|dc.description.abstract||The neutron spectrum and angular distributions of neutron groups from the reaction Al^27 (d,n)Si^28 were obtained by the method of proton recoils in nuclear emulsions. A thin aluminum target was bombarded with 2.16 Mev deuterons from the M. I. T. Rockefeller Van de Graaff generator, and neutrons were detected by means of 400 micron Ilford C-2 emulsions placed at nine angles to the incident beam. The plates were scanned with a Leitz binocular microscope equipped with a moving stage, at 1000 magnification. Neutron spectra were obtained at eight angles; O°, 10°, 20°, 30°, 45°, 60°, 90°, and 120°. A total of 12,500 tracks was scanned. Excited states of Si^28 were obtained from these measurements at 1.78 ± 0.10, 4.54 ± 0.2, 4.95 ± 0.2, 6.24 ± 0.06, 6.88 ± 0.06, 7.39 ± 0.06, 7.89 ± 0.06, 8.31 ± 0.10, 8.57 ± 0.08, 9.37 ± 0.04, 10.00 ± 0.10, and 10.25 ± 0.06 Mev. The cross-section for formation of the 9.37 state at 0° is 1O.1 millibarns per steradian, within a factor of two.
A second bombardment for the same reaction was made with a bombarding energy of 6.00 Mev at the M. I. T. -0. N. R. Van de Graaff generator, in order to obtain valid stripping angular distributions. 400 micron Ilford C-2 emulsions were used as before, and were placed at nine angles to the incident beam, at 15° intervals, from 0° to 135°. Neutron spectra were obtained at six of these angles by the methods described above. The angular distributions obtained were compared with the Butler stripping theory in order to obtain the parities and limits on the spins of the states in Si^28 which were reached in the reaction. The angular distributions of neutron groups corresponding to the levels at 1.78, 6.24, 7.90, 8.57, and 9.39 Mev states are adequately described by l=0 distributions. If these groups correspond to more than one unresolved level, as is the case with the 8.57 Mev state, then the spin and parity of the level whose crosssection is largest is 2^+ or 3^+. The angular distribution of the unresolved states at 4.5 and 5.0 Mev was obtained, and the principal peak matches a Butler l=1 distribution. One of the states at 4.5 and 5.0 Mev thus has odd parity, and a spin of l, 2, 3, or 4. Because of deviation from the l distribution at higher angles it is quite possible that the other state has an angular distribution corresponding to l-=2 or 3. The states at 6.88 and 7.39 Mev were poorly resolved, and did not fit Butler distributions very well. The 7.39 state has a distribution which may be either l=1 or l=2, and the 6.88 state distribution may be l=0 or l=l, with l=1 more likely. It is quite possible that the groups corresponding to these "states" are actually composite groups of unresolved states in Si^28. An l=2 distribution was obtained for the ground state of Si^28 as expected. The cross-section for formation of the 9.39 Mev state of Si^28 at 0° at 2.16 Mev born barding energy is 10.1 ± 5 millibarns per steradian, and at 6.00 Mev bombarding energy 30.6 ± 8 millibarns per steradian. The angular distributions obtained from this exposure followed the Butler predictions quite closely, out to the largest angles studied. The angular distributions obtained at the 2.16 Mev bombarding energy showed poor agreement with the predictions of the Butler stripping theory, which is not expected to be valid in this energy region. The angular distributions of the levels at 6.24, 8.28, 8.57, and 9.39 Mev excitation showed the typically forward stripping distribution, but had isotropic backgrounds and a considerable cross-section at backward angles. The angular distributions of the remainder of the levels were isotropic within statistics. A thorough analysis of the low bombarding energy angular distributions has not been carried out, but it is suggested that a comparison with the stripping theories of Tobocman and Kalas, and of Dabrowski, would be of value.
A thin target of isotopic boron has been bombarded with 7.03 Mev protons. The neutrons from the B^11(p,n)C^11 reaction, studied by means of nuclear emulsions, indicate an excited state of C at 2.01 ± 0.06 Mev.
The react10n P ^31(p,n)S^31 has been studied at Ep=17.2 Mev. The p energy spectrum of the neutrons was determined by means of proton recoil measurements in nuclear emulsions. The mass excess, M - A, of S^31 was calculated to be -10.04 ± 0.20 Mev. Excited states of S^31 have been located at 1.15 ± 0.15, 2.28 ± 0.20, 3.35 ± 0.20, 4.51 ± 0.15, 5.94 ± 0.30, and 6.41 ± 0.20 Mev.||en_US