T. Ohta

Development of high intensity laser-electron photon beams up to 2.9 GeV at the SPring-8 LEPS beamline

Abstract A laser-Compton backscattering beam, which we call a ‘Laser-Electron Photon’ beam, was upgraded at the LEPS beamline of SPring-8. We accomplished the gains in backscattered photon beam intensities by factors of 1.5–1.8 with the injection of two adjacent laser beams or a higher power laser beam into the storage ring. The maximum energy of the photon beam was also extended from 2.4xa0GeV to 2.9xa0GeV with deep-ultraviolet lasers. The upgraded beams have been utilized for hadron photoproduction experiments at the LEPS beamline. Based on the developed methods, we plan the simultaneous injection of four high power laser beams at the LEPS2 beamline, which has been newly constructed at SPring-8. As a simulation result, we expect an order of magnitude higher intensities close to 10 7 xa0s −1 and 10 6 xa0s −1 for tagged photons up to 2.4xa0GeV and 2.9xa0GeV, respectively.

Distillation of hydrogen isotopes for polarized HD targets

Abstract We have developed a new cryogenic distillation system to purify Hydrogen-Deuteride (HD) gas for polarized HD targets in LEPS experiments at SPring-8. A small amount of ortho-H 2 ( ∼ 0.01 % ) in the HD gas plays an important role in efficiently polarizing the HD target. Since there are 1–5% impurities of H 2 and D 2 in commercially available HD gases, it is necessary to purify the HD gas up to ∼ 99.99 % . The distillation system is equipped with a cryogenic distillation unit filled with many small stainless steel cells called “Heli-pack”. The distillation unit consists of a condenser part, a rectification part, and a reboiler part. The unit is kept at the temperature of 17–21xa0K. The Heli-pack has a large surface area that makes a good contact between gases and liquids. An amount of 5.2xa0mol of commercial HD gas is fed into the distillation unit. Three trials were carried out to purify the HD gas by changing temperatures (17.5xa0K and 20.5xa0K) and gas extraction speeds (1.3xa0ml/min and 5.2xa0ml/min). The extracted gas was analyzed using a gas analyzer system combining a quadrupole mass spectrometer with a gas chromatograph. One mol of HD gas with a purity better than 99.99% has been successfully obtained for the first time. The effective NTP (Number of Theoretical Plates), which is an indication of the distillation performances, is obtained to be 37.2±0.6. This value is in good agreement with a designed value of 37.9. The HD target is expected to be efficiently polarized under a well-controlled condition by adding an optimal amount of ortho-H 2 to the purified HD gas.

Development of portable NMR polarimeter system for polarized HD target

Abstract A portable NMR polarimeter system has been developed to measure the polarization of a polarized Hydrogen-Deuteride (HD) target for hadron photoproduction experiments at SPring-8. The polarized HD target is produced at the Research Center for Nuclear Physics (RCNP), Osaka university and is transported to SPring-8. The HD polarization should be monitored at both places. We have constructed the portable NMR polarimeter system by replacing the devices in the conventional system with the software system with PCI eXtensions for Instrumentation (PXI). The weight of the NMR system is downsized from 80 to 7xa0kg, and the cost is reduced to 25%. We check the performance of the portable NMR polarimeter system. The signal-to-noise (S/N) ratio of the NMR signal for the portable system is about 50% of that for the conventional NMR system. This performance of the portable NMR system is proved to be compatible with the conventional NMR system for the polarization measurement.

POLARIZED HD TARGET FOR FUTURE LEPS EXPERIMENTS AT SPRING-8 IN JAPAN

We are carrying out hadron photoproduction experiments by using polarized photon beams with energies of 1.5-2.9 GeV at SPring-8 in Japan. In 2005, we started developing a polarized HD target for future LEPS experiments using both the polarized photon beams and the polarized target. To introduce a polarized target plays an important role in upgrading the LEPS experiments to the next higher step. The measurement of double polarization asymmetries is expected to give important informations to investigate the nucleon hidden structure, hadron photoproduction dynamics, and exotic hadron property. We report on the present status of the development of the polarized HD target at RCNP. We will carry out a test experiment to confirm that the polarized HD target can be transported from Osaka university to SPring-8 without any problems in 2010. If we succeed in the test experiment, we will carry out a long experiment to take physics data in 2011-2012.

