From figures given by Cotser-Mullen, the assembled core was 6.25 inches in
diameter, but the tamper bore within which it resided was 6.5 inches in diameter
and 7 inches long. The enclosing tamper was 18 inches long by 13 inches in
diameter. These dimensions are sketched in Fig. P.3, which is not to scale. With
these dimensions, the assembled core had a volume of 214.76 in
3 = 3519.24 cm
3 ,
and the tamper a volume of 2156.9 in
3 = 35345.3 cm
3 . With respective densities of
18.71 and 15.63 gr cm
−3 , their masses were M core = 65.8 kg and M tamp = 552.5 kg.
However, it is estimated that the core of this device comprised only *80%
235
U,
with the balance being
238 U, so in many calculations I will use an operative mass of
0.8(65.8 kg) * 52.6 kg, rounded to 53 kg. Data on fissile and tamper materials are
gathered in Table P.1. Figure P.4 shows some Little Boy test bombs.
Fig. P.3 Side-view cross-sectional sketch of dimensions of the assembled Little Boy core. Not to
scale
Table P.1 Data on fissile and tamper materials. A is atomic weight and q is density
Material
A
gr mol
-1
q
gr cm
-3
235
U
235.04
18.71
239
Pu
239.05
15.6
Aluminum
26.982
2.699
Beryllium oxide
25.01
3.02
Depleted U (DU;
238
U)
238.05
18.95
Lead
207.2
11.35
Tungsten carbide (WC)
195.85
15.63
Preamble
xv