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We selected SN1006, the brightest and closest to Earth of all supernovas historically observed, for a study of 14C 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 14N(n,p)14C. Cellulose from single-year tree rings from ad 1003 to ad 1020 was measured to determine ∆14C. Three years after the first visual observation of SN1006, ∆14C 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 14C requires a total production of neutrons of 17.1 × 107n cm−2e, implying an input of 11.3 × 104 ergs cm−2e γ-ray energy. This requires the total supernova γ-ray energy (>10 MeV) to have been 1 × 1050 ergs.

The formation of the observed solar cosmic ray (SCR) composition remains an open question.It has become particularly acute after the discovery of 3He-rich events. The 3He/4He abundance ratio revealed in such events exceeds substantially (up to four orders of magnitude) that in the solar atmosphere.The data available on the 3He-rich events are discussed and a list of all such events known up to date is presented. Most of the 3He-rich SCR events can be associated with the corresponding optical flares on the Sun, with X-ray and radiobursts.An analysis of the models of 3He enrichement proposed up to now shows that only preferential 3He heating by plasma mechanisms can provide the observed high enrichment levels (3He/4He ~ 1).A model involving preferential heating of 3He by induced scattering on ions of the ion acoustic waves generated by flare associated electrons in the solar atmosphere is considered in detail. This model can account for the major properties of the 3He-rich flares.Observational implications of the 3He-rich solar flare model are analyzed; the predictions of the theory are compared with the experimental data available, and promising avenues of further relevant experimental and theoretical research are considered.

A liquid scintillation counting apparatus that enables highly accurate measurements of 14C has been constructed at the Solar-Terrestrial Environment Laboratory, Nagoya University. The main aim of the project is high precision year-by-year measurements of the 14C content in tree rings of an old cedar tree from Yaku Island, Japan. We present the results of 14C measurements on tree rings from the Agematsu region for recent decades to confirm the validity of the system.