Proposal for a nuclear gamma-ray laser of optical range

A possibility of the amplification of the 7.6 eV γ radiation by the stimulated γ emission of the ensemble of the (229m)Th isomeric nuclei in a host dielectric crystal is proved theoretically. This amplification is a result of (1) the excitation of a large number of (229m)Th isomers by laser radiation, (2) the creation of the inverse population of nuclear levels in a cooled sample owing to the interaction of thorium nuclei with the crystal electric field or with an external magnetic field, (3) the emission or absorption of the optical photons by thorium nuclei in the crystal without recoil, and (4) the nuclear spin relaxation through the conduction electrons of the metallic covering.     

A free-electron laser generated gamma-ray beam for nuclear physics

The High Intensity Gamma Ray Source (HIγS), a collaborative project between TUNL and the Duke Free Electron Laser Laboratory, is described. An initial experiment and plans for a future research program are discussed briefly.     

Gain requirement for a gamma-ray laser

A simple expression for gain saturation is presented for a laser filament emitting in a single transverse mode. Values of the gain exponent in the range 20 ? αl ? 30 are found, giving a maximum increase of ～ 10¹¹ in axial intensity.     

Radiation machines for gamma-ray laser research

In the basic research efforts to define the optimum isomers for making a gamma-ray laser, a variety of radiation sources have been used to find the nuclear gateways that make the idea possible. The radiation sources have several roles to play in the gamma-ray laser process, including pumping isomers to excited states with long lifetimes and in subsequently pumping these to short-lived states that quickly decay. This paper reviews the technology of the radiation sources and the desirable characteristics relative to pumping and triggering in gamma-ray laser research. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effect of uncertainties in nuclear decay data on coincidence summing calculations for gamma-ray spectrometry

All nuclear decay data have uncertainties. It is not obvious how these uncertainties affect the detection efficiencies in gamma-ray spectrometry performed with HPGe detectors and in close geometry with cascading gamma-rays. This paper presents examples based on Monte Carlo simulations. It shows that for certain cases the uncertainty in the detection efficiency can be significantly greater than the uncertainty of the nuclear decay. This should thus be taken into account when performing a complete uncertainty budget for close geometry measurements.     

Analysis of evaluated nuclear structure data

General analysis of the consistency of nuclear data and verification of the optimal values of excited state energies, presented in the evaluated nuclear structure data file (ENSDF) (October 2005) have been performed. As optimality criteria, we chose the Pearson and Romanovsky criteria. As a result, along with finding some misprints, it was revealed that the level energies are not optimal for a large number of the ADOPTED LEVELS, GAMMAS sets included in the ENSDF. The use of the standard GTOL program (7.1a version), which calculates the optimal values of the nuclear level energies from the energies of the transitions positioned in a scheme, made it possible to significantly improve the statistical consistency of the schemes.     

Dynamical symmetries in contemporary nuclear structure applications

In terms of group theory—the language of symmetries, the concept of spontaneous symmetry breaking is represented in terms of chains of group-subgroup structures that define the dynamical symmetry of the system under consideration. This framework enables exact analytic solutions of the associated eigenvalue problems.     

Development of underwater laser cutting technique for steel and zircaloy for nuclear applications

In nuclear field, underwater cutting and welding technique is required for post-irradiation examination, maintenance, decommissioning and to reduce storage space of irradiated materials like used zircaloy pressure tubes etc., of nuclear power plants. We have developed underwater cutting technique for 4.2 mm thick zircaloy pressure tubes and up to 6 mm thick steel using fibre-coupled 250 W average power pulsed Nd:YAG laser. This underwater cutting technique will be highly useful in various nuclear applications as well as in dismantling/repair of ship and pipe lines in water.     

Status of research in gamma-ray lasers

This article reviews conceptual devices designed to generate coherent high-quantum-energy radiation by stimulating nuclear transitions in solids; and delineates some of the promising areas of research. Solid state γ-ray lasers can benefit from (1) Mössbauer effect or recoilless emission, which suppresses first-order Doppler broadening, and brings the emitting nuclei close to a common resonant frequency; and (2) Borrmann effect, which suppresses non-resonant scattering and absorption, and may allow a crystal lattice to act as a distributed resonator. I discuss some of the basic physics that governs the performance of conceptual γ-ray lasers, and some of the classic approaches to design. Many of these early schemes were shown to be unworkable decades ago, but re-emerge in different forms generally without attention to the fallacies already revealed. Other schemes have languished for lack of a champion. I also describe some exciting new approaches, particularly those utilizing techniques for suppressing resonant absorption, which can realize gain without a true inversion. Finally, I submit some recommendations for future research.     

