Spectroscopy of superheavy hydrogen isotopes in stopped-pion absorption by nuclei

The structure of levels of superheavy hydrogen isotopes ^4–6H is analyzed on the basis of a record statistics of experimental data on the absorption of negatively charged pions by light nuclei. Qualitatively new experimental data are obtained for the spectroscopy of the superheavy hydrogen isotopes ⁵H and ⁶H. Peaks due to four resonance states of ⁵H are observed in the missing-mass spectra for the reaction channels ⁹Be(π ^?, pt)X and ⁹Be(π^?, dd)X. A structure that is associated with four resonance states of ⁶H is observed in the missing-mass spectra for the reaction channels ⁹Be(π^?, pd)X and ¹¹B(π^?, p ⁴He)X. On the basis of the results presented for ground-state parameters, it can be concluded that the binding energy of superheavy hydrogen isotopes decreases as the number of neutrons increases. Excited levels of the isotopes ⁵H and ⁶H are observed for the first time. On the energy scale, all of these states lie above the threshold for decay to free nucleons.     

Coulomb breakup of neutron-rich isotopes of light nuclei

The effects of higher order multipole transitions, in particular, E2 and E1–E2 interference, in the Coulomb dissociation of neutron-rich nuclei ¹¹Be, ¹⁴B, ¹⁵C, and ¹⁹C on Pb targets at energies of 72, 86, 550, and 77 A MeV, respectively, within the framework of the eikonal-approximation approach are studied. The main steps involved in the derivation of the explicit expressions corresponding to dipole, quadrupole, and dipole-quadrupole-interference terms are outlined. The calculations reveal that the contribution of E2 transitions to the total cross section is finite but small, while that ofE1–E2 interference is nil.Nevertheless, the E1–E2 interference term introduces small distortions in the peak of the relative-energy spectrum. The calculated results are compared with the corresponding data and the comparison favors a value of 0.530 MeV as the ground-state binding energy of ¹⁹C. The text was submitted by the authors in English.     

Study on antiprotonic atoms of light nuclei and isotopes

New data on strong interaction effects in light antiprotonic atoms (N, ¹⁶O, ¹⁸O, S) are presented. For the first time an isotope effect could be observed in p?-¹⁶O/¹⁸O which is used to gain new information about the p?-n interaction in nuclei. A comparison between all existing p?-atomic data and an optical model calculation is performed, yielding a set of fit parameters for the potential.     

Search for superheavy hydrogen isotopes in pion absorption reactions

Review of the experimental results on the search for and the spectroscopy of the superheavy hydrogen isotopes ^4–7H obtained in stopped π^?-meson absorption by ⁹Be and ¹¹Be nuclei is presented. Study of light neutron-rich nuclei is a principal line in developing modern views on the properties of nuclear forces and determination of nuclear properties near the drip line. The present method of investigation relies on precision measurements of energy of charged particles emitted after pion absorption by nuclei. Important advantages of this method are the practically accurate initial state energy and momentum, as well as the possibility to study a wide range of excitation energy. In the frames of this method new results were obtained on level structures of the isotopes ^4–6H and indications on ⁷H production. Comparison with other experimental and theoretical results is performed.     

Decay of μ-mesic molecules formed by isotopes of hydrogen and helium nuclei

Gammay-ray spectra from μ-mesic molecules formed by isotopes of hydrogen and helium nuclei are calculated. The life times of the mesic molecules are obtained.     

Search for light neutron-rich isotopes in stopped pion absorption

The results based on the spectroscopy of superheavy hydrogen isotopes (^4?7H), heavy helium isotopes (^6,7He), and heavy lithium isotopes (^7?12Li) produced in stopped pion absorption by light nuclei were analyzed. Search for nuclear states was performed in inclusive and correlation measurements of missing mass spectra. A broad range of excitation energies studied in correlation measurements provided the possibility of search for isobaric analog states and cluster resonances. A comparison with experimental and theoretical results of other authors was conducted.     

Production of light nuclei in the reactions of protons with separated tin isotopes

The cross sections for the production of ⁷Be, ²²Na, ²⁴Na, ²⁸Mg, ³⁸S, ³⁸Cl, and ³⁹Cl nuclei from ¹¹²Sn, ¹¹⁸Sn, ¹²⁰Sn, and ¹²⁴Sn targets irradiated with 0.6-, 1.0-, and 8.1-GeV protons were measured by the method of induced activity. In analyzing resulting data, it was established that the above nuclei are produced in the fragmentation process and that the reaction cross section is a power-law function of the mass and charge numbers of fragmentation products. A strong dependence of the reaction cross section on the nucleonic composition of the targets and of the products is observed. The measured cross sections, together with data available in the literature, are discussed within various assumptions.     

