The results are presented from an experiment to measure the probabilities of γ-quanta emission from the first excited states of daughter nuclei formed in α-decay chain of the 226Ra nucleus. The use of fast temporal digitizers of the shape of the signal from a semiconductor α-detector and a germanium γ-detector of large volume allows the probabilities of the decay of the first excited states to be estimated at the level of 10–5 from the main mode of decay.

The results are presented from an experiment to measure the probability of internal bremsstrahlung upon the α-decay of the 214 Po nucleus using a large-volume germanium detector and fast-time digitizers of signals from gamma and alpha detectors. Satisfactory agreement is obtained betw een the experimental data and the results from calculations in the literature, performed with the realistic and oscillatory nuclear potentials.

Efficient direct electron acceleration in the plasma channel with injection through the breaking of plasma waves generated by parametric instabilities was demonstrated experimentally and reproduced in the 2D3V PIC simulations. The electron bunch was produced using the specific plasma profile containing arbitrary sharp, ∼0.5λ, gradient at the vicinity of 0.1–0.5 critical density and a long tail of a tenuous preplasma. Such a preplasma profile was formed by an additional nanosecond laser pulse with intensity of 5 × 1012 W cm−2. In the case of optimal preplasma parameters femtosecond laser pulse with an intensity of 5 × 1018 W cm−2 and an energy of 50 mJ generates a collimated electron bunch having divergence of 50 mrad, exponential spectrum with the slope of ∼2 MeV and charge of tens of pC. The charge was confirmed measuring neutron yield from Be(g, n) photonuclear reaction with threshold of 1.7 MeV. By the contrast, a ring-like electron beam with divergency of 300 mrad and significantly lower charge is generated if the prepulse intensity drops to 5 × 1011 W cm−2. The 2D PIC simulations confirmed beamed electron's acceleration in the plasma channel (so-called direct laser acceleration). This channel is formed in a long tail of teneous preplasma by the laser pulse specularly reflected from the arbitrary sharp gradient. The ring-like electron beam was attributed to the longer gradient case enlarging divergence of the reflected laser beam, preventing channel's formation and electron acceleration by the so-called vacuum laser acceleration, or VLA. We also showed that injected electrons appeared from the wave breaking of plasma waves of hybrid SRS-TPD instability for the both gradients. Electrons received an initial momentum from this breaking to be effectively injected into the plasma channel.

The hot plasma formed onto the surface of nanostructured targets by a relativistically intense (up to 4 × 1018 W/cm2), high contrast femtosecond laser radiation is studied. The nanoscale structures (pores, spheres, grass) were produced via laser ablation or chemical etching of bulk silicon and molybdenum. We report one of the first experimentally observed manifold enhancements of gamma yield at the background of hot electron energy growth from 200 to >600 keV, compared to the case of initially flat substrate in the relativistic regime of interaction. The efficiency of hot particle production is significantly affected by the shape of the structures. Experimental results are supported by 2D3V Particle-In-Cell simulations of laser–plasma interaction. It is shown that a laser-based plasma source, formed onto the surface of a solid target may be utilized for phase contrast X-ray imaging in a wide energy range of photons.

The processes and problems of big bang nucleosynthesis are considered. Powerful laser pulses allow us to obtain high energy density in matter. Thus, laboratory modeling of big bang nucleosynthesis becomes feasible. Results of experiments on the picosecond laser facility 'Neodymium' and on the femtosecond terawatt laser are reported. Further investigations of this topic are discussed.

The possibility of studying photonuclear reactions near the threshold by means of powerful femtosecond lasers is explored by considering the example of deuteron photodisintegration. The respective experiment was performed by employing the terawatt femtosecond laser facility of the International Laser Center at Moscow State University. The radiation from this facility is characterized by a pulse energy of up to 50 mJ, a duration of 50 fs, a repetition rate of 10 Hz, and a wavelength of 805 nm. This provides a power above 10 18 W/cm 2 . Intense relativistic-electron and photon beams of energy up to 10 MeV were obtained after the optimization of relevant experimental parameters, including the focus of the laser beam, its time structure, and the choice of target. The use of these beams made it possible to study neutron generation in heavy water, to measure the time of neutron moderation, and to determine the detection efficiency. The experimental data obtained in this way are in qualitative agreement with the results of simulations based on the GEANT-4 and LOENТ code packages and indicate that it is possible to create a neutron source on the basis of the aforementioned laser. The cross section measured for deuteron photodisintegration complies with theoretical estimates available in the literature.

A large-volume germanium detector coupled with fast signal digitizers is proposed for use in experiments to study interference effects in yields of the bremsstrahlung radiation that accompanies alpha decays of heavy nuclei. When wavelet processing is applied to the signals from detectors, the time resolution can be as fine as ~30 ns for a detector with a volume of ≥100 cm3. This method is used to measure experimentally the probability of the emission of γ-quanta from excited states of daughter nuclei produced in the α-decay chain of 226Ra.

