Talk:Californium

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Article changed over to new Wikipedia:WikiProject Elements format by mav 08:17, 31 Mar 2004 (UTC). Elementbox converted 11:47, 17 July 2005 by Femto (previous revision was that of 23:40, 10 July 2005). /archive1

Initial price of californium?

The article states that Californium was sold by the Atomic Energy Commission starting in the 1970s for $10 a microgram. Several other sources, however, given different figures. An October 1968 newspaper article (The Spokane Daily Chronicle) gives a figure of $100 per tenth of a microgram - there's also an amusing quote from Seaborg in the article, he called californium "a bargain at almost any price". A November 1968 article in the Leader Post (see here) cites the same figure of $100 per tenth of a microgram. This price was repeated in a number of newspapers at around the same time - with the equivalent per pound price arousing considerable interest. On balance, these sources seem to make a much more credible case that Californium first went on sale in 1968 for $100 per tenth of a microgram - rather than the 1970s for $10 a microgram figure currently included. What's not clear, though, is whether anyone actually bought it at this price. It would be great if someone could help clarify. Sir Nils (talk) 19:24, 1 July 2011 (UTC)

I did some digging but could not verify with a more reliable source than a newspaper that Cf was sold prior to the 1970s. So I'm not comfortable mentioning that. But that is enough for me to copyedit the sentence to get rid of the impression that it was sold starting in the 1970s. I'm not concerned by the price being much higher in the late 1960s; Cf became easier to synthesize as time went by and the AEC set up the Cf-252 sale program specifically to encourage study of the element. --mav (reviews needed) 03:04, 4 July 2011 (UTC)

Introduction: absence from Earth's crust

I have removed the phrase "this short half-life means the element is not found in the Earth's crust." It is already stated that the element does not occur naturally, and that it was artificially produced. The half life is not a definitive reason for absence: absence of that which does not naturally occur scarcely needs explanation. Custard is not found in the Earth's crust either. Kevin McE (talk) 06:28, 21 July 2011 (UTC)

It's not the same thing. Every one of the 288 nuclides that has a half life long enough to have existed from the solar system's primordial cloud (with nucleosynthesis in the supernovae that seeded it with elements heavier than carbon) exists primordially on Earth. If Cf had an isotope with a half life longer than Pu-244, it would exist as a primordial nuclide also. The fact that it doesn't means it must exist as a non-primordial or not at all.

In this case, it is apparently not at all. Absense of a long-lived nuclide means no primordial element, but not necessarily no natural occurence. There exist an additional 50 or so short lived radionuclides that exist naturally on Earth due to cosmogenesis (C-14), radiogenesis (Fr, Ra, Rn, etc), and natural nucleogenic processes (some Pu-239). No Cf appears to exist in that fashion, however. Its only route would be neutron absorption nucleogenesis (geonuclear transmutation) in the crust, and there just aren't enough neutrons around these days to do the job. SBHarris 06:45, 21 July 2011 (UTC)

To sum up, yes, not only lifetime but also the bombarding particle (required for synthesis from lighter elements) is important. The custard comparison is invalid - all chemical elements found in custard occur in the Earth's crust. Materialscientist (talk) 07:12, 21 July 2011 (UTC)

Yes, obviously the custard example was tongue in cheek. But Californium (not unlike custard) is only known to have existed by human intervention: there is no assertion in the article that it ever has existed naturally. Without evidence of that, the rate of decay is irrelevant to its absence from the earth's crust today. It seems to be a presumed reason for an assumed change in prevalence. Kevin McE (talk) 19:22, 21 July 2011 (UTC)

SBHarris can answer better, but for what I know, the rate of decay is very relevant simply because it gives a rough estimate whether an isotope could have survived from the time when the Earth wasn't a solid yet and its particles were originating from the outer space. In other words, if the half-life is short, the element can't be primordial, and this is the primary selection factor for occurrence. However, it doesn't necessarily mean the isotope does not occur in the crust, because an unstable isotope can still be formed in detectable amounts by natural irradiation, provided both the precursor and the irradiating particles are abundant enough. (Here again, the half-life - of precursor though - is a major factor, because if it is too short, the precursor decays before conversion.) Materialscientist (talk) 23:41, 21 July 2011 (UTC)

