Oak Ridge National Laboratory is home to the High Flux Isotope Reactor (HFIR), a high-flux research reactor, and the Spallation Neutron Source (SNS), the world's most intense source of pulsed neutron beams. The unique co-localization of these two sources provided an opportunity to develop a suite of complementary small-angle neutron scattering instruments for studies of large-scale structures: the GP-SANS and Bio-SANS instruments at the HFIR and the EQ-SANS and TOF-USANS instruments at the SNS. This article provides an overview of the capabilities of the suite of instruments, with specific emphasis on how they complement each other. A description of the plans for future developments including greater integration of the suite into a single point of entry for neutron scattering studies of large-scale structures is also provided.

The suite of small‐angle neutron scattering instruments at Oak Ridge National Laboratory

This article reviews the physics and technology of producing large quantities of highly spin-polarized 3He nuclei using spin-exchange (SEOP) and metastability-exchange (MEOP) optical pumping. Both technical developments and deeper understanding of the physical processes involved have led to substantial improvements in the capabilities of both methods. For SEOP, the use of spectrally narrowed lasers and K-Rb mixtures has substantially increased the achievable polarization and polarizing rate. For MEOP nearly lossless compression allows for rapid production of polarized 3He and operation in high magnetic fields has likewise significantly increased the pressure at which this method can be performed, and revealed new phenomena. Both methods have benefitted from development of storage methods that allow for spin-relaxation times of hundreds of hours, and specialized precision methods for polarimetry. SEOP and MEOP are now widely applied for spin-polarized targets, neutron spin filters, magnetic resonance imaging, and precision measurements.

Optically polarized 3 He

We have obtained improvement in the 3He polarization achievable by spin-exchange optical pumping (SEOP). These results were primarily obtained in large neutron spin filter cells using diode bar lasers spectrally narrowed with chirped volume holographic gratings. As compared to our past results with lasers narrowed with diffraction gratings, we have observed between 5% and 11% fractional increase in the 3He polarization PHe. We also report a comparable improvement in PHe for two small cells, for which we would not have expected an increase from improved laser performance. In particular, prior extensive studies had indicated that the alkali-metal polarization was within 3% of unity in one of these cells. These results have impact on understanding the maximum PHe achievable by SEOP, whether the origin of the improvement is from increased alkali-metal polarization or decreased temperature-dependent relaxation. We conclude that the most likely explanation for the improvement in PHe is increased alkali-metal po...

On the limits of spin-exchange optical pumping of 3He

We are developing a neutron polarizer with polarized 3 He gas, referred to as a 3 He spin filter, based on the Spin Exchange Optical Pumping (SEOP) for polarized neutron scattering experiments at Materials and Life Science Experimental Facility (MLF) of Japan Proton Accelerator Research Complex (J-PARC). A 3 He gas-filling station was constructed at J-PARC, and several 3 He cells with long spin relaxation times have been fabricated using the gas-filling station. A laboratory has been prepared in the MLF beam hall for polarizing 3 He cells, and compact pumping systems with laser powers of 30 W and 110 W, which can be installed onto a neutron beamline, have been developed. A 3 He polarization of 85% was achieved at a neutron beamline by using the pumping system with the 110 W laser. Recently, the first user experiment utilizing the 3 He spin filter was conducted, and there have been several more since then. The development and utilization of 3 He spin filters at MLF of J-PARC are reported.

/pdf/development-and-application-of-a-3he-neutron-spin-filter-at-118o49tzsr.pdf

Development and application of a 3He Neutron Spin Filter at J-PARC

We propose a precise method to calibrate the coil constants of spin-precession gyroscopes and optical atomic magnetometers. This method is based on measuring the initial amplitude of Free Induction Decay (FID) of noble gases, from which the π/2 pulse duration can be calculated, since it is inversely proportional to the amplitude of the π/2 pulse. Therefore, the coil constants can be calibrated by measuring the π/2 pulse duration. Compared with the method based on the Larmor precession frequency of atoms, our method can avoid the effect of the pump and probe powers. We experimentally validated the method in a Nuclear Magnetic Resonance Gyroscope (NMRG), and the experimental results show that the coil constants are 436.63±0.04 nT/mA and 428.94±0.02 nT/mA in the x and y directions, respectively.

/pdf/a-method-for-calibrating-coil-constants-by-using-the-free-2dh3kal5k4.pdf

A method for calibrating coil constants by using the free induction decay of noble gases

Polarized 3He Neutron Spin Filters at Oak Ridge National Laboratory

The Hybrid Spectrometer (HYSPEC) is a new direct geometry spectrometer at the Spallation Neutron Source at the Oak Ridge National Laboratory. This instrument is equipped with polarization analysis capability with 60° horizontal and 15° vertical detector coverages. In order to provide wide angle polarization analysis for this instrument, we have designed and built a novel polarized 3He filling station based on the spin exchange optical pumping method. It is designed to supply polarized 3He gas to HYSPEC as a neutron polarization analyzer. In addition, the station can optimize the 3He pressure with respect to the scattered neutron energies. The depolarized 3He gas in the analyzer can be transferred back to the station to be repolarized. We have constructed the prototype filling station. Preliminary tests have been carried out demonstrating the feasibility of the filling station. Here, we report on the design, construction, and the preliminary results of the prototype filling station.

Spin exchange optical pumping based polarized 3He filling station for the Hybrid Spectrometer at the Spallation Neutron Source.

We constructed a compact in situ polarized 3He neutron spin filter based on spin-exchange optical pumping which is capable of continuous pumping of the 3He gas while the system is in place in the neutron beam on an instrument. The compact size and light weight of the system simplifies its utilization on various neutron instruments. The system has been successfully tested as a neutron polarizer on the triple-axis spectrometer (HB3) and the hybrid spectrometer (HYSPEC) at Oak Ridge National Laboratory. Over 70% 3He polarization was achieved and maintained during the test experiments. Over 90% neutron polarization and an average of 25% transmission for neutrons of 14.7 meV and 15 meV was also obtained.

Development of a compact in situ polarized 3He neutron spin filter at Oak Ridge National Laboratory

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Polarized 3He Neutron Spin Filters at Oak Ridge National Laboratory

Spin exchange optical pumping based polarized 3He filling station for the Hybrid Spectrometer at the Spallation Neutron Source.

Development of a compact in situ polarized 3He neutron spin filter at Oak Ridge National Laboratory