3He Target Research Articles

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.

A new type of liquid- 3He target system using small mechanical refrigerators

A new type of liquid- 3He target has been developed for photoabsorption experiments at intermediate energies. Using the cooling power of liquid 4He at reduced vapour pressure, 3He gas is liquefied into a cylindrical target cell of 180 ml and is maintained at 2.0 K during the experiment. Evaporated 4He gas is evacuated by a rotary pump and returned into the 4He bath in the cryostat, where two small mechanical refrigerators with cooling capacities of 3 W at 4.3 K and 10 W at 20 K are operated for the purpose of 4He recondensation. A maintenance-free operation of more than 1000 hours has become possible by adopting the 4He circulation system.

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.

Spin-polarized 3He nuclear targets and metastable 4He atoms by optical pumping with a tunable, Nd:YAP laser

Several Nd:YAP lasers were constructed which could be broadly tuned in the 1083-nm region which includes the helium 23S-23P transition, using a Lyot filter and thin, uncoated etalons within the laser cavity. 1 W of power could be extracted at 1083 nm through a 1% transmitting output coupler. This laser beam was used to optically pump metastable 4He and 3He 23S helium atoms in a weak discharge cell, spin polarizing the metastable ensemble. In a 3He cell the polarization is transferred to the nuclear spin system. A 3He target cell at 0.3 Torr was polarized to 52% in a few minutes. We describe the application of this system to the design of polarized targets for experiments in nuclear physics.

Results on the performance of a liquid H 2 and 3He target

In this paper we present a H 2 and 3He condenser to be used as a target for intermediate energy nuclear physics experiments. Here we summarize the test results on its working performance.

Results on the performance of a liquid H2 and 3He target

In this paper we present a H2 and 3He condenser to be used as a target for intermediate energy nuclear physics experiments. Here we summarize the test results on its working performance.

Test and analysis of a liquid 3He target for intermediate energy physics experiments

Experiments with a liquid 3He target with convectional circulation and a liquid 4He cooling system are described. A theoretical treatment is given which agrees with the experimental results. If properly constructed, the target can take up more than 1 W. In that case the 3He leaving the reaction region must have a temperature near 3 K, which is higher than the temperatures measured directly. A small expansion vessel on top of the heat exchanger appeared to be important for the functioning of the target under conditions of high power dissipation. On the basis of our calculations, the variation of the experimental averaged target thickness with the beam power of the NIKHEF 3He target at Amsterdam can be largely explained.

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.

Elastic scattering of α particles on light nuclei at Pα=7 GeV/ c

Elastic scattering differential cross sections of α particles have been measured at P α =7.0 GeV/ c ( T N =1.05 GeV ) on 1H, 2H, 3He and 4He target up to a momentum transfer of ∼4 (GeV/ c) 2. A preliminary interpretation of the data is given in the framework of the Glauber theory.

A study of the 6Be system by use of the reaction [formula omitted]5Li(g.s.) between 17 and 30 MeV with a polarized target

The differential cross section of the reaction 3He( 3He, p) 5Li(g.s.) has been measured at 26 MeV and the analyzing power A γ in the energy range 17–30 MeV with the use of a polarized 3He target. The data are compared with existing microscopic multi-channel calculations to the 6Be system. The influence of the J π = 4 + channels turned out to be too strong. The deviations from the antisymmetry to 90° c.m. of the analyzing power angular distribution γ ( θ) are discussed with respect to the purely direct transfer model for identical particles in the entrance channel.

Experimental study of coherent pion production in [formula omitted] and a test of the reaction mechanism

Pion production through the 4He( 3He, π +) 7Li reaction leading to the first three levels of the 7Li nucleus has been measured at two incident energies close to threshold (280.5 and 266.5 MeV). A model previously used to analyse doubly coherent pion production on a 3He target was found to give a good description of the present data.

Magnetic transition of solid 3He observed by polarized neutrons

Measurements of the transmission of polarized neutrons through a weakly polarized solid 3He target are reported. Temperatures down to 0.45 mK have been reached. This permits experimentation on the melting curve below the temperature of the magnetic transition. The Kapitza resistance is estimated.

A liquid 3He target system for use at intermediate energies

A liquid 3He target system, with remote instrumentation and handling capabilities, has been developed for experiments using the 180–525 MeV TRIUMF cyclotron. 3He gas is liquified, by means of a 4He cryostat, into a cylindrical target cell (4.4 cm diameter, 1.6 cm thick) and maintained during operation at ∼1.6 K. This provides an areal target density of ∼2.7×10 22 3He nuclei/cm 2 (128 mg/cm 2), suitable for intermediate energy proton scattering.

Status Report on the University of Manitoba Cyclotron

A comprehensive upgrading of the University of Manitoba cyclotron (20-50 MeV H-) as a low energy research facility, has been in progress since 1974. When completed, the cyclotron is expected to provide polarised H- and D- beams with currents in excess of 15 nA in addition to existing beams of unpolarised ions. Along with a polarised 3He target which is currently under construction this upgrading will add a new dimension to the facility.

Polarization enhancement of an optically pumped 3He target and a simple polarization measuring method

It is shown that the polarization of an optically pumped 3He target can be essentially enhanced by a reflector at the back of the target. Furthermore a better method of producing the optical signal for the polarization measurement is presented.