A nuclear amusement - Tungsten

[Richard Hull]

A quick glance at the chart of the nuclides shows that naturally occuring, earthbound tin is perhaps on of the most isotopically rich of all of the elements. None of its ten or more natural isotopes are radioactive.

Tunsgten, on the other hand, is naturally radioactive and over 30%, by weight, is W-184 with the longest half life of most any natural element with such a large isotopic percentage factor. (3x10e17 years)!!! That's 300 quadrillion years! It decays down to Hafnium via alpha particle emission.

Now what kind of counts should we expect from how big a piece of pure tungsten? 184 grams of W-184 is a mole, but we need about 613 grams or 1.35lbs of real pure, earthly tungsten to contain that 1 mole of W-184 atoms. (~6X10e23 atoms)

Now that means that the 1.3 pound chunk of nautral Tungsten will decay at a rate of ~1 million atoms/year or 2 disentegrations/minute (2 CPM). As the radiation is alpha and would likely not penetrate more than a few atoms thickness in tungsten, we would expect virtually zero counts to be recorded off of a bulk piece of tungsten.

Is tungsten radioactive? Yes! All tunsten is radioactive. As a matter of fact a large fraction of all tungsten is radioactive. Can you really measure its radioactivity with normal equipment? No!

This begs the question how was W-184 created. Man knows of no real fusion process yet studied that could possibly fuse matter into this massive atom. Most stars we study fade out at iron. Obviously, we have a lot to learn. The generally allowed handwaving exposition by modern physics is that such massives are the result of ancient massive supernovae explosions. Sounds nice, but how accurate is it. Anyone ever made measurements inside a supernova core?

Massive atoms like W-184 that are in such huge natural abundances and that are also ever so slightly unstable fascinate me. Quadrillions of years.........Amazing.

Richard Hull

[guest]

For what it worth, The reason why heavy elements are abundant, is because when the universe was younger, it was made up of nearly pure hydrogen. This permitted huge quantities of massive stars (stars with diameters out to the orbits of Jupiter and Saturn). These stars only live for a couple of million years before they go nova, creating all the wonderful elements we now have. There are a still a few of these massive stars (Orion has one), but the conditions for supporting them largely, no longer exist.

[Richard Hull]

Hydrogen still makes up about 99.9% of the mass of the universe. (According to the powers that be.) In spite of Billions of years of turnin' and burnin', nature's fusion systems are blessedly poor and slow in their action. Still got lotsa' H to burn. The heavier elements are sort of concentrated on the slag heaps that acrete around stars. Once again, where we live and work is atypical of the universe as a whole. Pretty much a heap of dead, neutralized matter warmed just enough by the nearby star to allow low order biological systems to crawl outta' th' ooze and provide for some interesting chemistry reshuffling outer electron orbitals.

Virtually 100% of this energy that drives us and that we later retrieve and use is due to solar UV light cocking a whole bunch of chemical potential energy guns which we biologics (flora and fauna) release latter as needed for warmth, growth and transportation.

All of this can only happen in the most microthin zones about any stable star system. These zones of good chemistry are defined pretty much by an ideal energy density of UV light in the range of 100-300 nm.

Richard Hull

[ChrisSmolinski]

FWIW, according to Science News, researchers at the Institute for Space Astrophysics in Orsay, France have found that Bi-209 is actually radioactive - via alpha decay, with a half life of 1.9e19 years. Apparently this was postulated 50 years ago. They used bolometers to make the measurements, not direct measurement of the radiation (hey, this stuff has a half life two orders of magnitude longer than the W-184 Richard was talking about!)

Here is the link, but I think you may need to be a subscriber to view it: http://www.sciencenews.org/20030503/note16.asp

IMHO, I suspect the harder we look, the more "stable" nuclides we'll discover to actually be unstable. First we're told that everything from Bismuth on down is stable. Well, except for Technecium and Promethium. Then there are isotopes of Vanadium and Rubidium, which also don't seem to be completely stable either. I stumbled on an interesting list here: http://www.don-lindsay-archive.org/crea ... _list.html

So now Bismuth-209 gives up the the title of heaviest stable nuclide, with Lead-208 the current champion. "Stable" may just mean "less unstable", though. Iron death of the universe?

[Richard Hull]

Thanks Chris. I have heard for years that naturally occuring bismuth was thought to be radioactive. Bi-209 is the sole natural bismuth isotope! Thus, all extant natural bismuth is a pure radioactive! The alpha decay would be the only way it could decay, of course. Giant longer half life elemental atoms have to ditch an alpha.

Richard Hull

P.S. didn't get the URL to show the article as I am not a subscriber, it said. RH

[ChrisSmolinski]

Here is the text of the article, appologies for poor formatting:

Not even bismuth-209 lasts forever
http://www.sciencenews.org/20030503/note16.asp

Peter Weiss

Many heavy elements radioactively decay into lighter
ones, although some do it
faster than others. For decades, textbooks have
listed bismuth-209 as the
heaviest naturally occurring atom that never decays.
A new experiment shows
that the textbooks are wrong.

Using exquisitely sensitive, heat-detecting
instruments known as bolometers,
Pierre de Marcillac and his colleagues at the
Institute for Space Astrophysics in
Orsay, France, chanced upon signs that more than 100
bismuth-209 atoms had
each spat out a helium nucleus—also known as an
alpha particle—to become a
lighter atom of thallium-205.

Theorists had predicted this particular decay more
than 50 years ago. However,
after a series of experiments conducted between 1949
and 1972 failed to turn up
any evidence of the breakdown, those predictions
faded into obscurity.

The rare disintegrations, reported in the April 24
Nature, were finally spotted as
de Marcillac and his coworkers searched for
something else—a hypothetical
particle, the neutralino, that might be a component
of the universe's so-called
dark matter (SN: 1/25/03, p. 51: Available to
subscribers at
http://www.sciencenews.org/20030125/fob2.asp).

During a routine check for contamination in their
bolometers, which happen to
be built around crystals containing bismuth, the
team noticed an unexpected
alpha decay not listed in any reference tables.

Even so, those disintegrations occur so infrequently
that an atom of bismuth-209
can still last just shy of forever. On the basis of
the new decay data, the team
calculates a half-life for bismuth-209 of some 19
billion billion years—roughly
1.4 billion times the current age of the universe.

Researchers didn't have to wait anywhere near that
long to detect the telltale
alpha decays because the huge number of bismuth
atoms in even a single
bite-size bolometer crystal guarantees that some
atoms will break down in a
matter of days, if they break down at all, de
Marcillac says.