Yes. All elements heavier than boron are made in type IIa supernovas. There is every reason to think that such supernovas make every nuclide that CAN be made. If none are left of some of these > 4.6 billion years later, it's because they are radioactive with half lives too short for enough to still be detectable now, AND there are no routes to them having been naturally produced in some process, SINCE the supernova. The short-lived transactinides past plutonium illustrate all that very well. The lighter radioactives are usually made naturually from something heavier, such as fission producing Tc and Pm. But most heavy radioactives with short half lives have no way to be made naturally, except a way that occured too long ago (in supernovae) for them to survive to today. Cf is one of these. And BTW, please capitalize Cf, but not californium. SBHarris 02:43, 23 July 2011 (UTC)

Stability

From the article:

The most stable of californium's twenty known isotopes is californium-251, which has a half-life of 898 years; this short half-life means the element is not found in the Earth's crust.[note 1] Californium-252, with a half-life of 2.645 years, is the most common isotope used and is produced at the Oak Ridge National Laboratory in the United States and the Research Institute of Atomic Reactors in Russia.

This may be a silly question, but based on the half-life as stated above, isn't Ca-252 more stable than Ca-251? It's half-life is almost 3 times as long. Kleuske (talk) 07:23, 21 July 2011 (UTC)

2.645 means a bit more than two and half years. Materialscientist (talk) 07:58, 21 July 2011 (UTC)

I suspect Kleuske has fallen victim here to differences between how decimal and thousand separators are handled in the MOS and the way they are handled in his/her native culture. As a reminder, here are the relevant quotations from the MOS: "Use commas to break the sequence every three places: 2,900,000" and "use a period character between the integral and the fractional parts of a decimal number, not a comma or a raised dot (6.57, not 6,57 or 6·57)." --Khajidha (talk) 14:42, 21 July 2011 (UTC)

And I am a native user of that convention, and still read it the wrong way. I find it awkward to read decimal parts of years. It might be clearer to give the half-life of Cf-252 in days (although "966 days" may cause confusion of a different sort). -- Donald Albury 15:37, 22 July 2011 (UTC)

Just cut a decimal place or two. then the number will be shorter either way and won't look like a Euro style thousands separator. Plus it's un-needed precision for prose.TCO (reviews needed) 01:49, 23 July 2011 (UTC)

Yep, shortening to 2.64 years does the trick. SBHarris 02:30, 23 July 2011 (UTC)

More information

The "Universitium" + "Ofium" + "Californium" + "Berkelium" anecdote (http://elements.vanderkrogt.net/element.php?num=98) should perhaps be mentioned. Double sharp (talk) 12:59, 19 January 2012 (UTC)

Natural Occurrence

This article states that californium is the heaviest element to occur naturally on Earth. What is the source for that statement and is it reliable? Every source I have seen states that plutonium is the last known naturally occurring element on Earth/in the Earth's crust. — Preceding unsigned comment added by 72.84.185.135 (talk) 16:31, 27 October 2012 (UTC)

Emsley, John (2011). Nature's Building Blocks: An A-Z Guide to the Elements (New ed.). New York, NY: Oxford University Press. ISBN 978-0-19-960563-7. Double sharp (talk) 02:35, 28 October 2012 (UTC)

Critical mass

Under "Applications", it says, "Californium-251 has a very small critical mass (about 5 kg)...." It should probably be stated that this is a calculation/extrapolation, as enough californium to directly test this has probably never been produced, and probably shouldn't be, because nuclear blasts are devastating and, in this case, would spray highly radioactive californium into the environment. Also, how credible are such estimates of critical mass?--Solomonfromfinland (talk) 08:03, 5 May 2013 (UTC)

[1] Double sharp (talk) 13:18, 6 May 2013 (UTC)

In case this wasn't clear: yes, it is a calculation, but a reliable one. I have edited the article to make it clear that it is a calculation. Double sharp (talk) 15:54, 19 October 2013 (UTC)