L.M. Bollinger

Measurement of the Time Dependence of Scintillation Intensity by a Delayed‐Coincidence Method

A new method for the measurement of the time dependence of the light intensity from scintillators is described. An important aspect of the method is the ease with which it can be applied to all modes of excitation. The results of measurements on the time dependence of the scintillators for several modes of excitation are presented.

Neutron detection with glass scintillators

Abstract A systematic study is made of the characteristics for neutron detection of boron- and lithium-containing glass scintillators. The results of measurements of the optical transmission, the pulse-height distribution, and the time dependence of scintillation intensity are presented. A careful study of the pulse-height distributions for thermal neutrons shows that a major part of the width of the distributions can be accounted for in terms of well-understood statistical fluctuations. Problems associated with the application of the scintillators are considered, with special emphasis on application to time-of-flight neutron spectroscopy. As part of these considerations, a Monte Carlo calculation is performed to obtain a complete understanding of the time uncertainties involved in the capture of neutrons in the scintillators. It is concluded that the lithium glass in an excellent detector of neutrons when large uncertainties in time ( > 0.3 >sec) can be tolerated, the boron glass excels when intermediate accuracy (≈ 30 nsec) in timing is required, but neither kind of glass is suitable for most experiments that require fast timing.

High-sensitivity neutron-capture gamma-ray facility

Abstract An exceptionally sensitive experimental system for the measurement of neutron-capture gamma rays is described and the characteristics of the system are examined critically. The results of measurements on the gamma-ray spectra from neutron capture in 6 Li, 10 B, 12 C, 13 C and 14 N are reported. Some of these data are used to derive an accurate calibration of the efficiency of the Ge(Li) gamma-ray spectrometer used in the measurements.

Beam buncher for heavy ions

Abstract An ion beam buncher has been developed for efficient pulsing of heavy ions into a tandem accelerator. The buncher consists of a single acceleration gap, with aligned grids, which is excited by an rf voltage with a sawtooth waveform. The sawtooth is generated by combining an rf sine wave with its first three higher harmonics. The amplitudes of the second, fourth and sixth harmonics induced by the pulsed beam in a resonant cavity provide an immediate indication of the pulse width. Time-of-flight measurements yielded pulses 0.6 and 0.9 ns wide (fwhm) for 1 H and 12 C beams, respectively, with over 75% of the dc beam compressed into the pulses.

Boron‐Loaded Liquid Scintillation Neutron Detectors

The general problems involved in constructing boron‐loaded liquid scintillation neutron detectors are considered. The characteristics of particular counters which have been successfully used in neutron transmission measurements by the time‐of‐flight method are then described. The design of these counters was guided by the results of a Monte Carlo study of neutron capture in a boron‐poisoned medium. This calculation gives the probability of neutron capture as a function of neutron energy, counter thickness, and time. The calculated results are compared with experimentally determined efficiencies. The advantages and problems encountered in using the boron‐loaded liquid scintillator with the Argonne fast neutron chopper are discussed.

Split Ring Resonator for the Argonne Superconducting Heavy Ion Booster

A split-ring resonator for use in the ANL superconducting heavy-ion linac was constructed and is being tested. The electromagnetic characteristics of the 98-MHz device are the same as the unit described earlier, but the housing is formed of a new material consisting of niobium sheet explosively bonded to copper. The niobium provides the superconducting path and the copper conducts heat to a small area cooled by liquid helium. This arrangement greatly simplified the cryogenic system. Fabrication of the housing was relatively simple, with the result that costs have been reduced substantially. The mechanical stability of the resonator and the performance of the demountable superconducting joints are significantly better than for the earlier unit.

Glass Scintillators for Neutron Detection

The characteristics for neutron detection of some clear boron-containing glass scintillators are discussed. The pulse-height response of the glasses GL- 127 and GI-55 to thermal neutron capture is given. Tests on small samples of the two glasses indicate they can be used as detectors for slow neutrons. (C.J.G.)

The positive-ion injector of ATLAS: Design and operating experience

Abstract The recently completed positive-ion injector for the heavy-ion accelerator ATLAS is a replacement for the tandem injector of the present tandem-linac system. Unlike the tandem, the new injector provides ions from the full range of the periodic table. The concept for the new injector, which consists of an ECR ion source on a voltage platform coupled to a very-low-velocity superconducting linac, introduces technical problems and uncertainties that are well beyond those encountered previously for superconducting linacs. The solution to these problems and their relationship to performance are outlined, and experience in the operation of ATLAS with its new injector is discussed.

The ATLAS Positive-Ion Injector project

The goal of the Argonne Positive Ion Injector project is to replace the ATLAS tandem injector with a facility which will increase the beam currents presently available by a factor of 100 and to make beams of essentially all elements including uranium available at ATLAS. The beam quality expected from the facility will be at least as good as that of the tandem based ATLAS. The project combines two relatively new technologies — the electron cyclotron resonance ion source, which provides ions of high charge states at microampere currents, and rf superconductivity which has been shown to be capable of generating accelerating fields as high as 10 MV/m resulting in an essentially new method of acceleration for low-energy heavy ions.

Ultra-Short Pulies of Heavy Ions

The bunching requirements for a heavy-ion tandemlinac accelerator are defined and a bunching system to satisfy these requirenents is outlined. This discussion introduces an experimrent on the bunching of 45 MeV 16O ions by means of a ¿/2 superconducting-helix resonator. The measured ion-bunch width is 64 psec, a value daminated by the resolution width of the ion detector. By correcting for the detector-resolution width one infers that the ion bunch itself is <40 psec wide.