Evidence for a K<Superscript>π</Superscript> = 1/2<Superscript>+</Superscript> isomer in neutron-rich <Superscript>185</Superscript>Ta

In this paper we present for the first time the measured delayed neutron (DN) yields and time spectra from high-energy protons interacting with thick ^natPb targets. The 1GeV protons from the accelerator impinged on targets of different thicknesses producing a huge number of spallation-fission products, some of which can be DN precursors. After the beam is switched off, the DNs were detected with optimized ³He counter. The production yields of light DN precursors as ¹⁷N and “usual” fission products as ⁸⁷Br and ⁸⁸Br, which dominate the total DN activity, are obtained both for thin and thick targets. These new data are of great interest for the new generation high-power spallation targets based on liquid-metal technologies. Our findings also should help to constrain the physics models within the simulations codes.     

Measurement of the cross sections for the production of the isotopes <Superscript>74</Superscript>As, <Superscript>68</Superscript>Ge, <Superscript>65</Superscript>Zn,and <Superscript>60</Superscript>Co from natural and enriched germanium irradiated with 100-MeV protons

The cross sections for the production of the radioactive isotopes ⁷⁴As, ⁶⁸Ge, ⁶⁵Zn, and ⁶⁰Co in metallic germanium irradiated with 100-MeV protons were measured, the experiments being performed both with germanium of natural isotopic composition and germanium enriched in the isotope ⁷⁶Ge. The targets were irradiated with a proton beam at the facility for the production of radionuclides at the accelerator of the Institute for Nuclear Research (INR, Moscow). The data obtained will further be used to calculate the background of radioactive isotopes formed by nuclear cascades of cosmic-ray muons in new-generation experiments devoted to searches for the neutrinoless double-beta decay of ⁷⁶Ge at underground laboratories.     

Negative-muon capture in <Superscript>150</Superscript>Sm

The energy and time spectra of γ rays emitted during negative-muon capture in ¹⁵⁰Sm were studied. The total muon lifetime in ¹⁵⁰Sm was measured. The yields of several radioactive isotopes in this reaction were determined. The partial γ-ray yield upon muon capture by a ¹⁵⁰Sm nucleus were measured.     

Study of the excitation of high-spin isomers in <Superscript>190</Superscript>Ir and <Superscript>196,198</Superscript>Au in the near-threshold region

The isomeric ratios of the yields for ^190m,g Ir and ^196m,g Au have been measured in the (γ,n) reaction in the near-threshold region at γ-ray energies of 12 and 12.5 MeV. The isomeric ratios for ^198m,g Au have been measured in the (d,p) and (n,γ) reactions. The statistical nature of the (γ,n) and (n,γ) reactions is shown.     

Study of fusion and nucleon transfer channels in the <Superscript>197</Superscript>Au + <Superscript>6</Superscript>He reaction in an energy range of <Superscript>6</Superscript>He to 20 Mev/A

New data on the cross sections of reactions occurring during the interaction of ⁶He nuclei with ¹⁹⁷Au at energies of ⁶He from 40 to 120 MeV are presented. The experiments were performed in the ACCULINNA secondary beam separator of the Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research. To identify the reaction products, the activation method for measuring the gamma activity of the target assembly of thin foils was used. The excitation functions for fusion reactions involving the evaporation of up to ten neutrons from the compound nucleus as well as reactions with the emission of charged particles and nucleon transfer in the investigated energy region are obtained. Data analysis was carried out using two codes: ALICE-MP and NRV. The cross sections for the (⁶He, xn) reactions occurring through the compound nucleus are mostly in agreement with the results of model calculations based on the statistical approach. It is shown that, up to the energies of 114 MeV, the cross-section drop in the complete fusion reactions is negligible. The experimental excitation functions of reactions leading to the formation of isotopes of mercury and gold (transfer reaction) indicate that the main contribution to their formation is made by direct processes and that evaporation reactions (⁶He, pxn) and (⁶He, αxn) play a minor role, as is evidenced by a comparison of the measured cross sections with the calculation results.     

