Can Radioisotope Generators Really Put an Elephant to Sleep?

[Nomy-the wanderer]

We've an old professor, can make an elephant sleep, bad notes, bad lectures and no real source for what we are studying...The thing is people just copy and paste his notes but ican't do that, i don't have this ability, i need some proper notes about generators, using sublimation, chromatography methods...

If anyone has a link please...Because I've been searching for a decade now. I'm not that good at chemistry BTW.

 

[Astronuc]

I believe you mean - Radioisotope thermoelectric generator

For starters - http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator

http://saturn.jpl.nasa.gov/ spacecraft /safety.cfm - RTG's used on Cassini spacecraft

and discussion of RTG's and alternatives for Cassini (Cassini Environmental Impact Statement Supporting Study)

DOE Report on Nuclear Power in Space, including discussion on RTG's -
http://www.ne.doe.gov/pubs/npspace.pdf

What specifically would you like to know about RTG's?

 

[chroot]

Or perhaps he means 'generators,' which are used in nuclear pharmacy, to generate a steady supply of short-lived isotopes from other longer-lived isotopes?

- Warren

 

[Astronuc]

Ah, in that case, I think one is looking for neutron activation perhaps, in which stable nuclei (of mass A) absorb neutrons, which produce a population of radionuclei (of mass A+1, and possibly A+2).

In that case, the principles of neutron activiation analysis would apply.

 

[Nomy-the wanderer]

Actually he is a she :D

Anyway yes Chroot was right, I'm talking about those generating a supply of short-lived isotopes from a longer-lived ones, and specifically as I've just stated in the other post, those that use separation methods like sublimation and chromatography methods...

OH! i forgot the most important thing, forget about neutrons now, we r talking Radiochemistry, I'm sorry i donno how i forgot to mention that...Radiochemistry is one of my most hated subjects, it started with a bit of nuclear physics, that was nice, was nothing that new back then, and then they started the separation techniques, it's not difficult to understand if u've at least some proper notes, our library is kinda useless...

Mah, anyway i don't want to give u headache, the example the professor used was generating Tc from Mo (99) using both sublimation and chromatography, but it's pretty uncealr here...

 

[Astronuc]

Well, there are two main issues here: 1) the physics of radionuclide production and 2) the chemical aspects.

So let's look at the example of ₄₃Tc⁹⁹ from ₄₂Mo⁹⁸ in which ₄₂Mo⁹⁹ is an intermediate step.

Ref:
http://wwwndc.tokai.jaeri.go.jp/CN04/CN010.html

Note: half-lives -
₄₂Mo⁹⁹ - 2.747 d
₄₃Tc⁹⁹ - 211,000 yrs.

The Mo-99 isotope will decay rapidly and after 30 days (~1 month) it's activity will have decreased by a factor of about 2000, leaving mostly Tc-99 - if the initial Mo sample is mostly pure Mo-98.

If one looks at the Chart of Nuclides, one finds that the abundance of Mo-98 is 24.13% of natural Mo, so one has to separate Mo-98 from the other isotopes, which could be done by a number of means, such as mass spectrometry or gas centrifuge of a fluroride compound, for example MoF₆.

http://www.webelements.com/webelements/compounds/text/Mo/F6Mo1-7783779.html

Purified Mo-98 can then be irradiated in a neutron flux, which produces Mo-99. Fortunately, if some Mo-100 is produced that's not a problem since it is a stable nuclide. Then the sample if removed from the neutron flux at some point, and the Mo-99 is allowed to decay for say 1 or 2 months, and then it is mostly Tc-99 distributed in Mo-98. Then again the sample could be dissolved and the Tc chemically separated from Mo.

Similar process applies to other radionuclides.

 

[daveb]

In nuclear pharmacy, the generators are Mo-99 (there are others such as Sr-82/Rb-82, etc.). These have a column of Mo-99 in an alumina matrix. Each end connects to a needle at the top of the shielded moly core. Tc-99m is extracted by a process called "milking" the generator, where a vial of saline is placed on one needle, and a evacuated vial on the other. The vacuum in the one vial draws the saline through the column, and the Tc-99m comes along with it (as well as some Mo-99 and Tc-99 if it hasn't been recently milked), into the evacuated vial. There are only 2 makers of genreators inthe US right now - Mallinckrodt http://www.mallinckrodt.com/" . If you want a pretty good book, Saha's Fundamentals of Nucler Pharmacy is a great resource, as is Mosby's Handbook of Nuclear Medicine.

 

[Nomy-the wanderer]

That was an enlightment.. Thx guys for the help, also I've found an illustrative drawing + the explanation u gave. let's see...

Note: half-lives -
42Mo99 - 2.747 d
43Tc99 - 211,000 yrs.

I think that's quite opposite to the purpose of a generator as far as i understand, we need a large flux of the produced isotope (high activity) and a very short half life, to prevent any complexes caused by excess radiation...In the same time the gamma energy is of 140 Kev,also this amount of energy wouldn't harm the patient organs...I think the Tc produced is Tc99-m which has a half life of 6 hours, that is long enough to be used and short enough to be safe.

The question is if the regular Tc99 is produced, wouldn't that make it more complicated to deal with generators and kinda unsafe?

Saha's Fundamentals of Nucler Pharmacy

I think I've seen that somewhere, i'll look for it.

 

[Astronuc]

I had forgotten about Tc<sup>99m[/sub] which undergoes Isomeric Transition (IT) which is a gamma decay. See - http://wwwndc.tokai.jaeri.go.jp/cgi-bin/nuclinfo2004?43,99

That is the short half life (6 hrs) to which one is referring, and if one has significant activity with this isotope then the corresponding activity of the longer half-life state Tc99 is considerably lower.</sup>

 

[Nomy-the wanderer]

Thx Astronuc, things are clear now...

 

[daveb]

There isn't any danger from Tc-99 to the patient. Even if the drug is a sulfur colloid, which stays in the patient forever, the activity of Tc-99 is indistinguishable from background. The typical Tc-99m dose is about 30 mCi at the time of injection. At a half life of ~ 6 hours, even if all of it turns into Tc-99, with its half life of `210,000 years, the activity of Tc-99 in the patient's system is 30mCi*6hours/210,000 years which is about 100 pCi - a very tiny activity.

 

[Nomy-the wanderer]

My main concern was about the long T1/2 which makes it difficult to handle later, not as danger cause to the patient...Contamination problems, waste issues...etc that's what i was talking about.

 

[daveb]

Well, the Tc-99 from the core itself is indistinguishable from background. You can pick up impurities in the core, most of which are beta emitters, but even this is generally less than 2mR/hr if completely unshielded. These last about 2 to 4 years (it's hard to quantify these nuclides in anything other than a well shielded well with an NaI crystal). They're pretty easy to shield, though, since the actual cores themselves are about half the size (height) of a pencil.

As for disposal, even the Tc-99 itself is only around 500 nanocuries.