[show abstract][hide abstract] ABSTRACT: We describe a Fast Neutron Imaging Telescope (FNIT) that is sensitive to neutrons in the energy range 3–100 MeV, optimized to study solar neutrons in the innermost heliosphere. The detection principle is based on multiple elastic neutron–proton scatterings in stacked organic scintillator layers. Plastic scintillator provides the proton target and is an efficient detector of charged particles. At the upper and lower face of each scintillator plate orthogonally oriented wavelength shifting fibers (∅ ∼ 1 mm) collect and guide the scintillation light to a multi-anode photomultiplier tube (MAPMT). The relative anode signals of the MAPMT register the interaction location while the total intensity of the signal is a measure of the recoil proton energy. Elastic scattering kinematics allows one to determine direction and energy spectrum of the primary neutron flux. A performance evaluation prototype has been built, and we show results from first laboratory measurements. We then present Monte Carlo simulation results to outline the performance of an optimized design.
[show abstract][hide abstract] ABSTRACT: We have developed a Monte Carlo code based on Geant4 to simulate the interaction of cosmic rays with the Martian atmosphere and soil. The code allows to compute the flux of secondary particles in the atmosphere and at ground level.The application allows to predict the radiation level on the Martian surface due to galactic cosmic rays and the effects of solar energetic particle events. We discuss main aspects of the code and present first simulation results.
Advances in Space Research 07/2013; · 1.18 Impact Factor
[show abstract][hide abstract] ABSTRACT: The radiation dose rates at flight altitudes can increase by orders of
magnitude for a short time during energetic solar cosmic ray events, so
called ground level enhancements (GLEs). Especially at high latitudes
and flight altitudes, solar energetic particles superposed on galactic
cosmic rays may cause radiation that exceeds the maximum allowed dosage
limit for the general public. Therefore the determination of the
radiation dose rate during GLEs should be as reliable as possible.
Radiation dose rates along flight paths are typically determined by
computer models that are based on cosmic ray flux and anisotropy
parameters derived from neutron monitor and/or satellite measurements.
The characteristics of the GLE on 15 April 2001 (GLE60) were determined
and published by various authors. In this work we compare these results
and investigate the consequences on the computed radiation dose rates
along selected flight paths. In addition, we compare the computed
radiation dose rates with measurements that were made during GLE60 on
board two transatlantic flights.
Journal of Physics Conference Series 02/2013; 409(1):2166-.
[show abstract][hide abstract] ABSTRACT: An overview is presented of basic results and recent developments in the field of cosmic ray induced ionisation in the atmosphere,
including a general introduction to the mechanism of cosmic ray induced ion production. We summarize the results of direct
and indirect measurements of the atmospheric ionisation with special emphasis to long-term variations. Models describing the
ion production in the atmosphere are also overviewed together with detailed results of the full Monte-Carlo simulation of
a cosmic ray induced atmospheric cascade. Finally, conclusions are drawn on the present state and further perspectives of
measuring and modeling cosmic ray induced ionisation in the terrestrial atmosphere.
Space Science Reviews 04/2012; 137(1):149-173. · 5.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: A brief review of the research of atmospheric effects of cosmic rays is presented. Numerical models are discussed, that are
capable to compute the cosmic ray induced ionization at a given location and time. Intercomparison of the models, as well
as comparison with fragmentary direct measurements of the atmospheric ionization, validates their applicability for the entire
atmosphere and the whole range of the solar activity level variations. The effect of sporadic solar energetic particle events
is shown to be limited on the global scale, even for the most severe event, but can be very strong locally in polar regions,
affecting the physical-chemical properties of the upper atmosphere, especially at high altitudes. Thus, a new methodology
is presented to study cosmic ray induced ionization of the atmosphere in full detail using realistic numerical models calibrated
to direct observations.
[show abstract][hide abstract] ABSTRACT: The calculation of particle trajectories in the Earth's magnetic field has been a subject of interest since the time of Störmer.