Yields of hydrogen and helium isotopes in fragmentation of carbon ions with the energy of 0.3 GeV/nucleon

Data on the yields of hydrogen isotopes (p, d, t) and helium isotopes (from ³He to ⁸He) at the angle of 3.5° in fragmentation of the carbon ions with the energy of 0.3 GeV/nucleon on the beryllium target are reported. The momentum spectra of the fragments in the rest frame of the fragmenting nucleus are measured in a considerably larger momentum range than in the previous experiments.     

\alpha-decay spectroscopy of light odd-odd Bi isotopes - I: 188,190Bi nuclei

Detailed fine-structure -decay studies of ^188,190Bi were performed using the complete-fusion reactions of ^50,52Cr ions with a ¹⁴²Nd target at the velocity filter SHIP. The evaporation residues were separated in-flight and subsequently identified on the basis of recoil- , recoil- - /X-ray and excitation function measurements. Improved data on the -decay of ^188,190Bi were obtained and a number of new low-lying excited states in the daughters ^184,186Tl were observed. An intruder, presumably 10^- state was identified in ¹⁸⁴Tl, extending the systematics of such states in the odd-odd Tl nuclei beyond the neutron mid-shell at N = 104. Some technical aspects of experiment at recoil separators are also discussed.Received: 14 March 2003, Revised: 1 May 2003, Published online: 2 September 2003PACS: 23.60.+e decay - 27.70.+q - 27.80.+w C.D. OLeary: Present address: Department of Physics, University of York, York, UK.M.J. Taylor: Present address: Department of Physics and Astronomy, Rutgers Univesity, NJ, USA.L. Weissman: Present address: NSCL, Michigan State University, East Lansing, MI 48824-1321 USA.K. Heyde: Present address: EP-ISOLDE, CERN, CH-1211, Geneva 23, Switzerland.     

Energy spectra of neutrons emitted following the absorption of stopped negative pions in light nuclei

Energy spectra of neutrons emitted following the absorption of stopped negative pions in carbon, nitrogen and oxygen were measured from about 2.5 MeV up to the kinematical limit. The experiments were carried out at the biomedical pion channel πE3 of the Swiss Institute for Nuclear Research (SIN). The evaporation part of the spectra was extrapolated to zero energy using the formula of Le Couteur. Various parameters like mean neutron energies and neutron multiplicities are given. The data are compared with experimental data obtained by other authors and with results of intranuclear cascade calculations.     

Search for superheavy hydrogen isotopes <Superscript>4,5</Superscript>H in reactions of pion absorption by <Superscript>10,11</Superscript>B nuclei

The results of searching for production of superheavy hydrogen isotopes ^4,5H in reactions of absorption of stopped π^? mesons by ^10,11B nuclei are reported. A peak near 3 MeV was observed in the missing mass spectra measured in the reactions ^10,11B(π^?, t⁴He)X, ¹⁰B(π^?, d⁴He)X, and ¹⁰B(π^?, t³He)X. A structure caused by two ⁵H states with the resonance energies E _R = 5.2 and 10.4 MeV was observed in the missing mass spectra measured in the reactions ¹¹B(π^?, d⁴He)X, ¹¹B(π^?, t³He)X, and ¹⁰B(π^?, d³He)X.     

Deformation in the light Br isotopes

The nuclear ground state spins of the odd-A Br nuclides^{75, 77, 79}Br with Z=35 are all 3/2⁻. Nilsson orbital calculations show that the 35^th proton occupies the f_5/2 [301]3/2⁻ orbital for ε<0.20 and the p_3/2 [312]3/2⁻ orbital at larger deformations. The magnetic moments of these two states differ by a factor of two, giving clear evidence for the magnitude of the ground state deformation. Low Temperature Nuclear Orientation measurements made in Oxford and Bonn on^{76, 77g}BrFe prepared at ISOLDE, and on line at the SERC Daresbury Laboratory on^{72, 74m, 75}BrFe, have yielded the magnetic moments of these isotopes, using a two non-zero field model with magnetic hyperfine fields of +81.38(6) T and 26(2) T. The spin of the⁷³Br ground state is also deduced. An interpretation of the ground state configurations of these isotopes is given.     

