Clyde Wiegand

Detection Efficiency of Plastic Scintillator for Neutron Energies 4 to 76 Mev

The neutron detection efficiency of plastic scintillator counters 15 cm thick has been determined for neutron energies from 4 to 76 Mev. Neutrons in this energy range were obtained by scattering a 205‐Mev neutron beam from a hydrogen target. A proton‐range telescope selected the forward‐scattered protons from the n‐p reaction, thus monitoring the flux of monoenergetic neutrons scattered in a prescribed direction. Near 10 Mev the efficiency is 30%, and it slowly decreases to 20% at 76 Mev.

Distributed Coincidence Circuit

A coincidence circuit using the traveling wave principle as applied to distributed amplification is described. The resolving time is about 10−8 sec. when the device is used in connection with scintillation detectors.

Experiments on N-P Scattering with 260-Mev Neutrons

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High Energy Neutron Detector

A neutron detector which utilizes the fission of bismuth and responds only to neutrons of energy greater than about 50 Mev is described. The efficiency is low (about 10−6), but the instrument is suitable for monitoring a high energy neutron beam and for beam attenuation measurements.

A high-resolution Si(Li) spectrometer with thermoelectric cooling

Abstract A Si(Li) spectrometer cooled by a thermoelectric refrigerator exhibited a peak width of 258 eV fwhm for X-rays of 5.9 keV. The measured electronic noise was equivalent to 224 eV fwhm.

K− decay, hydride bonds, and Z-dependence in kaonic atoms

Abstract The observed low values and striking variations in kaonic X-ray intensities were found to be not due to K− decay. Measurements on H2O and CH show greatly reduced X-ray intensities apparently due to the presence of the hydride bonds. A simple cascade calculation with an initial distribution in n = 30 that is statistical out to various lmax gave agreement with our absolute X-ray intensities. A correlation between lmax and atomic spacing is suggested.

An electronic data-acquisition system for use with a complex nuclear physics experiment

Abstract An electronic data-acquisition system is used with a nuclear physics experiment of such complexity that data processing required a high-speed computer. The system acquires data from 168 signal channels of scintillation counters and four channels of chronotron circuits. It has the capacity to store 10 events during the 0.1-sec-long Bevatron beam pulse. The storage time for the information from each event, consisting of 168 bits from the counters plus 12 bits from the chronotrons, is 40μsec. In the interval between beam pulses, the stored information is punched onto paper tape in a form suitable for computer input. This report describes the over-all characteristics and operation of the system. The specific parts of the system and techniques for semi-automatic testing are given in the companion reports.

Observation of dynamic E2 mixing via kaonic X-ray intensities

Abstract We have observed a nuclear resonance effect between a kaonic atom and a nuclear transition in 98 Mo. Our measurement gave 98 Mo (n=6→5) 92 Mo (n=6→5) = 0.16 ± 0.16 instead of the no-mixing value of 1. Dynamic E2 mixing caused kaons to be strongly absorbed from the 98 Mo atomic state n =6, l =5 in agreement with theoretical predictions.

Example of an Antiproton-Nucleon Annihilation

The existence of antiprotons has recently been demonstrated at the Berkeley Bevatron by a counter experiment. The antiprotons were found among the momentum-analyzed (1190 Mev/c) negative particles emitted by a copper target bombarded by 6.2-Bev protons. Concurrently with the counter experiment, stacks of nuclear emulsions were exposed in the beam adjusted to 1090 Mev/c negative particles in an experiment designed to observe the properties of antiprotons when coming to rest. This required a 132 g/cm2 copper absorber to slow down the antiprotons sufficiently to stop them in the emulsion stack. Only one antiproton was found in stacks in which seven were expected, assuming a geometric interaction cross section for antiprotons in copper. It has now been found that the cross section in copper is about twice geometric, which explains this low yield.

A precision beta gauge using a plastic scintillator and photomultiplier detector

We describe the use of a plastic scintillator photomultiplier detector combination in applications involving the precision beta-gauge measurement of small mass deposits of thin substrates. The requisite precision (±2 μg/cm2) places stringent requirements on the beta-particle counter and associated electronics. The scintillator based system is shown to be equivalent if not superior to previously employed semiconductor detectors with respect to long-term counting stability.