The H7 system was populated in the H2(He8,He3)H7 reaction with a 26 AMeV He8 beam. The H7 missing mass energy spectrum, the H3 energy and angular distributions in the H7 decay frame were ...reconstructed. The H7 missing mass spectrum shows a peak, which can be interpreted either as unresolved 5/2+ and 3/2+ doublet or one of these states at 6.5(5) MeV. The data also provide indications of the 1/2+ ground state of H7 located at 1.8(5) MeV with quite a low population cross section of ∼25 μb/sr within angular range θc.m.≃(17°-27°).
The extremely neutron-rich systems 7H, 6H were studied in the 2H(8He, 3He)7H and 2H(8He, 4He)6H proton and deuteron pickup reactions with a 26 AMeV secondary 8He beam produced at the new ACCULINNA-2 ...fragment separator. In addition, the same proton and deuteron pickup reactions were generated using the 42 AMeV 10Be beam, and the population of low-lying 9Li and 8Li states was measured in reactions 2H(10Be,3He)9Li and 2H(10Be,4He)8Li, respectively. The latter were used as reference measurements in order to check the setup calibration over the excitation energy of 7,6H and to determine the real experimental energy resolution which was compared with Monte Carlo calculations. The corresponding results obtained for the superheavy hydrogen systems 7H, 6H are presented and discussed. Typical excitation spectra of the 9Li and 8Li nuclei are also shown.
A neutron spectrometer based on stilbene crystals has been developed by the Flerov Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research (Dubna, Russia). The timing resolution ...is determined as a function of the signal amplitude (σ
T
= 0.18 ns at an amplitude of 1 MeV in the electron equivalent). The measured energy resolution of the detecting modules for γ rays is σ
E
/
E
= 4.5% at
E
= 1 MeV. The quality of the
n
–γ discrimination is investigated. It is shown that reliable discrimination is possible, beginning with a deposited energy of 100 keV in the electron equivalent, which corresponds to the kinetic energy of recoil protons of ∼700 keV. The neutron spectrometer helps to significantly expand the experimental capabilities and to carry out correlation experiments with radioactive beams on the ACCULINNA-2 fragment separator at a new level of quality.
The extremely neutron-rich system H6 was studied in the direct H2(He8,He4)H6 transfer reaction with a 26A MeV secondary He8 beam. The measured missing mass spectrum shows a broad bump at ≈4-8 MeV ...above the H3+3n decay threshold. This bump can be interpreted as a broad resonant state in H6 at 6.8(5) MeV. The population cross section of such a presumably p-wave state (or it may be few overlapping states) in the energy range from 4 to 8 MeV is dσ/dωc.m.≃190-80+40μb/sr in the angular range 5°<θc.m.<16°. The obtained missing mass spectrum is practically free of H6 events below 3.5 MeV (dσ/dωc.m. 5μb/sr in the same angular range). The steep rise of the H6 missing mass spectrum at ≈3 MeV allows us to derive the lower limit for the possible resonant-state energy in H6 to be 4.5(3) MeV. According to the paring energy estimates, such a 4.5(3) MeV resonance is a realistic candidate for the H6 ground state (g.s.). The obtained results confirm that the decay mechanism of the H7 g.s. (located at 2.2 MeV above the H3+4n threshold) is the "true"(or simultaneous) 4n emission. The resonance energy profiles and the momentum distributions of fragments of the sequential H6→H5(g.s.)+n→H3+3n decay were analyzed by the theoretically updated direct four-body-decay and sequential-emission mechanisms. The measured momentum distributions of the H3 fragments in the H6 rest frame indicate very strong "dineutron-type"correlations in the H5 ground state decay.
The extremely neutron-rich system H7 was studied in the direct H2(He8,He3)H7 transfer reaction with a 26 AMeV secondary He8 beam Bezbakh et al., Phys. Rev. Lett. 124, 022502 ...(2020)PRLTAO0031-900710.1103/PhysRevLett.124.022502. The missing mass spectrum and center-of-mass angular distributions of H7, as well as the momentum distribution of the H3 fragment in the H7 frame, were constructed. In addition, we carried out another experiment with the same beam but a modified setup, which was cross-checked by the study of the H2(Be10,He3)Li9 reaction. A solid experimental evidence is provided that two resonant states of H7 are located in its spectrum at 2.2(5) and 5.5(3)MeV relative to the H3+4n decay threshold. Also, there are indications that the resonant states at 7.5(3) and 11.0(3)MeV are present in the measured H7 spectrum. Based on the energy and angular distributions, obtained for the studied H2(He8,He3)H7 reaction, the weakly populated 2.2(5)-MeV peak is ascribed to the H7 ground state. It is highly plausible that the firmly ascertained 5.5(3)-MeV state is the 5/2+ member of the H7 excitation 5/2+-3/2+ doublet, built on the 2+ configuration of valence neutrons. The supposed 7.5-MeV state can be another member of this doublet, which could not be resolved in Bezbakh et al. Phys. Rev. Lett. 124, 022502 (2020)PRLTAO0031-900710.1103/PhysRevLett.124.022502. Consequently, the two doublet members appeared in the spectrum of H7 in the work mentioned above as a single broad 6.5-MeV peak.
