We have performed the first direct measurement of the ^{38}K(p,γ)^{39}Ca reaction using a beam of radioactive ^{38}K. A proposed ℓ=0 resonance in the ^{38}K+p system has been identified at 679(2) keV with an associated strength of 120_{-30}^{+50}  meV. Upper limits of 1.16 (3.5) and 8.6 (26) meV at the 68% (95%) confidence level were also established for two further expected ℓ=0 resonances at 386 and 515 keV, respectively. The present results have reduced uncertainties in the ^{38}K(p,γ)^{39}Ca reaction rate at temperatures of 0.4 GK by more than 2 orders of magnitude and indicate that Ar and Ca may be ejected in observable quantities by oxygen-neon novae. However, based on the newly evaluated rate, the ^{38}K(p,γ)^{39}Ca path is unlikely to be responsible for the production of Ar and Ca in significantly enhanced quantities relative to solar abundances.

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Differential Cross Section of the pn ! pp͑ ͑ ͑ 1 S 0 ͒ ͒ ͒p 2 Reaction Extracted from pd ! pppp 2The double differential cross section for pn ! pp͑ 1 S 0 ͒p 2 at three beam energies has been extracted from the quasifree process pd ! pppp 2 . A comparison is carried out with single differential cross section measurements for 3 He͑p 2 , pn͒n, where the pion is thought to be absorbed onto a pp͑ 1 S 0 ͒ "diproton" state. A significant difference is observed in the shape of the angular distribution between the production and absorption data. This difference is ascribed to the effects of the 3 He nuclear environment characterizing the absorption process; however, an adequate theoretical explanation is not available. [S0031-9007 (98)06103-1]