Radiocarbon Production by the Gamma-Ray Component of Supernova Explosions

Abstract

We selected SN1006, the brightest and closest to Earth of all supernovas historically observed, for a study of 14 C production by e − ,e + -bremsstrahlung cascades initiated by hard γ rays (>10 MeV) from that event. During the cascade, bremsstrahlung energies eventually fall within a giant (n,γ), (n,2γ) cross-section, peaking at 23 MeV and approaching effectively zero below 10 MeV and above 40 MeV. The neutrons are absorbed primarily in the reaction 14 N(n,p) 14 C. Cellulose from single-year tree rings from ad 1003 to ad 1020 was measured to determine ∆ 14 C. Three years after the first visual observation of SN1006, ∆ 14 C rose and remained above pre-ad 1009 values until ad 1018. Comparison of the 7 years before ad 1009 with the 9 years following show an average increase of 6.1 ± 1.6 (s.d.)‰ (significant at the 99.6% confidence level). Such a pulse of 14 C requires a total production of neutrons of 17.1 × 10 7 n cm −2 e, implying an input of 11.3 × 10 4 ergs cm −2 e γ-ray energy. This requires the total supernova γ-ray energy (>10 MeV) to have been 1 × 10 50 ergs.