12
ORIGIN AND NATURE OF RADIOACTIVE DEBRIS
WORLDWIDE EFFECTS OF ATOMIC WEAPONS
To
From the data summarized by Brewer, we may arrange the oxides in
1000
the order of increasing volatility as follows:
Vaporization Temperature (°K)
(Pressure == 1 atm)
Oxide
= 10°
(scole right)
noe
e
100
3
THO, 2 eee eee eee
0 &
Bed eee eects
Al,Og . 0. ec eee eee
4300 (decomposes)
3800 (decomposes)
SO ween tea eae
3500
:
E io*
:
\
‘
i? ioe?
7©
&
re
se ys?
“
<a,
Surf
se tg?
2
va
“
“
aoa oO!
a8 "19°
t
a
Oo
€ "I0!
Fig. 1—-Time-temperature relations
FejOy occ eee
molecules is formed, (Oxygen gas at 1 atm pressure is 50 per cent dissociated at 3800°K. )
The relative stability of gaseous oxide molecules is given roughly by
the D, value, which is the heat of dissociation of the molecule into the
component atoms in the ground state at O°K. Values of D, have been
summarized by Brewer."’ The following are some gaseous oxides in the
order of decreasing stability: UO, ZrO,, SiO, AlO, StO, and FeO.
Although most of the fission products exist as oxides, some are present
with very electropositive elements such as cesium and rubidium from the
fireball and sodium from the dust in the air; silver, palladium, and
rhodium are very likely to be in metallic form; whereas xenon and krypton
remain in the atomic gaseous state.
.
As the materials cool, condensed phases will be formed from the gaseous
oxide molecules.he order of condensation of the various oxides will
eT
Te
eee
CTT en
+t
3800
~
the relative volatility of the oxides. The volatility of the oxides is not
necessarily related directly to the stability of the gaseous molecules, but
may best be related to the temperature at which the vapor pressure has a
specified value.
2060 (decomposes)
Condensed phases will form at some time when the temperature ts
between 5000°K and 2000°K, which on a time scale for a 20-KT bomb
means between 1 and 5 sec after detonation. The actual condensation may
occur in a very short time. At 3.5 sec the temperature will have reached
2500°K and the fireball will have attained its maximum radius and will
contain approximately 2000 tons of air. If we assume that it contains
100 Ib of unused plutonium or uranium,’ a total of 1 kg of fission
products, and 1 ton of bombstructure, the material in the fireball will
then have the following composition:
Ait... 2... ee eee ee 2X 108 gm (99.99%)
Bombstructure .........
108 gm (0.1%)
Fission products ........
10% gm (0.00005%)
PuorU............... 5 X 104 gm (0.0025%)
in other forms: iodine and bromineexist as halide ions, probably combined
os
4570
MgO 2... cect ee ee
33590
|©
3400 (decomposes)
BaO ow. eee ees
3000
SID, cece teens ~ 2800 (decomposes)
Time (sec)
2
4670
(PuO) «0... ccc eee (~4500)
©) rar (~4500)
La,O, occ cece cece eee nan eas
4470
CaO occ ccc e eee
z
13
With this composition and the relative volatilities of the oxides in
mind, let us now consider which oxides are likely to condense first and
the probable form of the condensed particles. It should be noted that the
condensable material is extremely dilute compared with that used in the
4
TART OLY
ra
RMVDIAIUEUT SS
3
LEEERIUE
ret
TITySe
COTES oTT
experiments
are
carried out.
If we consider ZrO,, which has the highest vaporization temperature
of any of the oxides of the fission products, then, assuming a maximum
fission yield of 5 per cent and a total pressure of t atm, the partial pzessure