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Re: Bismuth breaks half-life record
John
Thanks for the information. I checked my old Table of Isotopes (Ledeer at
al, Sixth Ed. 1967). The Bi-209 half-life there is >2 x 10^18 and the alpha
energy is ? 3.0 MeV. It looks like the theory I learned in graduate school
was better than I thought at the time!
_______________________
John R Johnson, PhD
idias@interchange.ubc.ca
----- 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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