Tin-113

At 3.72e+14 Bq/g — 1.00e+4 Ci/g — a gigabecquerel of Sn-113 amounts to 2.69 µg, which is why activity rather than mass is how anyone states the quantity. Tin-113 decays by electron capture with beta-plus with a half-life of 115.09 days, falling to 83.47% of today's activity in a month and 11.08% in a year.

1 GBq at 1 m reads 0.0706 mGy/h, and 1 Ci at the same distance 2.61 mGy/h, from an air kerma rate constant of 0.0706 mGy·m²/(GBq·h) — 1.1× less than Cs-137 and 4.3× less than Co-60, and 31 of 96 among the photon emitters carried here.

7 lines clear the 20 keV cutoff, but 4 of them carry 90% of the dose rate. The leading one is 391.7 keV at 48.7% of the total — its emission probability is 64.97%, which is also the highest.

Shielding barely arises: 0.0684 mm of lead halves the air kerma rate and 5.78 mm takes it to a tenth, thicknesses a source capsule is likely to exceed on its own. Steel does the halving in 0.332 mm. Reaching 20 µSv/h from 1 GBq at a metre takes 2.01 mm of lead. The tenth-value layer runs 84.4 times the half-value layer, not the 3.32 a single energy would give.