The fundamental problem is that the trajectory-tracing process involves using mathematical equations that have `no solution
in closed form'. This difficulty has forced researchers to use the `brute force' technique of numerical integration of many
individual trajectories to ascertain the behavior of trajectory families or groups. As the power of computers has improved
over the decades, the numerical integration procedure has grown more tractable and while the problem is still formidable,
thousands of trajectories can be computed without the expenditure of excessive resources. As particle trajectories are computed
and the characteristics analyzed we can determine the cutoff rigidity of a specific location and viewing direction and direction
and deduce the direction in space of various cosmic ray anisotropies. Unfortunately, cutoff rigidities are not simple parameters
due to the chaotic behavior of the cosmic-ray trajectories in the cosmic ray penumbral region. As the computational problem
becomes more manageable, there is still the issue of the accuracy of the magnetic field models. Over the decades, magnetic
field models of increasing complexity have been developed and utilized. The accuracy of trajectory calculations employing
contemporary magnetic field models is sufficient that cosmic ray experiments can be designed on the basis of trajectory calculations.
However, the Earth's magnetosphere is dynamic and the most widely used magnetospheric models currently available are static.
This means that the greatest uncertainly in the application of charged particle trajectories occurs at low energies.
Space Science Reviews 04/2012; 93(1):305-333. · 5.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: The radiation dose rates at flight altitudes may be hazardously
increased during solar cosmic ray events. Within the scope of this paper
we investigate the total accumulated radiation doses, i.e. the
contribution of galactic and solar cosmic rays, during the two extreme
solar cosmic ray events on 29 September 1989 and on 20 January 2005
along selected flight profiles. In addition, the paper discusses the
consequences of possible solar cosmic ray flux approximations on the
results of the radiation dose computations.
Astrophysics and Space Sciences Transactions 04/2011; 7(2):105-109.
[show abstract][hide abstract] ABSTRACT: A high-time resolution Neutron Monitor Database (NMDB) has started to be realized in the frame of the Seventh Framework Programme of the European Commission. This database will include cosmic ray data from at least 18 neutron monitors distributed around the world and operated in real-time. The implementation of the NMDB will provide the opportunity for several research applications most of which will be realized in real-time mode. An important one will be the establishment of an Alert signal when dangerous solar cosmic ray particles are heading to the Earth, resulting into ground level enhancements effects registered by neutron monitors. Furthermore, on the basis of these events analysis, the mapping of all ground level enhancement features in near real-time mode will provide an overall picture of these phenomena and will be used as an input for the calculation of the ionization of the atmosphere. The latter will be useful together with other contributions to radiation dose calculations within the atmosphere at several altitudes and will reveal the absorbed doses during flights. Moreover, special algorithms for anisotropy and pitch angle distribution of solar cosmic rays, which have been developed over the years, will also be set online offering the advantage to give information about the conditions of the interplanetary space. All of the applications will serve the needs of the modern world which relies at space environment and will use the extensive network of neutron monitors as a multi-directional spectrographic detector. On top of which, the decreases of the cosmic ray intensity – known as Forbush decreases – will also be analyzed and a number of important parameters such as galactic cosmic ray anisotropy will be made available to the users of NMDB. A part of the NMDB project is also dedicated to the creation of a public outreach website with the scope to inform about cosmic rays and their possible effects on humans, technological systems and space-terrestrial environment. Therefore, NMDB will also stand as an informative gate on space research through neutron monitor’s data usage.
[show abstract][hide abstract] ABSTRACT: SONNE, the SOlar NeutroN Experiment proposed for Solar Probe Plus and
developed at the University of New Hampshire (UNH), is designed to
measure solar neutrons from 1-20 MeV and solar gammas from 0.5-10 MeV.
