Beam collimation and bolusing material optimizations for 10boron neutron capture enhancement of fast neutron (BNCEFN): definition of the optimum irradiation technique.

PURPOSE: In boron-10 neutron capture enhancement of fast neutron irradiation (BNCEFN), the dose enhancement is correlated to the 10B concentration and thermal neutron flux. A new irradiation technique is presented to optimize the thermal neutron flux. METHODS AND MATERIALS: The coupled FLUKA and MCNP-4A Monte Carlo codes were used to simulate the neutron production and transport for the Nice and Orleans facilities. RESULTS: The new irradiation technique consists of a 20-cm lead blocks additional collimator, placed close to the patient's head, which is embedded in a pure graphite cube. A 24-fold thermal neutron flux increase is calculated between a 5 x 5 cm2 primary collimated field, with the patient's head in the air, and the same field size irradiated with the optimum irradiation technique. This increase is more important for the p(60)+Be Nice beam than for the p(34)+Be Orleans one. The thermal neutron flux is 2.1 x 10(10) n(th)/Gy for each facility. Assuming a 100 microg/g 10B concentration, a physical dose enhancement of 22% is calculated. Moreover, the thermal neutron flux becomes independent of the field size and the phantom head size. CONCLUSION: This technique allows conformal irradiation of the tumor bed, while the thermal neutron flux is enhanced, and spreads far around the tumor.

Combined use of FLUKA and MCNP-4A for the Monte Carlo simulation of the dosimetry of 10B neutron capture enhancement of fast neutron irradiations.

Boron neutron capture enhancement (BNCE) of the fast neutron irradiations use thermal neutrons produced in depth of the tissues to generate neutron capture reactions on 10B within tumor cells. The dose enhancement is correlated to the 10B concentration and to thermal neutron flux measured in the depth of the tissues, and in this paper we demonstrate the feasibility of Monte Carlo simulation to study the dosimetry of BNCE. The charged particle FLUKA code has been used to calculate the primary neutron yield from the beryllium target, while MCNP-4A has been used for the transport of these neutrons in the geometry of the Biomedical Cyclotron of Nice. The fast neutron spectrum and dose deposition, the thermal flux and thermal neutron spectrum in depth of a Plexiglas phantom has been calculated. The thermal neutron flux has been compared with experimental results determined with calibrated thermoluminescent dosimeters (TLD-600 and TLD-700, respectively, doped with 6Li or 7Li). The theoretical results were in good agreement with the experimental results: the thermal neutron flux was calculated at 10.3 X 10(6) n/cm2 s1 and measured at 9.42 X 10(6) n/cm2 s1 at 4 cm depth of the phantom and with a 10 cm X 10 cm irradiation field. For fast neutron dose deposition the calculated and experimental curves have the same slope but different shape: only the experimental curve shows a maximum at 2.27 cm depth corresponding to the build-up. The difference is due to the Monte Carlo simulation which does not follow the secondary particles. Finally, a dose enhancement of, respectively, 4.6% and 10.4% are found for 10 cm X 10 cm or 20 cm X 20 cm fields, provided that 100 micrograms/g of 10B is loaded in the tissues. It is anticipated that this calculation method may be used to improve BNCE of fast neutron irradiations through collimation modifications.

Light induced H2 evolution in a hydrogenase-TiO2 particle system by direct electron transfer or via rhodium complexes.

Three different hydrogenases (isolated from Clostridium pasteurianum, Desulfovibrio desulfuricans strain Norway 4 and D. baculatus 9974) added to a suspension of TiO2 (anatase) powder are able to catalyze H2 evolution under band gap illumination of the semiconducting particles, and in the presence of EDTA or methanol as electron donor. This H2 production can be obtained by the direct electron transfer from the conduction band of the TiO2 particles to the active site of the enzyme at pHs higher than 7. This mediator-independent charge transfer is more efficient with C. pasteurianum and D. baculatus 9974 hydrogenases, and in the presence of methanol. Rhodium tris- and bis-bipyridyl complexes can act efficiently as electron carriers from the supporting particles to the adsorbed enzyme molecules in cases where the direct transfer is inefficient.

Performance of sulfur dioxide passive monitors.

