The GALPROP program for cosmic-ray propagation: new developments

TL;DR

The paper addresses the need for accurate cosmic-ray isotopic propagation by preserving spatial transport while handling complex fragmentation networks. It introduces an explicit, iteratively solved reaction-network extension to GALPROP, with $z_h=4$ kpc and diffusion described by $D=D_0\beta(p/p_0)^{1/3}$, enabling isotopic predictions for a network of 87 nuclei. Key findings include plausible reproduction of B/C with reacceleration and preliminary predictions for $^{10}$Be$/\,^9$Be, $^{26}$Al$/\,^{27}$Al, $^{36}$Cl$/Cl$, and $^{54}$Mn$/Mn$, suggesting halo-height implications in the $4$–$12$ kpc range, albeit limited by cross-section uncertainties. This framework offers a physically grounded alternative to leaky-box models and is poised to leverage ACE/ISOMAX data and future cross-section improvements for improved isotopic constraints and gamma-ray predictions.

Abstract

The cosmic-ray propagation code GALPROP has been generalized to include fragmentation networks of arbitrary complexity. The code can now provide an alternative to leaky-box calculations for full isotopic abundance calculations and has the advantage of including the spatial dimension which is essential for radioactive nuclei. Preliminary predictions for sub-Fe/Fe, 10Be/9Be, 26Al/27Al, 36Cl/Cl, and 54Mn/Mn are presented in anticipation of new experimental isotopic data.

Figures (4)

• Figure 1: Model isotopic fluxes at 2 GeV/nucleon as function of $Z$; individual $A$ values are marked. NB: This plot is illustrative of the method but not to be taken as predictions for evaluation purposes.
• Figure 2: Left: B/C interstellar and modulated to 500 MV for diffusive reacceleration model with $z_h$ = 4 kpc. Data compilation: Webber et al. (1996). Right: The same for sub-Fe/Fe $(Z=21-23/\,^{56}$Fe). Data: $\diamond$ -- Engelmann et al. (1990), $\triangle$ -- Binns et al. (1988).
• Figure 3: Model interstellar and modulated (500 MV) ratios. Left: $^{10}$Be$/\,^9$Be. Data from Lukasiak et al. (1994a) ( (0,4) -- Voyager--1,2, (0,2)$\bigcirc$ -- IMP--7/8, $\triangle$ -- ISEE--3) and Connell (1998) ($\bullet$ -- Ulysses). Right: $^{26}$Al$/\,^{27}$Al. Data: (0,2)$\bigcirc$ -- Lukasiak et al. (1994b), $\bullet$ -- Simpson and Connell (1998). Note that the data points shown are at the measured (not interstellar) energies.
• Figure 4: Model interstellar and modulated (500 MV) ratios. Left: $^{36}$Cl$/\,$Cl. Data: Connell et al. (1998); Right: $^{54}$Mn$/\,$Mn. Data: $\bullet$ -- Duvernois (1997), (0,2)$\bigcirc$ -- Lukasiak et al. (1995), $\triangle$ -- Leske (1993).