[Isotope-prod] Meeting notes

[George Neil]

Thanks Joe!  It would be useful if you could dig up that information 
when you get back.
George


On 9/17/2015 3:15 PM, Joseph Grames wrote:
> Sorry if I'm redundant, been gone for awhile.
>
> Some thoughts...
>
> 1.  Equilibrium temperature of vacuum window will come to same value within radius of a raster pattern so even if raster size is kept small (sorry don't know size off target) to match target there is a big advantage to making beam profile as large as sample since average power goes out like 1/r^2.  If helpful, rostering at small angle and low energy can be done with few tune Litz wire dipoles at rates up to ~10kHz with simple current driver, I think.
>
> 2.  The vacuum window can be thicker where the beam does not strike and vice versa to improve mechanical strength.  There is a beryllium vendor I've worked that will machine windows, I can get their info when back in town next week.
>
> 3.  A thermal model should be run when some geometry is considered - we've had really good success providing information for thin targets and windows for Mott and PEPPo and getting results quickly - for thick targets we provide energy deposit profile but for thin targets the estimate Pavel suggests make this even easier to do.
>
> Joe
>
> Sent from my iPhone
>
>> On Sep 17, 2015, at 8:28 PM, Pavel Degtiarenko <pavel at jlab.org> wrote:
>>
>> Hi George and All,
>>
>> The second important engineering question, the answer to which could severely limit our options, is:
>>
>> What is the maximum beam current that the vacuum window, separating the beam vacuum and the irradiation setup, could let through without breaking the vacuum. The beam size should be small (~0.2x0.2mm max) and the beam should not be rastered.
>>
>> Beam current is the right parameter here, as for thin windows the energy loss is only weakly dependent on energy. For crude estimates it can be assumed to be ~2 MeV/(g/cm^2) - and can be calculated precisely if needed. Beam cannot be rastered because Radium target is small (and I guess it will be quite difficult to move the target in sync with the rastered beam).
>>
>> Beryllium water-cooled vacuum window comes to mind. Still, I would expect it's a challenge to hold milliampere-range currents in these conditions. This limitation may force us to lower the beam currents and go to higher energies to provide for the activation power in the target.
>>
>> One "crazy" option that may have to be considered, is to have the window itself move in a circular motion, together with the last straight section of the beamline, that would have to be mounted on a flexible vacuum bellows... "Rastering" the window itself...
>>
>> Regards,
>> Pavel
>>
>>
>>> On 09/12/2015 10:01 PM, Pavel Degtiarenko wrote:
>>> 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
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