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LLNL'S PRECISION COMPTON SCATTERING LIGHT SOURCE*
F.V. Hartemann#, F. Albert, S. G. Anderson, A.J. Bayramian, R.R. Cross, C.A. Ebbers, D. J.
Gibson, T.L. Houck, R.A. Marsh, M. J. Messerly, V. A. Semenov, M.Y. Shverdin, S.S. Wu, R.D.
Scarpetti, Jr., C.W. Siders, D.P. McNabb, R.E. Bonanno, and C.P.J. Barty, LLNL, Livermore, CA
C.E. Adolphsen, A. Candel, T.S. Chu, E.N. Jongewaard, Z. Li, C. Limborg-Deprey, S.G. Tantawi,
A.E. Vlieks, F. Wang, J.W. Wang, F. Zhou, and T.O. Raubenheimer, SLAC, Stanford, CA 94025,
Continued progress in accelerator physics and laser
technology have enabled the development of a new class
of tunable x-ray and gamma-ray light sources based on
Compton scattering between a high-brightness, relativistic
electron beam and a high intensity laser pulse produced
via chirped-pulse amplification (CPA). A precision,
tunable, monochromatic (< 0.4% rms spectral width)
source driven by a compact, high-gradient X-band linac
designed in collaboration with SLAC is under
construction at LLNL. High-brightness (250 pC, 2 ps, 0.4
mm.mrad), relativistic electron bunches will interact with
a Joule-class, 10 ps, diode-pumped CPA laser pulse to
generate tunable y-rays in the 0.5-2.5 MeV photon energy
range. This gamma-ray source will be used to excite
nuclear resonance fluorescence in various isotopes. Fields
of endeavor include homeland security, stockpile science
and surveillance, nuclear fuel assay, and waste imaging
and assay. The source design, key parameters, and current
status will be discussed, along with important
applications, including nuclear resonance fluorescence
and high precision medical imaging.
INTRODUCTION AND OVERVIEW
The nascent field of nuclear photonics is enabled by the
recent maturation of new technologies, including high-
gradient X-band electron acceleration, robust fiber laser
systems, and hyper-dispersion CPA . Recent work has
been performed at LLNL to demonstrate isotope-specific
detection of shielded materials via NRF using a tunable,
quasi-monochromatic Compton scattering gamma-ray
source operating between 0.2 MeV and 0.9 MeV photon
energy. This technique is called Fluorescence Imaging in
the Nuclear Domain with Energetic Radiation (or
FINDER). This work has, among other things,
demonstrated the detection of 7Li shielded by Pb, utilizing
gamma rays generated by a linac-driven, laser-based
Compton scattering gamma-ray source developed at
LLNL [2-4]. Within this context, a new facility is
currently under construction at LLNL, with the goal of
generating tunable y-rays in the 0.5-2.5 MeV photon
energy range, at a repetition rate of 120 Hz, and with a
peak brightness in the 102 photons/(s x mm2 x mrad2 x
* This work performed under the auspices of the U.S. DoE by LLNL
under Contract DE-AC52-07NA27344 and by DHS DNDO.
Figure 1: the MEGa-ray facility.
This section is a brief summary of the main properties
of Compton scattering. The incident electron and photon
4-momenta are given by u, = (y,u) and k = (k,k); the
scattered photon 4-wavenumber is q = (q,q) , and the
electron 4-velocity after the interaction satisfies energy-
momentum conservation: v, = u, +X(nk - q'), where
X is the reduced Compton wavelength and n is the
harmonic (multi-photon) number. From these parameters,
the incident and scattered light-cone variables can be
computed , along with the Compton formula:
2 -u( +p) A A
'~~''L 2 [y-ucos(e+q)]
Here, s is the angle between the electron initial velocity
and the mean electron beam axis; p is the angle of
incidence of the laser photon(s); -AA' corresponds to
radiation pressure; finally, the result is given for on-axis
radiation (0 = 0). The relativistic Doppler upshift,
radiation pressure, and recoil are the main contributions to
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Hartemann, F.; Albert, F.; Anderson, S.; Bayramian, A.; Cross, R.; Ebbers, C. et al. LLNL's Precision Compton Scattering Light Source, article, September 14, 2010; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc864444/m1/3/: accessed June 24, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.