I think there are good reasons to use electron-volts. Perhaps the most basic is that it is generally understood to mean energy per photon. If joules would used, some way of indicating energy per photon rather than for the beam would have to be appended. The NIST Codata value for the electron volt is 1.602 176 487(40) x 10^-19 J. I think it is known with reasonable precision (uncertainty beginning in 9th significant figure)
--- On Thu, 12/3/09, Bill Hooper <[email protected]> wrote: From: Bill Hooper <[email protected]> Subject: [USMA:46239] Use of atto and yocto To: "U.S. Metric Association" <[email protected]> Date: Thursday, December 3, 2009, 3:43 PM It is also worthy of note that the GeV (gigaelectronvolts) was used as the energy unit. In this type of work, there are valid reasons why joules cannot be used; basically, they don't know precisely how many gigaelectronvolts there are in a joule. That is why the GeV (and eV, keV and MeV) are permitted for use with SI. Regards, Bill Hooper
