Limits on light-speed anisotropies from Compton scattering of high-energy electrons.

The possibility of anisotropies in the speed of light relative to the limiting speed of electrons is considered. The absence of sidereal variations in the energy of Compton-edge photons at the European Synchrotron Radiation Facility's GRAAL facility constrains such anisotropies representing the first nonthreshold collision-kinematics study of Lorentz violation. When interpreted within the minimal standard-model extension, this result yields the two-sided limit of 1.6×10(-14) at 95% confidence level on a combination of the parity-violating photon and electron coefficients (κ(o+))(YZ), (κ(o+))(ZX), c(TX), and c(TY). This new constraint provides an improvement over previous bounds by 1 order of magnitude.

Measurements of H-->D-->(gamma-->,pi) and implications for the convergence of the Gerasimov-Drell-Hern integral.

We report new measurements of inclusive pi production from frozen-spin HD for polarized photon beams covering the Delta(1232) resonance. These provide data simultaneously on both H and D with nearly complete angular distributions of the spin-difference cross sections entering the Gerasimov-Drell-Hearn (GDH) sum rule. Recent results from Mainz and Bonn exceed the GDH prediction for the proton by 22 microb, suggesting as yet unmeasured high-energy components. Our pi0 data reveal a different angular dependence than assumed in Mainz analyses and integrate to a value that is 18 microb lower, suggesting a more rapid convergence. Our results for deuterium are somewhat lower than published data, considerably more precise, and generally lower than available calculations.

Simultaneous photoproduction of eta and pi0 mesons on the proton.

The analysis of the gammap-->etapi(0)p reaction has been performed using data from the GRAAL experiment. The total and differential cross sections and the beam asymmetry have been obtained from threshold up to 1.5 GeV of beam energy. The two resonances S11(1535) and Delta(1700) are expected to be excited in the intermediate states of this reaction. The results are used to test predictions based on the assumption that both resonances are dynamically generated from the meson-baryon interaction provided by chiral Lagrangians. The term involving the Delta(1700) excitation, followed by the decay into etaDelta(1232), is found to be dominant.

Double pi(0) Photoproduction on the Proton at GRAAL.

The double pi(0) photoproduction off the proton has been measured in the beam energy range of 0.65-1.5 GeV. The total and differential cross sections and the Sigma beam asymmetry were extracted. The total cross section measured for the first time in the third resonance region of the nucleon shows a prominent peak. The interpretation of these results by two independent theoretical models infers mostly the selective excitation of P11- and D13-nucleon resonances.

Photon beams for radiosurgery produced by laser Compton backscattering from relativistic electrons.

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 CO2 (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 x 10(10), 1.8 x 10(10), 6.5 x 10(8), 2.2 x 10(8), 8.6 x 10(7) and 7.8 x 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 CO2 laser, a 3 MeV photon beam 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 mrad only had to be considered due to the larger angular energy and yield spread). With a lower electron energy of 138 MeV and a CO2 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.