Polarized Target Materials Research Articles

Polypropylene track membranes as a promising material for targets with polarized protons

Polypropylene track membranes made by irradiation of polypropylene films with a beam of high-energy heavy ions followed by chemical etching of latent ion tracks are proposed for being used as a polarized target material. To give membranes paramagnetic properties needed for allowing dynamic polarization of nuclei, the nitroxyl radical 2,2,6,6-tetramethylpiperidine-1-oxyl was introduced in the samples by the thermal diffusion technique. Using the electron paramagnetic resonance method, we obtained information on paramagnetic centers in the polymer matrix of the membranes and determined the nitroxyl radical concentration and rotational mobility of the spin probe in them.

Local field in LiD polarized target material

We have experimentally studied the first and the second moments of D, 6 Li and 7 Li (I> 1 2 ) NMR lines in a granulated LiD-target material as a function of nuclear polarizations and the data has been compared with a theory elaborated by Abragam, Roinel and Bouffard for monocrystalline samples. The experiments were carried out in the large COMPASS twin-target at CERN. The static local magnetic field of the polarized nuclei was measured by frequency shift between the NMR-signals in the two oppositely polarized cells and lead to the first moment, whereas the investigation of the second moment was done through Gaussian approximation. The average field magnitude in granulated material was estimated 20% larger than the value given by the calculations for monocrystalline samples of cylindrical shape. The second moment shows a qualitative agreement with the theory but it is slightly larger at the negative than at the positive polarization. In a polarized mode, the moments depend on the saturated microwave field.

Polarization reversal by adiabatic fast passage in various polarized target materials

Spin-polarization reversal by the use of the adiabatic fast passage mechanism has been investigated in a variety of polarized target materials. The high efficiencies achieved open the way to the application of the AFP method in operational polarized solid targets.

Cross-relaxation between protons and 13C nuclei

In an applied microwave field, the free electron spin-spin interaction reservoir in polarized target material couples strongly to the Zeeman interaction reservoirs of different nuclei. This leads to an effective cross-relaxation between different nuclei, which was studied at different levels of microwave power between protons and 13C nuclei in the large SMC target using butanol as material.

Present status of polarized solid-state targets for experiments with real and virtual photons

The current situation of the polarized solid-state targets for experiments with real and virtual photons is reviewed.The present situation in phototproduction and deuteron photodisintegration experiments at intermediate energies can be improved by the use of tagged photons and a frozen spin polarized target.The discovery of ammonia as polarized target material and its very good polarization resistance to radiation damage makes improved experiments also with electron beams possible.

Present status of polarized targets for high intensity photon and electron beams

The discovery of ammonia as polarized target material and its very good polarization resistance to radiation damage makes improved experiments with photon and electron beams possible. Dilution refrigerators are now standard equipment in most laboratories where polarized targets are in operation. The frozen spin technique can be employed in tagged photon beams. A first measurement of the electromagnetic formfactors of the deuteron by means of electron scattering from a tensor polarized ND 3 target was performed in Bonn.

Dynamic nuclear polarization of irradiated targets

We report studies of dynamic nuclear polarization of irradiated targets. The polarized target operated at a magnetic field of 5 T and a temperature of 1 K and was irradiated with the 20 GeV electron beam at the Stanford Linear Accelerator. Our results indicate that the temperature at which the target is irradiated is important. The maximum proton polarization attained with radiation was measured for some seven hydrogen-rich compounds. Irradiated NH 3 and ND 3 were polarized to high values of P p ⋍ 0.75 and P d ⋍ 0.25 with short values of polarization growth time T p, and with radiation resistance of the polarization about a factor of 30 greater than for normal chemically-doped hydrocarbons. Hence, irradiated NH 3 and ND 3 appear very promising as practical polarized target materials.

Dynamic nuclear polarization in irradiated ammonia below 0.5 K

We have reached +90.5% and −93.6% dynamic proton polarization in solid NH 3 using paramagnetic radicals created by proton irradiation of 40 Mrad total dose. The dynamic polarization experiments were performed at 25 kG field in a dilution refrigerator. These results may indicate a breakthrough in the development of better polarized target materials for high-energy physics experiments.

Dynamic polarization in radiation resistant materials

Measurements of spin effects in small cross section processes have shown the need for more radiation resistant polarized target materials. We have examined the dynamic polarization of a number of substances which are known to be highly resistant to the formation of color centers with particular emphasis on toluene. We have also examined the relation between the maximum polarization and characteristic radiation flux constant to obtain a figure of merit for new materials.

Radiation damage in polarized target materials

We examine some of the parameters which influence the decay of the polarization of polarized targets in an intense proton beam. We find that the usual characteristic flux for the polarization to drop to 1/e of its initial value does not provide a sufficient criterion to specify the radiation resistance of target materials. We give a more detailed method of evaluation including an empirical formula for the effect of annealing on the target polarization.

Quantity production of polarized target material

A simple, inexpensive device for quickly making large quantities of small, uniform, frozen beads of alcohol for polarized targets is described. It has been successfully used at Stanford Linear Accelerator Center for about two years.