Technology (NIST) Center for Neutron Research. Sealed 3He cells, polarized by spin-exchange optical pumping, are used as polarizer and analyzer. The polarization of the neutrons incident on the sample is inverted by flipping the polarization of the 3He gas in the polarizer, with only a small effect on the analyzer cells. The cell fabrication process, 3He spin flipper, and the holding magnetic field are discussed and we present the results of a first on-linetest.

Characterization of glasses for 3He neutron spin filter cells

Polarized 3He neutron spin filters are suitable devices for polarizing neutrons at spallation neutron facilities because of the wide coverage in energy range and the large solid-angles. The glass cell plays an important role in the 3He spin filters. In order to get good quality of glass cells, the investigation on the microscopic structure would be helpful. In this paper, we report on the results of X-ray diffraction for several glasses. We observed a correlation between the position of the first peak and the helium permeation velocity. We also observed a small difference in the diffraction curve among GE180 glasses with different thermal treatment. Desirable structure for 3He spin filters is discussed.