A method is outlined for determining the total number of photons at each energy for a given irradiation from a betatron, assuming the bremsstrahlung photon distribution to be represented by an equation of Schiff and the response of an r-meter to be proportional to the absorption cross section for photons in the wall material.The resulting activities produced by gamma-neutron reactions in Cu 63 , Cu 65 , Sb 121 , Sb 123 , and Ta 181 have been measured as functions of the maximum photon energy of the betatron. In each case the activity was normalized to saturation per gram for 100 roentgens of radiation.A method is also outlined whereby these activation curves may be analyzed to give the photo-neutron cross section as a function of energy. The cross section for Cu 63 obtained by this method has its maximum at 17.5 Mev with a resonance half-width of 6 Mev and an integrated area of 0.7 Mev-barn. Maxima for the other nuclides are at somewhat lower energies and have essentially the same half-width.

A careful examination of the C n (y,n)O l and O u (y,n)0 15 reactions, resulting from irradiating samples with betatron bremsstrahlung, has revealed discontinuities in the yields as a function of peak bremsstrahlung energy. These discontinuities are interpreted to indicate the presence of strong photon absorption levels in the C 12 and O 16

ARSTRACT 'I'he reaction Xij8(r,77)Ni" has been it~vcstigated between 12-and 24-Mev maximum photon energy. The absolute yield value a t 22 Mev was found to be much lower than reported previously. Also, a shorter half-life of Ni57 was obtained. The cross section was determined using two different methods.'Manuscript rcceived February 16, 1050.

The cross-sectional curves for the reactions F 19 (T, n)F 18 and F 19 (Y, 2W)F 17 have been determined by measurement of the induced positron activities. The (7, n) cross-sectional curve rises almost vertically from the threshold to a value of about 2 mb, remains constant for about 3 Mev, and then increases again to a maximum value of 3.48 mb at 20 Mev. The (7, 2n) cross-sectional curve has a peak value of 0.66 mb at about 26 Mev. The integrated cross sections for the (7, n) and (7, 2n) reactions are 0.039 and 0.0024 Mev-barns, respectively. However, the (7, 2n) reaction is evaluated only up to its peak position at 26 Mev. A new value of 60±1 seconds is reported for the F 17 activity.

On the basis of the work done by Darling and Dennison on the water vapor molecule, the vibrational constants of acetylene are calculated, taking into account the resonance interaction arising from the near equality of the fundamentals ν1 and ν3. Seventeen band centers are known experimentally. The band centers depend on the 10 constants χi, χik and γ which are functions of the potential constants. The expressions for the vibrational energies of the band centers are set up, those for interacting doublets or triplets being found by perturbation methods. The 10 constants are determined and the positions of eight bands calculated to check the results. The agreement is very satisfactory. The positions of 10 other bands not yet observed are predicted.