by Akira Masaike

this review is on “Proceedings of the 11th International workshop on Polarized Sources and Targets”

the introduction stated that using thermal polarization (brute force method) in low temperature, ~ 0.01K and high magnetic field~10T can produce proton polarization as high as 76%. another way is using dynamical method by paramagnetic materials, (was proposed by Overhauser) the coupling between electron spin and proton spin can polarize proton in higher temperature and lower magnetic field. Abragam proved that by using paramagnetic impurity can also work for non-metallic materials.

Abragam and Jeffries used La_2 Mg_3 (NO_3)_{12} 24 H_2O (or called LMN), containing small percent of neodymium to polarize proton spin by dynamic nuclear polarization at 1963. but the LMN crystal is not good for inelastic reaction because of the low dilution factor ( the ratio of polarized proton to total number of nucleon ), and this produce a lot other un-wanted reactions. and also the crystal is damaged under scattering by relativistic particles.

organic materials are tested and a major breakthrough is by using butanol with water doped with porphyrexide in 1969 by Mango t al.. the polarization is 40% at 1K and 2.5T.  and also, diol with Cr^{5+} were polarized to 45% at 1K and 2.5T by Glättli et al. Masaike et al. was polarized diol up to 80% at temperature lower then 0.5K. Burtanol in ^3He cryotat also polarized upto 67%. All these were done in 1969.

deuteron in deuterated organic material can also be polarized. the principle is called “the equal spin temperature model”

\displaystyle P = B_I( \frac{\mu B }{ 2 k_B T_s} )

B_I is Brilluin function and T_s is the nuclear spin temperature.

Spin Frozen Target is a technique that the polarized proton spin last long enough with ESR radiation. the theory was developed around 1965 by Schmugge and Jeffries and constructed by Rusell at 1971 in Rutherford laboratory.

NH_3 or ammonia has high dilution factor. it was polarized to 70% by doped with ethylene glycol Cr^{5+} complex at 0.5K and 2.5T by Scheffler and Borghini at CERN at 1971. but ammonia has slow growth of polarization and may explode by high intensity proton irradiation at 1983 at CERN.  but later, it was overcomed by Meyer et al. at Bonn. Thanks to Meyer, ammonia becomes a popular polarized target.

High polarization of H, D and ^6Li in dilution refrigerator were found in Bonn around 2005. The COMPASS experiment in CERN use target of $latxe ^6LiD$ at polarization 50% at 300mK and 2.5T.

Hydrogen deuteride (HD) has the highest dilution factor and in principle, both can be polarized. the relaxation properties at 0.5K depends on ortho-para and para-ortho conversions of $latxe H_2$ and $latxe D_2$. The polarization for proton and deuteron of 60% and 14% by brute force method at 10mK and 13.5T was done by Grenoble-Orsay group at 2004.

Crystal of Naphthalene (77K) and p-tarphenyl (270K) doped with pentacene have been polarized in 0.3T by Iinuma et al. at 2000. the high temperature and low magnetic field is due to the paramagnetic excited state in pentacene and diamagnetic on ground state. the population of Zeeman  sublevels of the lowest triplet state is 12% for m=+1, 76% for m=0 and 12% for m=-1 regardless of temperature and magnetic field strength. by using ESR radiation and the “integrated solid effect”, the proton can be polarized and remain polarized after the electrons go back to ground state. 70% polarization at liquid nitrogen temperature.