Nuclear Instruments and Methods in Physics Research最新文献

The CADIM apparatus is a combination of : (a) a microscope equipped with a motorized stage and a drawing attachment; (b) high precision digitizers of X, Y and Z coordinates; (c) television camera, monitors and tape recorder; (d) a microcomputer and its peripherals. In addition to fast scanning and measurements in nuclear emulsion, it enables the performing of a direct visual comparison between the topology of an event seen in emulsion and its reconstructed topology from the data taken by associated electronic detectors. The use of television techniques allows image display and storing. This apparatus will be used in the first place for the CERN hybrid experiment WA71 searching for beauty particles.

A lifetime measurement method using active targets is discussed. A new high precision monolithic target of germanium with 100 and 50 μm resolution is described and the results of tests with high energy beams are presented.

Results are presented of longitudinal position measurements using charge division readout. The use of the limited streamer mode gives large current pulses and allows one to achieve an rms resolution of less than 2 mm for a wire of length 5000 mm.

We tested a multistep proportional chamber of 20 × 20 cm² activ area, conceived to localize single vacuum ultraviolet photons. The detector has a capability of imaging large multiplicities of Cherenkov rings with a high density of detected photoelectrons and uses tetrakis(dimethylamine)ethylene, with a threshold of 5.4 eV, as the photoionizing vapour. Time slicing in a conversion gap reduces the multiplicity at a given instant of time by a large factor and permits the use of simple methods of localization. Separation of the amplifying gaps solves the problems of photon feedback encountered, at high gains, with single-step detectors. We also discuss an application of this chamber for the detection of superheavy monopoles if they have a speed in the range of the electron drift velocity.

Several new types of photodetector have been developed for use in severe environmental conditions; four types of phototube are especially designed to be operated in high magnetic fields of several kilogauss or more. A photomultiplier which is designed for use under pressures as high as 600 atm has stable gain and energy resolution under such high pressures. And a 15 inch diameter spherical photocathode photomultiplier has also been developed for high pressure use when packed in a special strong glass housing. There is another photomultiplier which can be operated in temperatures over 175°C, such as in oil well logging works.

When used in lead-scintillator sandwich calorimetry, scintillating optical fibres offer a new way to achieve fine grain sampling and thereby to improve the energy and spatial resolution of a technique still unbeaten for timing and compactness. A small calorimeter element made of planes of 0.9 mm diameter fibres alternating with Pb plates has been built and tested in an electron beam. An energy resolution of $\text{σ}{}_{\mathrm{E}}\text{/√E⋍9.8}\text{and}\text{7.8\%}$ was obtained with 1 and 0.5 mm Pb plates, respectively. The parameters of the fibres have been measured. Calculations performed with a refined version of the EGS code reproduce these results and suggest improved Pb-fibre calorimeters rivalling with Pb glass in energy resolution.

The construction and performance of a prototype scintillator lead photon calorimeter using a double wavelength shifter optical readout is described. The calorimeter is divided into 4 individual cells, each consisting of 44 layers of 3 mm lead plus 1 cm thick scintillator. The edges of each scintillator plate are covered by acrylic bars doped with a wavelength shifting material. The light produced in each scintillator plate is first converted in these bars and then converted a second time in a set of acrylic rods, which run longitudinally through the calorimeter along the corners of each calorimeter cell. A photomultiplier is attached to each of these rods at the back end of the calorimeter. The energy resolution obtained with incident electrons in the energy range of 2–30 GeV is σ/E = 0.12/√E. The uniformity of response across the front face of each cell was measured. Showers within each cell can be localised with an accuracy of better than σ = 7 mm.

Tracks in a high pressure streamer chamber were holographically recorded. The chamber was filled with a mixture of helium and methane and operated in a pressure range of 4 to 13 atm. At a pressure of 13 atm, a streamer diameter of ∼ 25 μm was observed. The influence of electron diffusion and streamer size on the spatial resolution is discussed.