[ RadSafe ] Po-210 & Lethality

james.g.barnes at att.net james.g.barnes at att.net
Wed Nov 29 17:14:44 CST 2006

Look at it from this perspective, and perhaps it will help:

1)  ARS is a defined syndrome for cumulative, external exposure.  The general progression is hemopoetic, GI tract, CNS.  But keep in mind that someone with GI tract involvement, ALSO has hemopoetic.  It's just that the GI tract damage is what eventually kills him or her (or kills him or her faster than the hemopoetic damage would).  This is all based on a smooth progression as the total dose increases.  It is interesting to consider if one ONLY had GI tract issues, whether it would be as fatal as having GI tract issues AND blood-forming organ disruption.

2)  It is a bit harder to define ARS in an internal situation.  Here, as you note, because of isotope distribution (what organs, what cells in those organs, etc.), you won't get a universal exposure of the entire body, so you probably don't get the "syndromes" we are used to discussing for external exposure.  Usually, one or two specific organs get highly exposed, and other organs get significantly less dose.  So, from a deterministic viewpoint, the danger is in enough cellular disruption occurring that the organ can no longer function adequately enough to support healthy bodily function, which brings on illness and possibly death (I won't say cell killing, as a damaged cell may be a worse situation than a dead cell due to cell signaling, altered immune response, etc. etc.)  Every other organ in the body may be functioning just fine, yet the victim gets sick.

3)  I know of no really good numbers for how much dose that involves.  You have to be careful with this as (as I'm sure you know) 500 RAD to the entire body is not the same thing as 500 RAD to one organ as the former simultaneously irradiates ALL organ systems, while the latter only affects one or two.  The best I've found is a Table in Blatz's "Radiation Hygiene Handbook" (Table 19-4)(1959!) which lists a number of organ specific doses and resulting effects (e.g., 1,000 R to the lung produces swelling and ulceration, 2,000 R to the kidneys produces vascular damage, etc.).  Taking that as a basis, it's probably safe to say that organ disruption (greater or lesser) could be expected somewhere between 500 - 1000 Rad.  A radiation oncologist could probably give us some more focused information on this point (or perhaps some of our Medical Physicist colleagues).

4)  The health effect would center on whether those disrupted organs were critical to life or an adjunct to life.  Losing lung function is a whole lot nastier than losing gall bladder function.  Blatz lists heart and muscle as being in the 10K Rad range, so that would probably be the last to go.  Blood marrow is, of course, pretty sensitive to radiation, and losing one's immune system due to white cell killoff is pretty unpleasant.

5)  It would take a LOT of flux (activity) to deliver that much energy into the tissues of the affected organ body.  Alpha delivers more energy / particle simply based upon the physical behavior of the particle during an interaction.  This involves the LET, of course; the faster you lose energy per cm, the more dose you deposit.  So, by nature, an alpha dumps more dose than, say, a beta, because it has more energy to lose and it loses it faster (this isn't quite what the QF is addressing, as others have noted; this is more about the behavior of the dose deposition process, and is really more about LET).  Cancer is not the end point here; immediate cellular / organ functional disruption is.

Further, microeffects now become important because an "averaging" of dose over an entire organ probably isn't meaningful.  The fact that the arterial walls have become dangerously inflamed due to alpha exposure may the be driving issue, and that isn't very amenable to dose averaging.

6)  Now, we generally assume that the specific activity of the alpha emitters is relatively low, so it would take a lot of MASS to deliver that much activity and dose.  Requiring a lot of mass makes it less likely than one could intentionally or unintentionally administer enough of the material to approach these deterministic doses.

7)  However, Po-210 is a HIGH specific activity, thus one could deliver that much dose without too much mass. You're not constrained by having to shove in 1,000 grams of stuff to get the high doses; it's on the order of milligrams.  So now you don't need lots of mass to get a high dose effect in the organ.

So Po-201 doesn't fit our usual paradigm for internal exposures, which is discomforting to say the least.  Not least of which is that somebody actually sat down and figured all of this out so that they could use the material to kill.  That's tough to take.

Jim Barnes

-------------- Original message from Pete_Bailey at fpl.com: -------------- 

> Was wondering how (mechanism) does the alpha emitter 
> present an acute exposure-lethality combination ? 
> First off, was death due to the Hemopoietic syndrome ? 
> Gastrointestinal Syndrome ? I doubt , but was it, CNS Syndrome ? 
> Other systemic failure brought on by compromised organ failure/functions ? 
> I guess I'm struggling with the alpha Mev to Joules/Kg 
> and the number of alphas ( i.e., uCi) needed to kill enough 
> organ cells of enough important organs to cause a fairly rapid death ( 
> days/weeks). 
> While is has to be soluble enough to disperse 'everywhere' in the body, 
> it has to be of a form that wants to stay in the body; i.e., a long bio 
> half life.... 
> The material is in a chemical form that seeks , or at least 
> travels trough, the blood forming organs, wiping them out ? 
> I don't know, something just doesn't 'feel right'..... 
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