 |
| Complete
Majorana Instrument, shielding
removed. |
A very rare form of nuclear disintegration
called double beta decay was observed
for the first time in 1986. This process,
in which a nucleus emits two electrons
and two antineutrinos, was observed
in an isotope of selenium by Michael
Moe and colleagues at the University
of California, Irvine, with Office
of Science support. Later, double
beta decay was seen in other nuclei,
including forms of calcium, germanium,
and molybdenum. The methods developed
for the experiment are being used
to search for another rare decay mode,
neutrino-less double beta decay, in
which only the two electrons are emitted.
This process could occur only if an
electron neutrino is its own antiparticle
and if neutrinos have mass, in violation
of the Standard Model (physicists'
current theory of matter and the forces
of nature). Given the prevalence of
neutrinos in the universe, even a
tiny mass could account for much of
the mysterious "dark matter" that
emits no visible radiation but constitutes
90 percent of the mass of the universe.
Scientific Impact:
The measurement of the double beta
decay rate provides key information
that will be needed to determine neutrino
mass once neutrino-less double beta
decay is observed. In addition, the
ultrasensitive techniques developed
for these experiments are being used
to search for other forms of dark
matter.
Social Impact: Although
research on double beta decay is new,
single beta decay has many applications,
including diagnostic and therapeutic
medicine, and archeological dating.
For example, doctors can examine functional
images of patients' organs using positron
emission tomography or treat thyroid
disorders using a radioisotope of
iodine, and carbon-14 dating is used
to establish the age of ancient objects.
Reference: "Double
Beta Decay," S. P. Rosen and Michael
K. Moe, Scientific American
November, 1989, p. 30.
URL:
http://majorana.pnl.gov
Technical Contact:
Dr. Peter Rosen, peter.rosen@science.doe.gov
Press Contact: Jeff
Sherwood, DOE Office of Public Affairs,
202-586-5806
SC-Funding Office:
Office of High Energy and Nuclear
Physics |
