At 10:26 AM Wednesday 11/9/2005, Robert G. Seeberger wrote:
http://www.spacedaily.com/news/physics-05zq.html
If subatomic particles had personalities, neutrinos would be the
ultimate wallflowers. One of the most basic particles of matter in the
universe, they've been around for 14 billion years and permeate every
inch of space, but they're so inconceivably tiny that they've been
called "almost nothing" and pass straight through things - for
example, the Earth - without a bump.
So it's easy to see why no one thought they existed until the 1930s,
and why it wasn't until the 1950s that scientists were finally able to
confirm their inconspicuous presence. It's also easy to see why their
masses, once believed to be zero, remain so elusive, but could help
unlock the universe's mysteries on everything from dark matter to the
births of galaxies.
With a Precision Measurement Grant from the National Institute of
Standards and Technology that will provide up to $150,000 in funding
over three years, Florida State University research physicist Edmund
G. Myers, in Tallahassee, Fla., and student researchers hope to meet
part of that challenge by measuring the precise difference in mass of
tritium, a form of hydrogen, and helium-3 atoms. This will help pin
down the mass of the electron neutrino.
To make such a measurement, Myers will use the state-of-the-art
Penning trap that he brought to FSU from the Massachusetts Institute
of Technology in 2003. It's arguably the most precise equipment made
for the purpose of determining atomic mass.
"With neutrino mass, the game is to keep lowering the upper limit
until you find it," Myers said.
Right now, that ceiling is around 2 electron Volts (eV). Myers' work,
combined with results from other experiments, could drop this by a
factor of at least 10, to 0.2 eV or even lower. By comparison, an
electron, which is probably the lightest commonly known subatomic
particle, has a mass of 511,000 eV.
Myers was one of two recipients of this year's Precision Measurement
Grants, which the National Institute of Standards and Technology has
been awarding since 1970. Among the 34 applications, Myers' research
stood out because it so snugly fit the institute's mission to support
physics research at the most fundamental level, said Peter Mohr, the
institute's grant program manager.
"What he's doing is very precise measurements," Mohr said. "The
results are very important."
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I'm having a bit of trouble envisioning how voltage is equivalent to
mass.
I'm guessing that voltage in the electrical sense is not exactly the
same as eV in the electron sense, or is it?
Voltage is electrical pressure. Is eV the pressure an electron exerts
on its environment?
An electron volt is a unit of *energy*: the
amount of energy imparted to an electron when it
moves through a potential difference of one volt.
By Einstein's equation E=mc^2, mass and energy
are equivalent. The mass of an electron is
equivalent to about 511 thousand electron volts
worth or energy. So, rather than calling it
9.1×10^-31 kilograms, physicists especially in
the atomic and nuclear field say that the mass of
an electron is "511 keV" or "0.511 Mev," both
because (1) it is shorter and simpler than
carrying along that big negative exponent on the
mass in kilograms and (2) it relates the
mass-equivalent of a particle to the amount of
energy the particle receives when accelerated
through a voltage in the laboratory (or in
nature, or by the electron gun in a TV picture
tube or the like), which for a light particle
such as an electron can easily be comparable to
or even greater than the energy equivalent of its
mass. It also makes it easier when dealing with
annihilation reactions and pair production: the
mass of an electron or positron is 0.511 MeV, and
so the spectrum of a positron emitter shows a
peak at that energy due to the gamma rays
produced when the positrons emitted by the decay
of the radioactive substance annihilate with electrons in the surroundings.
xponent
I'm A Dummy Maru
Nah, you just haven't spent enough time hanging
out in unclear physics labs . . .
Or Maybe You Already Have A Life Maru
--Ronn! :)
"Since I was a small boy, two states have been
added to our country and two words have been
added to the pledge of Allegiance... UNDER
GOD. Wouldn't it be a pity if someone said that
is a prayer and that would be eliminated from schools too?"
-- Red Skelton
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