Measurement of (p,n) thresholds at tandem energies
Phillips, Gerald C.
Master of Arts
The "counter ratio" technique of Bonner, et al., for measuring neutron thresholds has been extended to bombarding energies greater than 6 MeV. Neutron background problems had previously precluded neutron threshold measurements with this technique at these energies. A system was developed which allowed the beam to be stopped 30 ft. away from the thin foil target in a heavily shielded cave. No slits were used other than those of the analyzing magnet, and they were shielded. A remotely retractable plunger permitted accurate alignment of the beam by minimizing the beam current on a Ta disk with a 3/16" aperture. The slow counter consisted of 2 BF3 tubes imbedded in paraffin through which the beam passed. Improvement in background by a factor of 5 or better over stopping the beam in a Ni58 slug at the target was achieved. Thresholds were measured for various (p,n) reactions, and the results are given as follows according to the form, reaction (level in'residual nucleus) threshold energy in MeV: C13(p,n)N13(0) 3.235, (2) 6.965; Al27(p,n)Si27(0) 5.800, (1) 6.611, (2) 6.793, (3) 8.046, (4) 8.549; Cr52(p„n)Mn52(1) 5.975, (2) 6.149; Ni58(p,n)Cu58(0) 9.509; Ni60(p,n)Cu60(0) 7.025, (1) 7.092, (2) 7.325; Ni62(p,n)Cu62(0) 4.812, (1) 4.852, (2) 5.109. Many resonances were seen in the various compound nuclei.