Emission patterns of neutral pions in 40 A MeV Ta+Au reactions

Differential cross sections of neutral pions emitted in 181Ta + 197Au collisions at a beam energy of 39.5A MeV have been measured with the photon spectrometer TAPS. The kinetic energy and transverse momentum spectra of neutral pions cannot be properly described in the framework of the thermal model, nor when the reabsorption of pions is accounted for in a phenomenological model. However, high energy and high momentum tails of the pion spectra can be well fitted through thermal distributions with unexpectedly soft temperature parameters below 10 MeV.Comment: 16 pages (double-spaced), 5 figures; corrections after referee's comments and suggestion

Systematics of pion emission in heavy ion collisions in the 1A GeV regime

Using the large acceptance apparatus FOPI, we study pion emission in the reactions (energies in GeV/nucleon are given in parentheses): 40Ca+40Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), 96Ru+96Ru (0.4, 1.0, 1.5), 96Zr+96Zr (0.4, 1.0, 1.5), 197Au+197Au (0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include longitudinal and transverse rapidity distributions and stopping, polar anisotropies, pion multiplicities, transverse momentum spectra, ratios for positively and negatively charged pions of average transverse momenta and of yields, directed flow, elliptic flow. The data are compared to earlier data where possible and to transport model simulations.Comment: 56 pages,42 figures; to be published in Nuclear Physics

Age-dependent calibration factors for in-vivo monitoring of 131I in thyroid using Monte Carlo simulations

International audienceFollowing a nuclear incident, 131I monitoring is usually carried out by performing in vivo measurements of the retained activity in the thyroid. The measurement equipment needs to be calibrated in order to convert thyroid count rates into retained activity. This calibration relies on measurements or Monte Carlo computations using appropriate anthropomorphic model of the thyroid gland contaminated with a known activity of the radionuclide of interest. Several factors influence the calibration procedure, such as the geometry, the individual anatomical characteristics, and the presence of 131I in other organs and tissues of the body. In particular, given their age-dependent anatomical changes, appropriate values of detector efficiencies for children are necessary to reduce results uncertainties when children are involved. In this study, Monte Carlo simulations for several detectors and phantoms of different ages have been performed to investigate the variation of the detection efficiency with distance, age and thyroid volume. It was found that the counting efficiency varies linearly with the thyroid volume and inversely with the squared detector-phantom distance. Age-dependent correction factors to be applied to the adult calibration factor have been derived and can be used when calibration factors for children are not available. © 2019 Elsevier Lt

The influence of nuclear models and Monte Carlo radiation transport codes on stray neutron dose estimations in proton therapy.

Purpose: This study investigates the influence of several Monte Carlo radiation transport codes and nuclear models on the simulation of secondary neutron spectra and its impact on calculating and measuring the neutron doses in proton therapy. Materials and methods: Three different multi-purpose Monte Carlo radiation transport codes (FLUKA, MCNPX, Geant4) were used together with different available nuclear models, to calculate secondary neutron energy spectra at various points inside a water tank phantom with PMMA walls using a 10 × 10 cm2 rectangular, mono-energetic proton beam (110 MeV, 150 MeV, 180 MeV, 210 MeV). Using Kerma approximation secondary neutron doses were calculated applying fluence-to-dose equivalent conversion coefficients in water. Moreover, the impact of varying spectra for electrochemically etched CR39 detector calibration was analyzed for different codes and models. Results: In distal positions beyond the Bragg peak, results show largest variations between the codes, which was up to 53% for the high energy neutron fluence at 16 cm from the Bragg peak of the 110 MeV proton beam. In lateral positions, the variation between the codes is smaller and for the total neutron fluence within 20%. Variation in the nuclear models in MCNPX was only visible for the proton beam energies of 180 and 210 MeV and modeling the high energy neutron fluence which reached up to 23% for 210 MeV at 11 cm lateral from the beam axis. Impact on neutron dose equivalent was limited for the different models used (<8%) while it was pronounced for the different codes (45% at 16 cm from the Bragg peak of the 110 MeV proton beam). CR39 calibration factors in lateral positions were on average varying 10% between codes and 5% between nuclear models. Conclusions: This study demonstrated a large impact on the neutron fluence spectra calculated by different codes while the impact of different models in MCNPX proved to be less prominent for the neutron modeling in proton therapy

EURADOS intercomparison exercise on MC modeling for the <em>in-vivo</em> monitoring of Am-241 in skull phantoms (Part I).

An intercomparison on in-vivo monitoring for determination of 241Am in three skull phantoms was launched by EURADOS in 2011. The project focused on the measurement and estimation of 241Am activity in the human skull. Three human skull phantoms of different complexity were used. A Monte Carlo (MC) exercise with the voxel representations of the real phantoms was also launched in September 2012. The main goals of the project were to investigate the use of MC techniques for efficiency calibrations for body monitoring systems for a special calibration exercise and compare the approaches of participating laboratories. The full MC exercise consisted of three tasks with increasing difficulty, to test the extent of the skills of each participating laboratory. The first task in this intercomparison was to simulate a specified detector and a well defined semi-skull phantom. All parameters of the simulation, including photon yield, material property and geometry were fixed. This paper provides an overview of the participants&#39; results and analyses of the issues presented by this first task. The majority of the responses did not need any correction and the number of incorrect results was less than in a previous exercise of a similar kind. Overall knowledge in this research area utilising MC techniques appears to have improved and the repetition of the intercomparison exercise has positively affected the skills of the participating laboratories

Monte Carlo calculation of organ and effective dose rates from ground contaminated by Am-241: Results of an international intercomparison exercise

International audienceAn intercomparison exercise is described that examines Monte Carlo modelling of anthropomorphic voxel phantoms in an idealized ground-contamination photon exposure scenario. Thirteen participants calculated and submitted organ and effective dose rates for comparison against a set of verified reference solutions. The effective dose rates are shown to agree with the reference value to within reasonable statistical uncertainties in five of the cases, though in only one of those was similar agreement also demonstrated in the evaluation of all requested organ dose rates. Orders-of-magnitude differences in doses are seen for some of the other participants, both internally within their own dataset and also relative to the reference solutions. Following limited feedback and suggestions from the organizer, up to two sets of revised solutions were resubmitted by some of the participants; these generally exhibited improved agreement, though not always. The overall observations and conclusions from this intercomparison exercise are summarized and discussed

EURADOS intercomparison exercise on MC modelling for the in-vivo monitoring of AM-241 in skull phantoms (Part II and III)

International audienceAn intercomparison on in-vivo monitoring for determination of Am-241 in three skull phantoms was launched by EURADOS in 2011. The project focused on measurement and estimation of the activity of Am-241 in the human skull. Three human skull phantoms of different complexity were used. A Monte Carlo (MC) intercomparison exercise with the voxel representations of the physical phantom was launched additionally in September of 2012. The main goals of the action were (1) to investigate the different methodologies for developing MC calibrations that might arise from a complex radiological assessment and (2) to compare individual approaches of the participating laboratories in order to determine international guidance for best practice. The MC exercise consisted of three tasks with increasing difficulty, in order to test the extent of skills needed by the participating laboratory. The first task was to simulate a given detector and a well-defined semi-skull phantom. The second and third tasks presented in this paper-introduced more complex simulations with individual geometry and real detector modelling. The paper provides an overview of the participant's results, analyses of the observed issues concerning tasks two and three, and a general evaluation of the whole project. © 2015 Elsevier Ltd