SONNE is a double scatter instrument that employs imaging to maximise
its signal-to-noise ratio by rejecting neutral particles from non-solar
directions. It is intended for an inner heliosphere space mission to
detect solar neutrons close enough to the Sun (0.2-0.4 AU), where these
lower-energy neutrons exist in sufficient numbers. Using laboratory and
simulated data, we produce an instrument response matrix for FNIT that
we are then able to test. A crucial aspect for the inversion of data
from such an instrument is identifying suitable regularisation
techniques needed to deconvolve the data it produces. Here we shall
present work done to test the FNIT response matrix by employing Tikhonov
regularisation. Using simulated `fake' data, we show that zeroth-order
Tikhonov regularisation produces the most encouraging reconstruction of
the incident spectrum. First- and second-order Tikhonov regularisation
produce unsatisfactory results because the choice of the smoothing
parameter - essential for the deconvolution - cannot be determined
automatically because the Picard condition is not met for the higher
order regularisations. Hence zeroth-order Tikhonov regularisation seems
to be the most suitable deconvolution technique for FNIT's needs.
American Astronomical Society Meeting Abstracts #216; 05/2010
[show abstract][hide abstract] ABSTRACT: Currently a cosmic ray cloud connection (CRC) hypothesis is subject of an intense controversial debate. It postulates that galactic cosmic rays (GCR) intruding the Earth's atmosphere influence cloud cover. If correct it would have important consequences for our understanding of climate driving processes. Here we report on an alternative and stringent test of the CRC-hypothesis by searching for a possible influence of sudden GCR decreases (so-called Forbush decreases) on clouds. We find no response of global cloud cover to Forbush decreases at any altitude and latitude.
Geophysical Research Letters, v.37 (2010). 01/2010;
[show abstract][hide abstract] ABSTRACT: The Cassini-Huygens mission has provided a new vision of the atmosphere of Titan since its arrival at Saturn in 2004. One of its main result is the discovery of a complex molecule formation in the upper atmosphere, and the discovery of an ion layer in the troposphere, at 65 km. In this work, we show the results of a recent modeling of ion production in the whole atmosphere of Titan, and its comparison with the Cassini-Huygens results. We show that the three layers where aerosols are detected, upper atmosphere, mesosphere, and lower atmosphere, corresponds to the main regions of ion production. These productions are caused by photons and electron impact in the upper atmosphere, protons from the magnetosphere of Saturn in the detached haze layer, and galactic cosmic rays in the main haze layer. We therefore suggest that these ionization are at the origin of the haze layer, and that the upper atmosphere should be considered as the third haze layer of Titan.
[show abstract][hide abstract] ABSTRACT: SONNE, the SOlar NeutroN Experiment proposed for Solar Probe Plus, is designed to measure solar neutrons from 1-20 MeV and solar gammas from 0.5-10 MeV. SONNE is a double scatter instrument that employs imaging to maximize its signal-to-noise ratio by rejecting neutral particles from non-solar directions. Under the assumption of quiescent or episodic small-flare activity, one can constrain the energy content and power dissipation by fast ions in the low corona. Although the spectrum of protons and ions produced by nanoflaring activity is unknown, we estimate the signal in neutrons and γ−rays that would be present within thirty solar radii, constrained by earlier measurements at 1 AU. Laboratory results and simulations will be presented illustrating the instrument sensitivity and resolving power.
[show abstract][hide abstract] ABSTRACT: Over the last two decades, models of the Earth’s magnetospheric magnetic field have been continuously improved to describe
more precisely the different magnetospheric current systems (magnetopause current, symmetric and partial ring currents, tail
currents and field aligned currents). In this paper we compare the different Tsyganenko models and the Alexeev and Feldstein
model in the context of cosmic ray physics. We compare the vertical cutoff rigidity and asymptotic direction of vertical incidence
obtained with these models for the January 20, 2005, ground level enhancement and for the big magnetic storm of April 6, 2000.
For the event of January 20, 2005, we study the impact of the differences in asymptotic direction obtained with the models
on the radiation dose computation at aircraft altitude. For the magnetic storm of April 6, 2000, we discuss the importance
of the different magnetospheric current systems in causing cutoff rigidity variations. Finally we summarise the advantages
and drawbacks of the different models in the context of space weather.
