STUDIES OF (p,n) REACTIONS IN THE PROTON ENERGY RANGE FROM 2 TO 10 MEV

Reaction thresholds have been studied for (p,n) reactions on B11, F19, Al27, Si30, P31, K39, Ni58, and Ni60. Using the C13(p,n)N13 and Cu65(p,n)Zn66 thresholds, which have previously been measured with precision, to calibrate the magnetic beam analyzer of the tandem accelerator, and the H2(O16,n)F17 threshold to establish the linearity of this calibration to an equivalent proton energy of 14.57 Mev, threshold energies of 3.019±0.004, 4.229±0.006, 5.800±0.008, 5.174±0.030, 6.456±0.020, 7.227±0.070, 9.480±0.025, and 7.016±0.015 Mev, respectively, have been established. These data are in reasonable agreement with the available positron decay data except in the case of Ca39 where an unexplained discrepancy exists. Resonances of total width less than 20 kev have been observed in the neutron-excitation curves of the Al27(p,n)Si27 and Si30(p,n)P30 reactions corresponding to excitations of approximately 17 Mev and 13 Mev in the compound systems Si28 and P31, respectively. In the latter case isolated resonances are found without overlapping broad resonances. The reaction threshold falls between resonances and is not directly observable; the counter-ratio technique was calibrated for use in such situations. Neutron yield measurements have been made on thick targets of C, Al, Ni60O, Ni58O, Ni58, W, Pb, Au, Th, and U as functions of the incident proton energy in the energy range from 4 to 10 Mev.