Penning-trap mass measurements on <Superscript>92, 94-98, 100</Superscript>Mo with JYFLTRAP

Penning-trap measurements on stable ^{92, 94-98, 100}Mo isotopes have been performed with relative accuracy of \(\ensuremath 1\cdot 10^{-8}\) with the JYFLTRAP Penning-trap mass spectrometer by using ⁸⁵Rb as a reference. The Mo isotopes have been found to be about 3keV more bound than given in the Atomic Mass Evaluation 2003 (AME03). The results confirm that the discrepancy between the ISOLTRAP and JYFLTRAP data for ^101-105Cd isotopes was due to an erroneous value in the AME03 for ⁹⁶Mo used as a reference at JYFLTRAP. The measured frequency ratios of Mo isotopes have been used to update mass-excess values of 30 neutron-deficient nuclides measured at JYFLTRAP.     

Momentum distributions of <Superscript>4</Superscript>He nuclei from the <Superscript>6</Superscript>He and <Superscript>6</Superscript>Li breakup

Experimental data on the momentum distributions of ⁴He nuclei originating from ⁶He and ⁶Li breakup on various targets are presented over a wide beam energy range. The experiment with ⁶He was performed at the DRIBs accelerator complex for radioactive beams at the Joint Institute for Nuclear Research (JINR, Dubna). The intensity of the ⁶He beam used was 5 × 10⁶ particles per second and its energy was 10 MeV per nucleon. The momentum distributions of breakup products were measured by means of the MSP-144 magnetic spectrometer. The distribution width was shown to be virtually independent of the target mass. A small value of this width, σ ～ 28 MeV/c, confirms the presence of a halo in ⁶He. The measurements performed with ⁶Li beams of energy 18 and 46 MeV per nucleon at the U-400M accelerator yielded a width value of σ ～ 50 MeV/c for the momentum distributions of ⁴He nuclei, which is intermediate between that for ⁶He and those for stable nuclei. A compilation of the widths of the momentum distributions of fragments originating from the breakup of various nuclei is presented versus the binding energy of one or two neutrons in these nuclei, the target mass and the projectile energy.     

Investigation of spatial distribution of <Superscript>137</Superscript>Cs in soil in area of location of the Armenian NPP

Problem of evaluation of spatial distribution of ¹³⁷Cs in soil and of direct radiation impact of the Armenian NPP on population dwelling in the region of its location, on the background of global radioactive fallouts and aftermaths of the Chernobyl accident is solved. Content of radiationdangerous radionuclide ¹³⁷Cs in soil on the territory with radius 50 km including the NPP area has been investigated. Points of monitoring have been chosen on the basis of analysis of meteorological data and calculation of the distance where emissions from NPP have maximal concentration in air. The obtained results agree well with the data of UN Scientific Committee of Radiation Action.     

One-neutron stripping reactions of <Superscript>11</Superscript>Be and <Superscript>19</Superscript>C on light target

We have calculated the one-neutron absorption cross-section and the longitudinal momentum distribution of the core fragment coming out from the breakup of ¹¹Be and ¹⁹C on ⁹Be target at 63 MeV/A and 88 MeV/A beam energies respectively. The reaction mechanism is treated within the framework of the eikonal approximation. The effective range of the nuclear interaction between the core and the valence neutron within the projectile has been determined by comparing the predicted stripping cross-section with the recently measured one. The effective range for ¹⁹C has been found to be smaller than that for ¹¹Be. It qualitatively indicates that ¹⁹C is slightly more halo than ¹¹Be. The smaller width, predicted as well as measured, of the LMD of ¹⁸C than ¹⁰Be also strengthens this fact. The experimental data concerning the LMD of core fragments have been well represented.      

Cosmogenic radionuclides <Superscript>14</Superscript>C and <Superscript>10</Superscript>Be: Solar activity and climate

The problem of the use of such cosmogenic nuclides as ¹⁴C and ¹⁰Be in natural archives for reconstruction of both the solar activity and the cosmic-ray intensity is discussed. The climate-dependent processes of the formation, transport, and deposition of these nuclides to Earth’s archives must be taken into account for adequate processing of information derived from such archives.     

