The K<Superscript>-</Superscript>α scattering length and the reaction dd↦αK<Superscript>+</Superscript>K<Superscript>-</Superscript>

We present predictions for the K^-α scattering length obtained within the framework of the multiple-scattering approach. Evaluating the pole position of the K^-α scattering amplitude within the zero-range approximation, we find a loosely bound K^-α state with a binding energy of E_R = - 2,..., - 7 MeV and a width Γ_R = 11,..., 18 MeV. We propose to measure the K^-α scattering length through the final-state interaction between the α and K^--meson produced in the reaction dd↦αK⁺K^-. It is found that the K^-α invariant-mass distribution from this reaction at energies near the threshold provides a new tool to determine the s-wave K^-α scattering length.     

Nuclear quadrupole moments of 5/2<Superscript>-</Superscript> and 9/2<Superscript>-</Superscript> states in <Superscript>169</Superscript>Ta

The nuclear spectroscopic quadrupole moments for the πh_9/25/2^-, 1/2^-[541] and the πh_11/29/2^-, 9/2^-[514] isomeric states in ¹⁶⁹Ta have been measured employing the time differential perturbed angular-distribution technique following the nuclear reaction ¹⁵⁹Tb(¹⁶O, 6nγ)¹⁶⁹Ta at beam energy 104 MeV. The ratio of the intrinsic quadrupole moments has been derived as 1.87(13) from the measured quadrupole precession frequencies of the corresponding states. The model-independent analysis of the equilibrium deformation indicates strong prolate- and oblate-driving nature of the 1/2^-[541] and 9/2^-[514] orbitals in ^169,171Ta isotopes, respectively.     

High-spin states in <Superscript>36</Superscript>Ar and their underlying shell model configurations

Eight high-spin states in ³⁶Ar below 10MeV excitation energy, among them a prospective J ^π = 8^- state at 9408keV and the J? 8 levels of the recently discovered superdeformed rotational band, have been observed by n-γ coincidence measurements with the ³³S(α, nγ) reaction at E _α = 14.4 and 13.4MeV. High-spin assignments of, respectively, J ^π = 6⁺ and 5^- were obtained for the E _p = 1209 and 1462keV (E _x = 9682 and 9927keV) resonances of the ³⁵Cl (p,γ) reaction by a measurement of γ-ray angular distributions. The spectrum of the high-spin and of the E _x? 7.4MeV levels is decomposed according to the underlying shell model configurations with n = 0, 1, 2, 4 particles excited from the N = 2 into the N = 3 major shell. The role of four-particle excitations, all connected with large prolate distortions, is elucidated for the entire A = 36-40 mass region. Received: 21 December 2001 / Accepted: 25 March 2002     

Total strength of the magnetic dipole resonance in <Superscript>31</Superscript>P

The γ decay of the resonance-like structure observed in the ³⁰Si(pγ)³¹P reaction in the energy range E _p = 1.4–2.7 MeV of accelerated protons has been investigated. The excitation function of this reaction and the spectra and angular distributions of the γ rays formed in the decay of resonances with E _p = 1482, 2350, and 2505 keV have been measured. The M1 resonance on the ground and the first excited states of ³¹P with E _p = 1266 keV is identified. The total strength of the M1 resonance on the ground state of this nucleus is determined. The position and total strength of this resonance on the ground state are explained taking into account pairing forces.     

Electronic structure of defective lithium cobaltites Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CoO<Subscript>2</Subscript>

X-ray absorption, resonant X-ray emission, and X-ray photoelectron spectroscopical methods have been applied for the study of the electronic structure of defective lithium cobaltites Li _x CoO₂ (0.6≤x≤1.0). Resonant O K α X-ray emission spectra of LiCoO₂ showed localized excitonic states due to a dd transition between occupied and unoccupied Co 3d states. On the base of measurements of Co 3s X-ray photoelectron, Co 2p, and O 1s X-ray absorption spectra, it was established that in defective cobaltites the electronic holes are localized mainly in O 2p states. An evidence of phase separation in Li _x CoO₂ has been found. It was shown that the semiconductor-to-metal transition in Li _x CoO₂ (x<0.76) at about 160 K is not accompanied by changes in the Co 3d electronic configuration which remains 3d ⁶.     

