Charles C. Foster

A Facility for Studying Neutron Energy Spectra at Intermediate Energies

Apparatus for measuring neutron energy spectra in the 50-200 MeV range is described. The apparatus, installed at the Indiana University Cyclotron Facility, consists of a beam swinger to change the angle of incidence of the beam on target, 100 m flight paths, large, subnanosecond neutron detectors, and a system for deriving phase stabilized timing signals.

Features of the analyzing powers in deuteron elastic scattering near 80 MeV

Abstract Measurements of the differential cross section and vector ( A y ) and tensor ( A yy ) analyzing powers are reported for deuteron elastic scattering on 58 Ni at 80 MeV. A smooth exponential decline in the cross section is present at large scattering angles. Both A y and A yy rise to large, positive values beyond 60°. These effects are understood in terms of a semiclassical description of the scattering involving only the real central and spin-orbit potentials. A comparison is made to optical-model calculations using global potentials. Additional calculations show that the T R and T P tensor potentials have small but distinguishable effects on the tensor analyzing powers.

Variable Depth Bragg Peak Method for Single Event Effects Testing

The Variable Depth Bragg Peak (VDBP) method for measuring the Single Event Effects (SEE) cross-section of an integrated circuit (IC) in a closed package as a function of ion linear energy transfer (LET) is described. The method uses long-range, high-energy heavy ions that can penetrate the package and deposit charge in the devices sensitive volume (SV), the depth of which is not known. A series of calibrated energy degraders is used to vary the depth of the Bragg peak relative to the devices sensitive volume. When the Bragg peak is located at the sensitive volume, the measured SEE cross-section is a maximum, as is the LET, which is calculated using a Monte Carlo-based program, TRIM that takes both straggling and spread in beam energy and angle into account. Degrader thickness is varied and the change in LET is calculated while the corresponding cross-section is measured. Good agreement was obtained between the LET-dependence of the single event upset (SEU) cross-section for a 4 Mbit memory in an unopened package using the above method and that for an identical de-lidded part previously measured.

Proton irradiation effects on advanced digital and microwave III-V components

A wide range of advanced III-V components suitable for use in high-speed satellite communication systems were evaluated for displacement damage and single-event effects in high-energy, high-fluence proton environments. Transistors and integrated circuits (both digital and MMIC) were irradiated with protons at energies from 41 to 197 MeV and at fluences from 10/sup 10/ to 2/spl times/10/sup 14/ protons/cm/sup 2/. Large soft-error rates were measured for digital GaAs MESFET (3/spl times/10/sup -5/ errors/bit-day) and heterojunction bipolar circuits (10/sup -5/ errors/bit-day). No transient signals were detected from MMIC circuits. The largest degradation in transistor response caused by displacement damage was observed for 1.0-/spl mu/m depletion- and enhancement-mode MESFET transistors. Shorter gate length MESFET transistors and HEMT transistors exhibited less displacement-induced damage. These results show that memory-intensive GaAs digital circuits may result in significant system degradation due to single-event upset in natural and man-made space environments. However, displacement damage effects should not be a limiting factor for fluence levels up to 10/sup 14/ protons/cm/sup 2/ [equivalent to total doses in excess of 10 Mrad(GaAs)]. >

Comparison of the 12C(p, n)12N and 12C(p, p′) reactions at Ep = 62 and 120 MeV☆

Abstract Measured 12 C(p, p′) and 12 C(p, n) 12 N reaction cross-section angular distributions leading to isobaric analog states are compared at 62 and 120 MeV bombarding energies. It is shown that the (p, p′) differential cross section is one-half the (p, n) differential cross section to the analog state. This relation and these reactions are demonstrated to be very useful for the determination of the detection efficiency of large volume neutron detectors at intermediate energies.