Analysis of <Superscript>8</Superscript>B Proton Halo Nucleus Scattered from <Superscript>12</Superscript>C and <Superscript>58</Superscript>Ni at Different Energies

Angular distributions in the elastic scattering of ⁸B from ¹²C and ⁵⁸Ni targets at different energies have been analyzed in the framework of the double-folding (DF) optical model. The real central part of the nuclear optical potential is obtained by folding the M3Y effective interaction with the cluster density distribution of the ⁸B nucleus. The experimental angular distributions have been successfully reproduced. This confirms the validity of the cluster structure of the ⁸B nucleus.     

Projectile fragmentation of <Superscript>40,48</Superscript>Ca and isotopic scaling in a transport approach

We investigate theoretically projectile fragmentation in reactions of ^40,48Ca on ⁹Be and ¹⁸¹Ta targets using a Boltzmann-type transport approach, which is supplemented by a statistical decay code to describe the de-excitation of the hot primary fragments. We determine the thermodynamical properties of the primary fragments and calculate the isotope distributions of the cold final fragments. These describe the data reasonably well. For the pairs of projectiles with different isotopic content we analyze the isotopic scaling (or isoscaling) of the final fragment distributions, which has been used to extract the symmetry energy of the primary source. The calculation exhibits isoscaling behavior for the total yields as do the experiments. We also perform an impact-parameter-dependent isoscaling analysis in view of the fact that the primary systems at different impact parameters have very different properties. Then the isoscaling behavior is less stringent, which we can attribute to specific structure effects of the ^40,48Ca pair. The symmetry energy determined in this way depends on these structure effects.     

Investigation of the <Superscript>232</Superscript>Th and <Superscript>238</Superscript>U photofission

The average angular momenta of the ⁸⁴Br, ¹³²Sb, ¹³³Te, and ¹³⁵Xe fission fragments, produced as a result of ²³²Th and ²³⁸U photofission by bremmsstrahlung γ photons with an endpoint energy of 8.5 MeV, have been determined by measuring the isomeric yield ratios. The experimental isomeric yield ratios have been calculated taking into account the contribution from β decay of isobaric nuclei to the yields of isotopes studied.     

Examination of the <Superscript>16</Superscript>O + <Superscript>28</Superscript>Si system with microscopic and phenomenological potentials

The ¹⁶O + ²⁸Si reaction has been widely studied both experimentally and theoretically and has been claimed to show indications of chaotic scattering. In order to examine this claim and to address whether reaction models such as the optical one could explain the experimental data, we have analyzed the ¹⁶O + ²⁸Si system within the framework of the optical model for ten energies from 29.0 to 45.0 MeV, by using microscopic folded potentials, which are based on M3Y nucleon-nucleon, alpha-alpha effective interactions and a phenomenological shallow potential. All potentials describe the individual angular distributions very well at forward angles. However, they fail to describe the individual angular distributions over the whole angular range up to 180°. Nevertheless, we have been able to explain the experimental data by modifying the surface region of the microscopic real potentials by adding two surface potentials. With these correction potentials, we have obtained very good agreement for the individual angular distributions over the whole angular range for the given energies as well as for the experimental data near the Coulomb barrier. The failure of these optical potentials in explaining the scattering observables of this reaction without corrections puts a question mark on the model and supports the idea of a chaotic behavior. The text was submitted by the authors in English.     

Measurement of <Emphasis Type="Italic">K</Emphasis><Superscript> + </Superscript><Emphasis Type="Italic">K</Emphasis><Superscript>-</Superscript> production in two-photon collisions in the resonant-mass region

K ⁺ K ^- production in two-photon collisions has been studied using a large data sample of 67 fb^-1 accumulated with the Belle detector at the KEKB asymmetric e ⁺ e ^- collider. We have measured the cross section for the process for center-of-mass energies between 1.4 and 2.4 GeV, and found three new resonant structures in the energy region between 1.6 and 2.4 GeV. The angular differential cross sections have also been measured.Received: 30 September 2003, Published online: 18 December 2003     

Photonuclear Reactions on Bypassed Nuclei <Superscript>84</Superscript>Sr and <Superscript>92</Superscript>Mo

The yields of photonuclear reactions on mixtures of natural isotopes of strontium and molybdenum that result in the formation and decay of bypassed nuclei ⁸⁴Sr and ⁹²Mo are measured and compared to theoretical results obtained using the TALYS code and calculations in the combined model of photonucleon reaction (CMPR). The need is demonstrated to consider isospin splitting in cases of photoproton reactions. The yields of the ⁹²Mo(γ,p)⁹¹mNb, ⁸⁴Sr(γ,p)⁸³Rb reactions that make the main contribution to the formation and decay of ⁸⁴Sr and ⁹²Mo in the p-process of nucleosynthesis differ from the TALYS and CMPR results by several hundred percent.     

