The behaviour of BGO sectors, designed for an electromagnetic calorimeter to be operated at up to 2 GeV, is considered in relation to the different terms that contribute to the overall BGO resolution and to the techniques that can be adopted to reduce them to a minimum. In particular, the measurements of light collection uniformity and energy resolution obtained on a large number of sectors are reported, and their effect on the overall BGO resolution analyzed

The study of meson photoproduction on the nucleon is a very important tool to complete the puzzle of baryon excited states. GRAAL aim is the measurement of cross sections and of beam asymmetries for all the photonuclear reactions accessible in the energy range from 600 MeV up to 1.5 GeV. In the following preliminary results of the Sigma beam asymmetry for omega photoproduction on the free proton in Hydrogen and on the quasi-free nucleon in Deuterium are shown. GRAAL is the first experiment in which both the charged and the radiative decay of omega meson are studied. Since the beam asymmetry is independent of the decay mode, the comparison of the results from the two channel allows an important check on data consistency. Results on the free proton are in good agreement with theoretical prediction from Zhao model and confirm the presence of P(13)(1720) state. The analysis performed for the radiative decay is applied to the process of. photoproduction on the quasi free nucleon in Deuterium.

The SPARX project consists in an X-ray-FEL facility jointly supported by MIUR (Research Department of Italian Government), Regione Lazio, CNR, ENEA, INFN and Rome University Tor Vergata. It is the natural extension of the ongoing activities of the SPARC collaboration. The aim is the generation of electron beams characterized by ultra-high peak brightness at the energy of I and 2 GeV, for the first and the second phase respectively. The beam is expected to drive a single pass FEL experiment in the range of 13.5-6 nm and 6-1.5 nm, at 1 GeV and 2 GeV respectively, both in SASE and SEEDED FEL configurations. A hybrid scheme of RF and magnetic compression will be adopted, based on the expertise achieved at the SPARC high brightness photoinjector presently under commissioning at Frascati INFN-LNF Laboratories (1,2). The use of superconducting and exotic undulator sections will be also exploited. In this paper we report the progress of the collaboration together with start to end simulation results based on a combined scheme of RF compression techniques.

The frontal collisions of a laser beam with relativistic electrons result in Compton-backscattered photons. The energy of these photons is dependent on the laser and electron energy in the range from kilo-electron-volts to tens of mega-electron-volts. In a sufficiently narrow backscattering angle the photons are nearly monochromatic. Over the past 30 years there have been several attempts to produce photon beams by laser backscattering from relativistic electrons stored in magnetic ring structures. One aim is to produce photons in the high mega-electron-volt energy range with fluxes useful for nuclear physics research; another is to produce photons in the high kilo-electron-volt energy range, which would be useful for medical applications, such as coronary angiography or treatment of tumour. Our present interest is to investigate the possibility of using 34 keV to 10 MeV photon beams for applications in stereotactic functional radiosurgery. We foresee the possibility of neurosurgical operations through the intact skull with precise and effective destruction of deeply lying millimetre-sized targets with minimal effects on intervening structures, high reproducibility and good prediction of the results. Our paper presents: a Monte Carlo study of radiosurgery based on cross firing with 34 keV to 100 MeV photon beams and 200 and 580 MeV proton beams, a theoretical description of the kinematics of Compton backscattering and estimates of the backscattered photon flux from several combinations of laser cavities at Nd:YAG (1.17 eV) and CO-2 (0.117 eV) laser energies and electron storage rings energies in the range 0.1-1.3 GeV. As examples, existing magnetic structures, such as the DA-PHI-NE Accumulator in the lower energy range and the Trieste Synchrotron Light Source ELETTRA in the higher energy range have been utilized in the calculations. The Monte Carlo study has shown that radiosurgery with photon beams of energies in mega-electron-volt energy range enables precise destruction of deeply lying millimetre-sized targets with minimal effects on intervening structures. Its precision is comparable to that of radiosurgery with 200-580 MeV proton beam, but our hope is that radiosurgery with lower energy photon beams could be more precise and less expensive. An average dose of 200 Gy can be delivered to a target of diameter 2 mm at the centre of an 18 cm diameter phantom in 1 h using photon beams of fluences 7.3 times 10-10, 1.8 times 10-10, 6.5 times 10-8, 2.2 times 10-8, 8.6 times 10-7 and 7.8 times 10-6 photons per second at 34 keV, 100 keV, 1 MeV, 3 MeV, 10 MeV and 100 MeV per cross section of beam of 2 mm diameter, respectively. 34-100 keV photon beams were studied in the hope of finding a strong enhancement of their efficiency if a stable high-Z element were to be introduced into the target's DNA. It is shown that, with a low-energy ring running at about 0.4 GeV and a Nd:YAG laser, it would be possible to obtain the required 3 MeV photon beam flux to deliver the average dose within 1 h, assuming an average distance between the source and the target of about 5 m. With a similar machine used at about 1.3 GeV and a CO-2 laser, a 3 MeV photon hewn is obtained and the exposure time can be reduced to less than 1 min, assuming a roughly 10 m distance between source and target (here a beam angle of 0.1 nuad only had to be considered due to the larger angular energy and yield spread). With a lower electron energy of 138 MeV and a CO-2 laser, a 34 keV photon beam can be produced. More than 45 h would be needed to deliver the same dose. We hope that this time could be shortened considerably if stable iodine were introduced into the target with the help of a DNA-seeking molecular carrier. In this case the geometrical precision would be further improved.

