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Comparison of measured (○, ×, and ∆) and calculated field components (solid lines) for BB z (r=0 cm, z), B z B (r=5cm, z), and BB r (r=5cm, z) of the RFSR. The solenoid is 30 cm long and the RFSR (i.e. the RF field) is 40 cm long.
Source publication
We have developed a radio-frequency resonant spin rotator to reverse the neutron polarization in a 9.5 cm x 9.5 cm pulsed cold neutron beam with high efficiency over a broad cold neutron energy range. The effect of the spin reversal by the rotator on the neutron beam phase space is compared qualitatively to RF neutron spin flippers based on adiabat...
Contexts in source publication
Context 1
... M is the length of the solenoid and L the length of the aluminum shield. The calculated fields shown in Fig. 5, are a sum of the first 40 terms of the slowly converging ...
Context 2
... B r B components at r=0 cm and 5 cm were mapped with 10-mm steps. The maximum of BB z on axis was measured to be 0.42 mT at the center of the solenoid and increasing slowly with r. On the axis B r B =0 mT and off axis BB r increases when approaching the ends of the solenoid. Neither field components were distorted much by the aluminum windows. In Fig. 5 we compare the measured B z B at r=0 cm (○) and r=5 cm (×), and BB r at r=5 cm (∆) with the corresponding calculated fields (solid lines). They agree within ...
Citations
... The direction of the magnetic field must be known to 0.1 • with respect to the detector to prevent the mixing of the parity-allowed nuclear spin asymmetry associated with k n · σ n × k γ,p . A resonant neutron spin rotator [396] has been used to alternate the spin direction on a pulse-by-pulse basis to reduce systematics associated with instrumental drift. These experiments use a novel double cos-theta RF coil with fringeless transverse fields that operates for both longitudinally and transversely polarised neutrons [397]. ...
Presently under construction in Lund, Sweden, the European Spallation Source (ESS) will
be the world’s brightest neutron source. As such, it has the potential for a particle physics
program with a unique reach and which is complementary to that available at other
facilities. This paper describes proposed particle physics activities for the ESS. These
encompass the exploitation of both the neutrons and neutrinos produced at the ESS for
high precision (sensitivity) measurements (searches).
... The direction of the magnetic field must be known to 0.1 • with respect to the detector to prevent the mixing of the parity-allowed nuclear spin asymmetry associated with k n · σ n × k γ,p . A resonant neutron spin rotator [396] has been used to alternate the spin direction on a pulse-by-pulse basis to reduce systematics associated with instrumental drift. These experiments use a novel double cos-theta RF coil with fringeless transverse fields that operates for both longitudinally and transversely polarised neutrons [397]. ...
Presently under construction in Lund, Sweden, the European Spallation Source (ESS) will be the world's brightest neutron source. As such, it has the potential for a particle physics program with a unique reach and which is complementary to that available at other facilities. This paper describes proposed particle physics activities for the ESS. These encompass the exploitation of both the neutrons and neutrinos produced at the ESS for high precision (sensitivity) measurements (searches).
... The neutron beam is 10 cm x 12 cm at the exit of the Fundamental Neutron Physics Beamline (FNPB) [1] at the Spallation Neutron Source at Oak Ridge National Laboratory. The beam passes through a supermirror polarizer [2] before entering the resonant frequency spin rotator (RFSR) [3]. The RFSR alternates the neutron spin over a sequence of 8 beam pulses in a ↑↓↓↑↓↑↑↓ pattern in order to cancel first and second order fluctuations in the beam intensity. ...
The NPDGamma experiment measures the parity-violating asymmetry in $\gamma$-ray emission in the capture of polarized neutrons on liquid parahydrogen. The sensitivity to the asymmetry for each detector in the array is used as a parameter in the extraction of the physics asymmetry from the measured data. The detector array is approximately cylindrically symmetric around the target and a step-wise sinusoidal function has been used for the sensitivity in the previous iteration of the NPDGamma experiment, but deviations from cylindrical symmetry necessitate the use of a Monte Carlo model to determine corrections to the geometrical factors. For the calculations, source code modifications to MCNPX were done in order to calculate the sensitivity of each cesium iodide detector to the physics asymmetry. We describe the MCNPX model and results from calculations and how the results are validated through measurement of the parity violating asymmetry of $\gamma$-rays from neutron capture on chlorine.
... Neutrons exit the 10 × 12 cm neutron guide on the Fundamental Neutron Physics Beamline (FNPB) [3] and enter a supermirror polarizer [4], after which is the NPDGamma apparatus [5,6]. Polarized neutrons then enter the resonant frequency spin rotator (RFSR) [7] and are rotated according to a pattern (↑↓↓↑↓↑↑↓) that cancels beam power fluctuations to second order and the signals from opposite spin states are used to isolate the asymmetry signal. The neutrons are incident on the 16-liter liquid hydrogen target [8] that is surrounded by 48 CsI(Tl) detectors arranged in 4 rings of 12 detectors each [9] that detect the γ-rays from neutron capture. ...
