Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives

A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.     

Express analysis of spectra in precision experiments

Some precision experiments require several tens of hours for measurements. In this case, it is important to take into account possible drift of the detection system parameters in time. An express analysis program has been developed for early detection of significant distortions in recorded spectra, their filtration, and correction of results. Original Russian Text ? N.A. Gundorin, N.D. Dikoussar, N.G. Maznyj, L.B. Pikelner, I.M. Salamatin, M.I. Tsulaja, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 2, pp. 261–263.     

Separation efficiency of the MASHA facility for short-lived mercury isotopes

The mass-separator MASHA built to identify Super Heavy Elements by their mass-to-charge ratios is described. The results of the off- and on-line measurements of its separation efficiency are presented. In the former case four calibrated leaks of noble gases were used. In the latter the efficiency was measured via 284 MeV $^{40}$ Ar beam and with using the hot catcher. The ECR ion source was used in both cases. The $\alpha $ -radioactive isotopes of mercury produced in the complete fusion reaction $^{40}$ Ar+ $^{144}$ Sm $\rightarrow ^{184-xn}$ Hg+xn were detected at the mass-separator focal plane. The half-lives and the separation efficiency for the short-lived mercury isotopes were measured. Potentialities of the MEDIPIX detector system have been demonstrated for future use at the mass-separator MASHA.     

DANSSino: a pilot version of the DANSS neutrino detector

DANSSino is a reduced pilot version of a solid-state detector of reactor antineutrinos (to be created within the DANSS project and installed under the industrial 3 GW_th reactor of the Kalinin Nuclear Power Plant—KNPP). Numerous tests performed at a distance of 11 m from the reactor core demonstrate operability of the chosen design and reveal the main sources of the background. In spite of its small size (20 × 20 × 100 cm³), the pilot detector turned out to be quite sensitive to reactor antineutrinos, detecting about 70 IBD events per day with the signal-to-background ratio about unity.     

Investigation of the reaction <Superscript>208</Superscript>Pb(<Superscript>18</Superscript>O, <Emphasis Type="Italic">f</Emphasis>): Folding angular distributions of fission fragments and gamma-ray multiplicity

Correlations between folding angular distributions of fission fragments and the gamma-ray multiplicity are studied for ¹⁸O + ²⁰⁸Pb interactions at energies of the beam of ¹⁸O ions in the range E _lab = 78–198.5 MeV. The probabilities are determined for complete-and incomplete-fusion processes inevitably followed by the fission of nuclei formed in these processes. It is found that the probability of incomplete fusion followed by fission increases with increasing energy of bombarding ions. It is shown that, for the incomplete-fusion process, folding angular distributions of fission fragments have a two-component structure. The width of folding angular distributions (FWHM) for complete fusion grows linearly with increasing energy of ¹⁸O ions. The multiplicity of gamma rays from fission fragments as a function of the linear-momentum transfer behaves differently for different energies of projectile ions. This circumstance is explained here by the distinction between the average angular momenta of participant nuclei in the fusion and fission channels, which is due to the difference in the probabilities of fission in the cases where different numbers of nucleons are captured by the target nucleus.     

Using pixel detectors in investigations of EC/EC decay

A new multi-detector spectrometer based on Timepix silicon pixel detectors is developed to investigate the 2νEC/EC decay of ¹⁰⁶Cd. The detectors have high efficiency for recording two low-energy KX radiation quanta emitted during 2νEC/EC decay. The ability of pixel detector to identify α, β, and γ particles and precisely localize them allows us to suppress background radiation efficiently. Test measurements for an assembly of two pixel detectors in an underground laboratory were performed. They showed the possibility of using them in the search for the 2νEC/EC decay of ¹⁰⁶Cd.     

Investigation of hyperfine quadrupole interactions in UGe<Subscript>2</Subscript> and UAl<Subscript>2</Subscript> compounds on <Superscript>111</Superscript>Cd probe nuclei by the perturbed angular correlation method

The parameters of nuclear quadrupole hyperfine interaction in intermetallic UGe₂ and UAl₂ compounds have been measured in a temperature range of 100–300 K using the perturbed angular γγ correlation method on ¹¹¹Cd probe nuclei. The results obtained for UGe₂ indicate a pronounced anisotropic character in the distribution of f electrons in agreement with the calculation of the electronic structure of this compound. The hybridization degree between f electrons of U and p electrons of Al in UAl₂ is lower than the hybridization degree between f electrons of U and p electrons of Ge in UGe₂.     

Investigation of the 2νEC/EC Decay of 106Cd

Search for the β⁺β⁺, β⁺ EC, and EC/EC modes of the ¹⁰⁶Cd decay was carried out with the TGV-2 (Telescope Germanium Vertical) low-background multidetector spectrometer installed at the Modane underground laboratory (4800 m w.e.). The measured foil samples ～50 μm thick and 52 mm in diameter were placed between the entrance windows of the neighboring detectors inside the cryostat. The total measurement time for 10 g of ¹⁰⁶Cd enriched to 75% was 8687 h. New limits (at the 90% confidence level, CL) were obtained for the ¹⁰⁶Cd half-lives against various branches of the decay to the ground state 0⁺ and excited states 2⁺ of the ¹⁰⁶Pd daughter nucleus. They are T _1/2(2νβ⁺β⁺) ≥ 6.0 × 10¹⁹ y, and T _1/2(2νβ⁺ EC) ≥ 5.9 × 10¹⁹ y, and T _1/2(2νEC/EC) ≥ 3.0 × 10²⁰ y for the transitions to the 0⁺ ground state of ¹⁰⁶Pd; T _1/2(2νβ⁺β⁺) ≥ 5.7 × 10¹⁹ y, T _1/2(2νβ⁺ EC) ≥ 5.9 × 10¹⁹ y, and T _1/2(2νEC/EC) ≥ 4.2 × 10¹⁹ y for the transitions to the 2⁺, 512-keV excited state of ¹⁰⁶Pd; and T _1/2(2νEC/EC) ≥ 3.1 × 10¹⁹ y for the transition to the 0 ₁ ⁺ , 1334-keV excited state of ¹⁰⁶Pd.     

Investigation of the 208Pb(18O, f) fission reaction: Mass-energy distributions of fission fragments and their correlation with the gamma-ray multiplicity

The mass-energy distributions of fragments originating from the fission of the compound nucleus ²²⁶Th and their correlations with the multiplicity of gamma rays emitted from these fragments are measured and analyzed in ¹⁸O + ²⁰⁸Pb interaction induced by projectile oxygen ions of energy in the range E _lab = 78–198.5 MeV. Manifestations of an asymmetric fission mode, which is damped exponentially with increasing E _lab, are demonstrated. Theoretical calculations of fission valleys reveal that only two independent valleys, symmetric and asymmetric, exist in the vicinity of the scission point. The dependence of the multiplicity of gamma rays emitted from both fission fragments on their mass, M_γ(M), has a complicated structure and is highly sensitive to shell effects in both primary and final fragments. A two-component analysis of the dependence M_γ(M) shows that the asymmetric mode survives in fission only at low partial-wave orbital angular momenta of compound nuclei. It is found that, for all E _lab, the gamma-ray multiplicity M_γ as a function of the total kinetic energy (TKE) of fragments, M_γ(TKE), decreases linearly with increasing TKE. An analysis of the energy balance in the fission process at the laboratory energy of E _lab = 78 MeV revealed the region of cold fission of fragments whose total kinetic energy is TKE ～Q _max.