Helium 3 Neutron Precision Polarimetry CHRISTOPHER CRAWFORD, ROEL FLORES, CHRISTOPHER MENARD*, ELISE MARTIN, University of Kentucky *present address: Washington University in St. Louis AMERICO SALAS-BACCI, SCOTT WILBURN, ANDI KLEIN, AARON COUTURE Los Alamos National Laboratory (LANL) LIBERTAD BARRON PALOS, QUIELA CURIEL, DANIEL MARÍN LÁMBARRI, PENELOPE RODRÍGUEZ, MIGUEL JUÁREZ Universidad Nacional Autónoma de México TOM GENTILE National Institute of Standards and Technology (NIST) SEPPO PENTILLA Oak Ridge National Laboratory (ORNL) Goal: Make a.03% precision neutron polarization measurement using two independent techniques. n n + n n p p p p n n p p n n + p p Extraction of the polarization: The first method used to find the neutron polarization uses the measurements of neutron flux from the monitors before and after the polarizer (indicated by M 1 and M 2. First, let us define the neutron polarization: where n + and n - refer to the two separate spin states. Now let us quantized the neutron flux after they pass through a 3 He cell: Clearly, when the 3 He cell is unpolarized, the number of neutrons transmitted through the polarizer depends only on the density of the 3 He (n), the length of the polarizer (l) and the 3 He cross section (σ), which is a function of neutron energy. As the monitor signals are simply the sum of the two neutron spin states, the transmission is: Taking the ratio of this transmission with the transmission through an unpolarized 3 He eliminates the exponential term, leaving only the hyperbolic cosine. Finally, the neutron polarization after the polarizer is: The Spin Flipper Support provided by: Department of Physics, University of Kentucky P-25 Division, Los Alamos National Laboratory (US Department of Energy) Department of Undergraduate Research, Washington University in St. Louis Polarizer and Analyzer: Contain polarized 3 He which acts as a spin filter to polarize neutrons. Contain coils for NMR and adiabatic fast passage -AFP Neutron Monitors: Contain unpolarized 3 He which acts as a neutron detector Spin independent transmissions Three total Ratios between monitors show polarization of 3 He and neutrons RF Spin Flipper (RFSF): NMR technique: uses a rotating magnetic field to flip the neutron spin of every other neutron pulse. Aspects of the experiment that I worked on: assembly of the instrument supports mapping the holding magnetic field building heating system for 3 He cells tuning of the RF spin flipper amplitude collecting data with a VME DAQ system wrote ROOT scripts to help analyze the data a second phase of the experiment involving neutron capture by deuterium general troubleshooting Experimental Setup Abstract: Neutron decay correlation experiments can provide a test of the Standard Model Measurement of correlation constants in abBA are limited by one’s knowledge of the neutron polarization. Using 3 He as a spin filter to polarize neutrons also provides an easy method for finding neutron polarization. We test this measurement by employing a second 3 He cell to analyze the neutron polarization from the polarizer. Abstract: Neutron decay correlation experiments can provide a test of the Standard Model Measurement of correlation constants in abBA are limited by one’s knowledge of the neutron polarization. Using 3 He as a spin filter to polarize neutrons also provides an easy method for finding neutron polarization. We test this measurement by employing a second 3 He cell to analyze the neutron polarization from the polarizer. 3 He as a spin filter Neutrons interact with polarized 3 He to form tritium and a proton In 3 He the proton spins are anti-aligned so the spin state is determined by the neutron For an incoming neutron to be captured, it’s spin state must be anti-aligned with that of the 3 He Neutrons with parallel spin pass unabsorbed. As a neutron detector Unpolarized 3 He results in a polarization independent neutron transmission. 3 He ionized in capture process and when placed in a high voltage field a signal proportional to the neutron flux is generated. Spallation source Chopper Neutron guide Beam monitors Polarizer RFSF Analyzer RFSF Experimental “cave” LH 2 moderator Beamline: Tungsten spallation source LH 2 moderator slows neutron to cold - thermal range Chopper eliminates wrap- around neutrons (too slow/fast) ≈21m aluminum neutron guide 20 Hz pulsed Allows for TOF spectroscopy Bragg edge Chopper open Neutron energy spectrum Negative profile due to a negative voltage signal from monitors Fast neutrons on the left Profile goes to zero when chopper is completely closed Bragg edges from the aluminum neutron guide 23 meV 2.1 km/s 3.7 meV.84 km/s 1.9 meV.6 km/s.92 meV.42 km/s wavelength(Å) TOF (ms)