The nuclear electric polarizability of 6He

We present an estimate of the nuclear electric polarizability of the 6He halo nucleus based on six-body microscopic calculations. Wave functions are obtained from semi-realistic two-body interactions using the hyperspherical harmonics expansion method. The polarizability is calculated as a sum rule of the dipole response function using the Lanczos algorithm and also by integrating the photo-absorption cross section calculated via the Lorentz integral transform method. We obtain alpha_E=1.00(14) fm^3, which is much smaller than the published value 1.99(40) fm^3 extracted from experimental data. This points towards a potential disagreement between microscopic theories and experimental observations.Comment: 8 pages, 8 figures, minor changes, added error analysi

Nuclear polarizability of helium isotopes in atomic transitions

We estimate the nuclear polarizability correction to atomic transition frequencies in various helium isotopes. This effect is non-negligible for high precision tests of quantum electrodynamics or accurate determination of the nuclear charge radius from spectroscopic measurements in helium atoms and ions. In particular, it amounts to $28(3)$ kHz for 1S-2S transition in 4He+.Comment: 11 pages, 4 figures, to be published in Phys. Rev. A. Revised version: misprints corrected, new references adde

Photodisintegration of light nuclei for testing a correlated realistic interaction in the continuum

An exact calculation of the photodisintegration cross section of 3H, 3He and 4He is performed using as interaction the correlated Argonne V18 potential, constructed within the Unitary Correlation Operator Method (VUCOM). Calculations are carried out using the Lorentz Integral Transform method in conjunction with an hyperspherical harmonics basis expansion. A comparison with other realistic potentials and with available experimental data is discussed. The VUCOM potential leads to a very similar description of the cross section as the Argonne V18 interaction with the inclusion of the Urbana IX three-body force for photon energies 45< w < 120 MeV, while larger differences are found close to threshold.Comment: 9 pages, 6 figure

Self-consistent continuum random phase approximation calculations of 4^4He electromagnetic responses

We study the electromagnetic responses of $^4$He within the framework of the self-consistent continuum random phase approximation theory. In this approach the ground state properties are described by a Hartree-Fock calculation. The single particle basis constructed in this manner is used in the calculations of the continuum responses of the system. Finite-range interactions are considered in the calculations. We compare our results with photon absorption cross sections and electron scattering quasi-elastic data. From this comparison, and also from the comparison with the results of microscopic calculations, we deduce that our approach describes well the continuum excitation.Comment: 6 pages, 1 table, 4 figures, accepted for publication in Physical Review

Two-body Photodisintegration of 4^{4}He with Full Final State Interaction

The cross sections of the processes $^4$He($\gamma,p$)$^3$H and $^4$He($\gamma,n$)$^3$He are calculated taking into account the full final state interaction via the Lorentz integral transform (LIT) method. This is the first consistent microscopic calculation beyond the three--body breakup threshold. The results are obtained with a semirealistic central NN potential including also the Coulomb force. The cross sections show a pronounced dipole peak at 27 MeV which lies within the rather broad experimental band. At higher energies, where experimental uncertainties are considerably smaller, one finds a good agreement between theory and experiment. The calculated sum of three-- and four--body photodisintegration cross sections is also listed and is in fair agreement with the data.Comment: 18 pages, 6 figure

МОДЕЛЮВАННЯ ІНФОРМАЦІЙНОГО ОБМІНУ ДАНИМИ У СИСТЕМІ КООРДИНАЦІЇ РУХУ ЗАЛІЗНИЧНОГО ТРАНСПОРТУ

In article the use of GSM technology for information exchange system to coordinate movement of mobile assets is justified. The urgency of assessing the quality of data services via GPRS is indicated. The technology of information exchange system to coordinate movement of mobile assets, the basic characteristics of the components of the data transfer system are examined. The task of assessing the GPRS network capacity based on the mathematical apparatus of queuing systems is put. A simulation model for the collection of navigation data is developed.Обґрунтовано застосування технології GSM для організації інформаційного обміну даними у системі координації руху транспортних засобів. Зазначена актуальність процесу оцінювання якості послуги передачі даних каналами GPRS. Розглянута технологія інформаційного обміну даними у системі координації руху транспортних засобів, описані основні характеристики компонентів системи передачі даних. Поставлена задача оцінювання пропускної здатності мережі GPRS на основі математичного апарату систем масового обслуговування. Розроблена імітаційна модель збору навігаційних даних

