Helium 3 Neutron Precision Polarimetry CHRISTOPHER CRAWFORD, ROEL FLORES, CHRISTOPHER MENARD*, ELISE...
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Helium 3 Neutron Precision Polarimetry CHRISTOPHER CRAWFORD, ROEL FLORES, CHRISTOPHER MENARD*, ELISE MARTIN, University of Kentucky *present address: Washington
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 MARN LMBARRI, PENELOPE RODRGUEZ, MIGUEL JUREZ
Universidad Nacional Autnoma de Mxico 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 (), 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 ones 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 ones 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,
its 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() TOF (ms)