T. B. Smith

Recent advances in spin-exchange pumped polarized 3He target technology

Abstract We have produced long lifetime 3 He spin-exchange cells from Corning 7056 glass. The lifetimes of single cells have approached the 3 He 3 He bulk-limited lifetime (250 h at a density of 8 × 10 19 cm −3 , (3 amagats)). Corning 7056 glass has the advantage of being a much easier glass for the glassblower to work, allowing for more complex cell designs. In our experiments at Michigan and at SLAC, we have implemented laser diode arrays for spin-exchange optical pumping. In particular, for experiment E154 at SLAC, we achieved high polarizations in high-density 3 He targets using laser diode arrays.

Spin exchange pumped 3He targets: progress and prospects

Abstract Polarized 3He has been used as a spin filter for neutron polarization, as a target to probe neutron structure, and in combination with 129Xe for precision measurement of fundamental physics. Spin exchange pumped masers of one and two species have run for weeks and allow CW measurement with precision trending as steeply as τ −3 2 . At SLAC, a program of experiments has studied the neutron spin-dependent structure function in deep inelastic scattering, exploiting the large neutron polarization in a polarized 3He target. Data from the most recent experiment provide new precise data with Bjorken x down to 0.014. Among the conclusions is the need to consider Q2 dependence in interpretation of the data and determination of sum rules (sums over the full range in x).

A measurement of parity-violating gamma-ray asymmetries in polarized cold neutron capture on Cl-35, Cd-113, and La-139

Abstract An apparatus for measuring parity-violating asymmetries in gamma-ray emission following polarized cold neutron capture was constructed as a 1/10th scale test of the design for the forthcoming n → + p → d + γ experiment at LANSCE. The elements of the polarized neutron beam, including a polarized 3 He neutron spin filter and a radio frequency neutron spin rotator, are described. Using CsI(Tl) detectors and photodiode current mode readout, measurements were made of asymmetries in gamma-ray emission following neutron capture on 35 Cl , 113 Cd , and 139 La targets. Upper limits on the parity-allowed asymmetry s n ·( k γ × k n ) were set at the level of 7×10 −6 for all three targets. Parity-violating asymmetries s n · k γ were observed in 35 Cl , A γ =(−29.1±6.7)×10 −6 , and 139 La , A γ =(−15.5±7.1)×10 −6 , values consistent with previous measurements.

A MEASUREMENT OF THE PARITY-VIOLATING GAMMA-RAY ASYMMETRY IN THE NEUTRON-PROTON CAPTURE

The {rvec n} + p {yields} d + {gamma} experiment under construction at LANSCE studies the weak interaction between neutrons and protons. The experiments will measure the directional dependence of the parity-violating {gamma}-ray asymmetry, A{sub {gamma}}, in the polarized cold neutron capture by para-hydrogen. The goal is to measure A{sub {gamma}} with uncertainty of 0.5 x 10{sup -8}, 10% of its predicted value. A{sub {gamma}} primarily isolates the {Delta}I = 1 component of the hadronic weak interaction and thus will determine the long-range weak pion-nucleon coupling constant H{sub {pi}}{sup 1}. The experiment is carefully designed for the LANSCE pulsed spallation neutron source to achieve the proposed statistical precision and to control systematic errors. We discuss the experiment and its status.

A novel approach for a spin-exchange high density {sup 3}He target

In the past decade high density polarized 3He fixed targets based on spin-exchange with optically pumped Rb have been used successfully in electron scattering experiments at MIT/Bates and SLAC, as a neutron polarizer, and with proton and pion beams at TRIUMF. In the near future similar targets will be used in physics programs at TJNAF and as neutron polarizers at Los Alamos. Until now, the typical spin exchange target was a sealed design, however there are several advantages to target cells that can be evacuated and filled with a variable pressure of polarized 3He. We have begun development of such an actively filled target, based on technology recently developed for NMR/MRI with hyperpolarized noble gases. The benefits and difficulties of constructing such a “flowing” high density 3He target system are discussed.