In his book "Principles of Stellar Evolution and Nucleosynthesis," Donald D. Clayton writes (p.593) that "The half-lives.... are so short that no detectable quantities of I-129 and Pu-244 exist today in the solar system. Their presence initially in the solar system can be inferred only by the detection of anomalies in the abundances of nuclei to which they decay. They are called extinct radioactivities."
On p. 604 & 605 Clayton writes that "Study of the extinct radioactivities abounds with complications..... Called the general anomaly, these overabundances are interpreted as being produced as fission fragments, and the only parent that seems to fit the necessary fission yields is the spontaneous fission of Pu-244..... Assuming that the duration of nucleosynthesis was several billion years or more and that its rate was constant, [the ratio Pu244/U235 remaining] at the end of nucleosynthesis [would be] = 0.051."
On the other hand, "Several authors have suggested that the material in the primitive solar nebula should have had a larger portion of 'last-minute' nucleosynthesis than would be expected on a continuous model.... Perhaps one should expect one or more supernovas to have exploded nearby, mixing their fresh radioactivities into the gas that would soon condense into the solar system. Such a model will be strongly suggested if Pu244/U238 ratios are consistently and unambiguously found to have larger values than uniform synthesis can provide."
The book is a 1968 publication, so much of these questions may long since have been resolved (can anyone provide a good update please ?). For one thing, the 'last-minute' nucleosynthesis is, I believe, the standard model now, and its assumed that the supernova(s) triggered or accelerated the collapse of the pre-solar gas & dust cloud.....
More recently (March 1999), a news story posted at
http://www.newscientist.com/cgi-bin/pageserver.cgi?/ns/19990710/newsstory10.html said that there should be trace amounts of plutonium-244 ( T1/2 = 81mln.yrs) in the environment, dating back some millions of years (depending on when the last "near-by" supernova star explosion occurred..).
I asked Andy Karam about it and he responded as follows (Wednesday, September 08, 1999):
"....this story deals more with recent deposition. I don't know as much about this except that supernovae
of the type they are talking about aren't likely to contribute very much mass (or many atoms) to the Earth and would leave a pretty small signal.
For more information on this, you might be interested in a paper by Ellis, Schramm, and Fields (the researcher noted in this article) that discusses looking for isotopic evidence of nearby supernovae.
To the best of my knowledge, this is the first discovery made using the ideas noted in the Ellis et al paper.
[regarding] extinct radioactivities.... the premise is that supernovae produce all sorts of TRU nuclides, including Pu-244. The supernovae from which the solar system formed likely occurred at least 5 billion years ago, so the amount of Pu-244 left is likely to be nearly undetectable today (62 half lives). However, people have looked for decay series nuclides and, more importantly, fission products. Examinations of meteorites have shown excess Xe-132, 134, and 136 that seems to match FP abundance found from Pu-244 in the lab. Current
meteorites seem to have a Pu-244/U-238 ratio of about 0.007:1, pretty low.
It's also interesting to note that combining Pu-244 data with that from I-129 (also formed in supernovae) helps to constrain the time between supernovae explosion and the formation of the solar system - about 130
million years is the best bet. Another extinct nuclide that has been detected (at least via indirect evidence) is Cm-247 (half life = 15.6 million years).
......
There is more information on this in a book called Radiogenic Isotope Geology by Alan Dickin (1995, Cambridge University Press)."
----------
Hope this helps. Please let me know Phil, if you find any other interesting stuff on this topic !
Jaro
-----Original Message-----
From: Philip Egidi [mailto:phil.egidi@state.co.us]
Sent: Wednesday September 04, 2002 7:00 PM
To: radsafe@list.vanderbilt.edu
Subject: Naturally occurring Pu-244
RADSTERS,
I have a time critical response to put out to a member of the public
about naturally occurring Pu-244.
I have looked at NCRP 94, Kocher, UNSCEAR, Eisenbud/Gessell, Schlien,
and the prestigious Google. I don't have a whole lot to show for it
yet.
Does anyone have (preferable electronic) any papers or references on
the occurrence and properties of naturally occurring Pu-244?
Thanks,
Phil Egidi
phil.egidi@state.co.us
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