On search and identification of relatively short-lived superheavy nuclei (<Emphasis Type="Italic">Z</Emphasis> ≥ 110) by fossil track studies of meteoritic and lunar olivine crystals

The main goal of the present work is the search for and identification of relatively stable nuclei of superheavy elements (SHE) (Z>110) in galactic matter by fossil track study of nonconducting crystals from the surface of meteorites and rocks from the lunar regolith. Nuclei of SHE are thought to be the products of nucleosynthesis in explosive processes in our Galaxy (supernova r-process nucleosynthesis and, especially, neutron-star formation, etc.). When accelerated to relativistic energies in the Galaxy, they can produce extended trails of damage in nonconducting extraterrestrial crystals. The lifetime of such SHE in galactic cosmic rays will range from 10³ to 10⁷ yr to be registered in extraterrestrial crystals. To search for and to identify the superheavy nuclei in the galactic cosmic rays, it was proposed to use the ability of nonconducting extraterrestrial crystals such as olivines, pyroxenes, and feldspars to detect and to store for many millions of years the trails of damage produced by fast Z≥23 nuclei coming to rest in the crystalline lattice. The track lengths of fast Z≥23 nuclei are directly proportional to Z² of these nuclei. The nuclei of SHE produce, when coming to rest in a crystal volume, tracks that are a factor of 1.6–1.8 longer than the tracks due to cosmic-ray Th and U nuclei. To identify the tracks due to superheavy nuclei, calibrations of the same crystals were performed with accelerated Au, Pb, and U nuclei. For visualization of these tracks inside the crystal volume, proper controlled annealing and chemical etching procedures were developed. Since 1980, fossil tracks due to Th and U nuclei have observed and unambiguously identified (1988) by subsequent calibrations of the olivine crystals with accelerated U, Au, and Pb ions. The number of tracks of Th and U nuclei measured in olivine crystals totaled more than 1600, as compared with the prior 30 events. The other approach to identifying SHE in nature is to search for tracks in phosphate crystals from spontaneous fission of Z ≥ 110 nuclei; these produce two-prong and three-prong fission fragment tracks and differ significantly from the tracks from spontaneous fission of ²³⁸U and ²⁴⁴Pu nuclei. Extraterrestrial phosphate crystals of lunar and meteoritic origin will be investigated. Such SHE nuclei can survive in crystals of extraterrestrial rocks and produce spontaneous fission tracks, if the lifetime is more than 5×10⁷ yr.     

The CAKE experiment: Progress and new results

CAKE (cosmic abundances below the knee energies) is a prototype balloon experiment for the determination of the charge spectra of the primary cosmic-ray nuclei with Z>28 and the search for exotic heavy particles in the primary cosmic radiation. CAKE is made of stacks of CR39^® and Lexan^® nuclear track detectors; it has a geometric acceptance of about 1.7 m² sr for Fe nuclei. Here, the scanning strategy and the algorithms used for tracking in automatic mode of the CR events are presented.     

Study of fossil tracks due to 50 < or = Z < or = 92 galactic cosmic ray nuclei in meteoritic crystals: results and perspectives

A new approach to the problem of investigation of charge and energy spectra of ultra heavy Galactic cosmic ray nuclei, based on fossil track study of extraterrestrial olivine crystals has been developed. The results of an investigation of ultra heavy Galactic cosmic ray nuclei (Z=50-92) in meteoritic olivine crystals are presented. The technique was based on calibration of olivine crystals with accelerated Xe, Au, Pb and U ions and well-controlled partial annealing of "fresh" and "fossil" tracks. It allows us to determine the charge spectra and abundances of cosmic ray nuclei based on fossil track length study in meteoritic and Moon crystals. The comparative studies of the spectra of "fossil' tracks and tracks due to 208Pb and 238U nuclei have shown that the group of 210 micrometers "fossil" tracks, first observed in 1980 at JINR is due to Th-U nuclei-products of recent r-process nucleosynthesis in our Galaxy. The method in principle allows one to resolve Pt-Pb peaks in fossil tracks, to establish the upper limit of the abundance of Z>110 nuclei in the Galactic cosmic rays at the level < or = 10(-3) to the abundance of actinide nuclei and to get information on the history of Z>50 cosmic ray nuclei in time interval up to 220 M.Y.     

Effects of superstrings in collisions

Superstring theory in d = 10 dimensions after Calabi—Yau compactification yields a minimum low-energy gauge group SU(3)_C × SU(2)_L × U(1)_Y × U(1)_E. The low-energy theory includes particles with the quantum numbers of 27 representations of E₆, each of which contains an extra neutrino ν^c conventionally called a “right-handed neutrino”. The contributions of ν and ν^c to through Z⁰ and Z_E mixing is calculated. Small contributions are found of the new right-handed neutrino and of the superstring boson Z_E to σ(e⁺e⁻ → γ + nothing).     

