nucteonics DATA SHEET No. 26 
Gamma-Ray Shielding 
Gamma-Ray Attenuation 
with Buildup in Water 
By DAVID G. CHAPPELL, Knolls Atomic Power Laboratory, General Electric Co., Schenectady, New York 
This nomogram gives the attenu- 
ation factor for a water shielding slab 
used with a point source of gamma 
radiation. Two predecessors that do 
the task for iron and lead have already 
been presented in NUCLEONIcS Data 
Sheet No. 18 (“Gamma Attenuation 
with Buildup in Lead and Iron”—NU, 
Jan. ’57, p. 52). 
Like its predecessors this nomogram 
includes the effect of buildup—the 
scattering of degraded radiation into 
the beam from all points of the slab. 
Absorption coefficients and buildup 
factors are taken from the report APEX 
176.* 
Attenuation factor 7), = B(uxr)e™?, 
where B is the buildup factor for this 
geometry, w is the linear absorption 
coefficient, and z is the shield thick- 
ness. It does not include any allow- 
ance for source-to-detector distance. 
Water density is taken as being equal 
to 1 gm/cm. 
Examples. (1) By how much will 
4-Mev gamma rays from a point source 
be attenuated in passing through a 
16-ft layer of water? The upper of the 
two sample lines shows that the answer 
is 7.5 X 1077. 
(2) We wish to,attenuate 6-Mev 
photons by a factor of 3.1 X 107%. 
How thick must a water slab be to do 
it? The lower of the two sample lines 
yields the answer: 5.5 ft. 
* * * 
I wish to acknowledge the assistance of Miss 
Janice L. Noble, who drew the nomogram. 
* Miscellaneous data for shielding cal- 
culations. Compiled by John Moteff. 
APEX 176 (1954). 
WATER 
(1.0 gm/cm3) 
Photon Energy (Mev) 
outside ; 6-20 tt mside ) 
= 3 
ms < = 
” = 
a wo 
a & a 
£ Si ' 
s Se ° 
fe & ~— 
— S ‘a 
2 2 
a ° 
nw de 
! c 
re S 
oa = 
o. ° 
S =y 
= rc 
ad 
a 
245 
