5.3.19.10. Cosmic-ray source mode

e-type = 25, 26 : These types reproduce the cosmic-ray energy and angular distributions in space and in the atmosphere, considering their absolute values. When e-type = 25, the numbers of particles generated in each bin are proportional to the calculated cosmic-ray spectra, while their weights are constant. When e-type = 26, the weights of particles generated in each bin are proportional to the calculated cosmic-ray spectra, while maintaining constant probabilities for all source energy bins.

In the cosmic-ray source mode, <source> of each multi-source should be 1.0. If totfact is set to the source area, e.g. \(\pi(r_2)^2\) for s-type = 9, the tally results are automatically normalized to (/sec). If totfact is given as a negative value, the same particle is generated in each multi-source section with weights adjusted according to the ratio of the cosmic-ray fluxes. Note that e-type as well as icenv should be same for all multi-sources in the case of at least one multi-source having e-type = 25 or 26.

Table 5.3.226 icenv

value	explanation
(D=0)	Cosmic-ray environment parameter.
1-5	Terrestrial galactic cosmic-ray mode based on PARMA/EXPACS. These values represent the cosmic-ray environments in the ideal atmosphere (=1), on the ground surface (=2), at the pilot and cabin locations in aircraft (=3 and 4), and the black-hole mode (=5). In the cases of icenv = 2-4, the local environment must be specified by environ. The black-hole mode is useful for simulations with ground because all albedo neutrons from the ground are excluded. In this mode, proj should be neutron, proton, ions with \(Z \le 28\), muons, photon, electron, or positron. Note that the results obtained with icenv= 1-5 are the same, except for proj = neutron, muon+, and muon-. For muons, the flux in the horizontal directions increases when icenv = 2 or 5 due to the ground-level correction of the muon fluxes. Energy-dependent angular distributions determined by PARMA/EXPACS can also be reproduced in this mode in the case of s-type = 9 and dir = iso, where the top of the atmosphere should be the z+ direction.
0	Galactic cosmic-ray mode in space based on the DLR model. In this mode, proj should be proton or ions with \(Z \le 28\). The influence of the Earth’s magnetosphere on typical low-Earth orbits can be considered when alti is specified.
-1	Free-space solar energetic particle mode based on the Tylka model. Currently, the time-integral SEP fluences for historically large solar particle events can be reproduced. In this mode, proj should be proton. If totfact is set to the source area, the tally results are automatically normalized to (/SPE) instead of (/sec).
-2	Trapped proton mode on a typical low-Earth orbit based on the AP-8 model implemented in SPENVIS. In this mode, proj should be proton.

Table 5.3.227 nm

value	explanation
(D=-200)	Number of energy groups. If it is given as a positive number, linear interpolation is assumed in a bin. If negative, logarithmic interpolation is assumed in a bin.

Table 5.3.228 eg1

value	explanation
	Minimum cut off for energy distribution [MeV/n]. The default value is 1.0e-8 for proj = neutron. For other projectiles, the default values are 1.0e-2 and 1.0 for the terrestrial mode (icenv > 0) and free-space mode (icenv <= 0), respectively.

Table 5.3.229 eg2

value	explanation
	Maximum cut off for energy distribution [MeV/n]. Default values are 1.0e4 for proj = neutron, photon, electron, positron, 1.0e8 for proj = muon+, muon-, 1.0e5 for the SEP mode, and 1.0e6 for other projectiles.

Table 5.3.230 ag1

value	explanation
(D=-1.0)	Minimum zenith angle for calculating terrestrial cosmic-ray fluxes in \(\cos\theta\).

Table 5.3.231 ag2

value	explanation
(D=1.0)	Maximum zenith angle for calculating terrestrial cosmic-ray fluxes in \(\cos\theta\). In the case of s-type = 9, the zenith angles of actual source particles are also limited between ag1 and ag2. For other cases, ag1 and ag2 influence only the energy spectrum, and the direction of the source particles is determined from dir, phi, and dom.

Table 5.3.232 solarmod

value

explanation

(D=0)

Solar modulation potential, the so-called W-index, used in the calculation of both terrestrial and free-space GCR fluxes. It is effective only for icenv >= 0. The GCR fluxes are anti-correlated with the W-index, whose values are approximately 0 and 150 for solar minimum and solar maximum conditions, respectively. If this parameter is not specified, the W-index is automatically determined based on the daily count rates of several ground-level neutron monitors on the date of interest specified by icyear, icmonth, and icday.

Table 5.3.233 icyear

value	explanation
(D=2009)	Year for calculating the W-index. It is effective only when solarmod is not specified and icenv >= 0. If a period between 1614 and 1950 is specified, monthly average solar activity estimated from sunspot observation data is used. If 1951 onward is specified, daily average solar activity estimated from ground-based neutron monitor count rates is used.

Table 5.3.234 icmonth

value	explanation
(D=10)	Month for calculating the W-index. It is effective only when solarmod is not specified and icenv >= 0.