The obsidian from Quiron (Salta Province, Argentina): a new reference glass for fission-track dating

In the course of a geochronological study of the volcanic activity in the Andean Cordillera in northern Argentina, we have found in the El Quevar volcanic complex a phenocryst poor obsidian (Quiron obsidian) showing an unusually high spontaneous track density. Defects which might produce “spurious” tracks are virtually absent. Application of fission-track dating using an absolute approach, based on the IRMM-540 standard glass for neutron fluence measurements, yielded an apparent age of and a plateau age of .A ⁴⁰Ar–³⁹Ar isochron age on biotite of was already available for the Quiron rhyolite. We determined further ⁴⁰Ar–³⁹Ar ages on several chips of the glass itself using two analytical approaches: total fusion with a focussed laser beam (LTFA) and a step-heating approach using a de-focussed laser beam (LSHA). We have obtained a weighted average of , an isochron age of and an integrated age of for LTF analyses, and a w.a. of , an iso.a. of and an int.a. of for LSH analyses (all age errors are 2σ).The Quiron obsidian is very easy to analyse for its high spontaneous track density and because microlites which might produce spurious tracks are very rare. Independent reference ⁴⁰Ar–³⁹Ar ages determined in different laboratories are available. For these reasons we believe that this glass may be very useful for testing fission-track system calibrations and apparent age correction procedures.Splits of obsidian Quiron will be distributed upon request to colleagues who intend to test it.     

Detecting galactic cosmic ray transuranium nuclei in olivine crystals from meteorites

Results from the experimental search for and identification of tracks from the superheavy and transuranium nuclei of galactic cosmic rays in pallacite olivine crystals, conducted as part of project OLIMPIA [1], are presented. To date, 170 crystals from Marjalahti and Eagle Station pallacites have been processed and 6800 tracks corresponding to nuclei with charges Z > 55 have been found; 45 of these are from nuclei with charges of 88 < Z < 92 and three super-long ones were produced by nuclei with Z > 105. The charge of one of these nuclei is estimated in the first approximation as Z = 119(+10,?6). Our data confirm the hypothesis of islands of stability for natural trans-Fermi nuclei.     

A search for superheavy nuclei tracks in extraterrestrial olivine crystals

A study is made for the search of superheavy nuclei in Marjalahti, Eagle Station and in other pallasite olivines. The olivine crystals are calibrated for heavy ion track lengths by using heavy ion beams from cyclotrons. The calibration for ultra heavy ions which are presently not available with sufficient energy to produce volume tracks in olivine crystals, is based on Katz and Kobetich model of track formation. The length spectrum of volume tracks, revealed by puncturing them with focussed Nd-glass laser beam, is measured and the abundances of different nuclei groups are calculated. Partial annealing has been used at 430°C for 32 hr which eliminates the interfering tracks due to nuclei of atomic numberS ≤ 50. During the scanning 4 cm³ olivine crystals, about 360 long tracks of uranium group as well as two very long tracks have been found. If these tracks belong to superheavy nuclei, the relative abundance of super heavies is found to be 6 × 10⁻¹¹ in galactic cosmic rays.     

Analysis of the results of calibrating meteoritic olivine crystals with238U nuclei at the Bevalac accelerator

The results are presented of calibrating the sensitivity of olivine crystals from meteorites by the²³⁸U nuclei produced at the Bevalac accelerator. The comparative studies of the spectra of the etchable track lengths due to the²³⁸U nuclei and to fossil tracks in these olivines have shown that the group of the 210 m fossil tracks observed in 1980 at the LNR, JINR is due to the galactic cosmic-ray nuclei of the Th-U group. As regards the origin of the 340–360 m group of fossil tracks which were considered in [2] to be candidates for superheavy nuclei in cosmic rays the presence of the track with a length of up to 360 m in the calibrating²³⁸U track length spectra indicates that the above interpretation has to be questioned. The possible ways of the unambiguous identification of the group of the abnormally long fossil tracks are discussed.In conclusion the authors express their deep gratitude to Academician G.N. Flerov for thoughtful guidance and permanent attention to this study. The authors wish to thank Dr. G.M. Ter-Akopian for very useful discussions and advice and also for his help during the calibrations on Bevalac, Dr. R.I. Petrova for her help in preparing olivine crystal mounts and for their subsequent annealing and etching, and Mrs. G.G. Bankova and G.P. Knyazeva for the thorough microscopic measurements of the²³⁸U track spectra.     

