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Re: Improper (?) use of MeV
From: Jim Lux[SMTP:jimlux-at-earthlink-dot-net]
Sent: Saturday, November 29, 1997 2:06 PM
To: Tesla List
Subject: Improper (?) use of MeV
> You are correct -- it is a common unit used for both subatomic particles
> but also for high potential generators. Most large electrostatic
> generators such as Van de Graaff generators operating up to 35 million
> volts commonly use the 35 MEV rating. It actually refers to the ability
to
> accelerate particles down an evacuated accelerator tube. We prefer to
use
> this unit because we had initial calibrations of some of our resonance
> transformers at 1 MEV using X-ray generation to determine output
potential.
A few problems I see with the above:
1) With an electrostatic accelerator (e.g.Pelletron, Dynamitron, or Van de
Graaf), you need to make the distinction between the terminal voltage
(measured in Volts, with the world record at 25+ MV) and the energy of the
particles being accelerated (measured in electron volts (eV):note the
lower case e). With multiply ionized heavy ion particles falling through a
field, the energy of the particle could be several times the accelerating
voltage, e.g. hundreds of MeV from an accelerator with 10 MV accelerating
potential. Another standard technique is to use the accelerator in a
"tandem" mode, where the particles are accelerated once going from ground
to the HV terminal, then "stripped" changing their charge, and accelerated
back from the HV to ground. In this case the energy of the particles would
be twice the terminal voltage: i.e. a 5MV accelerator can produce 10MeV
particles.
2) With a high voltage source, you can accelerate electrons and have them
hit a target, producing X-rays. An evactuated tube is necessary because
otherwise the electrons will hit something on the way before they get
moving. The spectrum of the Xrays is directly related to the energy
distribution of the electrons. There are a variety of ways to measure the
X-ray energy distribution.
3) You can also get emission of x-rays by bending the beam of particles,
via a mechanism called synchrotron radiation. The beam gets bent by means
of a magnetic field. Again, the spectrum of the x-rays depends on the
energy of the particles, how sharp the bend, etc.
4) You can produce very high energy particles with relatively low voltages
by passing the particle through an accelerating field more than once. I
don't know what voltage the SLAC runs at, but it sure isn't a GigaVolt, and
that energy of the electrons coming out is well above a GeV. Also, the
Tevatron, producing particles at Tera electron Volts, doesn't use a
TeraVolt.
So, at the end of my ember ( a small flame, as it were), my proposal is to
stop using the electron volt measurement, unless in the context of charged
particles, perhaps generated by a tesla coil.