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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 polarization. We have observed PHe of between 0.80 and 0.85 in several large cells, which marks a new precedent for the polarization achievable by SEOP. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Maintaining high levels of 3He polarization over long periods of time is important for many areas of fundamental and particle beam physics. Long measurement times are often required in such experiments, and the data quality is a function of the 3He polarization. This is the case for neutron scattering, where the 3He can be used to analyze the spin of a scattered neutron beam. For neutron scattering, the relatively small fluxes of polarized neutrons lead to experiment times longer than several days. Consequently, the Jülich Centre for Neutron Science (JCNS) is developing spin-exchange optical pumping (SEOP) systems capable of polarizing the 3He gas in place on a typical neutron instrument. With the polarizer we have constructed, a very high level of 3He polarization of 80.4%±1.5% was obtained and maintained with good time stability. Having such high levels of polarization that are stable over time will reduce the measurement times for such experiments and eliminate time-dependent data corrections. [ABSTRACT FROM AUTHOR]

Abstract: Polarized 3He has shown its unique characteristics in many areas of polarized neutron scattering, its ability to polarize neutrons at short wavelengths, accept wide-angle and divergent beams and low backgrounds enable new classes of experiments. While polarized 3He is not a steady state solution as commonly applied, the benefits have been shown to offset the drawbacks of polarizing and refreshing the polarization in the neutron spin filter cells. As an extension of this work, in-situ polarization using the spin-exchange optical pumping (SEOP) method was explored as a means to construct a system which could be used to polarize 3He in the state used for an effective neutron spin filter to constant polarization while on the neutron beam. An in-situ SEOP polarizer was constructed. This device utilized many devices and principles developed for neutron spin filters which are polarized off the beam line using either SEOP or metastability exchange optical pumping (MEOP) under the same research program. As a collimation of this work effects of extremely high neutron capture flux density incident on the in-situ polarizer were explored. [Copyright &y& Elsevier]

Abstract: We discuss the development and characterisation of a new in situ spin exchange optical pumping (SEOP) based 3He neutron spin filter polarisation device. We present results from a recent test of the prototype system developed with the Institut Laue-Langevin. The polariser was installed on the polarised reflectometer CRISP at ISIS in the analyser position. The 3He was pumped continuously in situ on the beamline. The system also integrated a 3He adiabatic fast passage spin flipper that allowed reversal of the 3He and therefore neutron polarisation state, allowing for measurement of all four polarisation cross-sections. The system was run for a number of days reaching a 3He polarisation of 63%. [Copyright &y& Elsevier]

Abstract: We present a detailed investigation into 3He neutron spin filter cells polarised by spin exchange optical pumping (SEOP). We include measurements of the absolute 3He polarisation using neutron transmission and characterisation of both the X-factor and 3He relaxation times () for a number of cells. For one cell we calculated a maximum 3He polarisation of 79% with a of 633h. The measured X-factor of this cell, , is low. For all cells polarisations of are observed. In addition we present 3He relaxation data for a new design of magneto-static cavity with a field of high homogeneity . This compact device provides a magnetic field in an orientation suitable for in situ optical pumping that minimises the field inhomogeneity contribution to the to 930h in a 1bar cell, the longest reported on beam thus far. The results suggest that high 3He polarisation with long relaxation times can now be routinely obtained with SEOP, enabling time independent incident beam polarisation to be easily implemented across many different neutron scattering instruments. [Copyright &y& Elsevier]

Polarized ³He spin filters are needed for a variety of experiments with slow neutrons. Their demonstrated utility for highly accurate determination of neutron polarization are critical to the next generation of betadecay correlation coefficient measurements. In addition, they are broadband devices that can polarize large area and high divergence neutron beams with little gamma-ray background, and allow for an additional spin-flip for systematic tests. These attributes are relevant to all neutron sources, but are particularly well-matched to time of flight analysis at spallation sources. There are several issues in the practical use of ³He spin filters for slow neutron physics. Besides the essential goal of maximizing the ³He polarization, we also seek to decrease the constraints on cell lifetimes and magnetic field homogeneity. In addition, cells with highly uniform gas thickness are required to produce the spatially uniform neutron polarization needed for beta-decay correlation coefficient experiments. We are currently employing spin-exchange (SE) and metastability-exchange (ME) optical pumping to polarize ³He, but will focus on SE. We will discuss the recent demonstration of 75 % ³He polarization, temperature-dependent relaxation mechanism of unknown origin, cell development, spectrally narrowed lasers, and hybrid spin-exchange optical pumping. [ABSTRACT FROM AUTHOR]

Abstract: We report progress in the development and application of neutron spin filters based on transmission through polarized gas. Tests and application of these devices are underway at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) and the Intense Pulsed Neutron Source (IPNS). The results of application to polarization analysis for diffuse reflectometry is discussed, along with an example of the issues in choosing the flipping ratio for such applications. The status of our development of polarized gas production using both spin-exchange (SEOP) and metastability-exchange (MEOP) optical pumping will be presented. For SEOP, we currently obtain 70–75% polarization in cells up to in volume. [Copyright &y& Elsevier]

We report results of a new technique to measure the electric dipole moment of 129Xe with ³He comagnetometry. Both species are polarized using spin-exchange optical pumping, transferred to a measurement cell, and transported into a magnetically shielded room, where SQUID magnetometers detect free precession in applied electric and magnetic fields. The result from a one week measurement campaign in 2017 and a 2.5 week campaign in 2018, combined with detailed study of systematic effects, is dA(129Xe) = (1.4 ± 6.6stat ± 2.0syst) × 10-28 e cm. This corresponds to an upper limit of |dA(129Xe)| < 1.4 × 10-27 e cm (95% C.L.), a factor of 5 more sensitive than the limit set in 2001. [ABSTRACT FROM AUTHOR]