Investigation of the
7
H-system in the experiment conducted at the fragment separator ACCULINNA-2 in the
8
He(
2
H,
3
He)
7
H reaction requires to detect the recoil
3
He ions with energy down to 6 ...MeV. For this purpose two
particle telescopes are used, with each telescope having in front a thin (20-μm) Si strip detector (
). The maps of thickness heterogeneity of the thin detectors were determined by measuring the energy losses of the
226
Ra α-particles. The adopted thickness normalization method provides a good identification of the
3
He nuclei being recorded in the presence of a high
4
He background. Two approaches were used for calculating the energy losses of the identified
3
He and
4
He reaction ejectiles and reconstructing their energy values available at the exit from the deuterium target. The developed techniques were applied for the
7
H missing-mass reconstruction.
The extremely neutron-rich systems 7H, 6H were studied in the 2H(8He, 3He)7H and 2H(8He, 4He)6H proton and deuteron pickup reactions with a 26 AMeV secondary 8He beam produced at the new ACCULINNA-2 ...fragment separator. In addition, the same proton and deuteron pickup reactions were generated using the 42 AMeV 10Be beam, and the population of low-lying 9Li and 8Li states was measured in reactions 2H(10Be,3He)9Li and 2H(10Be,4He)8Li, respectively. The latter were used as reference measurements in order to check the setup calibration over the excitation energy of 7,6H and to determine the real experimental energy resolution which was compared with Monte Carlo calculations. The corresponding results obtained for the superheavy hydrogen systems 7H, 6H are presented and discussed. Typical excitation spectra of the 9Li and 8Li nuclei are also shown.
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This work is devoted to studying the effects of non-magnetic shell coating on nanoparticles in a low frequency alternating magnetic field (LF AMF) on tumor cells in vitro. Two types ...of iron oxide nanoparticles with the same magnetic core with and without silica shells were synthesized. Nanoparticles with silica shells significantly decreased the viability of PC3 cancer cells in a low frequency alternating magnetic field according to the cytotoxicity test, unlike uncoated nanoparticles. We showed that cell death results from the intracellular membrane integrity failure, and the calcium ions concentration increase with the subsequent necrosis. Transmission electron microscopy images showed that the uncoated silica nanoparticles are primarily found in an aggregated form in cells. We believe that uncoated nanoparticles lose their colloidal stability in an acidic endosomal environment after internalization into the cell due to surface etching and the formation of aggregates. As a result, they encounter high endosomal macromolecular viscosity and become unable to rotate efficiently. We assume that effective rotation of nanoparticles causes cell death. In turn, silica shell coating increases nanoparticles stability, preventing aggregation in endosomes. Thus, we propose that the colloidal stability of magnetic nanoparticles inside cells is one of the key factors for effective magneto-mechanical actuation.
Search for the population of the low-energy continuum of tetraneutron system was performed for reactions of the \(^{8}\)He beam on deuterium target. These studies are performed for the data I.A. ...Muzalevskii et al., Phys. Rev. C 103, 044313 (2021), previously used for the studies of \(^{7}\)H and \(^{6}\)H in the \(^2\text{H}(^8\text{He},{^3\text{He}})^{7}\)H and \(^2\text{H}(^8\text{He},{^4\text{He}})^{6}\)H reactions. Evidence for a hump in the \(^4n\) continuum at \(3.5 \pm 0.7\) and \(3.2 \pm 0.8\) MeV, was observed in the \(^2\)H(\(^8\)He,\(^6\)Li)\(^4\)n and \(^2\)H(\(^8\)He,\(^3\)He)\(^7\)H\(\rightarrow ^3\)H+\(^4\)n reactions, respectively. The observed statistics is quite low (6 and up to 40 events) corresponding to very low cross sections of few microbarns or tens of microbarns. The background conditions for the \(^2\)H(\(^8\)He,\(^6\)Li)\(^4n\) reaction are shown to be good, favoring the physical nature of the observed events. The \(^2\)H(\(^8\)He,\(^3\)He)\(^7\)H\(\rightarrow ^3\)H+\(^4n\) process transforms to the \(^2\)H(\(^8\)He,\(^6\)Li\(^{\ast})^4n\) reaction in the limit of the highest \(^7\)H decay energies. The population of the low-energy region in the \(^{4}\)n spectrum is found to be perfectly correlated with the population of the lowest \(^{6}\)Li states in the \(^{3}\)He+\(^{3}\)H continuum. Theoretical calculations of \(^{8}\)He in a five-body \(\alpha\)+\(4n\) and of \(^{4}\)n in a four-body hyperspherical models are presented. The \(^{8}\)He wave function is shown to contain strong specific correlations, which may give rise to very low-energy structures in tetraneutron continuum in extreme-peripheral reaction scenarios.
A 64-channel readout and data-acquisition module is described in detail. It consists of an H12700 multianode photomultiplier tube, four PADIWA preamplifier boards, and a TRB v3 card that perform the ...functions of a time-to-digital converter and a data concentrator. The software modules that are necessary for operation of the prototype are described. The inter-channel delays are calibrated. The drift of individual delays does not exceed 0.5 ns for the entire measurement time. The spectra of the “time over threshold” (ToT) are investigated. The influence of periodic noise pickups and the need to improve circuit designs are revealed. The timing properties of the wavelength shifter and its effect on the detection efficiency for Cherenkov rings are investigated. The most intense component is characterized by a decay time of 1.1 ns and there are components with characteristic times of 3.8 and 45 ns. The influence of single-electron spectrum features on the detection efficiency for photoelectrons and the probability of false hits are determined. The total time resolution of 131 channels is 1.1 ns (FWHM). The results make it possible to use the investigated system of readout and data acquisition in the CBM experiment. Nevertheless, the elimination of the revealed shortcomings will provide the efficiency margin and improve the reliability of the system during long-term operation.
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