Performance of a Neutron Polarimeter to Measure the Electric Form Factor of the Neutron

Abstract We measured the analyzing power and the efficiency of a neutron polarimeter that was designed and constructed to measure the neutron electric form factorGEn. The measurement was carried out at the Indiana University Cyclotron Facility (IUCF) with the 14 C ( p , n ) 14 N reaction at a proton beamenergy of 138.4 MeV. The analyzing power, 〈Ay〉, averaged over the acceptance of the polarimeter is typically 0.44±0.02−0.03+0.04 at a neutron energy of 135 MeV. With a lead-steel wall, consisting of 4 in. of lead sandwiched between two 1 3 8 -in. steel plates, ahead of the polarimeter, the average analyzing power is the same within statistics, namely, 〈Ay〉 = 0.43 ± 0.02−0.03+0.04. The large systematic uncertainty quoted here is dominated by an uncertainty from the inability at the time of the experiment of measuring the longitudinal polarization component of the sideways polarized protons; this systematic uncertainty can be reduced significantly to 0.02 in any future calibration at the IUCF. In each case, the efficiency of the polarimeter is about 0.26% for 135 MeV neutrons at a pulse-height threshold of 4 MeV equivalent electron energy (MeVee) on the front detectors and 10 MeVee on the rear detectors. This analysis reveals a small analyzing power from the carbon in the front-analyzer detectors.

The 19F(p, n)19Ne and 39K(p, n)39Ca reactions at intermediate energies and quenching of the Gamow-Teller strength

Abstract The (p, n) reactions on 19 F and 39 K targets have been studied at 120 MeV and 160 MeV using the Indiana University Cyclotron time-of-flight facility. States up to 12 MeV excitation energy have been observed and angular distributions for these neutron groups are presented. The ground-state mirror transitions have accurately measured ft values. This information is used to normalize the zero-degree energy spectra to a scale of Gamow-Teller (GT) transition probability to obtain GT strenghts to excited states. The experimental sum GT strengths are smaller than the sum-rule-limit values showing strong evidence for GT quenching.

INPOL – the Indiana University Neutron Polarimeter☆

Abstract We describe the upgraded time-of-flight facility at the Indiana University Cyclotron which has been used to measure the polarization transfer induced in ( p → , n → ) reactions at intermediate energies, Ep=100–200 MeV. The Indiana Neutron POLarimeter (INPOL) is able to measure simultaneously two orthogonal neutron spin polarizations induced in charge exchange reactions with polarized proton beams oriented in each of the three spin states, normal ( N → ), sideways ( S → ) and longitudinal ( L → ).

A MONOCHROMATIC NEUTRON FACILITY FOR (N,P) REACTIONS

Abstract A neutron facility for the study of (n,p) reactions was set up at the Indiana University Cyclotron Facility. The neutrons were produced by the reaction 7 Li(p,n) 7 Be. The energy spread of the neutron beam is dominated by the thickness of the 7 Li production target. At the (n,p) target the collimated neutron-beam intensity is about 10 5 n/s/cm 2 for a 1 μA proton beam at 120 MeV on a 7 Li target 100 mg/cm 2 thick. The distance between the neutron production target and the (n,p) target, 3.14 m, makes it possible by time-of-flight to eliminate neutrons degraded below the maximum energy by scattering. Protons from the (n,p) reaction are detected simultaneously at three laboratory angles (7.5°, 12.5°, and 17.5°), in three particle telescopes each consisting typically of three hyperpure Ge elements. All three telescopes are mounted in a common cryostat. Spectra are obtained at other angles including zero by magnetically deflecting the (n,p) protons. Spectra recorded at E n = 118 MeV for (n,p) reactions on several light nuclei are presented.

VECTOR ANALYZING POWERS FOR VALENCE AND INNER SHELL PICKUP IN THE SN-116(D-],T)SN-115 AND SN-116(D-],HE-3)IN-115 REACTIONS

Abstract Differential cross-section and vector analyzing-power angular distributions were measured at Ed = 50 MeV for the 116Sn( d , t)115Sn and 116Sn( d , 3He)115In reactions in the angular range from 6° to 26° for excitation energies up to 25 MeV. In addition to transitions to low-lying states in 115Sn and 115In, data were obtained for the deep-lying hole states in 115Sn. DWBA calculations in general give a good account of the analyzing powers for pickup of the valence shell nucleons. For states at 1.47 MeV (unresolved multiplet) and at 1.65 MeV in 115In, new spin assignments could be made on the basis of the analyzing-power measurements. Analyzing powers for the deeply bound hole states indicate a strong overlap of the different subshell orbitals, although the gross structure peaks still contain characteristic analyzing-power signatures.