Fred E. Bertrand

A Total-Absorption Detector for 60-MeV Protons Using Lithium-Drifted Germanium

A lithium-drifted germanium diode has been used for total-absorption detection of 59-MeV protons from the Oak Ridge Isochronous Cyclotron. The detector is 1.9 cm in diameter, has a depletion depth of 6 mm, is cooled to less than 85° K, and is sealed in an aluminum can with a 0.0026-in.-thick window. The diode was oriented so that the protons entered in a direction parallel to the detector junction. The energy resolution attained for 59-MeV protons was 150 keV (FWHM), uncorrected for energy straggling in windows of 76 keV, for approximately 60 keV of beam resolution, and for electronic noise. The peak-to-total ratio, determined by using an anticoincidence collimator, was as high as 0.94, which is comparable to 0.96 observed elsewhere for NaI. When the collimator was moved along a line parallel to the junction and perpendicular to the beam, the energy resolution and peak-to-total ratios remained constant within the experimental accuracy over a 10-mm scanned distance. As the collimator was moved in a direction perpendicular to the junction and toward the depleted material, the peak-to-total ratio decreased, as was expected from multiple scattering calculations. When the diode was connected by a 125-ohm terminated coaxial cable to a fast amplifier, a rise time of 4-5 nsec was observed. Since the protons entered the detector parallel to the junction, pictures obtained show the superposition of nearly rectangular current pulses arising from hole and electron collection. The length of the pulses is correlated with the point of incidence of the collimated beam.

Breeding 10{sup 10}/s Radioactive Nuclei in a Compact Plasma Focus Device

In the early 90s, it was discovered that a Plasma Focus (PF) system self-creates a plasma-tarp in which high energy-threshold nuclear-reactions occur at high reaction rates. Short life radioisotopes (SLR)s such as {sup 18}F, {sup 17}F, {sup 15}O, {sup 14}O, {sup 13}N have been generated (10{sup 6} - 10{sup 8} per pulse) with a PF-machine using 7 kJ energy storage to produce the plasmas. {beta}{sup -} radioactivity from the SLRs is measured with rugged, Geiger counters inserted into the PF-chamber, and a specific SLR is identified by its half-life. The PF chamber (before discharge) is filled with a mixture of gases that constitutes the latter plasma-target--beam system, e.g., the elements required to produce specific SLRs through nuclear reactions. In this paper, arguments are presented showing that a modest sized PF-machine, using a 50-75 kJ fast capacitor-bank, when operated at pulse frequencies of 1-10 Hz can produce {ge} 10{sup 9} SLRs/pulse. This paper reports the result s of testing a PF as a breeder of SLRs with dual applications for: (1) Secondary Radioactive Nuclear Beams ion-sources (Z < 35), and (2) as a breeder of radioisotopes for biomedicine (Z {le} 10) and/or PET imaging.

A high resolution spectrometer system with particle identification for 1 through 60 MeV hydrogen and helium particles

Abstract A coincidence semiconductor spectrometer system based on a Ge(Li) total absorption detector has been applied to the simultaneous spectroscopy of all charge 1 and 2 particles from targets bombarded with protons with energy up to 62 MeV. Output spectra cover the range from the full energy down to a 1 to 5 MeV threshold which depends on particle type. The method for choosing the thickness for the two ΔE detectors is discussed and unusual features of the system are described. Particles too slow to penetrate the first ΔE counter were sorted according to mass using flight-time vs E discrimination while the more energetic particles were separated using two sets of ΔE × E discrimination. Germanium detectors thick enough to stop 60 MeV protons were used with particles entering perpendicular or parallel to the field lines, and in either case the only significant inactive region in the path of the detected particles was the protective foil over the Ge(Li) detector. The typical pulse-height resolution of the system was about 200 keV for 60 MeV protons, although a germanium detector used alone gave 55 keV resolution at this energy. Analysis was performed after the experiments using magnetic tapes written by an on-line computer; corrections to the pulse-height spectra for reaction and collimator tails are discussed. The electronic logic system is described, including portions for event characterization, for use of an “active” detector collimator, and for pileup pulse rejection based on timing information.

A Four Parameter E vs dE/dx and Tie-of-Flight Computerized Charged Particle Experiment

For detection of charged particles from 1 to 60 MeV, three solid state detectors are utilized in a dE/dx telescope configuration. Signals are summed digitally and displayed on a 2-dimensional flicker box and transmitted off-line to a larger computer for tail corrections, dead layer corrections, and final analysis. Time-of-flight is utilized for nonpenetrating particles. p, D, T, 3He, ?, etc. can be distinguished from 1 to 60 MeV with ~180 keV system energy resolution.

The Research Career of Subramanian Raman at Oak Ridge National Laboratory

Subramanian “Ram” Raman, a distinguished nuclear physicist and senior staff member of the Physics Division at Oak Ridge National Laboratory (ORNL), died April 8, 2003. In June 1966, Raman joined the staff at ORNL working in the Nuclear Data Project. This position provided him insights into important open questions in nuclear structure physics, and the power of “horizontal” compilations of properties across a broad range of nuclei. These insights would guide Raman’s research interests throughout his 36‐year career at ORNL.As shown by his great variety of publications, Raman’s research career was marked by an intense interest in all areas of nuclear physics. He published papers on topics ranging from detailed nuclear structure to giant resonances, to the search for superheavy nuclei, to the scattering of heavy ions. His research resulted in over 200 published papers and over 3000 citations of his work. It is however, his nuclear data evaluations, both horizontal and vertical, that we most often remember. Hi...

The New Giant Resonances — An Experimental Review

An interesting and important development in nuclear physics during the past 7 years has been the experimental observation of non-dipole giant resonances, the so called “new” giant resonances. Unlike the giant dipole resonance (GDR) which has been established mainly through the photo-nuclear reaction, the new giant resonances were first observed by and have been studied almost exclusively through inelastic scattering of medium-energy hadrons and electrons. (Reference 1 provides a review of this subject as of early 1976. I will refer to this review and the references therein in order to shorten the present reference list. More recent work will be explicitly referenced here.)