EM CALORIMETER COMPLEX FOREST FOR THE π0 AND η PHOTO-PRODUCTION EXPERIMENTS AT LNS-SENDAI

A large solid angle γ-ray detector system, FOREST, has been constructed at LNS-Sendai to study the π0 and η photo-production reactions. The FOREST detector consists of three electro-magnetic calorimeters: pure CsI crystals, Lead/SciFi blocks and Lead Glass Cherenkov counters. It covers about 90% of the total solid angle. A new data acquisition system for the FOREST detector has been developed to handle high rate trigger events with a high efficiency. To investigate performances of FOREST and the DAQ system, a test experiment has been conducted. The π0 and η mesons are clearly observed. A DAQ efficiency of 76% has been obtained at a 2 kHz trigger request.

Toroidally Shaped Hopg Crystals as Strongly Focusing Bragg Reflectors of Characteristic X-Ray Tube Radiation for Edxrf Analysis

The characteristic 17.441 keV Mo-Kα tube line yields an exceedingly strong reflection at a Bragg angle of 6.0710 on Highly Oriented Pyrolytic Graphite (IIOPG). Using doubly bent toroidally shaped crystals we were able to concentrate the characteristic radiation from a Mo anode fine focus tube onto a small focal spot area of about 1 mm. FWHM diameter, as was observed by an X-Ray sensitive CCD. The radiation of the Mo anode fine focus tube is emitted at a take-off angle of 60 into a total solid angle with an aperture of 120. About 90 percent of this primary radiation solid angle can be used for the desired Bragg reflection on the designed toroidal crystal surface. This feature ensures the high beam intensity needed for special excitation problems.

An Attempt to Detect the Neutrino

It has been shown by Chadwick and Lee(1), using a high-pressure ionization chamber, that if one neutrino is emitted by each disintegrating Ra E nucleus, then the neutrinos do not produce more than one pair of ions in 150 km. of air at N.T.P. Calculations based on the wave mechanics show that the ionization due to a neutrino having a magnetic moment of one Bohr magneton would be very easily detectable(2), whereas it has peen estimated that if the neutrino has no magnetic moment at all its encounters with nuclei will be as scarce as one in 1016 km. of water(3). I have investigated the matter again, using two Geiger-Müller counters, instead of an ionization chamber. The counters have the advantage of giving a discharge for a single pair of ions(4). The two counters of 15×5cm. were connected in parallel, and filled with air at 76mm. pressure. They were shielded on all sides by 45 mm. of lead. A source of 7 mg. of Ra (D, E, F) was placed at a distance of 11 cm. from the centres of the two counters, so that the total solid angle subtended by the counters at the source was 0·10, expressed as a fraction of the complete sphere. Assuming that both the disintegrating atoms of Ra D and Ra E give one neutrino, then the number of neutrinos crossing the counters per minute is 3·1 × 109. The average effective length of the path in the counter, reduced to N.T.P., is 0·3 cm., so in one min. the total range in air of all the neutrinos crossing the counters is 9·3 × 108 cm.