R.E. Bell

Comparison of leading-edge and crossover timing in coincidence measurements

Abstract The statistical limits of the resolving time are compared for leading-edge and crossover timing in coincidence measurements. The results show that leading-edge timing is always superior, the factor of superiority being greater for slower detector responses, i.e. for those cases where the convenience of crossover timing is the greatest. For NaI(Tl) scintillation counters, leading-edge timing gives better time resolution by a factor estimated to be 13.7.

Delayed protons following the decay of 40Sc

Abstract Delayed protons have been observed following the beta decay of 40 Sc to excited states of 40 Ca. The observation of these low-energy protons was made possible by using a very thin gas counter as a “d E ” detector. Eighteen proton groups between the energies of 1.08 and 3.95 MeV were resolved in the proton spectrum and their energies were measured to ≈ 30 keV. The relative intensities of these peaks were determined and relative log ft values were calculated.

DIRECT MEASUREMENT OF THE PRIMARY PHOTOELECTRON YIELD IN SODIUM IODIDE SCINTILLATION COUNTERS.

Abstract The number, P, of photoelectrons produced per keV of electron energy absorbed in an NaI(Tl) scintillation counter has been measured directly with a charge-sensitive amplifier. The values obtained for selected detectors lie in the region of P=10, in contradiction to a number of statements in the literature that P typically lies in the range from 1 to 3.

Inelastic scattering of 100 MeV protons from Mg and Si using a Ge(Li) total absorption proton counter

Abstract A cooled Ge(Li) detector was used as the total absorption proton counter for the energy analysis of 100 MeV protons scattered from targets of enriched magnesium (99.7 % 24 Mg) and silicon (natural isotopic composition). A total energy resolution of 400 keV (FWHM) was achieved; it is comparable to the best resolution presently attainable with magnetic spectrometers in the 100–200 MeV energy region. The measurements cover the 10°–60° lab angular region; and angular distributions are presented for 23 peaks in the energy spectra. A qualitative discussion of the excited states which correspond to the observed peaks is based mainly on the shapes of the distributions. Comparisons are made with results from similar experiments at 55 MeV and 185 MeV. Shapes of angular distributions for strongly excited 2 + , 3 − and 0 + transitions are independent of energy, but significant differences exist for 4 + transitions. The excitation of a previously unknown level in 28 Si at 11.45±0.12 MeV energy has been observed. The level most probably has J π = 5 − .

Comment on dead-time losses in a buffered data recording system.

Abstract This note comments on a recent paper of Overas 1 ) and points out that some of the same calculations had in fact been published earlier.

A scattering chamber-cryostat for 100 MeV protons using lithium drifted germanium detectors

Abstract A compact scattering chamber has been developed for the inelastic scattering of 100 MeV protons using Ge(Li) crystals as the total absorption proton detector. The Ge(Li) detector is mounted on a LN2 cooled copper cold finger and is directly preceded by a “window” anticoincidence plastic scintillator and brass collimator designed to limit detected events to a central region of the detectors sensitive volume. The detector platform is externally adjustable so as to insure coplanarity of the detectors symmetry axis with the proton beam axis. The chamber also provides the usual scattering facility requirements and can be mounted directly on a 25 liter Linde dewar. An overall experimental resolution of 0.38±0.02 MeV (fwhm) has been achieved for 100 MeV protons.

STATISTICS OF A TWO-PARAMETER ANALYZER WITH ASSOCIATIVE MEMORY.

Abstract This paper deals with pulse-height analyzers with associative memories of M words, where M is very much smaller than the total number of possible different channels. We show that if the first M channels to record one event each are stored, the probability that any given channel is included in the store is simply proportional to its counting rate. The counts per channel in a region of the spectrum are therefore indicated not only by the contents of the recorded channels, but also by the density of recorded channels. In general, if the first M channels to record n events each are stored, the inclusion probability is proportional to the channel counting rate raised to the n th power.

SQUARE ROOT GRAPH PAPER FOR NUCLEAR SPECTRA.

Abstract The advantages of using a newly available square root graph paper for nuclear spectra are illustrated by means of a sample spectrum plotted on linear, logarithmic, and square root scales.