Optimization of the heavy nuclei track etching in olivine crystals from meteorites

The investigation of the track etching velocity dependence for nuclei with Z50 on pH of the etching solution in the olivine crystals from Marjalahti and Eagle Station meteorites, containing galactic cosmic-ray nuclear tracks and also the crystals from Marjalahti meteorite, calibrated at the UNILAC (GSI, Darmstadt) with 14.17 MeV/N ²⁰⁸Pb nuclei, were performed.

The pH of the etching solution were changed from 7.8 to 9.4. It is shown that the optimal track etch condition were realised at pH of etching solution in the interval from 8.4 to 8.8.

The results of the Galactic cosmic-ray nuclei tracks with Z83 revealed in olivine crystals are presented. They were additionally irradiated at 90% to the surface with accelerated 14 MeV/N ¹³²Xe nuclei.     

Search for superheavy elements in galactic cosmic rays

The charge distribution of approximately 6000 nuclei with charge numbers above 55 in galactic cosmic rays has been obtained in the OLIMPIYA project. Three superheavy nuclei with the charge numbers in the range 105 < Z < 130 have been detected. The regression analysis has provided a more accurate estimate of the charge number of one of these nuclei (119 _?6 ⁺¹⁰ with a probability of 95%). Such nuclei should form stability islands. Their detection in nature confirms theoretical predictions and justifies efforts for their synthesis under terrestrial conditions. The model calculations performed in this work possibly can explain the results of some experiments on the investigation of the charge composition of cosmic rays in which particles with charge numbers in the range 94 < Z < 100 were detected (they cannot enter into the composition of primary cosmic radiation because their lifetime is very short). The calculations indicate that events with Z > 92 are due to the fragmentation of heavier nuclei from the stability island, rather than to methodical inaccuracies or fault of instruments. Several such events have been revealed. Thus, the track method makes it possible to obtain the results very important for understanding of the physical picture of the world. The results obtained within the OLIMPIYA project show that the study of tracks of galactic cosmic rays in olivine crystals from meteorites opens new capabilities for the investigation of fluxes and spectra in cosmic rays in the region of heavy and superheavy nuclei.     

Leptonic flavor-changing Z decays in SU(2)U(1) theories with right-handed neutrinos

We analyze possible lepton-flavor-violating decays of the Z⁰ particle in a minimal extension of the standard model, in which one right-handed neutral field for each family has been introduced. Such rare leptonic decays are induced by Majorana neutrinos at the first electroweak loop level and are generally not suppressed by the ordinary “see-saw” mechanism. In particular, we find that experimental bounds on branching ratios of the order of 10⁻⁵–10⁻⁶ attainable at LEP may impose constraints on lepton-flavor-mixing parameters and the masses of the heavy Majorana neutrinos.     

Color centers in the ionized and in the triplet state —Z 2 centers in ytterbium-doped KCl crystals

Z ₂ centers in Yb²⁺-doped KCl crystals are investigated by optical absorption experiments and by ESR experiments using the optically excited triplet state. Two mainZ ₂ center configurations have been found. One of them shows (100) axial symmetry and is optically orientable in the crystal. The other one possesses (110) symmetry elements. The measured fine structure constants are explained partly by dipole-dipole interaction of the two electronic magnetic moments partly by spin orbit interaction due to the Ytterbium impurity. The structure of the optical absorption spectra is attributed to as ²–s d charge transfer transition affected by the combined effect of crystal field and spin orbit interaction.     

Study of fossil tracks due to VH and VVH groups of cosmic ray nuclei in olivine crystals from Luna-16 and Luna-24

The olivine crystals from lunar regolith samples taken by the Soviet unmanned spacecrafts Luna-16 and Luna-24 were investigated. Eleven 0.5 –1.0 mm size olivine crystals were mounted in epoxy, polished and then etched in modified WO₄ solution. The Fe-group track densities up to 10⁸ tracks.cm⁻² (Fe-group) were measured under optical microscope. The tracks of length greater than 30 microns due to Z ≥ 36 cosmic ray nuclei are counted for VVH tracks density for all the crystals. The VVH / VH track densities ratio for these lunar olivine crystals varies from 1.25×10⁻⁴ to 2×10⁻³. It corresponds to the averaged depth of these crystals in lunar soil of 2–8 cm during galactic cosmic ray exposure. Lunar crystals are well suited for VVH track studies due to a very high track density. Two crystals were annealed at 430°C for 32 hrs. This procedure eliminates iron group tracks completely and leaves etchable tracks of nuclei with Z 50 even in the olivine crystals with Fe-group tracks up to 1–2×10⁸ tracks cm⁻². We were able to measure two tracks with the length 195 and 210μm which were produced by Th---U group of Galactic cosmic ray nuclei.     