The NPDGamma experiment measures the asymmetry in $\gamma$-ray emission in the capture of polarized neutrons on liquid parahydrogen. The beam polarization is measured using $^3$He spin analysis, but this measurement does not account for the contribution of depolarization from spin-flip scattering primarily due to orthohydrogen in the bulk liquid. This is a systematic effect that dilutes the experimental asymmetry and is modeled using Monte Carlo. Methods for tracking neutron spin in MCNPX were developed in order to calculate the average neutron polarization upon capture for use as a multiplicative correction to the measured beam polarization for the NPDGamma experiment.
... Similar ramping is done in resonant RF flippers, another kind of spin rotator, where the amplitude of the RF field is varied in phase with the ToF neutron pulses. In contrast to adiabatic RF flippers in the resonant flippers, the static magnetic field perpendicular to the RF field does not change in magnitude along the device [34,35]. This list of spinflipping devices is not extensive, but rather contains the main devices used so far for imaging; a more comprehensive list and history of polar izing and spinflipping devices can be found in [36]. ...
While neutron imaging is a well-established technique for investigations of inner structures and processes in materials, complex systems, and devices, the utilization of polarized neutron beams to visualize magnetic phenomena has been introduced only about a decade ago. In contrast to neutron scattering studies, where the interaction of the neutron’s magnetic moment with magnetic states of matter has been exploited for a long time, the direct visualization of magnetic fields in neutron imaging is a relatively new field and is still developing. Here, we give an overview of the status and provide approaches to visualizing magnetic fields with polarized neutrons, together with a report on the latest developments in attempting to record neutron tomographies for 3D reconstructions of magnetic vector fields.
... The NPDGamma experiment uses a resonant RF spin rotator (RFSR), also known as a Rabi coil, to rotate the neutron spins π radians, thereby isolating the small parityviolating signal and canceling several systematic uncertainties in the γ-ray asymmetry measurement [17]. The RFSR creates a magnetic field B RF = B RF cos(ω RF t)ẑ parallel to the neutron beam and on resonance such that the frequency of the RF magnetic field ω RF is equal to the Larmor frequency of the neutrons in the guide field ω 0 = γ n B 0 . ...
... The RF field in the RFSR is described by modified Bessel functions, and the spin equations of motion of neutrons traversing the RF field are solved numerically [17]. The spin-reversal efficiency in the RFSR is position dependent, and therefore the average spin-reversal efficiency of the neutron beam downstream of the RFSR is modeled by ...
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 $\sim10^9$ neutrons per second per cm$^2$ and a cross sectional area of 10$\times$12~cm$^2$. 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 $^{3}$He 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 $^{3}$He 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 $\gamma$-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.
... The robustness of signal contrast is a great advantage of TOF-MIEZE spectroscopy with pulsed neutron beam. The characteristics of the TOF-MIEZE technique can be beneficial for various experiments using resonance spin flippers in neutron scattering spectroscopy and in high-precision fundamental neutron physics 23,24 . ...
We propose a basic formula and demonstration for a high-resolution quasi-elastic neutron scattering (QENS) by combining the time-of-flight (TOF) method with Modulation of Intensity by Zero Effort (MIEZE) type neutron spin echo spectroscopy. The MIEZE technique has the potential to develop a unique approach to study on slow dynamics of condensed matter; however, the energy resolution is limited owing to the hypersensitivity of the MIEZE signal contrast to the echo condition, which is strongly affected by the alignment of the instruments and the sample. The narrow allowance of the optimal alignment is a major obstacle to the wide use of this technique. Combining the TOF method with MIEZE (TOF-MIEZE), the hypersensitivity of MIEZE signals is significantly alleviated with a short pulsed beam. This robustness is very useful to optimize experimental alignments and enables accurate measurements of QENS. The experimental results demonstrate the characteristic of the TOF-MIEZE technique and are well described by the formula presented in this study.
... The F 1 and F 2 flippers should now be operated in the time-of-flight mode whereby the rf-fields are ramped up and down in coordination with the neutron source. 20 As a proof of principle experiment, we believe our MICE setup works extremely well, in spite of the fact that after being placed between the test beam line HB-2D's polarizer and analyzer our two rf-flippers achieved a flipping ratio of only about 2. With upgraded polarizers and analyzers, we fully expect that an improved MICE will enable us collect high quality data on real samples. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. ...
