Radio-isotope production using laser wakefield accelerators

Abstract

A 10 Hz, 10 TW solid state laser system has been used to produce electron beams suitable for radio-isotope production. The laser beam was focused using a 30 cm focal length f/6 off-axis parabola on a gas plume produced by a high pressure pulsed gas jet. Electrons were trapped and accelerated by high gradient wakefields. excited in the ionized gas through the self-modulated laser wakefield instability. The electron beam was measured to contain in excess of 5 nC/bunch. A composite Pb/Cu target was used to convert the electron beam into /spl gamma/-rays which subsequently produced radio-isotopes through (/spl gamma/,n) reactions. Isotope identification through /spl gamma/-ray spectroscopy and half-life time measurements demonstrated that /sup 61/Cu was produced which indicates that 20-25 MeV /spl gamma/-rays were produced, and hence electrons with energies greater than 25-30 MeV. The production of high energy electrons was independently confirmed using a bending magnet spectrometer. The measured spectra had an exponential distribution with a 3 MeV width. The amount of activation was on the order of 2.5 /spl mu/Ci after 3 hours of operation at 1 Hz. Future experiments will aim at increasing this yield by post-accelerating the electron beam using a channel guided laser wakefield accelerator.