[show abstract][hide abstract] ABSTRACT: The physical processes affecting the dynamics of the Earth's particle radiation environment are reviewed along with scientific and engineering models developed for its description. The emphasis is on models that are either operational engineering models or 188 R. Vainio et al. models presently under development for this purpose. Three components of the radiation environment, i.e., galactic cosmic rays (GCRs), solar energetic particles (SEPs) and trapped radiation, are considered separately. In the case of SEP models, we make a distinction be-tween statistical flux/fluence models and those aimed at forecasting events. Models of the effects of particle radiation on the atmosphere are also reviewed. Further, we summarize the main features of the models and discuss the main outstanding issues concerning the models and their possible use in operational space weather forecasting. We emphasize the need for continuing the development of physics-based models of the Earth's particle radiation envi-ronment, and their validation with observational data, until the models are ready to be used for nowcasting and/or forecasting the dynamics of the environment.
Space Science Reviews 01/2009; 147:187-231. · 5.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: This review summarizes the history of cosmic ray research at Jungfraujoch, the installation of three neutron monitors in Switzerland, and highlights a few of the main results by the Cosmic Ray Group of the Physikalisches Institut, Universität Bern, Switzerland. In addition, the outstanding scientific and personal contribution of the late Hermann Debrunner, the longtime leader of the Bern Cosmic Ray Group, is honored.
Advances in Space Research 01/2009; · 1.18 Impact Factor
[show abstract][hide abstract] ABSTRACT: Close to the current solar activity minimum, two large solar cosmic ray ground-level enhancements (GLE) were recorded by the worldwide network of neutron monitors (NM). The enormous GLE on 20 January 2005 is the largest increase observed since the famous GLE in 1956, and the solar cosmic-ray event recorded on 13 December 2006 is among the largest in solar cycle 23. From the recordings of the NMs during the two GLEs, we determined the characteristics of the solar particle flux near Earth.
[show abstract][hide abstract] ABSTRACT: The capability to detect fast neutrons with good angular and energy resolutions is gaining increased interest for different applications such as non-destructive testing, homeland security, and space-borne solar physics. To the latter aim, we recently developed and tested a novel type of instrument, the Fast Neutron Imaging Telescope (FNIT), for neutron spectroscopy and imaging in the 1–20 MeV range. Assessments of the instrument prototype performances, based on Monte Carlo simulations and on results from calibration tests performed in a monoenergetic neutron beam, are presented here. The purpose of the study is twofold: (1) to provide a comprehensive characterization of the prototype response, notably in terms of efficiency, event selection, energy and angular resolution; (2) to validate the simulation tool to support data analysis and reduction, and also to help in the design of more complex fast neutron telescopes.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2009; 603(3):406-414. · 1.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: In January 2005 toward the end of solar activity cycle 23 the Sun was very active. Between 15 and 20 January 2005, the solar active region NOAA AR 10720 produced five powerful solar flares. In association with this major solar activity several pronounced variations in the ground-level cosmic ray intensity were observed. The fifth of these flares (X7.1) produced energetic solar cosmic rays that caused a giant increase in the count rates of the ground-based cosmic ray detectors (neutron monitors). At southern polar neutron monitor stations the increase of the count rate reached several thousand percent. From the recordings of the worldwide network of neutron monitors, we determined the characteristics of the solar particle flux near Earth. In the initial phase of the event, the solar cosmic ray flux near Earth was extremely anisotropic. The energy spectrum of the solar cosmic rays was fairly soft during the main and the decay phase. We investigated also the flux of different secondary particle species in the atmosphere and the radiation dosage at flight altitude. Our analysis shows a maximum increment of the effective dose rate due to solar cosmic rays in the south polar region around 70 degrees S and 130 degrees E at flight altitude of almost three orders of magnitude.
Science of The Total Environment 04/2008; 391(2-3):177-83. · 3.26 Impact Factor