The analysis of neutron diffraction experiments often assumes that neutrons are elastically scattered from the sample. However, there is growing evidence that a significant fraction of the detected neutrons is in fact inelastically scattered, especially from soft materials and aqueous samples. Ignoring these inelastic contributions gives rise to inaccurate experimental results. To date, there has been no simple method with broad applicability for inelastic signal separation in neutron diffraction experiments. Here, we present a simple and robust method that we believe could be suited for this purpose. We use two radio frequency resonant spin flippers integrated with a Larmor precession field to modulate the neutron intensity and to encode the inelastic scattering information into the neutron data. All three components contribute to the spin encoding. The Larmor field serves several additional purposes. Its usage facilitates neutron time-focusing, eliminates the need for stringent magnetic shielding, and allows for compact setups. The scheme is robust, simple, and flexible. We believe that, with further improvements, it has the potential of adding inelastic signal discrimination capabilities to many existing diffraction instruments in the future.
... IV, the linear and quadratic components of time-dependent detector gain drifts in a sequence can be greatly suppressed [60]. To achieve neutron spin reversal the experiment employed a radio-frequency resonant neutron spin rotator (RFSR) [61] which operates at 29 kHz for the 1 mT guide field. The neutron spin direction is reversed when the RFSR is on and is unaffected when it is off. ...
... The neutron spin direction is reversed when the RFSR is on and is unaffected when it is off. The spin-flip efficiency averaged over the beam cross section (5-cm radius) was measured to be 98.0% [61]. Possible false asymmetries of electronic origin without neutron beam may be measured in two ways. ...
... The resulting effect would appear as an addition to (i.e., reside on top of) the detector signal. This contribution was investigated by running the spin rotator electronics together with the detector array and DAQ and looking for a spin-correlated signal in the detectors [61]. The second type of asymmetry occurs when the magnetic field from the spin rotator leaks into the vacuum photodiodes of the γ -ray detectors and changes their gain. ...
The NPDGamma collaboration reports results from the first phase of a measurement of the parity violating up-down asymmetry Aγ with respect to the neutron spin direction of γ rays emitted in the reaction n⃗+p→d+γ using the capture of polarized cold neutrons on the protons in a liquid parahydrogen target. One expects parity-odd effects in the hadronic weak interaction between nucleons to be induced by the weak interaction between quarks. Aγ in n⃗+p→d+γ is dominated by a ΔI=1, 3S1-3P1 parity-odd transition amplitude in the n-p system. The first phase of the measurement was completed at the Los Alamos Neutron Science Center spallation source (LANSCE), with the result Aγ=[-1.2±2.1 (stat.)±0.2 (sys.)]×10-7. We also report the first measurement of an upper limit for the parity-allowed left-right asymmetry in this reaction, with the result Aγ,LR=[-1.8±1.9 (stat.)±0.2 (sys.)]×10-7. In this paper we give a detailed report on the theoretical background, experimental setup, measurements, extraction of parity-odd and parity-allowed asymmetries, analysis of potential systematic effects, and LANSCE results. The asymmetry has an estimated size of 5×10-8 and the aim of the NPDGamma collaboration is to measure it to 1×10-8. The second phase of the measurement will be performed at the Spallation Neutron Source at Oak Ridge National Laboratory.
... This challenge is solved by measuring the γ-ray asymmetry for opposing spin directions so that the asymmetry inherent in the experimental apparatus can be removed by averaging the γ-ray asymmetry for each spin direction. The NPDGamma experiment uses a resonant RF spin rotator [8] to flip the spins of the neutrons by 180°. In this device there is a static magnetic field, B 0 , parallel to the neutron spins and an RF magnetic field B rf = B rf cos(ωt)ẑ parallel to the neutron guide. ...
The NPDGamma experiment will measure the parity violating directional γ-ray asymmetry in the capture of polarized neutrons on protons n + p → d + γ. The γ-ray asymmetry results from the weak nucleon-nucleon interaction, and the largest contribution to the asymmetry comes from weak pion exchange according to the meson exchange model of the weak NN interaction. The n + p → d + γ reaction will provide a measurement of the weak pion-nucleon coupling constant H 1 π without nuclear structure uncertainties. The Fundamental Neutron Physics Beamline (FNPB) at the Spallation Neutron Source (SNS) will provide a pulsed beam of cold neutrons to the experiment. The neutrons are polarized by a supermirror polarizer and then captured on a liquid parahydrogen target. The emitted γ-rays are detected with a CsI(Tl) detector array. The accuracy of the measurement is dependent on how well the polarization of the neutron beam is known. The beam polarization will be measured with a polarized 3 He spin filter for different directional neutron polarizations set with a resonant RF spin rotator. Techniques to determine the properties of a 3 He cell as well as the method of measuring the neutron beam polarization will be discussed.
