The possible regimes of the propagation of a self-sustained fluorescence wave of long-lived nuclear isomers, which is initiated by transitions to the nearest short-lived level owing to the absorption of X-ray photons and inelastic collisions of electrons in a plasma, have been analyzed. It has been found that, when the energy exchange between the nuclear subsystem and plasma is due to absorption and emission of photons, the fluorescence wave can propagate in the fast (with a near-light velocity) deflagration regime induced by the radiative heat transfer mechanism. When the energy exchange between the subsystems is nonradiative, the (slower) detonation regime becomes significant. The implementation of each of the two regimes requires certain conditions on the characteristics of the system.

A process of nucleus excitation by photons under the mechanism of the inverse electron bridge (IEB) is examined provided the energies of atomic and nuclear transitions coincide. It is shown that in this case, the excitation of nuclei with EL [ML] transition with the energy omega(N) less than or similar to 10 keV is strengthened relative to the process of photoabsorption by nucleus by a factor of 1/(omega(N)r(0))(2(L+2)) [e(4)/(omega(N)r(0))(2(L+ 2))], where r(0) is a typical size of domain in the ion shell for accumulation of electronic integrals. In the Rb-84 nuclei the IEB cross section for the 3.4 keV M1 transition 6(-)(463.59 keV) <-> 5(-)(463.59 keV) can exceed even a photoexcitation cross section for the 3.4keV E1 transition with the reduced probability in the Weisskopf model B-W.u.(E1) = 1. This result can be important for understanding the mechanisms of atomic nucleus excitation in hot plasma. In particular, the considered process is capable to provide the existence of so called gamma luminescence wave or a nuclear isomer "burning" wave-an analog of self-maintaining process of triggered depopulation of nuclear isomer.

Within the frameworks of the nonrelativistic plane wave Born approximation (PWBA), the analytical formulas for cross sections of E1-E3 and M1-M2 excitation of nuclei to the low-energy isomeric state as a result of inelastic scattering of nonrelativistic electrons are derived in the present work. The PWBA cross section of E1 excitation of isomer Ta-181(m) (9/2(-), 6.237 keV) by electrons appeared to be two orders less than that one used in a number of works for calculation of isomeric nuclei yield under exposure of Ta-181-target hot dense laser plasma. To test the PWBA method we have calculated excitation cross sections of the nuclei Ta-181, Ag-110, Tm-169, and Hg-201 in a relativistic version of the Hartree-Fock-Slater method. It was established that the PWBA method overestimates E1 cross sections and underestimates E2 and M1 cross sections.

A brief description of the developed structural electric diagrams of 16-channel scintillation module for the underground EMMA experiment, the basic characteristics and parameters of the electrical diagrams of this module are presented. Multi-pixel photodiodes operating in a limited Geiger mode are used for photoreadout of the scintillator de- tectors in 16-channel scintillation module. The method of the automatic tuning of the photosensors gain based on the sta- bilization of an average counting rate of the scintillation de- tectors from gamma rays of a natural radioactive background is described.

Fast induced decay of the long-lived nuclear isomer $^{178}\mathrm{Hf}$${}^{m2}$ via an intermediate state is shown to be possible in a deuterium-tritium laser thermonuclear plasma as a result of inelastic scattering of $\ensuremath{\alpha}$ particles and fast electrons on isomeric nuclei. A similar phenomenon also takes place in deuterium-deuterium plasma, where the intermediate state is exited by protons, thermal electrons, and photons.

In this short note we present results of background measurements carried out with a polystyrene based cast plastic 12.0x12.0x3.0 cm^3 size scintillator counter with a wavelength shifting fibre and a multi-pixel Geiger mode avalanche photodiode readout in the Baksan underground laboratory at a depth of 200 meters of water equivalent. The total counting rate of the scintillator counter measured at this depth and at a threshold corresponding to ~0.37 of a minimum ionizing particle is approximately 1.3 Hz.

The results of a development of a scintillator counter with wavelength shifting (WLS) fibre and a multi-pixel Geiger-mode avalanche photodiode readout are presented. The photodiode has a metal-resistor-semiconductor layered structure and operates in the limited Geiger mode. The scintillator counter has been developed for the EMMA underground cosmic ay experiment.

Highly sensitive micropixel avalanche photodiodes with a metal-resistor-semiconductor structure (MRS APDs) operating in the restricted Geiger discharge mode and scintillation detectors with wavelength-shifting optical fibers developed for the T2K neutrino oscillation experiment have been investigated. Dependencies of basic MRS APD parameters on the bias voltage, photon wavelength, and temperature have been measured. Characteristics of the scintillation detectors with wavelength-shifting optical fibers and avalanche photodiodes are described.