Nuclear Instruments and Methods in Physics Research最新文献

We review the characteristics of compact precise drift chambers and present the essential features of a vertex detector for an experiment at LEP. We discuss the initial performance of a prototype chamber and illustrate its good two-particle resolution.

A gas scintillation drift chamber has been exposed to the heavy ion beam at Berkeley, Ca, USA. The drift velocity of an ar(98%)-N₂ (2%) gas mixture as a function of the reduced electric field has been measured. The detector provided a spatial resolution of 500 μm and an energy resolution of 6% for penetrating 518 MeV / nuc Fe-particles.

A portable, rugged, monitor has been designed and built for measuring the short-lived decay products of radon and thoron. The monitor is computer-based and employs a continuous filter strip which can be advanced at programmable time intervals to allow unattended continuous operation with automatic sampling, analysis and recording of radiation levels. Radionuclide analysis is carried out by two silicon diffused-junction alpha-detectors and electronic circuitry with multichannel spectral analysis capabilities. Standard gross α-count methods and α-spectroscopy methods can easily be implemented. The built-in computer performs a variety of operations via a specially designed interface module, including control and data recording functions, and computations, program storage and display functions. Programs and data are stored in the built-in casette tape drive and the computer integrated CRT display and keyboard allow simple, prompted menu-type operation of standard software. Graphical presentation of α-spectra can be shown on the computer CRT and printed when required on the computer built-in thermal printer. In addition to implementing the specially developed radionuclide analysis software, the operator can interact and modify existing software, and program new ones, through BASIC language programming, or employ the computer in a totally unrelated, general purpose mode. Although the monitor is ideally suited for environmental radon (thoron) daughter monitoring, it could also be used in the determination of other airbone radionuclides provided adequate analytical procedures are developed or included in the already existing computer software.

A two-stage nitrogen laser has been built and is presently being used to investigate properties of drift chambers. In this paper we present the measured parameters of this laser, the results of a study of the double track separation in a drift chamber of jet design and a measurement of the saturation effects in this chamber as a function of total gain. An understanding of the saturation effects is important for drift chambers with multiple hit capability. The laser technique reported here represents a major improvement in the simplicity of investigation of the double track separation and saturation effects. In addition, we have demonstrated the usefulness of this kind of laser in the development of high precision drift chambers working in a resolution range of ∼ 20–30 μm.

A two-arm semiconductor spectrometer for the detection of secondary charged particles, such as p, d, t, ³He, ⁴He and of their correlations in the process of stopped pion absorption by nuclei is described. The spectrometer consists of two telescopes of Si-detectors with a sensitive surface of 800 mm², two semiconductor detectors as monitors and the “live” target, a silicon surface barrier detector. The number of semiconductor detectors is 19.

A technique for pion stop selection in thin targets is described.

The problem of particle identification and of measurements of their energy with the help of a multicrystal semiconductor telescope is discussed. The technique provides an absolute normalization of spectra. The “alive” target helps to obtain more information on the process of pion absorption by Si-nuclei.

This paper presents a theoretical analysis of the development of fission-couple output in a long duration neutron pulse, and in a steady neutron flux. It also explains why the behaviour of the fission-couple is very different in the long duration pulse compared to that in a short neutron burst.

The pulse-height response and timing characteristics of bismuth germanate scintillator haven been determined for light and heavy ions (A ⩽ 35 E ⩽ 250 MeV). Timing resolutions of ⩽ 250 ps have been observed.

A group of 9 silicon surface-barrier detectors, 4 manufactured by ORTEC and 5 fabricated by the first author and his students. has been tested for their energy resolutions with oxygen ions of 36.750 and 50 MeV energy and sulphur ions of 51.086 MeV energy from the University of Pittsburgh Van de Graaff accelerator. Six of the detectors had previously been tested with oxygen ions of 25 and 50 MeV energy at Pittsburgh, and those results are compared with the present ones. It is now possible to conclude that the energy resolution of the best detectors is independent of oxygen ion energy between 36.750 and 50 MeV and is about 100 keV (fwhm). When tested with sulphur ions, 4 of the detectors showed anomalous effects, including peaks and smudges both below and above the main peak. Some of these could be eliminated by varying the reverse bias voltage across the detector, others could not. In particular, the ORTEC detector 40, used in the previous work as the standard detector presently available, did not show a single peak at any bias. It is an excellent detector for oxygen ions, but is not useful for sulphur ions. The energy resolution of the best detectors for 51.086 MeV sulphur ions is under 300 keV (fwhm).

Using single-wire position sensitive counters with a stainless-steel anode wire of 25 μm diameter, position sensing has been performed in the self-quenching streamer (SQS) mode. Overall position resolutions of 0.26 mm and 0.69 mm fwhm for 4.5 keV X-rays were obtained for 100 mm long and 1.82 m long counters, respectively, by means of standard NIM electronic circuits and a new ratio-to-digital converter (RDC). Problems in the application of SQS mode to position sensing are discussed.

Total and photopeak efficiency values of well and through-well type detectors have been evaluated for gamma-rays of energies up to 15 MeV. The influence on the calculated values due to the auto-attenuation of the primary beam in the source has been shown.