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Re: Bismuth breaks half-life record
It is hard for me to conceive of anything with a half-life of ~10^19 years
as "radioactive". Given enough time, all matter will eventually decay, since
the proton itself is reputed to decay with have a half-life of ~10^31yr.
Therefore, in a sense, everything could be considered "radioactive" (i.e.
no such thing as a stable element). It is also hard to understand the
special dread of long-lived radionuclides given that the longer the
half-life, the less radioactive anything is.
To avoid such perceptions, in a paper we gave about 20 years ago, we
proposed the radioactive designation be limited to those nuclides with
half-lives less than one million years. Those with half-lives between a
million and a trillion years would be "radiopassive", and those with a
half-life exceeding a trillion years would be designated "radioquiscent".
Somehow, the idea never caught on.
----- Original Message -----
From: John Jacobus <crispy_bird@YAHOO.COM>
To: radsafe <radsafe@list.vanderbilt.edu>
Sent: Thursday, April 24, 2003 11:45 AM
Subject: Bismuth breaks half-life record
> Bismuth breaks half-life record
> 23 April 2003
>
> Physicists in France have measured the longest ever
> radioactive half-life - over two billion billion years
> - in a naturally occurring element. Nőel Coron and
> colleagues at the Institut d'Astrophysique Spatiale in
> Orsay used a 'scintillating bolometer' at very low
> temperatures to detect the emission of alpha particles
> - charged particles that consist of two protons and
> two neutrons - as bismuth-209 decays into thallium-205
> (P de Marcillac et al. 2003 Nature 422 876).
>
> Bismuth-209 is thought to be the heaviest stable
> isotope that exists in nature. However, theory
> suggests that it should be metastable and decay via
> alpha-particle emission to thallium-205. This not easy
> to measure because of the very low decay probability.
> Moreover, the alpha particles generated have very
> little energy and are difficult to detect.
>
> The scintillating bolometer used in the experiment
> consists of two detectors enclosed in a reflecting
> cavity and cooled to 20 mK. The first detector is made
> of bismuth, germanium and oxygen and faces a second
> "light" detector made from a thin disk of germanium.
> The bolometer registers the temperature rise following
> the absorption of an alpha particle in the germanium
> target as a voltage pulse. The amplitude of the pulse
> is directly proportional to the energy released, and
> this allows the researchers to record a complete
> spectrum of all the "events" observed.
>
> The team performed two measurements, one with 31 grams
> of bismuth in the detector and the other with 62
> grams. The scientists registered 128 alpha-particle
> events over 5 days and found an unexpected line in the
> spectrum at 3.13 MeV - now attributed to bismuth-209
> decay. The half-life was calculated to be (1.9 +/- 0.2
> ) x 1019 years, which is in good agreement with the
> theoretical prediction of 4.6 x 1019 years. It is also
> longer than any previous measurement of a radioactive
> half-life
>
> The technique could be also be used to accurately
> detect beta and gamma decays. "The experiment is a
> by-product of our search for dark matter," team member
> Pierre de Marcillac told PhysicWeb. "Other kinds of
> decays such as protons from proton-rich nuclei could
> be studied by the same method but this will have to be
> proved!"
>
> Author
> Belle Dumé is Science Writer at PhysicsWeb
>
> Location: http://physicsweb.org/article/news/7/4/16
>
>
> =====
> -- John
> John Jacobus, MS
> Certified Health Physicist
> e-mail: crispy_bird@yahoo.com
>
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