The following four commercial sulfur dioxide passive monitors were tested for performance and realiability: DuPont Pro-Tek C-20 air monitoring badges; MSA Vaporgard Dosimeter tubes; REAL BioBadges; and 3M Sulfur Dioxide Nutshell monitors. The experiments conducted were designed to test factors critical to the operation of passive samplers: accuracy and precision; capacity; stability; analytical recovery; and the effects of exposure time, concentration, humidity, face velocity, orientation, chemical interference, and temperature. The DuPont Pro-Tek badges performed satisfactorily for all the factors tested, and the REAL BioBadges performed satisfactorily except for the instability of the SO2/tetrachloromercurate complex when stored. An alternate monitoring system, REAL BioBadges containing deionized water absorbent had a limited capacity. Only the MSA dosimeters exhibited unsatisfactory performance. The 3M Nutshell monitor was withdrawn by the manufacturer after only partial evaluation.

[Evaluation of the degree of protection provided by a cartridge-mask system during working with asbestos]. / Evaluation du degré de protection d'un système masque-cartouche lors d'un travail avec de l'amiante.

During removal of sprayed-on asbestos coating workers are exposed to high airborne fiber concentrations. The true protection of negative pressure respirators under working conditions was evaluated during an asbestos abatement project. A modification allowing air sampling inside the mask is described. The values for samples collected inside a full-face mask ranged between 0.4 and 5% of the concentrations measured outside. These values were considerably lower than those found inside a half-mask.

Isolation and characterization of the polypeptide components from light-harvesting pigment-protein complex B800--850 of Rhodopseudomonas capsulata.

The light-harvesting bacteriochlorophyll-carotenoid-protein complex B800--850 has been isolated from membranes of the phototroph-negative mutant strain Y5 of Rhodopseudomonas capsulata. The three polypeptides of the complex have been found to be soluble in chloroform-methanol (1:1, v/v) in the presence of 0.1 M ammonium acetate. They were extracted from the complex and separated by gel filtration on Sephadex LH-60 in the same solvent mixture. Minimum molecular weights based on amino acid composition are 12 000, 9300, and 5100. Values previously determined by sodium dodecyl sulfate/polyacrylamide gel electrophoresis are 14 000, 10 000 and 8000. The two smaller polypeptides (polarities 31% and 39%) are completely soluble in chloroform/methanol/ammonium acetate while the largest and most polar (41%) polypeptide is only partially soluble. The largest polypeptide contains no tryptophan. The middle polypeptide contains no cysteine and arginine, while the small polypeptide lacks cysteine. Methionine is shown to be the amino terminus for the small and middle polypeptides by two independent methods (Edman degradation and dansylation). Both methods also indicated that the N terminus of the 14 000 polypeptide seems to be blocked. Partial N-terminal amino acid sequences were obtained for the two smaller polypeptides. No homology between the two proteins was observed.

Hydrophobic membrane protein from chromatophores of Rhodospirillum rubrum. Structural and spectroscopic studies of monolayers and multilayers.

A hydrophobic, lipid- and pigment-free polypeptide from the chromatophore membrane of Rhodospirillum rubrum was spread from chloroform/methanol, pyridine and formic acid solutions at an air-water interface. Surface pressure versus area isotherms of the monolayers formed at the interface were partially dependent upon the spreading solvent used. From the surface area at 20 dynes/cm compression, an average molecular area of 12.9 nm2/molecule was calculated for a polypeptide monolayer spread from chloroform/methanol. Multilayers built up on germanium plates at different surface pressures were subjected to attenuated total reflection infrared spectroscopy. In all cases the amide I and II absorption bands were typical of alpha-helical and random conformations. Electron microscopy of transferred monolayers replicated by rotary platinum shadowing revealed domains of regular texture in specimens prepared at 20 dynes/cm. Such domains were virtually absent in specimens prepared at 10 and 30 dynes/cm. Light optical diffractometry of the ordered arrays yielded a smallest repetitive area of 13.5 nm2 which agrees well with the molecular area obtained from the monolayer surface. Although no drastic changes in secondary structure were detected in the course of this study, some conformational changes are indicated by solvent-dependent differences in the surface pressure versus area isotherms.