Nuclear Instruments and Methods in Physics Research最新文献

The possibility of using HgI₂ as a survey dosimeter with a tissue-equivalent response in the energy range 1 keV to 1 MeV is theoretically investigated and discussed. The response function of HgI₂ is evaluated and checked with experimental data. HgI₂ with an energy threshold, in the counting mode, can have a reasonable tissue-equivalent response in the range 100–600 keV with a minimum detectable exposure rate of about 20 μR/h.

The XL-100S is a microprogrammable device based on the Am2900 family of bit slices and designed for use in the multimaster environment of an XL System Crate. The processor conforms to the EUR 6500 CAMAC standard and can access up to 4 Mbyte of memory and 7 CAMAC branches. Processor operation, which is a sequence of predefined microcommands fetched from a 32-bit wide control store with capacity up to 64 kwords, can be initiated by any of eight external requests.

The architecture of the XL-100S allows it to emulate almost any mini- or micro-computer including floating point operations. The processor can be used for: fast physical event filtering and data preprocessing, flexible apparatus control, organization of sophisticated DMA transfer modes, etc. The device with 4 kwords of control store is housed in a single width CAMAC module.

A mode of operation is discussed for a detector using BaF₂ as the scintillator, and tetrakis(dimethylamine)ethylene (TMAE) as the photosensitive agent adsorbed on a NiCr layer to form a photocathode. The position resolution of the detector with a crystal 25 mm thick and 120 mm in diameter is measured to be about 3 mm fwhm. The physics of TMAE as a liquid is also discussed.

We present three methods for estimating the photoelectron yield from a photomultiplier illuminated by an LED. We show that the three estimates are consistent. These estimates disagree by ∼ 25% from the popular but incorrect assumption that the pulse height distribution is Poisson-like in the number of photoelectrons.

Further, computations involving Gaussian spreading and/or Landau fluctuations are then performed. These computations should model the behavior of actual scintillator or Cherenkov counters. These computations enable us to estimate how often a counter will miss a count.

The experimental apparatus and the results of a study on the gain variation of photomultipliers at high average anode current are described. This gain variation was found to depend on the secondary emission process on dynodes; the last dynode gives the largest contribution to the overall photomultiplier effect. This contribution has been isolated and measured. The phenomenon may be due to more than one physical effect. The dominant one turns out to depend on the power released on the dynode by the incident electrons. A physical model is discussed which can take into account the observed phenomena.

An algorithm is presented for the evaluation of radiation radiation distribution and their coefficients and their uncertainties in complicated cascade decays from oriented nuclear states.

We have implemented the Erskine formalism for signal development to study in detail the main operational characteristics of a MWPC with a cathode read-out, for both point-like and extended ionization tracks. A parametrization has been made of the width of the cathode charge distribution and of the ratio of cathode charge over tottal avalanche charge to be applied for a general class of MWPCs. The integral and the differential nonlinearity of position measurements based on the calculation of the centroid of the cathode signals has been studies as a function of the width of the cathode read-out strips. Left-right and top-bottom assignment capability and interpolation between anode wires has been modelled. The possibility of measuring the angle of incidence of an ionizing particle with a delay-line cathode read-out is suggested.

Nuclear track detection, scintillation counter surface monitoring, and radon assaying have been used to locate sites of low-level ²²⁶Ra contamination in a radon laboratory. Procedures instituted to contain the radon emanated from this contamination have been effective to the extent of a 7-fold reduction in the air-borne radon concentration in the laboratory.

The methods of counting fission tracks by two image analyzing computers and a spark counting system are compared with a standard microscopy technique. In this comparison, for automatic fission track counting, the two commercially available image analyzer instruments, the Quantimet 720 and the Leitz-Texture Analyzing System (TAS) and a specially designed spark counter, the UTASC system, have been used. The results showed that the relative counting efficiencies of the Quantimet 720, the Leitz-TAS and the UTASC system are 0.974±0.010, 0.988±0.013 and 0.955±0.010, respectively