Progress in the pumping of gamma-ray laser

A gamma-ray laser would stimulate coherent emission of radiation at wavelengths below 1 Å from excited states of nuclei. However, the difficulties in realizing such a device were considered insurmountable when the first cycle of study ended in1981. Since then, research on the feasibility of a gamma-ray laser has taken on a completely new character. A nuclear analog of the ruby laser has been proposed and many of the component steps for pumping the nuclei have been demonstrated experimentally. A quantitative model based upon the new data and the concepts of this decade shows the gamma-ray laser to be feasible if some real isotope has its properties sufficiently close to the ideals. The greatest positive impact has come from the discovery of giant resonances for pumping nuclei with photons that greatly reduce the levels of input power needed. Most recently, attention has been focused upon efforts to demonstrate prelasing levels of fluorescence from simulation nuclides and actual gamma-ray laser candidates. Problems being addressed are the acquisition of macroscopic samples of the best nuclei for testing and the demonstration of appropriate instrumentation.     

Three-dimensional microfluidic structure embedded in photostructurable glass by femtosecond laser for lab-on-chip applications

A new technology for rapid prototyping of lab-on-chip devices is described. Direct write of a near-infrared femtosecond laser forms three-dimensional (3D) latent images inside photostructurable glass. Modified regions are developed by a post-annealing and then preferentially etched away in dilute hydrofluoric acid solution with an etching selectivity of 40–50 times, resulting in the formation of true 3D hollow microstructures inside the glass. Microfluidic structures with microcells and microchannels embedded in the glass are fabricated by this technique. PACS 42.62.-b; 47.85.Np; 81.05.Kf     

Comparison of two position sensitive gamma-ray detectors based on continuous YAP and pixellated NaI(TI) for nuclear medical imaging applications

Dedicated position sensitive gamma-ray detectors based on position sensitive photomultiplier tubes (PSPMTs) coupled to scintillation crystals, have been used for the construction of compact gamma-ray imaging systems, suitable for nuclear medical imaging applications such as small animal imaging and single organ imaging and scintimammography. In this work, the performance of two gamma-ray detectors: a continuous YAP scintillation crystal coupled to a Hamamastu R2486 PSPMT and a pixellated NaI(TI) scintillation array crystal coupled to the same PSPMT, is compared. The results show that the gamma-ray detector based on a pixellated NaI(TI) scintillation array crystal is a promising candidate for nuclear medical imaging applications,since their performance in terms of position linearity, spatial resolution and effective field of view (FOV) is superior than that of the gamma-ray detector based on a continuous YAP scintillation crystal. However, a better photodetector (Hamamatau H8500 Flat Panel PMT, for example) coupled to the continuous crystal is also likely a good selection for nuclear medicine imaging applications.     

Comparison of two position sensitive gamma-ray detectors based on continuous YAP and pixellated NaI(TI) for nuclear medical imaging applications

Dedicated position sensitive gamma-ray detectors based on position sensitive photomultiplier tubes (PSPMTs) coupled to scintillation crystals, have been used for the construction of compact gamma-ray imaging systems, suitable for nuclear medical imaging applications such as small animal imaging and single organ imaging and scintimammography. In this work, the performance of two gamma-ray detectors：a continuous YAP scintillation crystal coupled to a Hamamastu R2486 PSPMT and a pixellated NaI(TI) scintillation array crystal coupled to the same PSPMT, is compared. The results show that the gamma-ray detector based on a pixellated NaI(TI) scintillation array crystal is a promising candidate for nuclear medical imaging applications, since their performance in terms of position linearity, spatial resolution and effective field of view (FOV) is superior than that of the gamma-ray detector based on a continuous YAP scintillation crystal. However, a better photodetector (Hamamatau H8500 Flat Panel PMT, for example) coupled to the continuous crystal is also likely a good selection for nuclear medicine imaging applications.     

Optical fibres for current measurement applications

The polarization properties of optical fibres are of interest in several different communications and measurement applications. This paper indicates the properties ideally required of a fibre for use in current measurement systems and describes an extremely low birefringence fibre which meets many of these requirements. Measurements of the polarization properties of this fibre are given and a laboratory prototype current measurement system using the fibre is described.     

Investigation of structural properties of lead strontium borate glasses for gamma-ray shielding applications

Glasses of the system PbO-SrO-B₂O₃ with the value of molar ratio R (=PbO/B₂O₃) in the region 0.14≤R≤2.0 were prepared using the melt quenching technique. In order to evaluate gamma-ray shielding properties for glass samples, mass attenuation coefficients have been calculated with the XCOM computer program. The longitudinal velocities of ultrasonic waves were measured in these glass samples at room temperature using the pulse echo technique. The results indicate that with increase in R value, stability of glass network decreases. Stability of glass network decreases indicate the increase in the number of borons with non-bridging oxygens at the expense of decrease of tetrahedral borate units. This feature may lead to open glass structure with lesser rigidity of the glass samples. DSC studies have been undertaken to measure the glass transition temperature and to get an idea about stability of the glass network with increasing R value.