UK DM project: radioactivity test results

Count rates for principal natural radioactivity sources

The table below gives a, b, and g count rates for the principal natural sources of radioactivity, assuming isotopes are present in their `natural' concentrations, and that U and Th chains are in equilibrium. The g activity is separated into that which is `coincident' with a or b (half-lives for g emission from excited states left by a, b decay are typically below 1ns) and `other', resulting from either electron capture or decay of long-lived excited states. A significant proportion of some (usually low energy) nuclear de-excitations proceed by emission of a `conversion electron' rather than a photon; since, in target materials, the former contribute to total background, these are also listed.

Source	parent decays	a	b	g coincident with a	g coincident with b	other g
U	1.11 × 10³	8.88 × 10³	6.60 × 10³	155 c.e.: 1.19 × 10³	2.30 × 10³ c.e.: 1.68 × 10³	0.1
Th	351	2.10 × 10³	1.40 × 10³	28.5 c.e.: 276	901 c.e.: 844	0
Rb	78	0	78	0	0	0
(⁸⁷Rb	280	0	280	0	0	0)
Lu	4.5	0	4.5	0	8.6 c.e.: 4.1	0
Sm	10.8	10.8	0	0	0	0
K	2.67	0	2.39	0	0	0.286
La	0.070	0	0.023	0	0.023	0.046
In	0.022	0	0.022	0	0	0

Notes:
Units are tru for 1 ppb of source, where: 1 tru = 1 a, b, g per day per kg, and 1 ppb = 1 part per (US) billion by weight, ie a concentration of 10^-9;
c.e.: `conversion electrons'.
An Excel spreadsheet which also gives rates for elements at their mean crustal abundances is here.