H. Tsubota

Angular Distributions of Fast Photoneutrons from Pb, Bi and Ta

Using a stilbene scintillation detector, the angular distributions of fast photoneutrons of energies greater than two bias values of 7.4 MeV and 8.7 MeV were measured for Pb, Bi and Ta at 25.5 MeV end point energy of the bremsstrahlung. For Pb and Bi, the angular distributions were found to be asymmetric about 90 degrees with respect to the gamma-ray beam axis and were strongly peaked in a forward direction, but in the case of Ta not so obviously. The angular distributions were fitted to W(θ)=A+Bsin 2 θ+Ccos θ, using a least squares analysis. The present experiment indicates that, in the high energy region of the (γ, n) spectrum, C/A increases with the detecting threshold energy for neutrons and on the otherwise B/A decreases with the energy.

Photoproduction of neutral kaons on a liquid deuterium target in the threshold region

The photoproduction process of neutral kaons on a liquid deuterium target is investigated near the threshold region, E{sub {gamma}}=0.8-1.1 GeV. K{sup 0} events are reconstructed from positive and negative pions, and differential cross sections are derived. Experimental momentum spectra are compared with those calculated in the spectator model using a realistic deuteron wave function. Elementary amplitudes as given by recent isobar models and a simple phenomenological model are used to study the effect of the new data on the angular behavior of the elementary cross section. The data favor a backward-peaked angular distribution of the elementary n({gamma},K{sup 0}){lambda} process, which provides additional constraints on current models of kaon photoproduction. The present study demonstrates that the n({gamma},K{sup 0}){lambda} reaction can provide key information on the mechanism of the photoproduction of strangeness.

Photo-production of neutral kaons on 12C in the threshold region

Abstract The kaon photo-production process on 12C has been studied by measuring neutral kaons in the photon energy range of 0.8–1.1 GeV. Neutral kaons were identified by the invariant mass constructed from two charged pions emitted in the K S 0 → π + π − decay channel. The differential and integrated cross sections in the threshold photon energy region were obtained. The obtained momentum spectra were compared with a Spectator model calculation using elementary amplitudes of kaon photo-production given by recent isobar models. The present results provide the first information on the n ( γ , K 0 ) Λ reaction, which is expected to play an important role in constructing models of strangeness production by electromagnetic interactions. The experimental results show that the cross section of C 12 ( γ , K 0 ) is of the same order as that of C 12 ( γ , K + ) and suggest that a slightly backward K 0 angular distribution is favored in the γ n → K 0 Λ process.

A study of photoreactions in 48Ti

Abstract A high resolution measurement of the 48 Ti(γ, n) cross section is reported. Evidence for isospin splitting of the giant dipole resonance is found to be consistent with the prediction. In addition the deformation splitting of the GDR is consistent with predictions of the dynamic collective model.

Photoprotons in Giant Resonance Region for 31P

S>The energy spectra of photoprotons were measured for /sup 31/P with the electrodisintegration at 90 deg . The differential cross sections of the ( gamma ,p/sub 0/) and the ( gamma ,p/sub 1/) reactions are derived from them. Many fine structures are found in the results. The most of the structures found in the spectra can be explained by the ( gamma ,p/sub 0/) component. The result of the ( gamma ,p/sub 0/)~ cross section is compared with the /sup 32/S( gamma ,p /sub 0/)/sup 31/P cross section. Both the results agree well with each other in the gross structures, but the absolute value of the /sup 31/P( gamma ,p/sub 0/)/ sup 30/S i differential cross section is much smaller than that of the /sup 32/S( gamma ,p/sub 0/)/su p 31/ P reaction. The ( gamma ,p/sub 1/) differential cross section seems to show some gross structures though the errors of the result are rather large. Discussions are made with a single particle excitation process of the valence nucleon. (auth)

Contribution of M1 and E0 transitions in 13C(γ, π−)13Ng.s. in the threshold region

