NUCLEAR-DEBRIS FORMATION
3s
the variation in rubidium distribution with sodium content at any give
temperature can be calculated, with appropriate corrections made fo
polymerization.
Considerations for the condensed phase are Similar to those fo
the vapor phase. Lapple™ has speculated on the existence of pure *Sr¢
particles, The most favorable situation for producing these would b
an air burst, where “Sr might be present in the condensed phaseat th
relatively high average concentration of 107° at.% of all atoms(e.g., .
20-kt air burst containing 1 ton of steel or aluminum). No such parti
cles have ever been reported. All observations indicate that the fissio:
products are highly dispersed on or throughout the substrate material
Future Plans
The described considerations all indicate the approximationsin.
volved in judging the behavior of tracer components by the propertie:
they exhibit at high concentrations. In our experiments the vapor con.
centration of rubidium was some millionfold greater than that in th
fireball. On the other hand, the excess rubidium served to approximati
the effect of macroscopic vapor concentrations of Na,O and K,O. Al.
though the latter effect was overcompensated in the condensed phase
the data provide upper limits of the distribution coefficients, and in:
number of instances these suffice. In the other instances the degree 0
approximation is probably not bad compared to other uncertainties wit!
which the fallout-formation model maker is faced. The wisest cours:
appears to consist in being aware of the difficulties, in making experi-
ments as realistic as feasible, andin judging the adequacy of the result:
by comparison with observations on nuclear debris in the light of senSitivity analyses of the prediction scheme.
With improved measurement techniques we have constructed <
furnace that consists of two zones at different temperatures. Whereas
our previous isothermal—isopiestic technique relied solely on source
dilution to limit the fission-product vapor concentration, our new biisothermal-isopiestic apparatus will permit attainment of lower vapo)
pressures by uSing a source that is cooler than the sample, besides
providing higher temperatures in the sample zone. With this apparatus
we expect to achieve more realistic conditions of concentation, tempera-
ture, moisture content, and soil volatility.
We are also developing a method of making dynamic studies at higt
temperatures. This method promises to permit the simultaneous in-
vestigation of many kinetic properties. If successful, this method wil!
permit a degree of realism far surpassing any thus far achieved. The
ultimate method would consist of temperature-programed inorganic
gas chromatography with a polydisperse fluidized bed, with humiditycontrolled air aS a carrier gas, carried out in both the presence anc
the absence of high radiation fields.