A. Mittler

Prompt fission neutron energy spectra induced by fast neutrons

Abstract Prompt fission neutron energy spectra for 235 U and 239 Pu have been measured for fission neutron energies greater than the energy of the incident neutrons inducing fission. The measurements were undertaken to investigate the shape dependence of the fission neutron spectra upon both the incident neutron energy and the mass of the nucleus undergoing fission. Measurements were made for both nuclides at incident neutron energies of 0.50, 1.50, 2.50 and 3.50 MeV. The data are presented either as relative yields or as ratios of measured spectra to that of 235 U at 0.50 MeV. Incident neutrons were produced by the 7 Li(p,n) 7 Be reaction using a pulsed, bunched proton beam from the 5.5 MV Vand de Graaff accelerator at the University of Massachusetts Lowell Radiation Laboratory. Fission neutrons were detected by a thin liquid scintillator with good time resolution capabilities. Neutron energies were determined by time-of-flight techniques with pulse-shape discrimination to reduce gamma-ray background levels. The measurements are compared to calculations using the Los Alamos model of Madland and Nix to test the predictive capabilities of the model. The calculations were performed prior to the measurements. The data are fit by the Watt equation to determine the mean energy of the spectra and facilitate comparison of the results to previous measurements.

Spin and parity assignments for 35Cl levels from the 31P(α, p)34S reaction

Abstract 35 Cl states at excitation energies between 9.9 and 11.8 MeV have been identified through sharp resonances in the 31 P(α, p o ) 34 S excitation functions at 25°, 105° and 155° for E α = 3.25–5.50 MeV. Forty-eight on-resonance angular distributions, normalized to an absolute cross section scale, have been subjected to single-level and two-level analyses resulting in spin and parity assignments for each resonance. Approximately half the resonances were of the pure single-state type, having unique angular distribution shapes. Data from 12 resonances of an earlier experiment 1 ) were analyzed with the same theory, extending the diagnostics down to a 35 Cl excitation energy of 9.1 MeV. A set of optical potentials consistent in all four reactions that this experimental program encompasses has been incorporated in the present analysis. Validity of the optical potential is demonstrated for α-particles elastically scattered by 31 P.

Spin and parity assignments for 23Na levels from the 19F(α, p)22Ne reaction

Abstract Resonances were found in the 120° and 160° excitation functions for the 19 F(α, p o ) 22 Ne reaction between E = 2.5 and 5.0 MeV corresponding to 23 Na levels at excitation energies between 12.56 and 14.51 MeV. Twenty-one on-resonance angular distributions were analysed with single-level and two-level theory to extract 23 Na spin and parity information. The results of an earlier experiment were analysed by the same procedure, extending the diagnostics down to a 23 Na excitation energy of 11.55 MeV. The analysis incorporated an optical potential for the α-particle consistent with previous channel-spin- 1 2 reaction studies and α-induced reaction data.

Neutron scattering cross sections up to 2. 4 MeV for the ground and first two excited states of /sup 232/Th

Differential cross sections have been measured at the University of Lowell for the ground and first two excited states of /sup 232/Th via the neutron time-of-flight technique. The following results are presented for neutron scattering cross sections: (a) excitation functions of /sup 232/Th in the incident energy range from 185 to 2400 keV for the 0/sup +/ ground state and the 2/sup +/, 49-keV state, and in the 480- to 2400-keV range for the 4/sup +/, 162-keV state; (b) angular distributions for the 0/sup +/ and 2/sup +/ states at 185 kev and for the 0/sup +/, 2/sup +/, and 4/sup +/ states at 550 keV. Level cross sections were obtained using these and previously measured angular distributions.

55Mn(n, n'γ) cross-section studies for En = 1.0–3.6 MeV

Abstract Absolute 55 Mn(n, n′γ) γ-ray production cross sections have been measured for 19 transitions from levels up to and including the 2429 keV state in 55 Mn over the energy range E n = 1.0–3.6 MeV. Angular distributions were also measured for 6 of the transitions. Branching ratios were extracted and total inelastic neutron cross sections were inferred for these 55 Mn excited states. The measured and inferred cross sections are compared with calculated cross sections using the statistical compound nucleus theory.

Recent Results of Neutron Inelastic Scattering to Higher-Excited Levels in 232Th and 238U

Neutron inelastic scattering cross sections for levels of 232Th and 238U between 680 and 1200 keV excitation energy have been measured in the neutron energy range 0.9–1.5 MeV. Nearly monoenergetic neutrons were generated using the 7Li(p,n) reaction initiated by a pulsed proton beam produced by a Van de Graaff accelerator using terminal pulsing in conjunction with a Mobley bunching system. Scattered neutrons were observed with a time-of-flight spectrometer with experimental parameters chosen to yield an overall energy resolution of 12–15 keV for inelastically scattered neutrons. Level cross sections were deduced from measured 125°-differential scattering cross sections. Excitation functions were compared with our own previous (n,n′γ) measurements, recent theoretical calculations and the ENDF/B-V evaluations.

Gamma radiation from neutron irradiated U-235

Abstract A U-235 scatterer has been irradiated with neutrons in the 100- to 500-keV range. Preliminary production cross sections have been determined for gamma rays following neutron inelastic scattering and for gamma rays originating in isomeric states of fission fragments.

Analysis of Van de Graaff ion source with Rutherford backscattering spectroscopy

Abstract A radio frequency (RF) ion source is utilized at the University of Massachusetts Lowell accelerator facility to produce a plasma from which positive ions are extracted and then accelerated. The interior surface of the source becomes contaminated with a dark coating after several hundred hours of usage which reduces the current output of the source. Rutherford backscattering spectroscopy (RBS) was employed to analyze the constituents of this coating. Procedures have been carried out to etch chemically this film and to refurbish the ion source.

Trace elemental analysis of coral and bone samples

Biomaterials have been developed for various medical applications. Strength factors as well as the deterioration rate of the biomaterials in the human body must be considered. Extensive research covers the use of hydroxyapatite, a coralline substance for biomedical applications. Coral, bone and hydroxyapatite were examined using external beam Proton Induced X-ray Emission (PIXE), Neutron Activation Analysis (NAA) and X-ray Diffraction (XRD) to determine the similarities among these materials.

The 14N(n, n'γ) cross section of the 2.313-MeV first excited state

The neutron-induced gamma-ray production cross section for the first excited state of 14 N was measured for neutron energies from 2.65 to 3.55 MeV at intervals of 100 KeV An angular distribution from 45 to 135 deg in 10-deg steps was measured at an incident neutron energy of 3.45 MeV Neutrons were produced by the 7 Li(p,n) 7 Be reaction using a pulsed proton beam from the University of Massachusetts Lowell 5.5-MV Van de Graaff accelerator. The interaction of neutrons from the 7 Li(p,n) 7 Be* reaction in the sample was taken into account. A calibrated 235 U fission chamber was used to measure the absolute incident neutron fluence. Gamma rays were detected by a Ge(Li) crystal surrounded by a NaI(Tl) anti-Compton annulus. This spectrometer was used in conjunction with the pulsed-beam time-of-flight technique to attenuate background. The measured cross section compares favorably with other experimental data and with the ENDF/B- VI evaluation.