T. A. Love

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.

Cross sections for gamma-ray production by fast neutrons for 22 elements between Z = 3 and Z = 82

Cross sections for the production of gamma rays with energies of 0.3 < E/sub ..gamma../ < 10.5 MeV have been measured as a function of neutron energy over the range 0.1 < E/sub n/ < 20.0 MeV. Results were obtained for 22 elements that are commonly encountered in the calculation of radiation effects. The measurements were made using a heavily shielded Nal detector in conjunction with the white neutron spectrum from the Oak Ridge Electron Linear Accelerator. Incident neutron energies were determined by time-of-flight over a 47-m flight path, while gamma-ray energy distributions were obtained from pulse-height unfolding techniques. Elemental differential cross sections are presented for Li, C, N, F, Mg, Al, Si, Ca, V, Cr, Fe, Ni, Cu, Zn, Nb, Mo, Ag, Sn, Ta, W, Au, and Pb.

Fission-Product Energy Release for Times Following Thermal-Neutron Fission of Plutonium-239 and Plutonium-241 Between 2 and 14 000 s

Absolute fission-product decay energy-release rates have been measured for thermal-neutron fission of 239Pu and 241Pu. Spectral data were obtained using scintillation spectrometers for beta and gam...

Method for Detecting Nonproportionality of Response for Gamma‐Ray Scintillators

A quantitative method for studying the relation between the light output from a scintillator and the amount of absorbed garuma energy is described. Curves are presented showing the nonproportionality of response for the gamma cascade in the decay of Bi207

Absolute Efficiency Measurements of NE‐213 Organic Phosphors for Detecting 14.5‐ and 2.7‐MeV Neutrons

The absolute efficiency of two NE‐213 organic phosphors for detecting 14.5‐ and 2.7‐MeV neutrons has been determined by the associated particle technique with the recoil particles from the T(d,n)4He and D(d,n)3He reactions. The output of the neutron detector was placed in coincidence with the helium recoil pulses and the efficiency of the detector was obtained as the ratio of the coincidence counts to the helium recoil counts. The scintillators were 12 cm in diameter and had thicknesses of 2.61 and 6.10 cm, and each was preceded by a 5‐mm thick NE‐102 plastic scintillator and followed by a 3.3‐cm (average thickness) Lucite light pipe. The detection efficiency, for neutrons striking the central 25% of the detector area, was measured as a function of the bias level on a tunnel diode driven by the current pulse from dynode 14 of a 58AVP multiplier phototube and also as a function of a bias threshold on the total light output. The bias level was calibrated in terms of the pulse‐height spectra resulting from t...

An experimental system for providing data to test evaluated secondary neutron and gamma-ray-production cross sections over the incident neutron energy range from 1 to 20 MeV

Abstract A system is described which allows simultaneous measurement of secondary neutron and gamma-ray production cross sections. Measurements can be made rapidly over wide energy ranges. An electron linac is used as a neutron source. Annular scattering samples located 47 m from the neutron source are viewed by a NE-213 scintillation counter. Multiparameter data acquisition is done by on-line computer for incident neutron energies from 1 to 20 MeV.

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.

Absolute yield of 140.5 keV gamma ray following decay of 99Mo

Abstract The absolute intensity for the dominant 140.5 keV gamma ray in 99Tc was determined to be 90.7 ± 0.6 per 100 99 Mo disintegrations for 99Mo decay in equilibrium with the decay of the 99Tc∗ daughter. Relative intensities for K X-ray and gamma rays emanating from 99Mo in equilibrium with its 99Tc∗ daughter were measured using several Ge photon detectors. These include a direct measurement of the very weak 142.6 keV gamma ray. Combining these intensities with an evaluated set of electron-conversion coefficients provided a set of absolute intensities and uncertainties for the observed gamma rays. A complete discussion of the method of analysis, showing relationships among uncertainties of measured and evaluated data, is given.

Fast forward neutron production in the 7Li(p,n)7Be reaction for 41- and 64-MeV protons

Abstract Measurements have been made by the time-of-flight technique of the neutron energy spectra observed at zero degrees from the 7 Li(p,n) 7 Be reaction using 41- and 64-MeV incident protons. The neutron production cross sections for the fast forward peak (corresponding to excitation of the ground and first excited states of 7 Be) has been found to be 33±6 mb/sr at a mean energy of 39 MeV and 36±4 mb/sr at 60 MeV. These results are compared with those reported elsewhere, and the suitability of such 7 Li targets as a source of monoenergetic neutrons is discussed.