Question

Give the half-life, decay mode and branching ratios, and major gamma rays (those with intensities greater than 30%) emitted by ¹³⁷Cs and ⁶⁰Co. The database at http://nucleardata.nuclear.lu.se/toi/nucSearch.asp may be useful. Note that even though the gamma rays are produced by transitions in the daughter nucleus, it is common to say that these photons are emitted by the parent nucleus.

Answer 1

Solution:

¹³⁷Cs:

(1) Half-life = 30.07 years

(2) Decay mode: About 95 percent decays by beta (β) emission to a metastable nuclear isomer of barium, barium-137m (^137mBa)

(3) Branching ratio: 100%

(4) Major gamma rays: Energy, E_γ (keV) = 661.657 with intensity, I_γ = 85.1% by beta (β) decay mode.

⁶⁰Co:

(1) Half-life = 5.2714 years

(2) Decay mode: ⁶⁰Co decays by emitting an electron (β decay) with a half-life of 5.27 years into an excited state of ⁶⁰Ni, which then decays very fast to the ground state of ⁶⁰Ni, via two gamma decays.

(3) Branching ratio: 100%

(4) Major gamma rays: Energy, E_γ (keV) = 1173.237 with intensity, I_γ = 99.973% and E_γ (keV) = 1332.501 with intensity, I_γ = 99.985% by beta (β) decay mode.