First observation of isomeric transition from <Superscript>148<Emphasis Type="Italic">m</Emphasis></Superscript>Pr and parity assignment for excited levels in <Superscript>148</Superscript>Pr

Internal conversion electrons from the decay of ¹⁴⁸Ce and ^148mPr have been measured with a Si(Li) detector. The radioactive sources were produced by the thermal neutron-induced fission of ²³⁵U, followed by an on-line mass separation. K- and L-conversion electrons of the isomeric transition from ^148mPr were newly observed at 34.6 and 70.8 keV, respectively. The M3 multipolarity was assigned to this transition from the experimental conversion coefficients, and, consequently, the 76.8 keV isomeric level was found to be a 4^- state. Parities of some excited levels in ¹⁴⁸Pr were also deduced.     

Inverse Quasifission in <Superscript>156,160</Superscript>Gd + <Superscript>186</Superscript>W Reactions

To investigate the impact shell effects have in the formation of neutron-rich fragments in multinucleon transfer reactions, a series of experiments to explore the binary channel in ^156,160Gd + ¹⁸⁶W reactions at energies near and above the Coulomb barrier is performed at the Flerov Laboratory’s U-400 accelerator using the CORSET setup. These experiments are aimed mainly at obtaining the production cross sections of leadlike fragments in the process of inverse quasifission. The mass, energy, and angular distributions of the binary reaction products are measured at energies of 860 and 935 MeV of ¹⁶⁰Gd ions and 878MeV in the case of ¹⁵⁶Gd ions. The excitation energies of primary fragments are estimated using their measured mass–energy distributions. Enhanced yields of products with masses of 200–215 amu are observed for both reactions. At energies above the barrier for side-to-side collisions (935 MeV), the yield of lead-like fragments is an order of magnitude larger than at energies near the Coulomb barrier, due possibly to the influence of orientation effects. The enhancement observed in the yield of reaction products with masses heavier than the target mass confirms that multinucleon transfer reactions can be used to obtain new neutron-rich isotopes, and to synthesize new superheavy elements.     

Light-charged-particle emission from hot <Superscript>32</Superscript>S<Superscript>*</Superscript>formed in <Superscript>20</Superscript>Ne + <Superscript>12</Superscript>C reaction

Inclusive energy distributions for light charged particles (p , d , t and have been measured in the ²⁰Ne (158, 170, 180, 200 MeV) + ¹²C reactionsintheangularrange$10^°$ - - $50^°$.Exclusivelight-charged-particleenergydistributionmeasurementswerealsodoneforthesamesystemat158 MeVbombardingenergybyin - planelightchargedparticle - - fragmentcoincidence.Pre - equilibriumcomponentshavebeenseparatedoutfromprotonenergyspectrausingthemovingsourcemodelconsideringtwosources.ThedatahavebeencomparedwiththepredictionsofthestatisticalmodelcodeCASCADE.Ithasbeenobservedthatsignificantdeformationeffectswereneededtobeintroducedinthecompoundnucleusinordertoexplaintheshapeoftheevaporated$d$,$t$energyspectra.Forprotons, evaporatedenergyspectrawereratherinsensitivetonucleardeformation, thoughangulardistributionscouldnotbeexplainedwithoutdeformation.Thedecaysequenceofthehot$³²S$nucleushasbeeninvestigatedthroughexclusivelight - - charged - particlemeasurementsusingthe$²⁰Ne$$(158 MeV) + $¹²C reaction. Information on the sequential decay chain has been extracted through a comparison of the experimental data with the predictions of the statistical model. It is observed from the present analysis that exclusive light-charged-particle data may be used as a powerful tool to probe the decay sequence of hot light compound systems.