Session XA

XA1. Modifications of the Proton-Proton Chain. A. G. W. Cameron, Atomic Energy of Canada Limited.—The unexpectedly large cross section measured ¹ for the He³(α,β)Be⁷ reaction implies that this reaction will complete the proton-proton chain in stars with higher temperatures and helium concentrations, supplanting the He³(He³,2p)He⁴ reaction. The energy generation rate is thus doubled because of the more efficient conversion of hydrogen into helium. From recent solar model calculations ² it appears that the He³(α,γ)Be⁷ process did not take place in the primordial sun, but now predominates within about the central seven percent of the radius. Be⁷ is ionized in the solar interior. the free electron capture rate has been estimated by replacing the wave function for a K electron at the nuclear surface by that for a free electron. this rate appears to be slightly smaller at the solar center than the rate for the Be⁷(p,γ)B³ process, which has been computed for direct nonresonant capture using a square well. If this is correct, then the very energetic B₃ neutrinos should have a flux at the earth of about 4×10₃ neutrinos cm⁻³ sec⁻¹, which can probably be detected using a 10 000 gal tank of CCl₄ in a mine (R. Davis, private communication). The modified proton-proton chain may produce the large lithium abundances in certain giant stars. Thanks are due W. A. Fowler for bringing the work of reference 1 to the writer’s attention before publication.