Fusion-fission dynamics in the superheavy nucleus production

The fusion-fission reaction mechanism leading to the massive nucleus formation is studied. We investigate the superheavy nucleus formation in heavy-ion induced reactions by analysing the evaporation residue (ER) production in order to study the fusion dynamics and the decay properties of nuclei close to the stability island at Z=114. We consider the ⁶¹Ni+²⁰⁸Pb, ⁴⁸Ca+²³⁸U and ⁴⁸Ca+²⁴⁴Pu reactions that lead to the Z=110, 112 and 114 superheavy elements respectively. By using the dinuclear system (DNS) concept of the two interacting nuclei we calculate the quasifission-fusion competition in the entrance channel and the fission-evaporation competition along the de-excitation cascade of the compound nucleus. The dynamics of the entrance channel allows us to determine the beam energy window which is favorable to the fusion, while the dynamic evolution of the compound nucleus on the shell correction to the fission barrier and the dissipative effects influence the fission-evaporation competition in order to obtain the residue nuclei from the superheavy nucleus formation. We also calculate the τ _n /τ_tot ratio at each step of the de-excitation cascade of the compound nucleus and we present a systematics of τ _n /τ_tot (at first step of the cascade) for many reactions that lead to nuclei with Z=102–114.     

An “instantaneous” distribution of the ionization-passive electrons and holes under irradiation of a dielectric by intense electron or laser beams

A method is worked out for calculation of an “instantaneous” energy distribution of the ionization-passive electrons and holes resulting from the electron-electron collisions before the onset of electron-phonon relaxation under 10⁻¹⁵–10⁻¹⁴ s irradiation of a dielectric by an intense electron or laser beam. The method is based on the solution of a system of integral-differential kinetic equations of general form. The Auger and impact ionization as well as hole recoil due to the momentum conservation law are taken into account in calculations. The “instantaneous” distribution is calculated in NaCl under irradiation of the sample by a high-density electron beam. The “instantaneous” distribution of ionization-passive electrons and holes is the initial one in solutions of all kinetic equations describing further relaxation of electron excitations in irradiated materials.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 15–22, November, 2004.     

Optical and electron spin resonance spectra ofZ 2(Eu) centers in alkali halide crystals

The ESR spectra ofZ ₂(Eu)-centers in KBr and KCl are presented and correlated to the optical absorption and the electron spin resonance of the Europium vacancy complex. The fine structure of theZ ₂ spectra can be described by a Spin-Hamiltonian with an axialb ₂ ⁰ -parameter only. At room temperature it amounts to 1,761 10^–4 cm^–1 for KBr, 1,854 10^–4 cm^–1 for KCl and 1,453 10^–4 cm^–1 for RbCl. Accordingly theZ ₂(Eu)-center must posses a strict axial 100-symmetry in these crystals.     

Study on the phase transitions by nuclear magnetic resonance of α-type RbAl(SO4)2·12H2O and β-type CsAl(SO4)2·12H2O single crystals

The thermodynamic properties, spin–lattice relaxation times, T₁, and spin–spin relaxation times, T₂, of the ²⁷Al, ⁸⁷Rb, and ¹³³Cs nuclei in MAl(SO₄)₂·12H₂O (M=Rb and Cs) crystals were investigated, and the two crystals were found to lose H₂O with increases in temperature. From our results for T₁ and T₂, we conclude that the discontinuities near T_d in the T₁ curves of the two crystals correspond to structural changes. In both crystals, below T_d the water molecules surrounding the Al³⁺ and M⁺ nuclei form distorted octahedra, whereas above T_d the water molecules around the Al³⁺ and M⁺ nuclei form regular octahedra and the environment of the Al³⁺ and M⁺ nuclei has cubic symmetry. Further, the T₁ for the ²⁷Al and ⁸⁷Rb nuclei in RbAl(SO₄)₂·12H₂O below T_d were found to increase with increasing temperature, whereas the T₁ for the ²⁷Al and ¹³³Cs nuclei in CsAl(SO₄)₂·12H₂O were found to decrease. It is possible that this difference is due to the different characteristics of α- and β-type crystals.     

Influence of the nuclear Meissner - effect on the ground - state rotational bands of deformed nuclei

The possible regions of singularities in ground-state bands of deformed nuclei such as those observed in ¹⁶⁰Dy and ¹⁶²Er isotopes are predicted on the basis of the nuclear Meissner effect. The singularities can occur at Z=66,68 or N=90,112(110) in rare-earth nuclei and 92?Z96 or 138?N?144 in the actinides.     

K–K excitations on as “primary” superfields

We show that the K–K spectrum of IIB string on is described by “twisted chiral” superfields, naturally described in “harmonic superspace”, obtained by taking suitable gauge singlets polynomials of the D3-brane boundary superconformal field theory.To each p-order polynomial is associated a massive K–K short representation with states. The quadratic polynomial corresponds to the “supercurrent multiplet” describing the “massless” bulk graviton multiplet.