C. Birattari

Secondary neutron and photon dose in proton therapy

BACKGROUND AND PURPOSE The dose due to secondary neutrons and photons in proton therapy was estimated with Monte Carlo simulations. Three existing facilities treating eye and deep-seated tumours were taken into account. The results of the calculations related to eye proton therapy were verified with measurements. MATERIALS AND METHODS The simulations were performed with the FLUKA code. Neutron fluence was measured inside an Alderson phantom (type ART) with activation techniques. RESULTS The maximum dose due to secondaries produced in a passive beam delivery system was estimated to be of the order of 10(-4) and 10(-2) Gy per therapy Gy for eye and deep tumour treatments, respectively. In the case of irradiations of deep-seated tumours carried out with an active system, the dose was of the order of 10(-3) Gy per therapy Gy. CONCLUSIONS The dose due to secondaries depends on the geometry of the beam delivery system and on the energy of the primary beam and is lower in the healthy tissues distant from the target volume.

An extended range neutron rem counter

Abstract Extensive Monte Carlo calculations have been carried out to assess the possibility of extending the sensitivity of a neutron rem counter of the Andersson-Braun type up to several hundred MeV. The validity of the model adopted has first been checked by comparing with experimental data the calculated response curve and the angular dependence of the sensitivity for a well known commercial rem counter. Next, a number of modifications to the configuration of the moderator-attenuator have been investigated. The response functions and angular distributions produced by two simple solutions yielding an instrument with a sensitivity extended up to 400 MeV are presented. The response of the original rem counter and of its two modified versions to nine test spectra has also been calculated. The resulting instrument is transportable rather than portable, but the availability of an extended range neutron survey meter would be of great advantage at medium and high energy particle accelerator facilities.

Similarity in metabolic patterns of different chemical species of vanadium in the rat

To gain information about the influence of the oxidation state of vanadium on its metabolic behavior, different 48V-labeled vanadium compounds, such as cationic VO2+(V), VO2+(IV), V3+(III), and anionic V4O12(3-)(V), VS4(3-)(V) species were prepared and intravenously injected into rats. The 48V radioactivity was measured in whole tissues as well as in nuclei, mitochondria, lysosomes, microsomes, and cytosols from liver and kidney homogenates. The distribution of 48V radioactivity between the plasma components was investigated using gel filtration of the 48V-labeled plasma. The findings indicate that there are common pathways of the different chemical forms of vanadium in animals. The similarities are referred to the distribution in different tissues and their intracellular distribution as well as to the transport in the blood, in which 48V was always found in the plasma bound to transferrin. The results obtained tend to exclude a possible influence of the oxidation state of vanadium on its metabolism and support the existence in the body of two mechanisms of conversion of different chemical forms of vanadium ions to one with the same valence.

Pre-equilibrium processes in (p,n) reactions

Abstract Cross sections of (p, n) reactions in 89 Y, 160 Gd and 169 Tm have been measured for incident proton energies from 5 to 45 MeV. The contributions to the cross section from compound-nucleus evaporation and from pre-equilibrium neutron emission are evaluated, and found to be in accord with the experimental results of this work, as well as with those previously reported in the literature for target nuclei of A > 60. In the equilibration process, the competition between particle emission and internal transition into states with higher exciton number is studied, and the relevant branching ratio is deduced.

Calibration of the neutron rem counter LINUS in the energy range from thermal to 19 MeV

Abstract LINUS is a neutron rem counter of the Andersson-Braun type with a modified moderator-attenuator and a calculated response function which extends up to 400 MeV. Preliminary experimental investigations with uncalibrated neutron sources have already confirmed the expected much increased sensitivity of this instrument with respect to conventional remmeters when exposed to radiation fields with a large component of high energy neutrons. The present paper reports on the calibration of the monitor with monoenergetic neutrons in the range from thermal to 19 MeV. At 14 MeV its response is about 40% larger than that of a conventional Andersson-Braun monitor and about 55% larger at 19 MeV. The angular dependence and the range of linearity of the response have also been investigated.

Preparation of high specific activity radiotracers for radioanalytical studies

High specific activity radiotracers are very suitable for studies related to the toxicological impact of trace elements onto human health. In order to investigate the metabolic behaviour of Low Level Exposure (LLE) to trace elements, it is necessary to carry out in-vitro and in-vivo experiments with tracers whose concentration is of the same order of magnitude as the present environmental exposure values (ng-μg/kg day). Preparations, separations and purifications of some No Carrier Added (NCA) radiotracers (48V,95m,96Tc,195m,g,197m,gHg,199Au,202Tl) produced by either cyclotron or nuclear reactor irradiation, are presented and discussed. This work reviews the more recent advances in this field carried out by our groups.

Thin-target excitation functions and optimization of simultaneous production of NCA copper-64 and gallium-66,67 by deuteron induced nuclear reactions on a natural zinc target

Copper-64 is a radionuclide suitable for labeling of a wide range of radiopharmaceuticals for PET imaging, as well as systemic or local radioimmunotherapy of tumors. Among the possible methods for cyclotron production of No Carrier Added (NCA) 64Cu (61Cu), we investigated the deuteron irradiation on natural Zn target, via (d,axn) and (d,2pxn) nuclear reactions. This paper reports the preliminary results about the experimental determination and theoretical calculation of thin-target excitation functions in the energy range up to 19 MeV for 61Cu, 64Cu, 66Ga, 67Ga, 65Zn and 69mZn. A fast selective radiochemical separation of NCA 64Cu from Zn target and Ga radionuclides, with quality control tests is described too.

Measurements and characterization of high-energy neutron fields

Abstract The application of the Monte Carlo code FLUKA in the simulation of the stray radiation field around high energy accelerators has been tested against experimental results obtained at the 250 GeV/ c hadron beam at CERN. The present paper demonstrates the validity of the code in predicting neutron spectra in very complex geometrical conditions with large attenuation factors involved. The same experimental data served as a confirmation of the behaviour of a modified Andersson-Braun rem counter with a response function extended up to hundreds of MeV (LINUS). The present results confirm previous experimental evidence of the much increased response of this monitor with respect to conventional instruments when used in radiation fields with a substantial high energy neutron component.

Kr(p, xn) excitation functions and 81Rb−81mKr generator studies

Excitation functions for (p, xn) reactions on natural thin krypton gas targets in the 10–45 MeV proton energy range were measured. Different thick target designs for 81Rb−81mKr production purposes were studied. Removability of 81mKr in water solution or in the gaseous phase for a cation exchange generator type was determined.

Preparation of 203Pb compounds for studies on pathway and effects of lead pollution.

Successful production of 203Pb radioisotope with the proton beam of the Milan AVF cyclotron has made possible to start a wide range research program on pathway and effects of lead pollution. Irradiation and radiochemical separation techniques are described in some detail together with the synthesis of 203Pb tetraethyl. Applications to environmental problems carried out so far include chemical biological and biochemical studies. Preliminary results and the relevant experimental details are reported concerning lead uptake by different biological systems, and the distribution of lead in the air.