Beta Decay ofB12

Abstract

The 3.23-MeV gamma-ray transition between the 7.66- and 4.43-MeV states of ${\mathrm{C}}^{12}$ has been observed in the beta decay of ${\mathrm{B}}^{12}$ by means of scintillation detectors and coincidence techniques. The ${\mathrm{B}}^{12}$ activity was made by the ${\mathrm{B}}^{11}(d, p){\mathrm{B}}^{12}$ reaction using a Van de Graaff accelerator and a beam-chopping system for irradiation and delayed counting. All parts of the target-collimator assembly were constructed of beryllium in order to minimize bremsstrahlung production. Beta rays were detected in an 8-in.-diam by ¼-in.-thick Pilot-B scintillator and gamma rays were detected in two 5-in.×5-in. NaI counters placed on opposite sides of the source. Gamma-gamma coincidence measurements were made by displaying the output of each NaI detector in coincidence with a channel centered on the full-energy-loss peak of 4.43-MeV gamma rays in the opposite NaI detector. The additional requirement of a coincidence with the beta-ray detector was imposed for beta-gamma-gamma coincidence experiments. In both types of measurements the full-energy-loss and one-escape peaks of the 3.23-MeV gamma rays were observed. Based on the average result of two previous nuclear reaction measurements of the fractional decay of the 7.66-MeV state by the emission of 3.23-MeV gamma rays the present observation of these gamma rays leads to a value of (1.7±0.5)% for the beta-ray branching of ${\mathrm{B}}^{12}$ to the 7.66-MeV state of ${\mathrm{C}}^{12}$.