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observed until the vial was opened.4. Composition of the radioactive gas. Gas chromatography with charcoal and silica gel columns was used to analyze 1 the chemical composition of the radioactive gas liberated from 9.5-mg/cm 2 polyethylene. The composition was found to be 57% methane, 36% acetylene, 6% ethylene, and 1 % ethane. No CO or C0 2 was observed.Absolute measurements of the C X2 {p,pn)C n cross section may have been affected by the loss of C 11 in those cases where thin plastic targets were used. Recent measurements in the Bev region 2 ' 3 have used polystyrene targets sufficiently thick so that the correction is less than 1 %. The loss effect may also account for some of the discrepancies in the C 12 (p, pn)C n / Al 27 (/>, 3/m)Na 24 cross-section ratios which have been reported.The authors wish to acknowledge helpful discussions with and the assistance of R.

Although the experimental pion angular and momentum distributions have not as yet been accurately determined, the known results 2 agree qualitatively with the prediction of the static model, that the positive meson prefers to go at right angles to the photon beam, with the energy of the 3-3 resonance. Precise measurements of these quantities will be of great interest to test the details of the theory to a greater extent than is possible from total cross-section data. In particular, a more precise treatment of the Bose symmetry of the final pions may be required than that given by Cutkosky and Zachariasen. 3 These authors treated the mesons (New York) 14, 229 (1961)]. He finds a very large enhancement that could account for the remaining discrepancy with plausible parameters. Unfortunately, his calculations do not go beyond 550 MeV. It is important to ascertain whether the rescattering term gets small again at higher energy. We have also computed the interference term between Figs. 1(a) and 1(b). For an effective TTTTTTT coupling A = 5 [J. S. Ball, Phys. Rev. 124, 2014 gives |A| <1.8] the cross section is increased by about 4 ph at 500 MeV and 10 M b at 700 MeV.

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