Gamma-ray lasing by free nuclei: Further concept elaboration

Two years ago at the First International Workshop on Gamma-Ray Laser a number of concepts of IGE experiments were presented for discussion. The Free Nuclei Concept (FNC) as an alternative to the solid state approaches of all kinds was one of them. The main motivation for elaboration of FNC was the attempt to solve the problem of observation and investigation of true amplification of gamma-ray beam by excited nuclei, just like in ordinary optical lasers, not only the detection of separate events of induced gamma-emission. I believe that the latter type of experiments, aimed at the verification of the applicability to nuclei of Einstein's general law of stimulated emission, may be attractive and elegant, but, to my mind, is missing the real target. The paper reaches the following conclusions: 1. the minimum number of active nuclei necessary for reliable detection of gamma-ray lasing is rather small; 2. also small is the volume of fiber-like amplification channel and consequently an extra 'hot' lab is not needed; 3. proposed 'two-level' scheme withdraws most of rigid requirements for the candidate isomer and opens the way to efficient use of the broad band non-coherent X-ray pumping; 4. proposed modification of relativistic Doppler method of frequency up-conversion by resonant electron scattering may be very efficient for pumping purpose and a lot of another experimental applications. To sum up, I believe that intensive experimental activity in the field of IGE problem and in particular in its FNC version must be launched immediately without any delay. (author)