M. Sanzone

Measurement of the total cross section for 238U photofission in the nucleon resonance region

Abstract We present the results of the photofission cross section for 238 U measured between 200 and 1200 MeV. In the ‡ region our results agree with existing data on the total photoabsorption cross section, while at higher energy they show no evidence of the higher nucleon resonances, clearly seen in the photon absorption on the photon, and a damping of the absolute value.

Absolute total photoabsorption cross sections on nuclei in the nucleon resonance region

Abstract We present the results of an absolute measurement of the photoabsorption cross section on Li, C, Al, Cu, Sn, and Pb between 300–1200 MeV. In the Δ region our results confirm that the strength is conserved, while in the higher resonances region they show a 7–15% damping and a possible mass-number dependence of the photoabsorption cross section.

Absolute measurement of the total photoabsorption cross section for carbon in the nucleon resonance region

Abstract We present the results of an absolute measurement of the total nuclear photoabsorption cross section for carbon in the higher nucleon resonance region. In the Δ region our results agree with existing data, while at higher energies they show a damping in the excitation of the higher nucleon resonances, clearly seen in the photon absorption on proton and deutron.

Performance of a BGO calorimeter in a tagged photon beam from 260 to 1150 MeV

Abstract 20 BGO crystals with photomultiplier readout that form one sector of a large solid angle BGO calorimeter, were exposed to an intermediate energy tagged photon beam. Linearity, multiplicity and resolution results are presented and discussed.

Compton scattering by the proton through θcms = 75° and 90° in the Δ-resonance region

Abstract Differential cross sections for Compton scattering by the proton have been measured in the energy interval between 200 and 500 MeV at scattering angles of θ cms = 75° and θ cms = 90° using the CATS, the CATS/TRAJAN, and the COPP setups with the Glasgow Tagger at MAMI (Mainz). The data are compared with predictions from dispersion theory using photo-meson amplitudes from the recent VPI solution SM95. The experiment and the theoretical procedure are described in detail. It is found that the experiment and predictions are in agreement as far as the energy dependence of the differential cross sections in the Δ-range is concerned. However, there is evidence that a scaling down of the resonance part of the M 1+ 3 2 photo-meson amplitude by (2.8 ± 0.9)% is required in comparison with the VPI analysis. The deduced value of the M 1+ 3 2 - photoproduction amplitude at the resonance energy of 320 MeV is: |M 1+ 3 2 | = (39.6 ± 0.4) × 10 −3 m π + −1 .

Scattering of photons by the proton through θcms = 90° in the Δ-resonance region☆

Abstract The differential cross section for the scattering of photons by the proton was measured in the energy range Eγ = 250−500 MeV at the scattering angle θcms = 90° ± 3°. The tagged photon beam of the MAMI accelerator was used and both the scattered photon and the recoil proton were detected. The data essentially are consistent with dispersion theories, and remove the discrepancy that has existed above 290 MeV between theory and earlier published experimental results.

Compton scattering by the proton through θcms = 75° in the Δ-resonance region

Using the tagged-photon beam of MAMI (Mainz) differential cross-sections for Compton scattering by the proton through θcms = 75° have been measured for the Δ-resonance region from 200 to 410 MeV. The data put a new constraint on the M1+32 photoproduction amplitude in the resonance, |M1+32| = (39.6 ± 0.4) · 10−3mπ+−1 at 320 MeV, which is (2.8 ± 0.9) % less than given by the recent analysis SM95 of the Virginia group.

The argon cluster beam installed in the ADONE storage ring

Abstract The argon cluster beam, with a maximum thickness of 1.5 × 10 14 atoms/cm 2 , installed at Frascation the ADONE storage ring, is described. The cluster beam works at room temperature and is used as radiator to produce an intense tagged photon beam with energy up to 1.2 GeV. The argon bea, properties were measured using electrons stored in ADONE; the results are in good agreement with the expected values. The apparatus can produce cluster beams of higher thickness and work with different gases. It is suitable for internal target experiments with the 1.5 GeV stored electrons.

High-energy photoprotons from 12C

Abstract The spectra of fast photoprotons from the reaction 12 C(γ, p) 11 B have been measured at 14 bremsstrahlung end-point energies from 50 to 80 MeV. The main feature of the observed cross sections are compatible with a direct interaction of the photon with single nucleons. The experimental results are discussed in terms of momentum distribution of 1p and 1s protons between 1.5 fm −1 and 2.0 fm −1 .

GRAAL: a polarized γ-ray beam at ESRF☆

The GRAAL facility produces a highly polarized gamma-ray beam by Compton scattering of laser photons on the electrons of the European Synchrotron Radiation Facility (ESRF) at Grenoble. Preliminary results have been obtained with the LAGRANGE detector showing its excellent performances.