Investigations of low- and high-spin states of <Superscript>132</Superscript>La

The fusion evaporation reaction ¹²²Sn(¹⁴N, 4n)¹³²La was used to populate the high-spin states of ¹³²La at the beam energy of 60 MeV. A new band consisting of mostly E2 transitions has been discovered. This band has the interesting links to the ground state 2^- and the isomeric state 6^-. A new transition of energy 351 keV connecting the low-spin states of the positive-parity band based on the πh _11/2 ⊗ νh _11/2 particle configuration, has been found. This has played a very important role in resolving the existing ambiguities and inconsistencies in the spin assignment of the band head. Received: 12 August 2002 / Accepted: 18 March 2003 / Published online: 7 May 2003     

Super-allowed α decay above doubly-magic <Superscript>100</Superscript>Sn and properties of <Superscript>104</Superscript>Te = <Superscript>100</Superscript>Sn ⊗ α

α-decay half-lives for ^{104, 105, 106}Te and ^{108, 109, 110}Xe close above the doubly-magic ¹⁰⁰Sn are calculated from systematic double-folding potentials. The derived α preformation factors are compared to results for ^{212, 213, 214}Po and ^{216, 217, 218}Rn above the doubly-magic ²⁰⁸Pb. α-decay energies of Q _α = 5.42±0.07MeV and 4.65±0.15MeV are predicted for ¹⁰⁴Te and ¹⁰⁸Xe; the corresponding half-lives are T _1/2 ≈ 5ns for ¹⁰⁴Te and of the order of 60μs for ¹⁰⁸Xe. Additionally, the properties of rotational bands in ¹⁰⁴Te are analyzed, and the first excited 2⁺ state in ¹⁰⁴Te is predicted at E _x = 650±40keV; it decays preferentially by γ emission with a reduced transition strength of 10 Weisskopf units to the ground state of ¹⁰⁴Te and with a minor branch by α emission to the ground state of ¹⁰⁰Sn.     

Ground-state measurement of Pr<Superscript>3+</Superscript> in Y<Subscript>2</Subscript>O<Subscript>3</Subscript> by photoconductivity

1 at % Pr³⁺-doped Y₂O₃ single-crystal fibers were prepared using a laser-heated pedestal growth method. The emission and excitation spectra of the fibers were measured. The emissions of 4f-4f transitions from ¹ D ₂ to the ³ H ₄ and ³ H ₅ states are found at 620 and 720 nm, respectively. The ³ P ₂, ³ P ₁, ¹ I ₆, and ³ P ₀ 4f-4f absorptions are observed at 456, 472, 482, and 492 nm, respectively. A 4f-5d absorption band is detected at 288 nm. Photoconductivity measurements show that the 4f-5f transition of Pr³⁺ around 285 nm produces a direct photocurrent. Taking the onset of photocurrent to be at 320 nm, the ground state of Pr³⁺ is determined at 1.7 eV above the valence band of the host. The text was submitted by the authors in English.     

Level structures in the <Stack><Subscript>49</Subscript><Superscript>107</Superscript></Stack>In nucleus and their microscopic description

Excited states of the ₄₉¹⁰⁷In nucleus were populated through the ⁷⁸Se ( ³²S , p2n) fusion-evaporation reaction at beam energy, E _lab = 125 MeV. The de-excitations were studied using in-beam g \gamma -ray spectroscopic techniques involving the Compton-suppressed clover detector array. The level scheme of ¹⁰⁷In consisting of about seven bands is established up to spin ∼ 45/2ℏ with the addition of 25 new transitions. Spins and parities of various levels have been assigned through the DCO and polarization measurements. The level structures observed in ¹⁰⁷In have been interpreted in the framework of a microscopic theory based on the deformed Hartree-Fock (HF) and angular-momentum projection techniques. Various bands are reproduced in band mixing calculations with the configurations involving high-W \Omega p \pi g _9/2 and n \nu d _5/2 orbits, and low-W \Omega p \pi g _7/2 , n \nu g _7/2 and n \nu h _11/2 orbits.     

The low-energy dipole structure of <Superscript>232</Superscript>Th , <Superscript>236</Superscript>U and <Superscript>238</Superscript>U actinide nuclei

In this study, I^p = 1⁺\ensuremath I^{\pi} = 1^{+} and I^p = 1^-\ensuremath I^{\pi} = 1^{-} dipole mode excitations are systematically investigated within the rotational and translational + Galilean invariant quasiparticle random-phase approximation for ²³²Th , ²³⁶U , and ²³⁸U actinide nuclei. It is shown that the investigated nuclei reach a B(M1) strength structure, which corresponds to the scissors mode. The calculated mean excitation energies as well as the summed B(M1) value of the scissors mode excitations are consistent with the available experimental data. The results of calculations indicate large differences to the rare-earth nuclei as is the case for the experiment: a doubling of the observed dipole strengths and a shift of the energy centroid to the lower energies by about 800keV. The calculations indicate the presence of a few prominent negative-parity K^p = 1^-\ensuremath K^{\pi} = 1^{-} states in the 2.0-4.0MeV energy interval. The occurrence of the negative-parity dipole states with the rather high B(E1) value less than 4MeV shows the necessity of explicit parity measurements for the correct determination of the scissors mode strength in ²³²Th , ²³⁶U , and ²³⁸U isotopes.     

