DYnamic Atmospheric Shower Tracking Interactive Model Application (DYASTIMA) is a standalone software application for the simulation of the cosmic ray secondary particles cascades that are produced in the atmosphere of a planet. DYASTIMA is an open software developed in Geant4. It can be used by the public and the scientific community with the only requirement being a reference to:

• Paschalis P. et al., New Astronomy 33, 26-37, 2014
• Agostinelli S. et al. (Geant4 collaboration), Nucl. Inst. Meth. A 506, 250-303, 2003
• Allison J. et al. (Geant4 collaboration), IEEE Trans. Nuclear Sci. 53, 270-278, 2006
• Allison J. et al. (Geant4 collaboration), Nucl. Inst. Meth. A 835, 186-225, 2016

The users can run DYASTIMA by downloading it from the external DYASTIMA site (click here).
Operating system requirements and other details can be found in following FAQs. Details on running the application can be found in the User Manual, found in the Publications section.

Geant4 is a complete toolkit developed in C++ for the simulation of the particles propagation through matter. It covers high and lower energy ranges as well. As a result, it can be used in a variety of applications, such as space science, medical physics, nuclear physics high energy physics, acceleration physics etc. It provides a great variety of options, accuracy as well as good support and updates, while it has more than 1000 citations. Therefore, Geant4 is an excellent environment for the simulation of the secondary particle cascades. The official Geant4 website is http://geant4.web.cern.ch/ in which the necessary references can be found.

The requirements for the execution of DYASTIMA are the following:

• A Microsoft Windows operating system
• The .NET library
• The Geant4 libraries
• The Geant4 datasets
• Enough free disc space, depending on the desired output
• An over-mid-range computer

The time of the execution depends on the simulation as well as the performance of the computer system used.

DYASTIMA performs a simulation in order to study the cascades. For this reason, if the user wishes to perform the simulation for selected input parameters, the downloading of DYASTIMA is necessary. Some pre-fixed scenarios (e.g. solar minimum/ maximum conditions in the Earth’s atmosphere) will be soon available in a database, for a user not wishing to run the software.

To perform the simulations, Geant4 libraries and datasets are required. DYASTIMA can automatically download all the required Geant4 files, allowing the users not to install Geant4 by themselves. More information can be found in the DYASTIMA Software User Manual, provided in the homepage.

DYASTIMA-R is an extension of DYASTIMA implemented in C++ using Geant4. It provides radiation dosimetry calculations by using the output of DYASTIMA. More specifically, the radiobiologigal quantities calculated are dose rate (Gy/h) and equivalent dose rate (Sv/h), as defined by ICRP and ICRU.

The results provided by DYASTIMA-R are validated according to the International Commission on Radiological Protection (ICRP) as well as the International Commission on Radiation Units and Measurements (ICRU) standards. The ICRU Report 84 provides reference data for ambient-dose-equivalent rates derived from onboard aircraftmeasurementsdue to the exposure to cosmic radiation exposure for:

• three flying altitudes (FL310, FL350, FL390) corresponding to the usual flying range of large passenger-jet aircraft flights,
• eighteen vertical geomagnetic cut-off rigidity values Rc (0 GV to 17 GV, with an increment of 1 GV) corresponding to the full range of geographic latitudes, and
• three time periods (Jan 1998, Jan 2000, Jan 2002) covering different periods of solar activity.

The recommended acceptable uncertainty limit for the comparison of the model-calculated values and the reference data is ±30%. It can be observed that from 0 GV to 10 GV, i.e. middle and high geographic latitudes, the DYASTIMA-R calculated values of ambient dose equivalent are in good agreement with the reference data, without exceeding the 30% uncertainty proposed by ICRU. Above 10 GV, a greater deviation is observed, without exceeding an uncertainty of 40.9% which is probably due to the perplexed geomagnetic field. Moreover, DYASTIMA-R tends to underestimate the ambient dose equivalent. These results are in good accordance with other models. The deviation may also be attributed to the input parameters of the simulation, as the atmospheric profile and the primary cosmic ray spectra are model dependent. Therefore, DYASTIMA is being constantly improved in order to provide more precise results.

• ICRU: "Reference Data for the Validation of Doses from Cosmic-Radiation Exposure of Aircraft Crew", Journal of the ICRU 10, Report 84, Oxford University Press
• ICRP: "Radiological Protection from Cosmic Radiation in Aviation", ICRP Publication 123, Ann. ICRP 45, 1-48, 2016.

The input parameters are defined by the user via a graphical user interface. The parameters required are:

• the general characteristics of the planet (radius, surface type, surface pressure, surface gravitational acceleration, magnetic field)
• the structure of the atmosphere (composition and temperature profile)
• the primary cosmic ray spectrum ((particle types, flux, zenith and azimuth range)
• the simulation geometry
• the physics interactions taking place between the cosmic ray particles and the molecules of the planet’s atmosphere (Geant4 reference lists)
• the tracking altitude
• the selection between the flat and the spherical model of the atmosphere
• optional energy cuts for the production, simulation or tracking of particles

There are several models / tools providing the primary cosmic ray spectrum. Indicative examples can be found at:

• CRÈME, https://creme.isde.vanderbilt.edu/
• SPENVIS, https://www.spenvis.oma.be/
• OMERE, http://www.trad.fr/en/space/omere-software/

A good approximation of the Earth’s atmosphere is provided by:

• the International Standard Atmosphere (International Civil Aviation Organization: "Manual of The ICAO Standard Atmosphere", Doc 7488-CD third ed., 1993)
• τhe US Standard Atmosphere (U.S. Government Printing Office: "U.S. Standard Atmosphere", 1976)

Both models are identical up to 32 km from the Earth’s surface.

DYASTIMA simulates the propagation of the particles from the top of the atmosphere and below. The magnetic field is not used for the simulation of the travelling of the particles inside the magnetosphere, but for the divergence of the primary and secondary particles’ path in the atmosphere.

The values of the north, east and vertical Earth’s magnetic field are available by the National Oceanic Atmospheric Administration (http://www.ngdc.noaa.gov/geomag/).

The output of DYASTIMA provides all the available information about the secondary particle cascades and tracking, such as:

• number,
• energy,
• direction,
• arrival time and
• energy deposit of the secondary particles at different atmospheric layers.

If DYASTIMA-R simulation is also performed, the dose rate and equivalent dose rate at the different atmospheric layers will also be calculated.

Description: Indicative values for a simulation of the air showers in the Earth’s atmosphere during solar minimum conditions.

• The CR spectrum is extracted from CREME model for solar minimum conditions
• The Earth’s atmosphere description is based on the International Standard Atmosphere model
• The values of the magnetic field (north, east and vertical) are found in http://www.ngdc.noaa.gov/geomag

References

• Tylka J. et al., IEEE Trans. Nucl. Sci. 44, 2150-2160, 1997
• Weller R. A. et al., IEEE Trans. Nucl. Sci. 57, 1726-1746, 2010
• Mendenhall M. H. and Weller R. A., Nucl. Inst. Meth. A 667, 38-43, 2012
• International Civil Aviation Organization, Doc 7488-CD third ed., 1993
• ICRP, ΙCRP Publication 123, Ann. ICRP 42, 2013
• ICRU, J. ICRU 10, Report 84, Oxford University Press, 2010

Screenshots of DYASTIMA application

The uploading date of each scenario included in the database is indicated next to the title of the corresponding scenario. In this way the user can identify the latest scenarios.

Request

Scenario description(*)
Purpose of scenario(*)
Area of interest(*)
References(*)
Simulation input		(Maximum file size is 5 MB)