Two hundred experimental photofissility data obtained in the quasi-deuteron region (~ 30-140 MeV) of photonuclear absorption covering the target nuclei 27Al, natTi, 51V, 154Sm, 174Yb, natHf, 181Ta, natW, natRe, natOs, natPt, 197Au, natTl, 208Pb, natPb and 209Bi have been analysed within the framework of the current two-step model for intermediate-energy photofission reactions. The incoming photon is assumed to be absorbed by a neutron-proton pair (Levinger's quasi-deuteron model), followed by a mechanism of evaporation-fission competition for the excited residual nuclei. The experimental features of photofissility have been reproduced successfully by the model.

The skyshine radiation phenomenon consists of the scattering of primary photon beams in the atmosphere above the roof of a medical linear accelerator facility, generating an additional dose at ground level in the vicinity of the treatment room. Thus, with respect to radioprotection, this situation plays an important role when the roof is designed with little shielding and there are buildings next to the radiotherapy treatment room. In literature, there are few reported skyshine-measured doses and these contain poor agreement with empirical calculations. In this work, we carried out measurements of skyshine photon dose rates produced from eight different 6 and 10 MV medical accelerators. Each measurement was performed outside the room facility, with the beam positioned in the upward direction, at a horizontal distance from the target and for a 40 cm × 40 cm maximum photon field size at the accelerator isocenter. Measured dose-equivalent rates results were compared with calculations obtained by an empirical expression, and differences between them deviated in one or more order of magnitude.

Cross section measurements for photofission induced in 209 Bi, nat Pt, 197 Au, nat Pt, nat W, 181 Ta, 51 V and nat Ti by 120 and 145 MeV quasi-monochromatic photon beams have been performed at the ROKK-1M facility (BINP, Novosibirsk). The fission yields have been obtained using Makrofol sheets as solid-state fission track detectors. Nuclear fissility values have been deduced on the basis of Levinger's modified quasi-deuteron model of photonuclear interaction, and compared with available literature data. The trend of fissility in the 60-145 MeV energy range has been analysed for various target nuclei as a function of energy and of the parameter Z 2 /A.

Photofission cross sections of 209 Bi, nat Pb, 197 Au, nat Pt, nat W, 181 Ta, 51 V and nat Ti nuclei have been measured at an incident photon energy of 100 MeV using monochromatic photons produced by Compton backscattering at the ROKK-1M facility (BINP, Novosibirsk). Detection of fission fragments has been performed by means of Makrofol track-etch detectors in close contact with metallic foils of the target elements. The values of fissility at 100 MeV deduced for the targets under investigation are found to range between 10 −4 and 10 −2 . The present results show consistency with the fissility trends calculated for 69 and 600 MeV monoenergetic photons using a formalism based on the current two-step model for intermediateenergy photofission reactions.

The effects of nucleon effective mass on the Pauli-blocking function are worked out. We have shown that such effects on the quasi-deuteron mechanism of photonuclear absorption are rather relevant. The Pauli-blocking function has been evaluated by applying a Monte Carlo calculation particularly suitable for simulation of intranuclear cascade processes of intermediate-energy nuclear reactions. The nucleon binding in the photonuclear absorption mechanism is taken into account accordingly.

Data related to 11 y of high-energy photon radiotherapy beam dosimetry are presented and analysed. Dosimetric evaluations were carried out using water phantoms and thimble ionisation chambers and are part of the radiation protection regulatory licensing process for medicine facilities of Brazilian government. Measurements were done at reference conditions for a standard absorbed dose of 100 cGy [cGy (=1 rad)]. The absolute per cent deviation between the measured and presumed delivered doses should not exceed the tolerance level of +/-3%. The first dosimetry survey from 1996 to 1998 showed a situation that was an object of concern. Deviations of 22 and 18.7% could be measured, although small deviations were also obtained. After 1998, the improvement in dosimetry quality control by the radiotherapy centres became clear, with most of the deviations situated within the +/-3% range. The decrease in the measured deviations presents the effective success of the Institute of Radiation Protection and Dosimetry audit programme for the improvement in the control of radiotherapy photon beams in Rio de Janeiro. Also, it is possible to recommend to Brazilian regulatory organisation a decrease in the tolerance level for dosimetric deviations in order to achieve a more precise dose delivered to patients in radiotherapy centres.

A study of photofission on " T a , ""W and ""Pt nuclei induced by monochromatic photons of 69MeV has been performed. The fission yields have been measured by using makrofoil sheets as fission-track detectors, in thick-target 277 geometry. The absolute photofission cross sections for the tantalum, tungsten and platinum targets are found, respectively, to be 4.8-t l.Opb, 5.2-t 1 I p b and 1O-t2pb, and the corresponding deduced fissilities are (3.2 -t 0.7) X (3.4 j: 0.8) X and (6.4 * 1.3) x NUCLEAR REACTIONS ""Ta(y, fission), ""W (7. Iission), and ""'Pt(7, fission) E? = 69 MeV; measured o(fission), deduced fissility.

The Brazilian national regulatory authority, National Commission of Nuclear Energy, requires that dose rates in the vicinity of teletherapy treatment rooms do not exceed the permissible limits for workers as well as members of the public, depending on the place considered. At the end of 2005, the Brazilian national regulatory authority reduced the permissible dose limit for controlled areas from 1000 to 400 microSv week(-1). Therefore, the aim of this work is to verify the adequacy of structural shielding to this new limit for telecobalt units that had their sources changed and clinic linear accelerators (ALs) installed before the end of 2005. Considering the ALs, measurements of dose rates in controlled areas did not exceed the new permissible limit, excepting for a single case. In the case of (60)Co units, a similar situation is observed for controlled areas, although several non-conformities to the limit of uncontrolled area could be observed.