Ab initio study of the photoabsorption of 4^4He

There are some discrepancies in the low energy data on the photoabsorption cross section of $^4$He. We calculate the cross section with realistic nuclear forces and explicitly correlated Gaussian functions. Final state interactions and two- and three-body decay channels are taken into account. The cross section is evaluated in two methods: With the complex scaling method the total absorption cross section is obtained up to the rest energy of a pion, and with the microscopic $R$-matrix method both cross sections $^4$He($\gamma, p$)$^3$H and $^4$He($\gamma, n$)$^3$He are calculated below 40\,MeV. Both methods give virtually the same result. The cross section rises sharply from the $^3$H+$p$ threshold, reaching a giant resonance peak at 26--27\,MeV. Our calculation reproduces almost all the data above 30\,MeV. We stress the importance of $^3$H+$p$ and $^3$He+$n$ cluster configurations on the cross section as well as the effect of the one-pion exchange potential on the photonuclear sum rule.Comment: 15 pages, 12 figure

New Constraints on Radiative Decay of Long-Lived Particles in Big Bang Nucleosynthesis with New 4^4He Photodisintegration Data

A recent measurement of $^4$He photodisintegration reactions, $^4$He($\gamma$,$p$)$^3$H and $^4$He($\gamma$,$n$)$^3$He with laser-Compton photons shows smaller cross sections than those estimated by other previous experiments at $E_\gamma \lesssim 30$ MeV. We study big-bang nucleosynthesis with the radiative particle decay using the new photodisintegration cross sections of $^4$He as well as previous data. The sensitivity of the yields of all light elements D, T, $^3$He, $^4$He, $^6$Li, $^7$Li and $^7$Be to the cross sections is investigated. The change of the cross sections has an influence on the non-thermal yields of D, $^3$He and $^4$He. On the other hand, the non-thermal $^6$Li production is not sensitive to the change of the cross sections at this low energy, since the non-thermal secondary synthesis of $^6$Li needs energetic photons of $E_\gamma \gtrsim 50$ MeV. The non-thermal nucleosynthesis triggered by the radiative particle decay is one of candidates of the production mechanism of $^6$Li observed in metal-poor halo stars (MPHSs). In the parameter region of the radiative particle lifetime and the emitted photon energy which satisfies the $^6$Li production above the abundance level observed in MPHSs, the change of the photodisintegration cross sections at $E_\gamma \lesssim 30$ MeV as measured in the recent experiment leads to $\sim 10$% reduction of resulting $^3$He abundance, whereas the $^6$Li abundance does not change for this change of the cross sections of $^4$He($\gamma$,$p$)$^3$H and $^4$He($\gamma$,$n$)$^3$He. The $^6$Li abundance, however, could show a sizable change and therefore the future precise measurement of the cross sections at high energy $E_\gamma \gtrsim$ 50 MeV is highly required.Comment: 10 pages, 7 figures, conclusion not changed, to be published in PR

About creation of a techological tomograph using the ELIAS accelerator

Estimates were made for the possibility of creating a technological tomograph based on the registration of Compton scattering of photons through the use of the Van de Graaff accelerator (ELIAS) at NSC KIPT. The GEANT3 package was used to simulate the process of production of a sharply directed bremsstrahlung beam, to define the converter thickness, and to determine the angular distribution and energy spectrum of photons. The computation of counting rate for the tomograph’s detector has shown that for materials of a density up to 3 g/cm3 the counting rate can reach 2600 counts/sec, this being quite sufficient for tomographs of this type

Test of J-matrix inverse scattering potentials on electromagnetic reactions of few-nucleon systems

The J-matrix inverse scattering nucleon-nucleon potentials (JISP), describing both two-nucleon data and bound and resonant states of light nuclei to high accuracy, are tested on the total photoabsorption cross sections of Deuteron, Triton, 3He and 4He. The calculations in the three- and four-body systems are carried out via the Lorentz integral transform method and the hyperspherical harmonics (HH) technique. To this end the HH formalism has been adapted to accommodate non-local potentials. The cross sections calculated with the JISP are compared to those obtained with more traditional realistic interactions, which include two- and three-nucleon forces. While the results of the two kinds of potential models do not differ significantly at lower energies, beyond the resonance peak they show fairly large discrepancies, which increase with the nuclear mass. We argue that these discrepancies may be due to a probably incorrect long range behavior of the JISP, since the one pion exchange is not manifestly implemented there.Comment: 18 pages, 4 figures, 1 tabl