Question

# Give the half-life, decay mode and branching ratios, and major gamma rays (those with intensities greater...

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.

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, Eγ (keV) = 661.657 with intensity, Iγ = 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, Eγ (keV) = 1173.237 with intensity, Iγ = 99.973% and Eγ (keV) = 1332.501 with intensity, Iγ = 99.985% by beta (β) decay mode.

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