April 14, 1951

The range-energy relation for beta particles up to 3 Mev is given by the
relations

• (a.) below 0.8 Mev R = 0.407 E1.38
• (b.) above 0.8 Mev R - 0.542 E - 0.133

In the above relations, R is expressed in gm/cm² and E in Mev. The calculated
end-point range of a 1 Mev beta spectrum is thus 0.41 gm/cm² which is equivalent
to 0.15 cm of Al.

The percent transmission of the beta particles of Bi210 through a series of Al
absorbers as obtained in our laboratories is tabulated below.^a (Maximum energy
of Bi210 [beta] particles - 1.17 Mev.)

	TABLE I
Absorber mg/cm²	Thickness (Al) mm	% Transmission
0	0	100
20	0.07	74
30	0.11	63
40	0.14	53
60	0.22	40
80	0.29	29
100	0.37	22
120	0.44	16
140	0.52	12
150	0.56	7.2
180	0.67	6.4
200	0.74	4.7
240	0.89	2.5
280	1.03	1.4
320	1.19	.86

Thin wall GM tubes are produced commercially with wall thicknesses of 30 mg/cm²
in Al, glass, or stainless steel, some of which are designed as dipping counters.
For the RaE (Bi210) spectrum this represents about 63% transmission. It thus
seems feasible to design stack and coolant monitors which will be sufficiently
sensitive to beta particles, regardless of the choice of the detecting element.

CC: Reactor Committee

^adata gathered by W. T. Withers