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We perform a proof-of-principle experiment for a nondestructive method for detecting the elemental and isotopic composition of materials concealed by heavy shields such as iron plates with a thickness of several centimeters. This method uses nuclear resonance fluorescence (NRF) triggered by an energy-tunable laser-Compton scattering (LCS) -ray source. One-dimensional mapping of a lead block hidden behind 1.5-cm-thick iron plates is obtained by measuring an NRF -ray of a lead isotope 208 Pb. We observe a 5512-keV -ray from 208 Pb excited by the quasi-monochromatic LCS -rays with energies up to 5.7 MeV. The edge position of the lead block is consistent with the exact position within the uncertainty.

A nondestructive assay system for radioactive waste management is proposed. The system utilizes nuclear resonance fluorescence triggered by a quasi-monochromatic high-flux gamma ray generated from the Compton scattering of laser photons by relativistic electrons. We employ an energy-recovery linac as an electron source and a mode-locked fiber laser followed by a laser supercavity as a photon source. The combination of these novel technologies realizes a gamma-ray flux much higher than existing sources using electron storage rings. The proposed gamma-ray source produces a quasi-monochromatic gamma ray with a flux of 10 10 /s/keV, which is high enough for industrial applications such as the nondestructive analysis of radionuclides in nuclear waste and the interrogation of fissile material in cargoes. The nuclear resonance fluorescence triggered by quasi-monochromatic gamma rays provides a versatile method of nondestructive analysis of both radioactive and stable nuclides.

The first observation of sustained saturation in a free-electron laser (FEL) oscillator at perfect synchronism of an optical cavity is presented. A simultaneous measurement of FEL power and absolute detuning length of the optical cavity ( deltaL) has clearly shown that the FEL efficiency becomes maximum at deltaL = 0.0+/-1 microm, although it has been considered that only a transient state exists at deltaL = 0 due to the well-known laser lethargy effect. The observed efficiency detuning curve is well reproduced by our numerical simulation including a small shot-noise effect.