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The concept of the graser (or gamma-ray laser) is discussed, and recent Russian and American proposals are surveyed. The difficulties in building a gamma-ray laser are outlined; and specific recommendations are made for delimiting the extent of NRL involvement in graser research in the near future.
This report is addressed to the problem of the state-of-the-art of gamma ray laser development. It is intended to identify the various disciplines and specific research areas which can best contribute to resolving the question of 'graser' feasibility. Topics discussed include the following: The basic mechanisms of laser action; Gamma ray emission from nuclear isomers; The resonance cross section; Nonresonant absorption; Photon kinetics; Inhomogeneous line breadths; Problems of pumping.
This report summarizes the IDA research effort in FY 1985 in investigating the feasibility of developing a gamma-ray laser.
Recent approaches to the problem of the gamma-ray laser have focused upon upconversion techniques in which metastable nuclei are pumped with long wavelength radiation. At the nuclear level the storage of energy can approach tera-Joules (10 to the 12th power J) per liter for thousands of years. However, any plan to use such a resource for a gamma-ray laser poses problems of a broad interdisciplinary nature requiring the fusion of concepts taken from relatively unrelated fields of physics. Since 1978 we have pursued an approach for the upconversion of longer wavelength radiation incident upon isomeric nuclear populations that can avoid many of the difficulties encountered with traditional concepts of single photon pumping. Recent experiments have confirmed the general feasibility and have indicated that a gamma-ray laser is feasible if the right combination of energy levels and branching ratios exists in some real material. Resolution of the question of the feasibility of a gamma-ray laser now rests upon the determination of: 1) the identity of the best candidate, 2) the threshold level of laser output, and 3) the upconversion driver for that material.
This report summarizes the IDA research effort in FY 1988 in investigating the feasibility of developing a gamma-ray laser.
This publication presents cleaning and etching solutions, their applications, and results on inorganic materials. It is a comprehensive collection of etching and cleaning solutions in a single source. Chemical formulas are presented in one of three standard formats - general, electrolytic or ionized gas formats - to insure inclusion of all necessary operational data as shown in references that accompany each numbered formula. The book describes other applications of specific solutions, including their use on other metals or metallic compounds. Physical properties, association of natural and man-made minerals, and materials are shown in relationship to crystal structure, special processing techniques and solid state devices and assemblies fabricated. This publication also presents a number of organic materials which are widely used in handling and general processing...waxes, plastics, and lacquers for example. It is useful to individuals involved in study, development, and processing of metals and metallic compounds. It is invaluable for readers from the college level to industrial R & D and full-scale device fabrication, testing and sales. Scientific disciplines, work areas and individuals with great interest include: chemistry, physics, metallurgy, geology, solid state, ceramic and glass, research libraries, individuals dealing with chemical processing of inorganic materials, societies and schools.
Recent approaches to the problem of the gamma-ray laser have focused upon upconversion techniques in which metastable nuclei are pumped with long wavelength radiation. At the nuclear level the storage of energy can approach tera-Joules per liter for thousands of years. However, any plan to use such a resource for a gamma-ray laser poses problems of a broad interdisciplinary nature requiring the fusion of concepts taken from relatively unrelated field of physics. Our research group has described several means through which this energy might be coupled to the radiation fields with cross sections for stimulated emission that could reach 10 to the minus 17th power sq. cm. Such a stimulated release could lead to output powers as great as 3 X 10 to the 21st power Watts/liter. Since 1978 we have pursued an approach for the upconversion of longer wavelength radiation incident upon isomeric nuclear populations that can avoid many of the difficulties encountered with traditional concepts of single photon pumping. Recent experiments have confirmed the general theory and have indicated that a gamma-ray laser is feasible if the right combination of energy levels and branching ratios exists in some real material. Of the 1,886 distinguishable nuclear materials, the present state-of-the-art has been adequate to identify 29 first-class candidates, but further evaluation cannot proceed without remeasurements of nuclear properties with higher precision.
This paper compares two processes that can occur, under different conditions, in the same system of nuclei: amplified spontaneous emission (ASE) and superfluorescence (SF). It concludes that the (Trammell and Hannon) conditions for the occurrence of ASE are more restrictive than those for the occurrence of SF. Therefore, the conclusion by some authors based on an analysis of ASE, that coherent electromagnetic emission from a nuclear system is not feasible, is incorrect. The paper examines the feasibility of nuclear SF in 60Co. It concludes that SF will occur in the excited state obtained by thermal neutron pumping with fluxes ranging from 10.18 to 10.23 neutrons per second.
The possibility of extending the laser principle into the hard x-ray region above a few keV depends upon the ability of a pump to create the critical density of population inversion for which gain overcomes loss by absorption. Although this critical density decreases with the wavelength of the radiation to be stimulated, the power required to generate it depends upon the lifetime of the state being pumped. The lifetimes of inner-shell vacancies of atoms are very short. Nuclear states, on the other hand, have much longer lifetimes, ranging from fractions of picoseconds to millennia. Moreover, in the so-called recoilless or Moessbauer transitions of nuclear isomers, it was observed that the resonance cross section often exceeds the nonresonant absorption cross section by several orders of magnitude: just the condition for lasing in an inverted population. If, other things being equal, the absorber foil of a Moessbauer experiment contained an excess of excited states, then, instead of the absorption dip normally observed at resonance, there would be an increase of intensity, and amplification by stimulated emission would be achieved. The problem in making a gamma-ray laser is, therefore, simply that of obtaining an inverted population without inhibiting the Moessbauer effect. Research on this problem is reviewed.