The probability of pion absorption by α-clusters in nuclei

A multistep direct reaction model with pickup is extended to described the formation of tritons and ³He-particles in nucleon- and pion-induced precompound reactions. In the latter ones, those tritons not accounted for by pickup can be explained as primary ones from absorption by α-clusters, for which a 10% probability is deduced.     

Fragmentation of light nuclei by intermediate energy photons

New data on the fragmentation of carbon nuclei by photons with energies from 800 to 1500 MeV, obtained in the collaboration GRAAL, are presented. These data include the yields of heavier fragments than nucleons. Comparison of new results with literature data, obtained with real and virtual photons in reactions with electrons and relativistic ions (Coulomb dissociation) is done using a general approach in frame of the Weizsäcker–Williams model. Possible reasons for the observed differences between them are discussed.     

Orbital rearrangement in light nuclei

Orbital rearrangement effects due to the removal of a proton are studied. Calculations in the nuclei¹⁶O,²⁰Ne, and⁴⁰Ca are performed using the Yale potential, and the Brink Boeker forceB1. The odd mass nuclei are not restricted to time reversal symmetry which prevents a large overestimation of the rearrangement energies. Although the orbital rearrangement energies are small (<1.5 MeV) utilizing density independent forces one can find larger changes in the wave functions due to the rearrangement as exhibit the discussion of the quadrupole moments and the mass distributions.     

Neutron periphery in light nuclei

A spatial configuration of light nuclei that involves two excess neutrons (⁶He, ¹⁰Be, and ¹²B) is studied by analyzing cross sections for various reactions on these nuclei: ⁶He(α, α)⁶He, ⁹Be(d, p)¹⁰Be, and ¹⁰B(t, p)¹²B. Pole dineutron-transfer mechanisms (dineutron configuration of the neutron periphery) and second-order mechanisms involving sequential neutron transfer (cigar-like configuration of the neutron periphery) are taken into account in the calculations. It is shown that the neutron periphery is drastically different in the nuclei in question: in ⁶He, there is a halo receiving a contribution from both configurations; in ¹⁰Be, there is an only slightly noticeable halo featuring a contribution of practically one neutron from the cigar-like configuration; and, in ¹²B, there is a neutron skin.     

Diffusion behavior of hydrogen isotopes in tungsten revisited by molecular dynamics simulations

Molecular dynamics simulations were performed to study the diffusion behavior of hydrogen isotopes in single-crystal tungsten in the temperature range of 300–2000 K. The simulations show that the diffusion coefficient of H isotopes exhibits non-Arrhenius behavior, though this deviation from Arrhenius behavior is slight. Many-body and anharmonic effects of the potential surface may induce slight isotope-dependence by the activation energy; however, the dependence of the pre-factor of the diffusion coefficient on the isotope mass is diminished. The simulation results for H-atom migration near W surfaces suggest that no trap mutations occur for H atoms diffusing near either W{100} or W{111} surfaces, in contrast to the findings for He diffusion near W surfaces. Based on the H behavior obtained by our MD simulations, the time evolution of the concentration distribution of interstitial H atoms in a semi-infinite W single crystal irradiated by energetic H projectiles was calculated. The effect of H concentration on H diffusion is discussed, and the applicability of the diffusion coefficients obtained for dilute H in W is assessed.     

Cluster structures in light nuclei

Clustering in light stable and unstable nuclei is discussed. After a brief review of the clustering in stable nuclei, we make a new prediction of the existence of the alpha cluster condensed states in ¹²C and ¹⁶O. Discussions of clustering in light unstable nuclei are made in the cases of Be and B isotopes up to the neutron dripline. Received: 1 May 2001 / Accepted: 4 December 2001     

Spectroscopy of the <Superscript>9</Superscript>Li isotope in stopped-pion absorption reactions

The origin of the ⁹Li isotope is sought in missing-mass spectra measured in ¹¹B(π⁻, d)X, ¹²C(π⁻, pd)X, and ¹⁴C(π⁻, dt)X stopped-pion absorption reactions. The parameters of the three observed low-lying excited states coincide with the literature data. A state with excitation energy E _x = 9.1 ± 0.1 MeV, lying above the threshold of ⁹Li decay into ⁶He + t, is observed for the first time.