H. Miyase

A study of the giant dipole resonance in doubly even tellurium and cerium isotopes

Abstract The partial photoneutron cross sections [σ(γ, n) + σ(γ, pn)] and σ (γ, 2n) of 124, 126, 128, 130 Te and 140, 142 Ce were measured in the giant dipole resonance region by means of the monochromatic photon beam installation at SACLAY. Absolute total photoneutron cross sections, Lorentz line parameters and integrated cross sections are evaluated. The experimental behaviour of the GDR for the above nuclei and in particular its spreading, is then tentatively interpreted in terms of the improved dynamic collective model using the concept of potential energy surfaces.

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.

ISOBARIC ANALOGUE RESONANCES IN PHOTOPROTON REACTIONS.

Abstract Photoproton energy distributions from 89 Y, 90 Zr, 139 La, 140 Ce and 141 Pr have been measured. Strong proton peaks through isobaric states are found in the cases of 90 Zr and 140 Ce. In the other cases no prominent peaks are observed.

Electrofission of 208Pb in the intermediate energy region.

The absolute electrofission cross section of {sup 208}Pb was measured in the energy range 35--250 MeV, and the photofission cross section was deduced by means of the virtual-photon technique. A structure observed in the ({gamma},{ital f}) curve, around 200 MeV, was interpreted on the basis of recent calculations for the thermalization process which were performed in the framework of the intranuclear cascade model.

Photoproduction of neutral kaons on C in the threshold region

Abstract The measurement of neutral kaon photoproduction in the threshold region is in progress at Laboratory of Nuclear Science, Tohoku University. One of the purpose of the experiment is to study electromagnetic strangeness production mechanism, which is necessary for hypernuclear spectroscopy by electromagnetic probes. We have observed K 0 s produced on a carbon target in a commissioning run. Data taking will start in 2003.

Photoproton reactions on 208Pb

Abstract Photoproton energy distributions have been measured for the (e, e′p) reaction at a number of bombarding energies. The results are used to obtain the (e, e′p) cross sections and isochromats. The (e, e′p) cross sections are analyzed to get the (γ, p) cross sections. The results and (γ, p) cross sections show a strong resonance around 25.0 MeV, whose energy and integrated cross section agree well with theory for IAR. Proton spectra emitted through the IAR are extracted from the photoproton spectra and also from the isochromats. Strong proton groups are found at around 15.3 MeV and 11 MeV corresponding to the h 11 2 proton hole state at 1.3 MeV and also neutron particle-hole states around 6 MeV in the residual nucleus. The result is in good agreement with estimates obtained from proton scattering on 208 Pb, showing the configuration of the IAR states.

Measurement of the 6Li(e,e′p) reaction cross sections at low momentum transfer

Abstract The triple differential cross sections for the 6 Li(e,e′p) reaction have been measured in the excitation energy range from 27 to 46 MeV in a search for evidence of the giant dipole resonance (GDR) in 6 Li. The cross sections have no distinct structures in this energy region, and decrease smoothly with the energy transfer. Angular distributions are different from those expected with the GDR. Protons are emitted strongly in the momentum-transfer direction. The data are well reproduced by a DWIA calculation assuming a direct proton knockout process.

Surprisal Analysis of the 63,65Cu (e, p0) Reactions

Surprisal analysis is applied to photoreaction. The statistical model of Hauser-Feshbach is extended to analyze the 63,65 Cu(γ, p 0 ) reactions. A unified understanding of the measured cross sections in the giant resonance energy region, which has yet to be achieved, is attempted.

Development of optical-pumping polarized deuteron target

An optical-pumping system of rubidium atoms for a laser-driven polarized deuteron target was constructed. The density and polarization of the rubidium atoms were measured using Faraday rotation. The rotation angle was determined within an error of 0.01°. Our preliminary result showed a polarization of 0.4 at a gas thickness of 4×1013 atoms/cm2.