nucreonics DATA SHEET No. 5 
Shielding Constants 
Tenth-Value Thicknesses for Gamma-Ray Absorption 
By JOHN MOTEFF 
Aircraft Nuclear Propulsion Department 
General Electric Company 
Cincinnati, Ohio 
Ficure&s 1-3 on this page provide data 
useful in gamma-ray shielding calcu- 
lations (1). Included are graphs of: 
tenth-value thicknesses, energy at 
which narrow-beam absorption coeffi- 
cients are a minimum, and flux equiv- 
alent to 1 r/hr. 
Tenth-value thicknesses (Fig. 1) 
were calculated from total absorption 
coefficients tabulated in G. R. White’s 
tables (2) using Ly, = 0.904/n. 
(Nore: Pb tenth-values are wrong in 
Fig. 4, Stanford Res. Inst. report, 
“Tndustrial uses . . . fission products” 
and Fig. 4, p. 57, NU, June ’54.) 
Energy range is that of principal 
interest to reactor and isotope work. 
For lead and tungsten the curves can 
be straight-line extrapolated to get 
values from 0.1 to 0.2 Mev, but the 
0.116-Mev K absorption edge in ura- 
nium makes extrapolation difficult. 
The thickness to attenuate by a fac- 
tor other than ten can be gotten by 
multiplying the tenth-value thickness 
by the common logarithm of the de- 
sired factor; thus, half-value thick- 
nesses are logio 2 = 0.3010 times tenth- 
value thicknesses. 
The use of tenth-value layers assumes 
“good,” narrow-beam absorption ge- 
ometry; that is, that attenuation is 
exponential with equal attenuation in 
equal thicknesses. For broad-beam 
poor-geometry absorption, build-up of 
scattered radiation has to be con- 
sidered (1, 3). However, good-geom- 
-etry values are a guide and give a 
lower limit for transmitted intensity. 
Figure 2 is based on Table 6 of ref. 
(3). Figure 3, flux equivalent to 1 r/hr, 
is based on the absorption coefficient of 
air (given in ref. (3), Table 10) and as- 
sumes that 1 r = 6.77 X 104 Mev/cm? 
of std. air, based on 32.5 ev/ion pair. 
BIBLIOGRAPHY 
1, J. Moteff. Miscellaneous data for shielding 
calculations, APEX 176 (1954) 
2. Gladys R. White. X-ray attenuation coeffi- 
cients from 10 kev to 100,Mev, NBS 1003 
EE MERE Rates 
For narrow - beam geometry, owe a 
ata 
no build- up factor used 
ap 
Ht Pa AT | | Lee 
Lae cones 
A aT | | 
ne 
10] 1 a- acne 
o 8 =e 
s rte cot alain 
= ST err e300 
2 4 [Leet | lea Pt ela 
2 3+ Let 4 = am FA 
3 Le = LL | | 
s 
z 2 if yy ea +_1 
= wl ai 
% i VW po 211.4 cot 
eo 
as ji ale ioe a 
i > Ee) 
4 
| AA 
| en 47 ABA 
at /aulinat 
03 040506 O08 2 
Gomma -Ray Energy (Mev) 
0.2 | 
FIG. 1. 
Thickness to attenuate narrow beam of gamma rays by a factor of 10 
{e} 
a bk a on 
oO 
E minimum (Mev) 
to} 
ie) 
oO 
Gamma-Ray Flux Equivalent to Ir/hr 
te} 
of » bom 
fo) 
O 10 20 30 40 50 60 70 80 90 
Atomic Number, Z 
01002004 O| 0204 | 2 
Gamma-Ray Energy (Mev) 
46 
y 
{\ 
[| \ 
Hae 
3. Soca Nuctzontcs 11, No. 8, 8.and No.9, FIG. 2. Energy at which narrow-beam FIG. 3. Gamma-ray flux equivalent to 
55 (1953) absorption coefficients are a minimum 1 r/hr as a function of gamma-ray energy 
210 
