NUCLEONICS DATA SHEET No. 10 
Shielding Constants 
Gamma-Ray Attenuation 
BY DAVID G. CHAPPELL 
Knolls Atomic Power Laboratory* 
General Electric Co. 
Schenectady, N. Y. 
IN CALCULATING ATTENUATION of 
gamma-rays, one must determine the 
mass absorption coefficient, um. The 
Hm for a number of elements has been 
calculated, (1). The value for other 
elements is obtained by interpolation. 
Hullings did this for five energy 
groups (2). Recently Moteff extended 
the list of available energy plots to 
25 elements (3). However, complete 
tables of um from 0.5 to 6 Mev, the 
usual range of interest, for all elements 
are still unavailable. The plot of 
Lm vs Z below facilitates interpolation 
to any atomic number and energy. 
The data is taken primarily from 
Moteff (3). 
Energies greater than 6 Mev have 
been neglected since for these energies 
and for Z = 30-94 unm is defined quite 
well by the 6-Mev curve, the locus 
of minimum absorption coefficient. 
This is generally used for shielding 
calculations for any energy above 6 
Mev (4). For Z = 1-29, u, deter- 
mined from the chart is slightly high 
for energies greater than 6 Mev. 
The nomogram on p. 41 can be 
used to convert u,, to the linear absorp- 
tion coefficient, u, by multiplying by 
212 
the density of the shield material, p. 
If » is connected to the shield thick- 
ness, z, the shield attenuation factor 
for a point source with unit build-up, 
e->, is obtained (6 = wr). The ap- 
proximate build-up factor, B, for most 
elements, but not lead, up to 3 Mev 
is 1+) and for lead over the same 
range 1 + 446. The corrected attenu- 
ation factor is B X e~». (This applies 
for atomic numbers greater than that of 
iron but definitely not for light elements 
like aluminum.) 
Source strength (y/cm?/sec) for an 
infinite plane source is approximately 
/2 X Q,, where Q, is the specific 
activity, y/cm3, of the soyrce material. 
If » is determined for the source y-ray, 
d can be read on the adjacent scale. 
BIBLIOGRAPHY 
1. G. R. White NBS 1003 (1952) 
2. M. K. Hullings, ORNL, CF 53-2-266 (1953) 
3. J. Moteff, APEX 176 (1954) 
4. R. Stephenson, “Introduction to Nuclear En- 
gineering,’ p. 185 (McGraw-Hill Book Co., 
Inc., New York, 1954). 
* Knolls Atomic Power Laboratory is 
operated by the General Electric Co. for 
the U.S. Atomic Energy Commission under 
Contract W-31-109 Eng-52. 
