Polarized 3He Target Research Articles

Few-body physics with polarized beams and targets at IUCF

An experiment utilizing a polarized 3He target and other 3-nucleon experiments at the Indiana University Cyclotron Facility are discussed. The 3 He ( p , pN) reaction has been used to investigate the spin dependent momentum distributions of protons and neutrons in 3He. It was found that with large momentum transfer the PWIA is valid, thus allowing extraction of the distributions directly from the data. A similar experiment is currently under preparation to investigate the spin structure of the deuteron via the 2 H ( p , pN) reaction. Other experiments will study n-d and p-d breakup spin observables in final state interaction kinematics where intermediate energy Faddeev calculations predict large 3-body force effects.

Polarized 3He project at RIKEN

A new approach to study the high momentum component of deuteron D-state wave function by measuring the polarization correlation coefficient, C ∥, for the 3 H e( d , p) 4He reaction has been proposed. In order to carry out the experiment, a spin exchange type polarized 3He target was constructed at RIKEN Accelerator Research Facility (RARF). The density of the target was 2.2 × 10 20 cm −3 (8.2 amagats), and the polarization was about 10%. The spin flip system worked well. The experiment has been carried out in November, 1996, at RARF, using a polarized deuteron beam of 270 MeV.

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

We have produced long lifetime 3He spin-exchange cells from Corning 7056 glass. The lifetimes of single cells have approached the 3He 3He 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 3He targets using laser diode arrays.

The HERMES experiment

HERMES, HERA Measurement of Spin, is an experiment underway at DESY to study the spin structure of the nucleon by using polarized internal gas targets in the HERA 27.5 GeV electron storage ring. Inclusive and semi-inclusive spin dependent deep inelastic scattering are simultaneously measured in a forward spectrometer. In 1995 the experiment was installed and commissioned and data were taken on a polarized 3He target as well as on unpolarized targets of hydrogen and deuterium. In this paper, several aspects of the spin structure of the nucleon which can be probed by HERMES are discussed. The experiment is briefly described and some preliminary results from 1995 running are presented.

An internal polarized 3He target for electron storage rings

We describe an internal polarized 3He target currently under construction which will be used in several electron storage ring experiments. The target is based on the technique of metastability exchange laser optical pumping, where the polarized atoms flow into a cryogenically-cooled storage cell. This novel technique allows for high precision measurements where the beam interacts with the pure atomic species. Both the HERMES experiment at DESY and the BLAST detector at the MIT Bates Laboratory will use the polarized 3He target in their measurements. Details of the target system, including the provisions needed to incorporate the target into the electron storage ring, are presented.

A method for the accurate determination of the polarization of a neutron beam using a polarized 3He spin filter

A new method for the accurate determination of the degree of polarization of a neutron beam which has been polarized by transmission through a spin polarized 3He cell is given. The method does not require the use of an analyzer or spin flipper nor does it require an accurate independent determination of the 3He polarization. The method provides a continuous on-line determination of the neutron polarization. The method may be of use in the accurate determination of correlation coefficients in neutron beta decay which provide a test of the standard model for the electroweak interaction. The method may also provide an accurate procedure for the calibration of polarized 3He targets used in medium and high energy scattering experiments.

SLAC measurements of the neutron spin-structure function

Results from a measurement of the neutron spin-dependent structure functiong1n(x) over a range inx from 0.03 to 0.6 and withQ2>1 (GeV/c)2 are presented. The experiment consisted of scattering a longitudinally polarized electron beam from the Stanford Linear Accelerator off a polarized3He target and detecting scattered electrons in two magnetic spectrometers. The results are interpreted in the quark-parton model and used to test the Bjorken sum rule.

Adiabatic spin rotator for a laser pumped polarized 3He target

An adiabatic spin rotator has been constructed for use with the TRIUMF optically pumped polarized 3He target. It consists of two orthogonal pairs of Helmholtz coils allowing adiabatic rotation of the 3He spin into any arbitrary direction. Thus, the target may be polarized alternately in the sideways, longitudinal, and normal directions allowing measurements of complete sets of spin observables in nuclear scattering experiments during a single experimental run. Recently the system was used to measure all parity-allowed spin correlation observables A 00 ij in 3 He( p , p) elastic scattering at 200 and 500 MeV. The system permits reasonably rapid spin reversals (30 s) with minimal polarization losses (< 1×10 −5 per spin reversal). This allows the target spin to be reversed frequently during an experimental run thus reducing systematic uncertainties from variations in the response of other components in the experimental setup.

A laser optically pumped polarized 3He target for storage rings

A polarized 3He target for use in a storage ring has been constructed and tested. The target employs an infrared laser to polarize 3He atoms by metastability exchange optical pumping in a Pyrex glass cell which is connected by a glass capillary to a windowless target storage cell. The target polarization direction is determined by a 3 mT magnetic field. With 3 W of incident laser power, equilibrium polarizations of 50% at a flow rate of 1 × 10 17 3He atoms/s have been routinely achieved. Two techniques have been investigated to rapidly reverse the 3He target polarization. Further, a scheme to interface the glass pumping cell with the storage ring vacuum has been developed.

A dense polarized 3He target based on compression of optically pumped gas

3He-gas is spin polarized by the method of optical pumping of metastables and metastability exchange in a low pressure gas discharge. At a pressure of p ≈ 1.5 Torr a volume of 1 l is polarized within about 30 s to a degree of 50% with 300 mW of incident light from an argon-ion laser pumped LNA laser, tuned to the λ = 1.083 μm resonance line. The polarized gas is compressed by a Toepler pump into a target cell of 120 cm 3 volume. In a first attempt a steady state polarization of 30% has been achieved in the target at a pressure of 685 Torr. The paper analyses the essential parameters governing this technique and pilotes its experimental realization.

