W. Benenson

Study of the 10Be(d, p)11Be reaction at 25 MeV

The distribution of the single-neutron strength up to an excitation energy Ex = 7.0 MeV in 11Be was investigated with the 10Be(d, p)11Be reaction at Ed = 25 MeV. The 12+, g.s., 12−, 0.320 MeV and 1.785 MeV states are found to be excited with significant strength. The angular distribution for the 1.785 MeV state is typified by an orbital angular momentum transfer ln = 2. This together with other available data indicate that its spin is Jπ = (52)+. The spectroscopic factors for these three states are compared to the shell-model calculations of Teeters and Kurath and of Cohen and Kurath.

Experiences using the open-source learning content management and assessment system LON-CAPA in introductory physics courses

We discuss the development and functionality of the LON-CAPA system with a particular focus on its homework and examination functionality. We also describe its more general approach to course management and its infrastructure for course content sharing and reuse. We then focus on measures of student learning and the effectiveness of different content types.

The polarization of T(p, n)He3 neutrons for proton energies from 2.9 to 12 MeV

Abstract The polarization of neutrons produced in the T(p, n)He3 reaction was measured for proton energies from 2.9 to 12 MeV. Polarizations were determined by scattering from helium in a high-pressure cell. By recording the helium recoils in coincidence with the scattered neutrons, background counts were reduced. A magnetic field produced by a solenoid was used to rotate the polarization vector of the neutrons. The polarization near 45° in the centre-of-mass system decreases from 0.26±0.03 at 2.9 MeV to −0.20±0.04 at 12 MeV, passing through zero at about 4.8 MeV. The angular distribution of the polarization changes considerably as the proton energy increases from 2.9 to 6 MeV. However, the shape of the 12-MeV distribution is similar to that at 6 MeV.

Excited state production and temperature measurement in a heavy ion reaction

An effective temperature inferred from the slope of kinetic energy spectra of the emitted fragments is not reflected in the relative populations of excited states of the emitted nuclei. We found that the excited state populations of 6Li, 7Li and 7Be emitted near 90° in the lab from the reaction of 490 MeV 14N with Ag are significantly lower than those expected on the basis of their effective temperature.

Excitation of giant resonances by inelastic

Inelastic /sup 3/He scattering at 71 MeV on twelve nuclei ranging from / sup 27/Al to /sup 209/Bi shows an enhancement of the continuum very similar to that observed in electron and proton scattering. The effect is ascribed to a giant multipole state. The strength of the excitation indicates an E2 character for thc state. (auth)

sup 3

Abstract The effect of the neutron to proton ratio of the colliding system on the isotope ratio of the emitted fragments (1 ⩽ Z ⩽ 5) was studied for for a variety of constant mass beam-target combinations. To extend the N Z ratio as far as possible, one of the projectiles employed, 40Cl, was a radioactive secondary beam. The isotopic ratios depend on the N Z of the target and beam in a way which is not consistent with N Z > equilibration on the timescale of the emission of intermediate-mass fragments.

He scattering

Abstract Using the A1200 beam analysis device at the National Superconducting Cyclotron Laboratory, we have measured the halflives of several nuclei along the rp-process path near the proton-drip line. Halflife results for 61 Ga, 63 Ge, and 65 As (0.15±0.03 s, 95 −25 +23 ms, and 0.19 −0.07 +0.11 s, respectively) and their implications for the rp-process are presented.

The use of radioactive nuclear beams to study the equilibration of the N Z degree of freedom in intermediate-energy heavy-ion reactions

The [ital rp] process provides a mechanism whereby energy is generated and proton-rich nuclei are synthesized in various astrophysical environments. Understanding this process requires knowledge of the half-lives, binding energies, and reaction cross sections for the nuclei along its path, which for [ital A][approx gt]60 lies near the proton-drip line. Using the A1200 radioactive-beam facility at the National Superconducting Cyclotron Laboratory, we have performed an experiment to measure the [beta]-decay half-lives of several [ital T][sub [ital z]]=[minus]1/2 nuclei in this mass region by identification and implantation of projectile fragments followed by a rapid beam cutoff and observation of the [beta] decay. Using this technique, the half-lives of [sup 61]Ga, [sup 63]Ge, and [sup 65]As (0.15[plus minus]0.03 s, 95[sub [minus]20][sup +23] ms, and 0.19[sub [minus]0.07][sup +0.11] s, respectively) have been measured and are found to be consistent with expectations from [beta]-decay theory for decay between mirror states with [ital Q][sub [beta]][similar to]9 MeV. In addition, the proton-rich nucleus [sup 66]Se has been observed for the first time. The experimental method used for this measurement and the implications of these results for the [ital rp] process are discussed.

Halflife measurements of the rp-process nuclei 61Ga, 63Ge, and 65As

Abstract The even-even cadmium isotopes have been studied by the (p, t) reaction at 42 MeV. A broad resonance-like structure is observed between 6 and 7 MeV excitation energy which has similar properties to the feature observed in (p, t) reactions in the tin isotopes. A second smaller bump at higher excitation energy appears to arise from pickup of two particles from deep orbits.

Half-life measurements for Ga-61, Ge-63, and As-65 and their importance in the rp process

Abstract Excited 7 2 − states to which enhanced L = 0 (p, t) transitions are observed have been identified in 41Ca at 2958 keV and in 57Co at 2611 keV. A comparison of these (p, t) transitions with those to the 0+ states in 40Ca at 3353 keV and in 58Ni at 2940 keV leads to the conclusion that these states are obtained by weak-coupling of a f 7 2 particle and hole, respectively, to the excited 0+ states of the doubly even cores. It is suggested that these cases are examples of a rather general weak-coupling phenomenon.