[Isotope-prod] Meeting notes

[Pavel Degtiarenko]

Hi George and All,

I have set up a toy FLUKA model for the Radium irradiation, that can 
simulate Ac-225 production. That is all extremely preliminary and would 
require independent verification. But one immediate engineering question 
came along, and in any case it will have to be answered before we could 
propose a solution for the Radium irradiation problem.

The question is: what is the maximum heat power that could be deposited 
safely and continuously into the Radium target.

In any realistic setup, power deposition in the target will be not 
small. The figure of merit, "Ac-225 hourly production per power in the 
target" in (mCi/hour)/kW, varies, depending on the setup, from about 6 
mCi/h/kW in the case when 150 MeV beam strikes directly at the target, - 
to about 22 mCi/h/kW at 75 MeV and with a 2 rad. lengths radiator in 
front of the target. The setup with thin radiator and sweeping magnet 
before the target can produce 13 mCi per hour in the target 10 cm away 
from the radiator at the full beam 150 MeV, 1 mA (150 kW), and the power 
in the target is evaluated to be about 700 W. The term "hourly 
production" here means that the target is irradiated for one hour, 
parent Ra-225 is produced, and then, in 15-20 days, Ac-225 daughter is 
"harvested".

One gram (one Ci) of Radium is a small target, I used a cylinder 1 cm 
length and 0.48 cm diameter.

Seems like for any setup we would need a reliable engineering evaluation 
of the methods of taking heat off the small target. That would be one of 
the critical parameters that set limits on possible solutions.

One approach could be to investigate the option to use a beryllia (for 
example, see http://www.sanjosedelta.com/beryllium_oxide.shtml) vessel, 
holding Radium, cooled from the outside (by water?..). It should be 
shaped appropriately (with cooling fins attached, or such). The 
irradiation could happen through the entrance beryllia window.

Radium boils at 1140 C, and beryllia can be operated at up to 1800 C. So 
I guess the option to remove Radium from one such vessel into another 
without a loss could be the distillation process again: heat everything 
above 1140 C and attach a fresh vessel with a colder bottom.
Actinium should mostly stay, as it boils above ~3000 C.

Best regards,
Pavel