H. Okuno

A Measurement of the air fluorescence yield

Abstract We measured the air fluorescence yield as a function of pressure with electrons between 1.4 and 1000 MeV by means of a 90Sr β source and an electron beam. Results indicate that the fluorescence yield is proportional to electron energy loss from 1.4 to 1000 MeV. The d E d x relativistic rise in air is detected. We describe the pressure temperature dependency of air fluorescence by a formula derived from simple kinetic theory. With the aid of the 1966 US Mid-latitude Standard Atmospheric Model, we calculate the altitude dependence of fluorescence yield of an 80 MeV electron which demonstrates how this measurement could improve the longitudinal particle density profile determination of extensive air showers (EAS) observed by detectors such as the High Resolution Flys Eye and the Telescope Array.

Scintillation and phosphorescence of PbWO4 crystals

There are two types of crystals with respect to luminescence. In dc measurement, type A gives a primary emission at 410–430 nm (blue) with a second one at around 500 nm. Type B gives only dominant emission at 480–500 nm (green). This apparent difference can be interpreted as follows; the characteristic scintillation of PbWO4 is dominantly blue and subdominantly green. Intense phosphorescence with a decay constant of about 15 ms exists only in Type B at about 500 nm with one to two orders of magnitude larger intensity than scintillation, hiding the blue scintillation in its tail. The cause of the phosphorescence may be Mo.

Trigger system for the TOPAZ detector at TRISTAN, KEK

Abstract A trigger system for the TOPAZ detector at the TRISTAN e + e − collider has been developed. The system consists of an energy trigger and a track trigger. The track trigger uses track information from the inner drift chamber, the time-of-flight counters and the time projection chamber. A three-dimensional track reconstruction is performed with high-speed logic arrays. The design and the performance are described.

The TOPAZ inner drift chamber

We have constructed a cylindrical drift chamber with anode and cathode delay-line readouts, which is the innermost tracking device of the TOPAZ detector. This inner drift chamber (IDC) is used for the tracking of charged particles in both rφ and rz planes. Fast track-finding logics have been developed for the event triggering. We describe the design, the construction and the performances of the IDC in the first beam run.

A CsI(pure) calorimeter for π0 detection at intermediate energies

Abstract A set of CsI(pure) crystals have been tested for use as an electromagnetic calorimeter for π0 detection in photonuclear reactions at photon energies below 1.2 GeV. Performances of the calorimeter including energy and position resolution are studied by using the electron and tagged-photon beams at the INS-Tokyo electron synchrotron. In the first experiment for the nuclear coherent π0 photoproduction carried out at INS, a π0 mass resolution of 7 MeV (rms) has been obtained in the π0 energy region between 0.5 and 1.0 GeV.

A new type of liquid-3He target system using small mechanical refrigerators

Abstract A new type of liquid- 3 He target has been developed for photoabsorption experiments at intermediate energies. Using the cooling power of liquid 4 He at reduced vapour pressure, 3 He gas is liquefied into a cylindrical target cell of 180 ml and is maintained at 2.0 K during the experiment. Evaporated 4 He gas is evacuated by a rotary pump and returned into the 4 He bath in the cryostat, where two small mechanical refrigerators with cooling capacities of 3 W at 4.3 K and 10 W at 20 K are operated for the purpose of 4 He recondensation. A maintenance-free operation of more than 1000 hours has become possible by adopting the 4 He circulation system.

Response of pure CsI to charged pions in the intermediate energy region

Abstract The response of a scintillation detector array consisting of 7 pure CsI crystals with a thickness of 13.5 radiation lenghths has been measured to electrons, positrons and charged pions with momenta ranging from 250 to 1000 MeV/ c . For electrons and positrons the detector provides a very linear response to the incident energy. High energy charged pions make a peak at around 150 MeV corresponding to the ionization energy loss. In addition to the peak, comparable yields which are caused by nuclear reactions are distributed up to the maximum available enegy and form a broad bump. The shape of the broad bump for positive pions is different from that for negative pions with the same momentum. A simulation with a GEANT program cannot reproduce the shape of the broad bump.

Mask system for the TOPAZ detector at TRISTAN, KEK

Abstract A new beam pipe with an optimally designed mask system has been incorporated into the TOPAZ detector at the TRISTAN e + e − collider. It has allowed successful operation of a high-precision vertex chamber installed at a distance of 55 mm from the beam line and of a hermetic calorimetry covering 99.8% of the solid angle. We report on the design of the mask system and our running experience.

The TOPAZ vertex chamber's ceramic endplates

Abstract The TOPAZ group working at the e + e − storage ring TRISTAN has installed a vertex chamber using slow gas based on a mini jet-cell design. A major feature of the chamber is the simplicity of its mechanical structure accomplished by using monolithic ceramic endplates. Ceramic has proved to be an excellent material for the precision construction necessary to obtain a high resolution vertex chamber. The mechanical structure of the chamber, the method used for the precise positioning of the wires and the properties of the ceramic endplates are presented.

Experimental study of the 3He(γ, pp)n reaction with polarized photons

The experimental study of the reaction 3He(γ, pp)n is being carried out in the photon energy range Eγ = 200–500 MeV at the Tokyo 1.3 GeV electron synchrotron. By use of the tagged and linearly polarized photon beam, and the π-sr magnetic spectrometer TAGX, a kinematically complete measurement of the reaction 3He(γ, pp)n will be made. The high statistics measurements of dσdΩ and Σ of the reaction 3He(γ, pp)n will clarify the photon absorption mechanism.