Laser polarized muonic atoms

Lasers are an important tool in the field of muon physics. A new application of lasers, namely producing polarized muonic atoms, is the subject of a new program at LAMPF. One technique already demonstrated is stopping unpolarized muons in a laser polarized 3He target. A more promising idea is to polarize neutral muonic helium by collisions with laser polrized Rb vapor. These methods for producing polarized muonic helium will be useful for measuring the spin dependence of nuclear muon capture and for determining the induced pseudoscalar coupling.

The [formula omitted] reactions and the components of the 3He wave function

Spin observables in exclusive and semi-inclusive quasi-elastic scattering of polarized electrons on a polarized 3He target provides us with a powerful way to disentangle the dominant components of its wave function. However, the contributions of Final State Interactions and Meson Exchange Currents are sizeable for large values of the missing momentum, in the kinematical domain covered by the present generation of electron accelerators (virtual photon momentum pf the order of 500 MeV/ c. They become small when the momentum of the virtual photon is larger than 1 GeV/ c.

New physics with polarized 3HE targets

Development of targets of polarized 3He for nuclear and particle physics is a major focus of effort by experimental physicists at present. This is motivated by many interesting and important experiments with beams from 5 MeV to 35 GeV. The target technologies are described and the physics outlined. Further, the need for a significant theoretical effort on the three body problem is detailed.

Electron scattering with polarized beams and 3He-targets

The first part of the paper deals with some typical experimental situations met in scattering of polarized electrons from unpolarized and polarized targets. One example described is the measurement of parity violation measured in quasi-elastic scattering of polarized electrons at the 300-MeV Mainz-Linac. The main problems posed by this kind of experiments lie in achieving the necessary statistical and systematic error limits which have to be well below 10 −6 in order to detect the parity violating asymmetry. Much larger asymmetries can be observed in parity conserving, purely electromagnetic scattering processes. However, they require polarized targets in addition or polarization analysis in the final state. Such experiments can reveal fundamental insight in the electromagnetic structure of the nucleons. The d( e , e′ n ) and 3 H e( e , e′ n) reactions are discussed as examples. The second part briefly reports on the status and performance of polarized GaAsP-electron sources. The third part deals with polarized 3He targets. Attempts to build a dense 3He target, obtained by compressing an optically pumped 3He vapour are described in particular.

A polarized 3He target for nuclear physics

A prototype polarized 3He target based on optical pumping of metastables has been constructed and tested. The target employs an infrared laser to polarize 3He atoms in a pyrex cell which is connected by a capillary to a copper cell at 87 K. With 20% polarization and thickness 4 × 10 18cm −2, the target has been routinely operated with 1 μA of 5 MeV protons passing through it. Using this technique it should be possible with increased laser power and lower temperatures to construct targets of 50% polarized 3He with foil windows and thickness 5 × 10 18cm −2, or windowless targets of thickness 10 16cm −2 for use in a storage ring.

Measurement of 3He depolarization rates during bombardment with a 4He beam

We have produced a polarized 3He target and measured the depolarization rate arising from bombardment with a 4He beam. The 3He is contained in a glass cell with Mo windows and is polarized by spin exchange with laser-optically-pumped Rb. Nitrogen (at least 60 Torr) is included in the cell for effective optical pumping. The nitrogen also suppresses contributions to the depolarization of 3He by destroying atomic ions, 3He+, and molecular ions, 3He2+. In a target with 430 Torr of 3He and 150 Torr of N2 the depolarization rate due to bombardment by a 180 particle-nanoampere 18 MeV 4He beam is found to be 1(3.5 h), which is consistent with the predictions of a detailed model of the effects of ionization by the beam.

A polarized 3He target for nuclear physics

A prototype polarized 3He target based on optical pumping of metastables has been constructed and tested. The target employs an infrared laser to polarize 3He atoms in a pyrex cell which is connected by a capillary to a copper cell at 87 K. With 20% polarization and a thickness of 4 × 10 18 cm −2, the target has been routinely operated with 1 μA of 5 MeV protons passing through it. Using this technique it should be possible with increased laser power and lower temperatures to construct targets of 50% polarized 3He with foil windows and a thickness of 5 × 10 18 cm −2, or windowless targets of thickness 10 16 cm −2 for use in a storage ring.

Eighth order solenoids

Eighth order solenoids for producing honogeneous magnetic fields were computed. One such solenoid, designed to contain a polarized 3He target, was built and tested. Compared to usual Helmholtz-type coils of similar size and efficiency the new arrangement can secure a high degree of homogeneity over a volume 15–60 times larger.

Optical nuclear polarization — Targets and sources

The nuclear polarization of3He by optical pumping using discharge lamps is described, as well as attempts (both successful and unsuccessful) to make a polarized3He target. Recent experimental results with a polarized3He target are presented. Experiments to polarize3He using a laser as a pumping light source are described, and the prospects for producing a dense polarized3He target are indicated. The polarization of other nuclei, especially Xe and Kr, by spin transfer from laser polarized alkalis is described.

Experience with a polarized 3He target for nuclear scattering experiments

A polarized 3He target, which uses conventional optical pumping with 4He discharge lamps, is described. Emphasis is given to the experience gained with its use during nuclear scattering experiments using proton beams from the University of Manitoba cyclotron. An analysis of possible errors in present and past experiments is given.