J. Heckmann

First results of the large COMPASS 6LiD polarized target

The COMPASS (NA58) experiment at CERN operates with a large solid polarized target (PT) to study the spin structure of the nucleon. The COMPASS PT system started its operation with the target material 6 LiD in 2001. Deuteron polarizations of þ54:2% and � 47:1% were achieved in a 3 He= 4 He dilution refrigerator at a magnetic field of 2: 5T : The equal spin temperature (EST) concept was found to hold among the deuteron, the 6 Li and the 7 Li nuclei during the dynamic nuclear polarization (DNP) process. The agreement with the EST concept allows the permanent monitoring of only one nuclear species by the nuclear magnetic resonance (NMR) method. r 2003 Elsevier Science B.V. All rights reserved.

The COMPASS Polarized Target in 2006 and 2007

The COMPASS experiment has been taking data since 2002. Its polarized target was upgraded during the 2005 CERN SPS shutdown. With the high acceptance magnet we obtained +56.0% and −53.0% deuteron polarization in 6LiD. In 2007 ammonia is used as a proton target which has a relaxation time of ∼4000u2009h at 0.6 T.

Recent developments in the field of polarized solid state target materials

With the help of systematic EPR and NMR studies under various conditions the polarization properties of some established target materials could be considerably improved. In 6LiD preliminary polarization results of the still ongoing investigations are 52%1 at 150u200amK and 18% at 1u200aK both at a magnetic field of 2.5u200aT. Radiation doped d-butanol was polarized up to 48%1 and 13% under the same conditions. Additionally first investigations were started into a group of materials, the alkanes, which have not been tested for polarization purposes so far. Difficulties specific to these compounds could be overcome with the result of promising +16.2%/−13.5% at 1u200aK/2.5u200aT in a hybrid sample of chemically doped n-pentane/butanol. In this context new insights could be also gained into the polarization physics of radiation doped polyethylene.

The Bochum Polarized Target

The Bochum ‘Polarized Target’ group develops the target material 6LiD for the COMPASS experiment at CERN. Several different materials like alcohols, alcanes and ammonia are under investigation. Solid State Targets are polarized in magnetic fields higher than B=2.5T and at temperatures below T=1K. For the Dynamic Nuclear Polarization process, paramagnetic centers are induced chemically or by irradiation with ionizing beams. The radical density is a critical factor for optimization of polarization and relaxation times at adequate magnetic fields and temperatures. In a high sensitive EPR—apparatus, an evaporator and a dilution cryostat with a continuous wave NMR—system, the materials are investigated and optimized. To improve the polarization measurement, the Liverpool NMR—box is modified by exchanging the fixed capacitor for a varicap diode which not only makes the tuning very easy but also provides a continuously tuned circuit. The dependence of the signal area upon the circuit current is measured and it i...