The new local interstellar spectra and their influence on the production rates of the cosmogenic radionuclides ¹⁰Be and ¹⁴C

Abstract

With Voyager1 crossing the outer boundary of our solar system at the end of 2012, for the first time in the instrumental era an unmodulated local interstellar spectrum (LIS) at galactic particle energies below ~500 MeV has been measured. On the basis of these as well as Payload for Antimatter Matter Exploration and Light‐nuclei Astrophysics (PAMELA) and Alpha Magnetic Spectrometer (AMS02) measurements, most recently, three new LIS models have been proposed in the literature. In this study we compare the newest LIS models to previously most often used ones. Thereby, we investigate and discuss the influence of these LIS models on the terrestrial production rates of the cosmogenic radionuclides 10Be and 14C, which are produced due to the interaction of galactic and solar cosmic rays with atmospheric constituents. After being transported within the atmosphere they are preserved in natural archives such as, e.g., ice sheets or tree rings, forming a unique tool to study the solar modulation of thousands of years back in time. To parameterize the heliospheric modulation we apply the force‐field approximation for the individual LIS models from which LIS‐dependent solar modulation parameter (ϕ) values are derived. Furthermore, we present updated sets of linear regression functions containing the opportunity to convert the LIS‐dependent ϕ values between the investigated LIS models. The results are then applied to a long‐term reconstruction of the solar modulation parameter.

Neutron Monitors and Cosmogenic Isotopes as Cosmic Ray Energy‐Integration Detectors: Effective Yield Functions, Effective Energy, and Its Dependence on the Local Interstellar Spectrum

“…The result of this method to reduction of values between various LISs differs from earlier methods based on refitting the spectra (Herbst et al, 2017;Usoskin et al, 2005). We note that with our method the values of the modulation potential are converted "absolutely," viz., the production/count/deposition rate is equalized Figure 8.…”

“…A good news is that the modulation potential can be converted from one LIS to the other using an ad hoc relation. This is typically done using a linear relation (Herbst et al, , ; Usoskin et al, ), so that ϕ computed for one LIS (e.g., B00) can be with high accuracy recalculated to another LIS linearly as …”

“…between different LIS models. We have checked that the use of Table 1 for reduction of between different LIS models gives the accuracy (in terms of NM count rates or production/deposition rates of cosmogenic isotopes) within 0.5% which is much better than the accuracy of the spectral refitting method, which may reach 5-10% ( Figure 5 in Herbst et al, 2017).…”

The Atmospheric Radiation Interaction Simulator (AtRIS): Description and Validation

“…Using the so‐called force field approximation (see, e.g., Caballero‐Lopez & Moraal, ; Moraal, , and references therein), a first‐order analytic solution of the transport equation (Parker, ), the primary GCR particle flux at 1 AU can be calculated as a function of solar activity based on only one free parameter, the solar modulation parameter ϕ . The upper panel of Figure is showing 10 different differential primary proton spectra based on the Local Interstellar Spectrum (LIS) model by (Herbst et al, ) during five different solar activity phases described by the solar modulation parameter ϕ . In addition, for the case of no modulation ϕ = 0 MV, we investigate the effects of geomagnetic shielding by using five different locations (here given by their different vertical cutoff rigidities, R C ).…”

“…We will validate our results against three of the published measurements performed on 16 April 1965, on 29 July 1967, and on 2 August 1969 (values given in their Table 4). Based on the LIS by Herbst et al () and the modified modulation parameter ϕ by Gieseler et al () the following corresponding ϕ values were used: ϕ 1965 = 380 MV, ϕ 1967 = 665 MV, and ϕ 1969 = 950 MV. For helium, the modulation parameter was one half of the proton ϕ .…”