Production of the cosmogenic isotopes ³H, ⁷Be, ¹⁰Be, and ³⁶Cl in the Earth's atmosphere by solar and galactic cosmic rays

Abstract

In a follow‐up study to the earlier work of Webber and Higbie (2003) on 10Be production in the Earth's atmosphere by cosmic rays, we have calculated the atmospheric production of the cosmogenic isotopes 3H, 7Be, 10Be, and 36Cl using the FLUKA Monte Carlo code. This new calculation of atmospheric yields of these isotopes is based on 107 vertically incident protons at each of 24 logarithmically spaced energies from 10 MeV to 10 GeV, 102 times the number used in the earlier calculation, along with the latest cross sections. This permits a study of the production due to solar cosmic rays as well as galactic cosmic rays at lower energies where isotope production is a very sensitive function of energy. Solar cosmic ray spectra are reevaluated for all of the major events occurring since 1956. In terms of yearly production of 10Be, only the February 1956 solar event makes a major contribution. For 36Cl these yearly SCR production contributions are 2–5 times larger depending on the solar cosmic ray energy spectra. We have determined the yearly production of 10Be, 36Cl, and other cosmogenic isotopes above 65° geomagnetic latitude for the time period 1940–2006 covering six solar 11‐year (a) cycles. The average peak‐to‐peak 11‐a amplitude of this yearly production is 1.77. The effects of latitudinal mixing alter these direct polar production values considerably, giving an average peak‐to‐peak 11‐a amplitude of 1.48 for the global average production.

A history of solar activity over millennia

“…Comparison of model computations with direct beryllium production experiments (Usoskin and Kovaltsov 2008b;Kovaltsov and Usoskin 2010), and also the results of modelling of the short-living 7 Be isotope (Usoskin et al 2009a) suggest that some numerical models (Masarik and Beer 1999;Webber and Higbie 2003;Webber et al 2007) tend to underestimate the production.…”

“…These questions need to be answered. Several attempts have been made to evaluate that from the cosmogenic isotope data (Lingenfelter and Hudson 1980;Usoskin et al 2006b;Webber et al 2007), but the result was grossly uncertain (Hudson 2010;Schrijver et al 2012), mostly because of the large model uncertainties of the radionuclide production. A new step forward has been done recently by Usoskin and Kovaltsov (2012), who analyzed two 14 C and five 10 Be records over the last millennia and searched for possible signatures of extreme SEP events.…”

“…The first models were simplified quasi-analytical (e.g., Lingenfelter 1963;O'Brien and Burke 1973) or semiempirical models (e.g., Castagnoli and Lal 1980). With the fast advance of computing facilities it became possible to exploit the best numerical method suitable for such problems-Monte-Carlo (e.g., Beer 1999, 2009;Webber and Higbie 2003;Webber et al 2007;Usoskin and Kovaltsov 2008b;Kovaltsov and Usoskin 2010;Kovaltsov et al 2012;Argento et al 2013). The fact that models, based on different independent Monte-Carlo packages, namely, a general GEANT tool and a specific CORSIKA code, yield similar results provides additional verification of the approach.…”

“…A new step in the modelling of isotope production was made by Masarik and Beer (1999), who performed a full Monte-Carlo simulation of a GCR-initiated cascade in the atmosphere and used cross sections of spallation reactions directly instead of the average "star" efficiency. Modern models (Webber and Higbie 2003;Webber et al 2007;Usoskin and Kovaltsov 2008b;Kovaltsov and Usoskin 2010;Poluianov et al 2016) are based on a full Monte-Carlo simulation of the atmospheric cascade, using improved cross sections. The global production rate of 10 Be is about 0.02 -0.04 atoms cm −2 s −1 (Masarik and Beer 1999;Webber et al 2007;Kovaltsov and Usoskin 2010;Poluianov et al 2016), which is lower than that for 14 C (about 2 atoms cm −2 s −1 ; see Sect.…”

Assessment of F200 fluence for major solar energetic particle events on the multi-millennial time scale

“…The usual proxy for the variability of cosmic rays and also for major SEP events is based on records of cosmogenic radionuclides, such as 10 Be measured in polar ice and 14 C measured in dendrochronologically dated tree rings [7,8]. A short list of possible candidates for major SEP events in the past was proposed recently [9] providing a statistic on the time scale of ten millennia.…”