Intensities of the 2158- and 2505-keV gamma rays in the decay of cobalt-60

The intensities of the weak 2158- and 2505-keV gamma rays following the β− decay of 60Co were measured by applying the photonuclear reactions 9Be(γ,n) and 2D(γ,n). The results obtained wereI(2158) = (2.0 ±1.3) ×10-5I(2505) = (0.9 ± 0.7) × 10-7photons per decay of 60Co. The present result for I(2158) agrees with other data found in the literature within stated errors, whereas that for I(2505) is significantly smaller than previous estimates.From the present value of I(2158), the rate B2 and logarithmic comparative half-life log f2t2 of the second-forbidden unique β− decay, which is intimately related to this intensity, was estimated as B2 ≤ (15.0 ± 9.8) × 10-3% and log f2t2 ≥ 10.4+ 0.2- 0.3, respectively.