K. Min

Spin-isospin excitation in 12C(γ, π+)12B∗ using tagged photons

The energy spectra of positive pions from the reaction 12C(γ, π+)12B∗ were measured at five angles, using quasi-monochromatic, tagged photons in the energy range from 176 to 182 MeV. Strong transitions to the isovector nuclear states in 12B at 0–1, 4.5, and 7.5 MeV were observed. The differential cross sections to these states have been obtained for the momentum transfers 0.5 < q < 1.2 fm−1. DWIA calculations have been carried out in momentum space for each observed state or group of states. Comparisons are made between the present data, previous data from bremsstrahlung experiments, and various DWIA calculations.

Differential elastic scattering cross sections of Fe and Ni from 10 TO 700 keV

Abstract Differential elastic scattering cross sections of neutrons from natural Fe and Ni were measured in the energy region between 10 and 700 keV. The measurements were made at six angles ranging from 30° to 150°, and the differential cross sections were determined relative to the known cross sections of natural Pb. The principal angular distribution results are presented in terms of the Legendre polynomial expansion coefficients as functions of energy. Two sets of coefficients corresponding to averaged values over 20 and 50keV are given. Comparisons are made with the available data on total and differential elastic scattering cross sections. The data are consistent with the interpretation that s-wave scattering is dominant throughout the region of measurement, while p-wave scattering becomes evident above 200 keV. There seems to be appreciable d-wave contribution above 400 keV. The gross features of angular distribution coefficients are characterized by resonant structure with widths of the order of 100 keV.

Distribution of spin-isospin strengths in 12B and 13B

Abstract The differential cross sections of the reactions 12,13 C( γ , π + ) 12,13 B were measured using tagged photons at the mean energy E γ = 191 MeV at five angles 35° ⩽ θ π ⩽ 145° corresponding to the momentum transfer to the nucleus 0.5 ⩽ q ⩽ 1.5 fm −1 . The major transition strengths leading to various excited states in 12,13 B, in both cases, are concentrated within a resonance centered at about 7 MeV excitation energy in 12,13 B (about 22 MeV in 12,13 C) with a full width at half maximum (FWHM) of about 12 MeV, reminiscent of the well-known electric-dipole gian resonances. The two reactions are compared in the context of the weak-coupling model.

Positive photopion production from 12,13C using tagged photons

Abstract Angular distributions of positive pions to residual states in 12 B and 13 B at excitation energies up to 20 MeV were measured using tagged photon facility at SAL. Strong spin-isospin flip ( Δ S=1, Δ T=1) states are clearly observed in the excitation spectra of both 12 B and 13 B. Present data were found to be in good agreement with existing data. J.C. Kim and H.T. Chung gratefully acknowledges the support of SNU Daewoo Research Fund. K. Shoda and H. Tsubota want to thank the Monbusho International Scientific Research Program No. 63044011 for supporting this work.

Angular distribution measurement of 14N(γ, π+) 14Cgs at Eγ=320 MeV

Abstract Differential cross sections for 14 N(γ, π + ) 14 C gs at a photon energy of 320 MeV, near the peak of the free nucleon delta resonance, have been measured at six angles ranging from 35° to 120°. Momentum-space calculations based on the distorted wave impulse approximation yield results which are lower than experiment by a factor of three.

A facility for measuring electro and photo-pion spectra in a high background environment

Abstract A QD spectrometer for use in high background (γ, π ) experiments is described. The spectrometer has a large solid angle (17 msr) and a short flight path (2.8 m). The experimental techniques employed are described, particularly those used in coping with the high background levels. These include a novel approach to dead time corrections.

pi. /sup +/ photoproduction from /sup 13/C

Differential cross section measurements were made for /sup 13/C(..gamma..,..pi../sup +/)/sup 13/B (g.s.) at 90/sup 0/ (lab) for pion energies of 18, 29, and 42 MeV, and for /sup 13/C(..gamma..,..pi../sup +/)/sup 13/B (E/sub x/ = 3.5 MeV) at 42 MeV. The ground-state results are compared to several distorted-wave impulse approximation calculations and to Helm model calculations. There are significant discrepancies between experiment and theory and among the theoretical results.