The environmental radiation field at the Martian surface consists mainly of Galactic Cosmic Rays (GCR) and charged particles ejected during the Solar Particle Events (SPE). Interactions between these ...radiation fluxes and the regolith result in a complex radiation field that varies both as a function of depth and time and can only be quantified using radiation transport models. We first describe here the main issues and constraints in deriving Martian dose rates. Preliminary results, obtained using the GEANT4 Monte Carlo simulation tool kit, suggest the surface dose rate is ∼63
mGy
a
−1 during quiet periods in solar activity. The accuracy of the model predictions has been tested by comparison with published observations of cosmic ray dose-rate variation in the Earth's atmosphere.
The flux dropout of relativistic electrons in the earth’s outer radiation belt, during the main phase of the 26 March 1995 magnetic storm is examined. Outer belt measurements by the Radiation ...Environment Monitor, REM aboard the STRV-1b satellite are presented to characterize this dropout. In order to simulate the dynamics of the electron belt during the storm main phase a particle tracing code was developed which allows to trace the trajectories of equatorially mirroring electrons in a dynamic magnetospheric electromagnetic field. Two simulations were performed in a non-stationary magnetic field, one taking only the induced electric field into account (fully adiabatic motion), and one with an additional non-stationary convection electric field. The simulations show, that adiabatic deceleration can produce the observed count rate decrease and also the observed inward motion of the count rate peak. The convection electric field causes diffusion, which can take particles from low
L values out to the magnetopause and contribute to an additional loss of particles, which is suggested by the observations.
The wide range of physics models available in GEANT4, as well as its outstanding geometry and visualization tools, has made it gain widespread use in several fields of physics, like high energy, ...medical, space, etc. Nevertheless the use of GEANT4 often requires a long learning-curve, which implies a good knowledge of C++ and the GEANT4 code itself. GAMOS facilitates the use of GEANT4 by avoiding the need to use C++, providing instead a set of user commands. One of the novelties of GAMOS with respect to similar simulation codes lies in its flexibility, which makes it appropriate for simulation in many physics fields. This flexibility is sustained by the wide range of geometrical configurations, primary generators and physics lists supported and by the comprehensive set of tools that help the user in extracting detailed information from the simulation through user commands. The use of the plug-in technology contributes to this flexibility, as it facilitates the extension of the framework to include extra functionality not foreseen by the framework authors. GAMOS counts already with several hundreds registered users in the five continents; while it is more frequently used in the medical physics field, its use has also been extended to other fields, like high energy physics, space physics, neutron shielding, etc.
The dynamics of the relativistic electron flux in the earth's outer radiation belt measured by the Radiation Environment Monitor aborad the STRV-1B satellite is presented from August 1994 to end of ...April 1996. During this period the earth's magnetosphere was driven by recurrent fast solar wind streams which had periodically compressed the magnetosphere and caused large variations of the trapped particle fluxes in the outer radiation belt. The periodic variations are characterized by a rapid depletion, strong and rapid increase and a more steady phase. The flux level reached depends on the velocity of the interacting solar wind stream. The effectiveness of the solar wind — magnetosphere interaction shows a semiannual modulation with a maximum during the equinoxes.
SONTRAC: An imaging spectrometer for MeV neutrons Miller, Richard S.; Macri, John R.; McConnell, Mark L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2003, Letnik:
505, Številka:
1-2
Journal Article
Recenzirano
An instrument capable of unambiguously determining the energy and direction of incident neutrons has important applications in solar physics, environmental monitoring, and medical/radiological ...sciences. The SOlar Neutron TRACking (SONTRAC) instrument is designed to operate in the neutron energy range of 20–250MeV. It is based on non-relativistic double scatter of neutrons off ambient protons within a block of scintillating fibers. Using this double-scatter mode it is possible to uniquely determine neutron energy and direction on an event-by-event basis. A fully operational science model of such an instrument has been built and its performance (energy resolution, angular resolution) calibrated at MeV energies. The science model consists of a 5×5×5cm3 cube of orthogonal plastic scintillating fiber layers. Two orthogonal imaging chains allow full 3D reconstruction of scattered proton particle tracks. We report the results of the instrument development and calibration efforts, and discuss ongoing developmental efforts to improve performance.
REM measurements aboard Mir during 1995 Bühler, P.; Desorgher, L.; Zehnder, A. ...
Advances in space research,
01/1998, Letnik:
21, Številka:
12
Journal Article
Recenzirano
Odprti dostop
Measurements of the South Atlantic Anomaly (SAA) made with the Radiation Environment Monitor (REM) aboard Mir from November 1994 to February 1996 are presented. During this period an increase of the ...SAA radiation by ≈25% is observed, which coincides with a lowering of the radio solar flux. Radio solar flux is one of the parameters controlling the earth's atmospheric distribution and with it the absorption of inner radiation belt protons forming the SAA. Due to the altitude gradient of the atmospheric density, the proton fluxes in the SAA are anisotropic (loss cone, east-west effect). The measured distribution can be accounted for by basic models.
We study the variation of the relativistic electron fluxes in the Earth's outer radiation belt during the March 26, 1995, magnetic storm. Using observations by the radiation environment monitor (REM) ...on board the space technology research vehicle (STRV-1b), we discuss the flux decrease and possible loss of relativistic electrons during the storm main phase. In order to explain the observations, we have performed fully adiabatic and guiding center simulations for relativistic equatorial electrons in the nonstationary Tsyganenko96 magnetospheric magnetic field model. In our simulations the drift of electrons through the magnetopause was considered as a loss process. We present our model results and discuss their dependence on the magnetospheric magnetic and electric field model, as well as on the prestorm fluxes used in the simulations. (Author)
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