The features of the Graal experiment at ESRF are presented. The obtained results are discussed and future developments outlined. The Graal experiment started data taking in 1997. It was run for one year with the green laser line giving rise to a photon beam of maximum energy of 1100 MeV and for one year with UV multi-line and the corresponding gamma-ray beam of 1470 MeV maximum energy. Asymmetry data and cross sections have been produced for eta, pi 0 and pi + photoproduction channels providing, for these reactions, the most extended and coherent data base available until now. Future developments of the experiment will include the study of the same channels with deuteron target and the study of the photoreaction mechanism on the quasi-free neutron. The use of a polarised target of new concept will allow to access double polarisation observables for meson photoproduction on polarised proton and polarised neutron. Finally the increase in the maximum photon energy, up to 1.8 GeV will allow to study in details eta' photoproduction and to reach the threshold for scalar mesons production

The Sigma beam asymmetry in eta' photoproduction off the proton was measured at the GrAAL polarised photon beam with incoming photon energies of 1.461 and 1.480 GeV. For both energies the asymmetry as a function of the meson production angle shows a clear structure, more pronounced at the lowest one, with a change of sign around 90 degrees. The observed behaviour is compatible with P-wave D-wave (or S-wave F-wave) interference, the closer to threshold the stronger. The results are compared to the existing state-of-the-art calculations that fail to account for the data.

We present the analysis of data performed in order to identify the events of the gamma + n -> pi(-) + p reaction obtained by bombarding a liquid Deuterium target with a polarised. beam of 0.55-1.5 GeV at the Graal-experiment. We show the effect of different kinematic and hardware constraints used to reduce the contamination coming from the concurrent reaction channels. By the simulation we estimate the contamination degree due to the other reaction channels so we can test the reliability of our method. We describe a new three-dimensional cut based on the Fermi momentum reconstruction and its effect on the suppression of the concurrent double charged pion photoproduction. We present the preliminary beam asymmetry Sigma of the pi(-) fotoproduction off quasi-free neutron up to about theta(c.m.), (pi-) = 165 degrees together with some theoretical multipolar analysis. For a comparison we also report the data present in literature on the same reaction for E(gamma) -850-1740 MeV and theta(c.m.), (pi-) <= 105 degrees.

The double polarization (beam-recoil) observables O(x) and O(z) have been measured for the reaction gamma p -> K(+) Lambda from threshold production to E gamma similar to 1500 MeV. The data were obtained with the linearly polarized beam of the GRAAL facility. Values for the target asymmetry T could also be extracted despite the use of an unpolarized target. Analyses of our results by two isobar models tend to confirm the necessity to include new or poorly known resonances in the 1900 MeV mass region.

The extraction of resonance parameters from meson photo-reaction data is a challenging effort, that would greatly benefit from the availability of several polarization observables, measured for each reaction channel on both proton and neutron targets. In the aim of obtaining such complete experiments, polarized photon beams and targets have been developed at facilities, worldwide. We report on the latest results from the LEGS and GRAAL collaborations, providing single and double polarization measurements on pseudo-scalar meson photo-production from the nucleon.

New experimental approach to study meson photoproduction in nuclei is discussed. It is based on the measurement of the recoil nucleon as a tagger for identification of the initial step of reaction. Propagation of mesons and nucleons within a nucleus is described by the Intra-Nuclear Cascade (INC) model. Simulations and preliminary experimental data for the deuteron target obtained at GRAAL are presented. (c) 2008 Elsevier B.V. All rights reserved.

The photoproduction of double pi(0) on the neutron is studied in the beam energy range of 0.6 up to 1.5 GeV, using a liquid deuterium target. The cross section and the beam asymmetry are extracted and compared to those previously obtained on a proton target. The theoretical interpretation of these results is given using different models. (c) 2007 Elsevier B.V. All rights reserved.

The total photoabsorption cross section on a free proton was measured at the GRAAL facility in the energy range E-gamma = 600-1500 MeV. The large-aperture LAGRAN gamma E detector and a liquid hydrogen target were used in the experiment performed with a back-scattered Compton gamma beam. To improve the accuracy, two alternative methods were employed. First, a subtraction method of using empty-target measurements allowed the cross section sigma(tot) to be evaluated directly because of a low level of the electromagnetic background. Second, an algorithm for evaluating sigma(tot) on the basis of summing the dominating partial cross sections was developed. Experimental results obtained for sigma(tot) by the two methods are compared with existing data.