HD gas analysis with Gas Chromatography and Quadrupole Mass Spectrometer

A gas analyzer system has been developed to analyze Hydrogen-Deuteride (HD) gas for producing frozen-spin polarized HD targets, which are used for hadron photoproduction experiments at SPring-8. Small amounts of ortho-H2 and para-D2 gas mixtures (�0.01%) in the purified HD gas are a key to realize a frozen-spin polarized target. However, there was an intrinsic diffi culty to measure these small mixtures in the HD gas with a quadrupole mass spectrometer (QMS) because D + and [H2D] + produced from the ionization of HD molecules were misidentified as H 2 and D2 molecules, respectively, and became backgrounds for the measurement of the H2 and D2 concentrations. In addition, the ortho-H 2 and para-D2 are not distinguished from the para-H2 and ortho-D2, respectively, with the QMS. In order to obtain reliable concentrations of these gas mixtures in the HD gas, we produced a new gas analyzer system combining two independent measurements with the gas chromatography and the QMS. Helium or neon gas was used as a carrier gas for the gas chromatography which was cooled at�110 K. The para-H2, ortho-H2, HD, and D2 are separated using the retention time of the gas chromatography and the mass/charge ratio. Although the para-D2 is not separated from the ortho-D2, the total amount of the D2 is measured without the [H2D] + background. The ortho-H2 concentration is also measured separately from the D + background. It is found that the new gas analyzer system can measure small concentrations of�0.01% for the otho-H2 and D2 with good S/N ratios.

Nuclear spin imaging with hyperpolarized nuclei created by brute force method

We have been developing a polarized HD target for particle physics at the SPring-8 under the leadership of the RCNP, Osaka University for the past 5 years. Nuclear polarizaton is created by means of the brute force method which uses a high magnetic field (~17 T) and a low temperature (~ 10 mK). As one of the promising applications of the brute force method to life sciences we started a new project, NSI (Nuclear Spin Imaging), where hyperpolarized nuclei are used for the MRI (Magnetic Resonance Imaging). The candidate nuclei with spin ½ are 3He, 13C, 15N, 19F, 29Si, and 31P, which are important elements for the composition of the biomolecules. Since the NMR signals from these isotopes are enhanced by orders of magnitudes, the spacial resolution in the imaging would be much more improved compared to the practical MRI used so far. Another advantage of hyperpolarized MRI is that the MRI is basically free from the radiation, while the problems of radiation exposure caused by the X-ray CT or PET (Positron Emission Tomography) cannot be neglected. In fact, the risk of cancer for Japanese due to the radiation exposure through these diagnoses is exceptionally high among the advanced countries. As the first step of the NSI project, we are developing a system to produce hyperpolarized 3He gas for the diagnosis of serious lung diseases, for example, COPD (Chronic Obstructive Pulmonary Disease). The system employs the same 3He/4He dilution refrigerator and superconducting solenoidal coil as those used for the polarized HD target with some modification allowing the 3He Pomeranchuk cooling and the following rapid melting of the polarized solid 3He to avoid the depolarization. In this report, the present and future steps of our project will be outlined with some latest experimental results.

Development of polarized HD target for SPring-8/LEPS experiment.

A polarized solid HD (Hydrogen - Deuteride) has been developed for near future photoproduction experiment at SPring-8/LEPS. The solid HD target is polarized by the static method in a strong magnetic field of 17 T and low temperature of about 15 mK at RCNP Osaka university. The solid HD target is transported from RCNP to SPring-8, under the condition of a magnetic field larger than 0.1 T for holding the polarization and low temperature lower than 4 K, in which we use five cryostats. We have achieved a polarization degree of 44 % and a relaxation time of 8 months for H. We have recently succeeded in the connection among three cryostats used at SPring-8. After succeeding all the target transportations, we will start the physics experiment at SPring-8.

Production of hyperpolarized nuclei for MRI

The project in producing the hyperpolarized 3He and 19F are addressed in pursuit of radiation free medical diagnosis. The program for production of the hyperpolarized 3He by the brute force method with the Pomeranchuk cooling and the rapid melting of the solid 3He started a few years ago, and is still on the way, while a new program for production of the hyperpolarized 19F by means of the PHIP (ParaHydrogen Induced Polarization) has just got started. Particular attention is placed upon a new idea of the hyperpolarization catalyst to be used for 19F.