A simplified digital spectrometer for studying gamma-rays with energies up to 100 MeV is presented and tested. The spectrometer only consisted of a fast digital oscilloscope and three scintillation detectors which can work in single or in coincidence modes: two BGO-detectors comprising empty set 7.62 x 7.62 cm BGO-crystals and one plastic detector which includes an organic polystyrene-based scintillator The basic properties of the spectrometer (energy resolution, time resolution, gamma-rays detection efficiency) were studied exhaustively also using Geant4-based Monte-Carlo simulation. Several numerical algorithms for processing of waveforms in offline mode were proposed and tested to perform digital timing, pulse area measurement and correction of pile-up events without rejection. As a result, the energy resolution of the spectrometer was up to 10% better than that was obtained by a common 10-bit CAMAC ADC with the same defectors. Furthermore, the pile-up processing algorithm based on the pulse shape analysis showed high efficiency under severe conditions (the portion of pile-up events was similar to 30%). The measured maximum acquisition rate of the spectrometer was 1.8 x 10(5) waveforms/s. (C) 2014 Elsevier B.V. All rights reserved.

The high energy bremsstrahlung γ-rays accompanying the spontaneous fission of 252 Cf were measured in the 10–70 MeV energy range. The photons were detected by two BGO scintillator detectors (ø7.6cm × 7.6cm) in coincidence with neutrons detected by plastic scintillator detector, in the 90° and 180° geometry of the two BGO detectors with respect to the axis of the plastic scintillator. The distance from the 252Cf source to the BGO detectors was 10 cm, and the one to the plastic detector was 50 cm. The fast digital shape analysis technique and the time-of-flight method were used to reject pile-up effects and cosmic ray background. The γ-ray emission probability of 3 × 10−8photon/(MeV × fission) at Eγ = 70 MeV was obtained.

The probability of high-energy γ-ray emission accompanying the spontaneous fission of 252Cf nuclei in the energy range of 5–60 MeV was measured experimentally. The γ rays were detected by a BGO detector with a size of ∅7.6 × 7.6 cm in coincidence with neutrons detected by an organic polystyrene-based scintillator with a size of ∅6.0 × 2.0 cm. To reject events associated with the cosmic background, we propose an original method that combines rapid digitizing of the pulse shape and the time-of-flight method.

The high energy bremsstrahlung gamma-rays accompanying the spontaneous fission of Cf-252 were measured in the 10-70 MeV energy range. The photons were detected by two BGO scintillator detectors (circle divide 7.6cm x 7.6cm) in coincidence with neutrons detected by plastic scintillator detector, in the 90 degrees and 180 degrees geometry of the two BGO detectors with respect to the axis of the plastic scintillator. The distance from the Cf-252 source to the BGO detectors was 10 cm, and the one to the plastic detector was 50 cm. The fast digital shape analysis technique and the time-of-flight method were used to reject pile-up effects and cosmic ray background. The gamma-ray emission probability of 3 x 10(-8)photon/(MeV x fission) at E gamma = 70 MeV was obtained.

We report our experimental results on hard X-ray generation and stability parameters of a laser-driven plasma X-ray source using a melted gallium target irradiated by 2 mJ 100 fs laser pulse at 1 kHz repetition rate. Intense characteristic K-shell emission, including Kα and Kβ, is observed against a background of broadband bremsstrahlung. High brightness and stability from pulse to pulse of hard X-ray source allow its use as a promising tool for different applications using table-top laser systems.

High energy bremsstrahlung emission during spontaneous fission of 252 Cf is observed. The new experimental method to detect rare coincident events by digital storage oscilloscope is used. The γ-rays with energies up to 60 MeV have been measured (by a BGO detector) in coincidence with neutrons detected by a plastic scintillator. The determination of γ-ray emission probability up to the value of about 8 × 10-9event/(MeV × fission) at Eγ= 60 MeV is achieved.

This paper presents the spectrum of the bremsstrahlung emission accompanying the α-decay of 226Ra (E α=4.8 MeV) by measuring the α−γ coincidences. We analyze the spectrum by using the model presented in our previous study on the α-decay of 214Po (E α=7.7 MeV). We compare the experimental data with the quantum mechanical calculation and find a good agreement between theory and experiment. We analyze the bremsstrahlung emission contributions from the tunneling and external regions of the nucleus barrier into the total spectrum, and find destructive interference between these contributions.

. We analyze the bremsstrahlung emission obtained by the α -γ coincidence measurements to investigate on the α -decay dynamics of the 214 Po nucleus. We performed the experiment using a radioactive 226 Ra source leading, by α -decays, to the 214 Po nucleus, and the apparatus with the Si detector for α -particles, the NaI(Tl) detector able to collect photons with energies up to about 1 MeV. We compare the experimental data with the quantum-mechanical calculations and find a good agreement between theory and experiment for photon energies up to 765 keV. In the experimental data of the bremsstrahlung spectrum one can see the presence of slight oscillations.