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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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