Photon Production 
10 
t=target thickness in 
ost radiation lengths 
2 06+ 
= 
s 
5 04} 
© 
0.2 
t=002 t=004 
0 100 200 300 
Energy x Angle (Mev-deg) 
FIG. 4 tells beam width by plotting relative intensity against 
FIG. 5 is total conversion efficiency for 
photon production from electron beam stopped in thick target. 
energy-angle product. 
on 
2) 
Concrete (145 Ib/ft?) 
iS) 
Barytes concrete 
(220 |b/ft3) 
Ye ee 
— ! 
4 6 8 
Photon Energy (Mev) 
Tenth-Value Thickness (in.) 
[Sal 
2 10 
FIG. 7 gives thicknesses of various common shielding materials 
required to reduce narrow, monoenergetic photon beam to one 
FIG. 8 shows buildup factors for 
tenth of its incident intensity. 
for electron energies of 10-20 Mev and 
targets thicker than 0.2 radiation 
lengths photon intensity at 90 deg can 
be as high as 5% of forward intensity. 
Total conversion efficiency. Figure 
5 gives thick-target photon-production 
efficiencies (4). For thick targets con- 
version efficiency varies linearly with 
atomic number (5). Figure 6 enables 
computation of conversion efficiency 
from target thickness (6). 
Spectrum shape. The number of 
photons in each energy interval of a 
bremsstrahlung spectrum is relatively 
independent of angle. The spectrum 
shape is shown by the table (7). 
Shielding. The narrow-beam ab- 
sorption coefficients of Fig. 7 (8) and 
aa 
40 @ 
30}- 
20 
Photon-Production Efficiency (%) 
I | | 
a 10 15 
Electron Energy (Mev) 
1OF~ yr | 
Or 
8+ Water -3 Mev 
Hi Iron-3 Mev 
| 
3 5 
S al 
2 Iron-6 Mev 
= 
aM 
3} Water - 6 Mev 
2 
J SE | 
1 4 =. 
| 25 3: 245 5 6 
Number of Tenth Value Layers 
etry. 
the buildup factors of Fig. 8 (9) are for 
shielding calculations. For approxi- 
mate calculations the spectrum of the 
table is replaced by an effective photon 
energy and Figs. 7 and 8 are used at 
that energy. For 20-Mev electrons 
the effective photon energy is ~7 Mev, 
and for 6-Mev electrons it is ~3 Mev. 
For more accurate treatment each 
component of the spectrum is treated 
separately. Figure 9 shows the equiva- 
lence between photon flux and dose rate 
in air. Figure 9, the table and Fig. 2 
can be used together to obtain the for- 
ward flux at each energy. Figure 4 
gives the flux in any other direction. 
The 1/r? falloff and the shielding atten- 
uation from Figs. 7 and 8 are then 
200 
100 Pb 
Radiation 
Energy Loss per Radiation Length (%) 
10 20 50 
Electron Energy (Mev) 
FIG. 6 is thin-target conversion efficiency, given by € = tk, 
where ft is target thickness and k is per cent of electron energy 
converted into photons per radiation length 
‘i 9 if 
Ww 
T 
Photon Flux Equivalent to | r/hr 
(105 photons/cm2/sec) 
ine) 
n sin n : Ls n 
4 
2h 
8 2 16 
Photon Energy (Mev) 
use with FIG. 7 to find actual attenuation in broad-beam geom- 
FIG. 9 shows equivalence of photon flux and dose rate 
to enable treatment of spectrum by energy intervals 
calculated for each energy group. 
Finally total dose rate is calculated 
from Fig. 9. 
* * * 
This data sheet is based on Report AM-100 
(Applied Radiation Corp., Walnut Creek, 
Calif., March 13, 1957). 
BIBLIOGRAPHY 
1. ‘‘American Institute of Physics Handbook,” 
D. E. Gray, ed., p. 839 (McGraw-Hill Book 
Co., New York, 1957) 
2. Report AM-102.(Applied Radiation Corp., 
Walnut Creek, Calif., 1957); NucLEONIcs 15, 
No. 11, 178 (1957) 
3. L. H. Lanzl, A. O. Hanson, Phys. Rev. 89, 959 
(1953) 
4. C. W. Miller, Paper 276 presented at Industrial 
Electronics Convention, Oxford, 1954 
5. W. W. Buechner, R. J. Van de Graaff, A. E. 
Burrill, A. Sperduto, Phys. Rev. 74, 1348 (1948) 
J. D. Lawson, Nuc.eontcs 10, No. 11, 61 (1952) 
. Nat’l Bu. of Standards Handbook 55 (1954) 
S. Block, private communication 
J. Moteff, APEX-176 (1954) 
PHN 
249 
