S.L. Blatt

AN IMPROVED HIGH-ENERGY GAMMA SPECTROMETER.

Abstract A large, anticoincidence-shielded NaI(Tl) spectrometer has been developed for studies of nuclear reactions yielding γ radiation in the energy range 10–40 MeV. Improvements over earlier detector systems produce a mono-energetic γ ray response shape with, around E γ = 22 MeV, a fwhm resolution of 3.5% and a full width at 1/10 maximum of 7.6%. Good resolution is maintained with total counting rates of several hundred thousand pulses/sec in the NaI(Tl) crystal.

COINCIDENCE LOSSES DUE TO PILE-UP IN CROSSOVER-TIMING SYSTEMS.

Abstract In coincidence experiments where fast timing information is derived from the zero-crossing point of a double-differentiated pulse, counting losses can occur if the crossover point shifts beyond the resolving time of the fast coincidence circuit. Pulse pile-up can produce such a shift and losses can be significant. Correction for or elimination of these losses is necessary wherever precision in the absolute number of coincidence counts, or the relative number at different energies and angles, is desired.

Total cross section measurements by X-ray detection of electron-capture residual activity☆

Abstract A method is presented for measuring total cross-sections for reactions producing final nuclei which decay by electron capture. The method involves the detection of the X-rays from the atom produced by the electron capture, by use of a Si(Li) detector. As an example, results are presented for the total cross section of the reaction 48Ti(α, n)51Cr in the bombarding energy range 5.0 to 11.0 MeV.

Characteristics of random-sum peaks in nuclear radiation spectra☆

Abstract The spectrum of pulse heights resulting from the pile-up of constant-amplitude pulses, randomly distributed in time, is discussed. The shape of the pile-up spectrum is sensitive in differing degrees to the various time constants involved in detection and electronic processing. Predictions are presented for n-pulse pile-up, including a formula for two-pulse summation which differs significantly from the usually quoted result. Experimental data, utilizing a pulse generator operating with random time intervals down to 8 ns, agree with the predictions.

Gain stabilization of scintillation and Cerenkov spectrometers at high counting rates

Abstract A photomultiplier gain stabilization system, capable of operation at rates well over 5×10 4 pulses/s, is described. Pile-up and dead-time effects, which hamper conventional systems at such rates, are minimized through the use of a fast-gated charge sensitive integrator directly coupled to the photomultiplier anode. Deviations in the time-averaged response to a reference light pulser are fed back to control the high-voltage supply. Rapid fluctuations due to variations in average dynode current are reduced through the use of active voltage divider chains. Stability, tested with a large NaI(Tl) crystal viewed by five photomultiplier tubes, is better than 0.7% over 24 h, and for counting rates charging from a few hundred counts/s to over 2×10 5 counts/s.

A real-time 448 000-channel multiparameter pulse-height analysis system☆

Abstract A multiparameter pulse-height analysis system, operating on a small multiprogrammed computer with auxiliary magnetic disk memory, has been developed. The method enables experimentalists to collect data in arrays up to 448 000 channels, at coincidence rates of over 300 per second. The data may be viewed as it is collected, and is ready, in histogram form, as soon as data-collection is completed.

The 46, 48Ti(p, α)43,45Sc reaction at intermediate energy

Abstract The 46, 48 Ti ( p , α) 43,45 Sc reaction has been studied at E p = 79.2 MeV. Differential cross sections and analyzing powers were measured for 12 levels in 43 Sc and 11 levels in 45 Sc. A striking j -transfer dependence is observed in the analyzing powers. The reaction is quite selective at this energy, populating the highest-spin states with the largest cross sections. DWBA calculations were performed for all states observed, and the results were found to represent the data for states of known J π quite well. Restrictions on the J π of a number of previously unidentified states were made. A semi-microscopic analysis, in which the form factors for the negative-parity states observed were derived from shell-model wave functions, produced fairly good agreement with the magnitudes of the cross sections for the known states, and resulted in further restrictions of possible J π for some levels.

New thick-target technique for charged-particle radiative capture studies☆

Abstract A technique is described wherein radiative capture cross sections can be measured over a wide range of energies, in a single run, using thick targets and high-resolution gamma-ray detectors. Results from 12 C( p , γ ) 13 N are presented.

Oscar: A multiprogrammed small computer system for experimental nuclear physics☆

Abstract The central component of the data acquisition and analysis system at the Ohio State University Van de Graaff Laboratory is an IBM 1800 computer, operating under a powerful multiprogramming monitor. The system has been designed to allow efficient usage of the computer resources by several experimentalists at once. Under typical conditions, the processor is shared concurrently by data acquisition and display routines, an “on-line” data reduction or experimental control program, and an “off-line” analysis or system updating job. Operations are enhanced by two interactive display units. The system has been found to be flexible, easy to program, and straightforward to interface.

A storage-CRT interactive display for nuclear physics computer systems

Abstract An interactive display system utilizing a storage-type CRT has been develop. It is found to be economical, easy to interface and program, and to provide several advantages over conventional systems.