1 Neutron polarizer development
Skills learned: magnetic resonance, magnetic field measurement, data analysis
The neutron polarizer for NOPTREX is based on spin-dependent neutron absorption in 3He nuclei polarized through spin-exchange optical pumping (SEOP) of alkali atoms in a glass vapor cell. We have such a device in hand at IU for students to tune the laser, tune magnetic fields, and perform nuclear magnetic resonance (NMR) measurements of the 3He polarization. In years 1 and 2 in Japan, the student will be involved in the analysis of the polarized neutron transmission data through a 139La target placed at the very end of the apparatus, whose large parity-odd asymmetry acts as a neutron polarization analyzer. The same plan will apply in year 3 if we get additional beamtime: if not the student will concentrate on data analysis and documentation of the device for scientific publications. The students will benefit from the development of skills that are broadly applicable in many scientific and technical areas, and the project will benefit from preparation and testing of the apparatus.
2 Neutron/photon spin interferometry
Skills learned: Neutron optics, data acquisition, laser/optics experience
The parity violating asymmetries sought in the NOPTREX collaboration rely on the production and control of polarized neutron spin filters. In addition, the experiment requires the ability to flip the spins of neutrons with exquisite precision. In order to test the accuracy of the apparatus components responsible for the production and control of neutrons, the student will design a spin interferometer at NUANS. Spin interferometry is an elegant technique where an incident beam of polarized neutrons is split and then recombined, forming an interference pattern. By inserting a spin flipper in an arm of the interferometer, the students will determine the phase shift induced and characterize components of the NOPTREX apparatus. In preparation for building the spin interferometer at NUANS, the student will work at BC with the PI on an optical analog of the neutron spin interferometer. The student will become familiar with the basic principles of interferometry by implementing a Mach-Zehnder interferometer on an optical bench. The student will gain an understanding of spin interferometry while characterizing components for future design of the NOPTREX experiment. The interferometer will be fabricated and tested over three years in Japan, with the same training activities repeated each year.
3 Neutron spin flipper development
Skills learned: Simulation, magnetic field measurement, data analysis
A neutron spin flipper between polarizer and targets alternates spin state on a pulse-by-pulse basis to isolate P -odd and T -odd effects from instrumental background. UK is designing a DC adiabatic spin flipper which uses a zero-crossing to reverse the direction of the spin with respect to the magnetic field. A basic design will be installed at J-PARC by the beginning of the IRES program, and be used to collect initial data. As part of the academic year training, the students will perform field calculations of the spin flipper coils for both the active and inactive states, and perform spin simulations of neutrons passing through the device to determine its efficiency. They will gain experience mapping the magnetic field of the prototype spin flipper at UK, and compare their results with their simulations, fitting out variations such as the orientation of the coil. This will prepare them with the physics knowledge and computational skills to perform a detailed analysis of the neutron polarization of J-PARC experiments during their summer research in Japan. As part of the ongoing R&D effort, each year, students will investigate more advanced field profiles with sharper zero crossings, and more adiabatic field profiles that yield higher spin flip efficiencies at lower energies. As better field profiles are discovered, they will design coil windings to produce these fields using the magnetic scalar potential method, 3-d print formers to keep the windings in position, and wind new coils. They will bring the new coils for the spin flipper at J-PARC. In Japan, the participant will collect and analyze diagnostic data on the coils in Nagoya, and analyze data on the neutron polarization taken at J-PARC.
4 Neutron spin transport coils
Skills learned: Magnetic field design, spin simulations, data analysis
Since the neutron spin precesses around stray magnetic fields, a uniform holding magnetic field is required to define the spin direction of the neutrons and preserve their polarization. While it is quite easy to generate a uniform magnetic field in free space with a large Helmholtz pair, it is more complicated on the neutron beamline with tight geometry and stray fields from the polarizer coils. UK will participate in the design spin transport coils on the ANNRI beamline. They will already be installed and used to collect data before the first IRES summer program. However, the undergraduate participant will take part in the design of spin transport coils for other projects, for example the nEDM@SNS, n2EDM and nn' experiments. Similar to the spin flipper, these designs will start with analytic field profiles, with which the student will simulate neutron spin precession using the Bloch equation. Once the field profile has been optimized, the student will input this field as boundary conditions into the finite element analysis software COMSOL and calculate the winding geometry using the magnetic scalar potential. Finally, the student will verify the resulting magnetic fields, and repeat the adiabaticity calculations. Given an acceptable design, the student will wind the coils, map out the magnetic fields and compare with simulations. In Japan, the student will analyze field maps of the spin transport coils as installed on ANNRI, and determine the neutron polarization after passing through the coils, which is an important component in the analysis of parity violation experiments. If variations are found, the student will work with Prof. Kitaguchi to design and wind correction coils for installation at J-PARC. This project is closely related to the spin flipper design, and these two participants would work closely together on their projects.
5 Gamma/neutron detection
Skills learned: Detector hardware and electronics, light yield characterization, interpreting data
A high efficiency current mode eV neutron detector is needed to measure resonances in the total neutron absorption cross section. IU and UK conducted measurements at J-PARC to develop the concept for a 10B+NaI(Tl) current mode detector, which is being constructed and tested at EKU. This array will also be used to search for new candidate nuclei for NOPTREX through angular parity-odd asymmetries. An array of 24 NaI(Tl) crystals will form modular detector elements with photo-multiplier tubes enclosed within a light-tight housing. For training each year, the student will characterize the performance of the prototype detectors by measuring the light yield of the crystals, the behavior of the low-noise preamplifiers and current integration circuit, and by interpreting and analyzing the resultant signals. The participants will collaborate to validate Monte Carlo simulations on the detector. They will will also collaborate with UK to develop more advance digital signal processing algorithms for the detector array data acquisition system. In Japan, the participants will analyze γ data from the 139La target in the detector array at J-PARC. They will also characterize elements of the detector array at NUANS with epithermal neutrons on different nuclear targets at Nagoya.
6 Systematic Error Analysis
Skills Learned: Neutron optics, scattering theory, Monte Carlo simulations, Python programming
An experimentally observed T-violating effect is expected to be extremely small; hence, it is im- portant 1) to understand sources of systematic errors and their behavior as a function of neutron energy, and 2) to optimize 10B+NaI(Tl) detector performance. In year 1, the student will develop a MCNP model of the 10B+NaI(Tl) detection system and analyze simulation results. They will be responsible for data analysis and tuning the simulations to reproduce the neutron transmission data as they collect it at the NUANS. Since time reversal in the NOPTREX experiment is realized through mechanical rotation of the apparatus, misalignment and non-uniformities of the polarized target and neutron beam energy distribution will lead to systematic errors. In year 2, systematic errors will be analyzed analytically using the approach outlined in and neutron energy dependence of the neutron forward scattering amplitude. Students will develop a Python-based software framework to calculate the neutron asymme- try and polarization, and systematic errors as a function of neutron beam parameters. Obtained results will be tested using measurements of the J-PARC neutron beam energy distribution. The year 3 student will learn how to use Geant4 and McStas particle propagation simulation software packages, build a computer model of the NOPTREX experimental setup based on results from years 1 and 2, and run simulations needed by Japanese colleagues for the enhancements of the apparatus.