Table 5.3.235 icday

value	explanation
(D=20)	Day for calculating the W-index. It is effective only when solarmod is not specified and icenv >= 0.

Table 5.3.236 depatom

value	explanation
	Atmospheric depth in g/cm\(^2\). It is effective only for the terrestrial mode (icenv > 0). If this parameter is not specified, the atmospheric depth is automatically determined from the altitude specified by alti, using the U.S. Standard Atmosphere. The value of depatom obtained from the default alti at sea level is approximately 1033 g/cm\(^2\).

Table 5.3.237 alti

value	explanation
(D=0)	Altitude in km for calculating the atmospheric depth when depatom is not specified and icenv > 0. It is also the mean altitude of the orbit in km when icenv = 0 or -2, where only low-Earth orbit (340 – 420 km) can be specified.

Table 5.3.238 rigid

value

explanation

Cut-off rigidity in GV, which indicates the minimum rigidity of cosmic rays that can penetrate the magnetosphere. For the terrestrial mode (icenv > 0), it indicates the vertical cut-off rigidity whose range is approximately between 0 and 18 GV. If this parameter is not specified, the vertical cut-off rigidity is automatically determined from glat and glong. For the free-space mode (icenv <= 0), all particles with rigidity below this value are not generated as source particles.

Table 5.3.239 glat

value	explanation
(D=90)	Geographic latitude for calculating the vertical cut-off rigidity. Positive and negative values indicate north and south latitude, respectively, in degrees. It is effective only when rigid is not specified and icenv > 0.

Table 5.3.240 glong

value	explanation
	Geographic longitude for calculating the vertical cut-off rigidity. Positive and negative values indicate east and west longitude, respectively, in degrees. It is effective only when rigid is not specified and icenv > 0.

Table 5.3.241 environ

value

explanation

Parameter representing the local environments used in the calculation of terrestrial neutron fluxes (icenv = 2-4), or the event index for the SEP mode (icenv = -1). For reproducing neutron fluxes on the ground (icenv = 2), this parameter indicates the fraction of water in the ground. For considering the disturbance of neutron fluxes due to aircraft structures (icenv = 3 and 4), the mass of the aircraft in units of 100 ton should be provided. Note that both parameters are not pure physical quantities and can be adjusted. For the SEP mode (icenv = -1), this parameter should be an integer corresponding to the selected SPE event.

5.3.19.10.1. References

• 20. Sato, Analytical Model for Estimating Terrestrial Cosmic Ray Fluxes Nearly Anytime and Anywhere in the World: Extension of PARMA/EXPACS, PLOS ONE 10(12): e0144679 (2015). DOI: 10.1371/journal.pone.0144679. T. Sato, Analytical Model for Estimating the Zenith Angle Dependence of Terrestrial Cosmic Ray Fluxes, PLOS ONE 11(8): e0160390 (2016). DOI: 10.1371/journal.pone.0160390.

• Matthia D, Berger T, Mrigakshi AI, Reitz G, A ready-to-use galactic cosmic ray model, Adv Space Res 51: 329-338 (2013). DOI: 10.1016/j.asr.2012.09.022.

• An anti-proton trace model coupled with the static geomagnetic field model T89 (Tyganenko (1989), Planetary and Space Science, 37(1), 5-20) was used in the calculation of geomagnetic transmission function. Kp index was assumed to be 3. For more detail, please refer to Sato et al. (2018), Radiat. Prot. Dosim. 180, 146-149.

• Orbits of International Space Station (ISS) with the inclination angle of 51.6 degree and the mean altitude range between 340 – 420 km are assumed.

• Tylka, A.J., Dietrich, W.F., A new and comprehensive analysis of proton spectra in ground-level enhanced (GLE) solar particle events, the 31st International Cosmic Ray Conference, Universal Academy Press, Poland (2009).

• The Space Environment Information System (2010). http://www.spenvis.oma.be/

• Sawyer D, Vette J (1976) AP-8 trapped proton environment for solar maximum and solar minimum, National Space Science Data Center, Report 76-06, Greenbelt, Maryland.

• NMDB: Real-Time Database for high-resolution Neutron Monitor measurements, http://www01.nmdb.eu/

• I.G. Usoskin, K. Mursula, S.K. Solanki, M. Schuessler, and G.A. Kovaltsov, A physical reconstruction of cosmic ray intensity since 1610, J. Geophys. Res. 107(A11), 1374 (2002). DOI: 10.1029/2002JA009343.

• Warning System for Aviation Exposure to Solar Energetic Particle, NICT, https://wasavies.nict.go.jp/FFPday.txt

• U.S. Standard Atmosphere, 1976, U.S. Government Printing Office, Washington, D.C., 1976.

• http://cosray.unibe.ch/~laurent/magnetocosmics/

• 20. Sato and K. Niita, Analytical Functions to Predict Cosmic-Ray Neutron Spectra in the Atmosphere, Radiat. Res. 166, 544-555 (2006). DOI: 10.1667/RR0610.1.