Abstract The angular distribution of the 1 2 − → 1 2 − transition in 13 C (γ, π − ) 13 N g.s. has been measured using 165 MeV electrons The data were taken at 6 angles between 50° and 150° including the forward and backward regions around the deep minimum of the cross section. Comparison of the theory with a non-local calculation shows that the M1 component alone reproduces the experimental data. This implies some suppression of the E0 component

A study of the decay modes of the g92 and i112 isobaric analog resonances in 209Bi using electrons and bremsstrahlung

Abstract Differential cross sections at several scattering angles and proton spectra around the g 9 2 spin-flip and i 11 2 non-spin-flip IAR in 209 Bi were measured with the (e, p) reaction using a broad-range magnetic spectrometer and 100 solid-state detectors. Experiments on the (γ, p) reaction using bremsstrahlung were also performed on the same subjects using the same detector system and geometry as for the (e, p) reaction experiments. Both data agree well with each other when the virtual photon theory is used. Strengths deduced for the resonance at the g 9 2 IAS at θ lab = 125.3° are in basic agreement with previous data which are in contradiction with the results of the (p, γ 0 ) reaction and β-decay. Proton decay modes of these resonances were deduced by the photondifference method. Proton groups emitted through the i 11 2 IAR are found to have a decay mode typical of the IAS and leave the residual nucleus in neutron l p-1 h states. The decay mode at the g 9 2 IAR shows an anomalous reaction process as do previous data on the f 7 2 spin-flip IAR in 139 La.

The (γ, p0) reactions in the giant dipole resonance region of 51V and 52Cr nuclei

Abstract The differential cross sections at 90° for the 51 V(e, p 0 ) 50 Ti and 52 Cr(e, p 0 + p 1 ) 51 V reactions have been measured over the giant dipole resonance region. These cross sections were used to obtain the differential cross sections of the 51 V(γ, p 0 ) 50 Ti and 52 Cr(γ, p 0 + p 1 ) 51 V reactions. The results show two peaks that appear at the same energies as the main peaks of the (γ, n) and (γ, p) cross section for both nuclei. The angular distributions of protons from the (e, p) reaction have also been measured at several points of the incident electron energy. The coefficients A 2 obtained by fitting with a series of Legendre polynomials, W ( θ ) = 1 + A 1 P 1 (cos θ )+ A 2 P 2 (cos θ ), varies with excitation energy. These results are discussed in terms of the direct-semidirect process considering isospin effects in the giant dipole resonance.

Negative Pion Photoproduction from ^15N at E_γ=170 MeV

The angular distribution of the 15 N(γ, π - ) 15 O(g.s.) reaction at E γ =170 MeV was measured using a liquid ammonia target at pion emission angles of θ π =70°, 90°, 110° and 130°. The result is compared with the DWIA calculations and other experimental data. A large discrepancy is observed between the experimental result and the theory. In contrast with the 13 C case, the E0 suppression is not clearly confirmed from the present analysis.The angular distribution of the 15 N(γ, π - ) 15 O(g.s.) reaction at E γ =170 MeV was measured using a liquid ammonia target at pion emission angles of θ π =70°, 90°, 110° and 130°. The result is compared with the DWIA calculations and other experimental data. A large discrepancy is observed between the experimental result and the theory. In contrast with the 13 C case, the E0 suppression is not clearly confirmed from the present analysis.

π+ photoproduction from 28Si leaving low-lying residual states

Abstract The energy and angular distributions of π + photoproduced from 28 Si were measured to study spin-isospin-flip transitions leaving the residual nuclei in states up to 2.5 MeV excitation energy. Dominant contributions were found for M1 transitions at around 1.3 MeV and 2.2 MeV in 28 Al. The strengths of these transitions have been deduced and compared with the results of (e, e′), (γ, γ′), (p, p′), ( π − , γ), ( μ − , γ) and charge-exchange reactions. The (γ, π + ) result agrees with the electromagnetic interaction case but not with the (p, p′) case, which supports the contribution of exchange currents in electromagnetic transitions.