New results from the HAPPEX Experiments at Q<Superscript>2</Superscript> = 0.1GeV/c<Superscript>2</Superscript>

The nucleon's strange electric and magnetic form factors G _E ^s and G _M ^s can be probed via parity-violating electron scattering. The HAPPEX Collaboration has made new measurements of the parity-violating asymmetry A _PV in elastic scattering of 3GeV electrons off hydrogen and ⁴He targets with 〈θ_lab〉 ≈ 6.0^° . For ⁴He the preliminary result is A _PV = (+ 6.43±0.23(stat)±0.22(syst))×10^-6 . For hydrogen the preliminary result is A _PV = (- 1.60±0.12(stat)±0.05(syst))×10^-6 . From these values we extract G ^s _E = 0.004±0.014±0.013 at 〈Q ²〉 = 0.077 GeV/c^2 , and G ^s _E +0.09G ^s _M = 0.004±0.011±0.005 at 〈Q ²〉 = 0.109 GeV/c^2 , both consistent with zero, providing stringent new limits on the role of strange quarks in the vector structure of the nucleon.     

Spectroscopic and structural proprieties of LiAr and LiAr<Subscript>2</Subscript> molecules

We determined and tried to understand the spectroscopic and structural properties of small LiAr and LiAr₂ molecules within a simple model considering LiAr as a result of interaction between a valence electron and a LiAr⁺ molecular ion. Potential energy curves, spectroscopic constants, and vibrational levels corresponding to the Li(2s, 2p, 3s, and 3p)+Ar dissociation are reported for the LiAr molecule. The depth of the potential well for the X ²Σ⁺ ground state is found to be 50 cm⁻¹ (the corresponding experimental value is (42.5±1.2) cm⁻1 [1]). R _e is determined to be 9.36 a.u. (the experimental value is 9.24 a.u.). For the first excited state A, R _e = 4.97 a.u. and D _e = 993cm ⁻¹ (the corresponding experimental values are 4.68 a.u. and (925−40) cm⁻¹, respectively [1]). The spacing between the vibrational levels for the ground and first excited states is in very good agreement with the experiment. For the ground state, the difference between our results and the data of the most recent experiment is about 1 cm⁻¹. The model has been extended to study the LiAr₂ molecule in two forms (linear and triangular). We have determined the potential energy surfaces of the states dissociating to Li(2s, 2p)+Ar₂ and thus found the triangular form to be more stable as compared to the linear one. We have also calculated the transition energy between the ground state and first excited states of this molecule. The emission spectrum of the Li(2s)+Ar₂→Li(2p)+Ar₂ transition in both forms redshifts as compared to the Li(2s)→Li(2p) atomic transition.     

Investigations into the alpha-decay of <Superscript>195</Superscript>At

The low-energy nuclear structure and decay properties of the neutron-deficient isotopes ¹⁹⁵At and ¹⁹¹Bi have been studied. ¹⁹⁵At was produced in the reaction ¹⁴²Nd(⁵⁶Fe,p2n)¹⁹⁵At and ¹⁹¹Bi as the daughter activity of ¹⁹⁵At. The activities were implanted in a position-sensitive silicon detector after being separated from the primary beam by a gas-filled recoil separator. The 1/2⁺ intruder state was determined to be the ground state in ¹⁹⁵At with an alpha-decay energy of E _α = 6953(3) keV and a half-life T _1/2 = 328(20) ms. Another state with an alpha-decay energy E _α = 7075(4) keV and a half-life T _1/2 = 147(5) ms was found to decay to a 148.7(5) keV excited state in ¹⁹¹Bi for which a spin and parity of 7/2^- were deduced. Consequently, the same 7/2^- character was assigned to the initial state at 32(7) keV in ¹⁹⁵At on the basis of unhindered alpha-decay. The 9/2^- state, being the ground state in heavier odd-mass astatine isotopes, was not observed. Received: 16 September 2002 / Accepted: 19 December 2002 / Published online: 25 March 2003 RID="a" ID="a"e-mail: heikki.kettunen@phys.jyu.fi RID="b" ID="b"Present address: Laboratory of Radiochemistry, P.O. Box 55, FIN-00014, University of Helsinki, Finland. RID="c" ID="c"Present address: Radiation and Nuclear Safety Authority, P.O. Box 14, FIN-00881 Helsinki, Finland. Communicated by W. Henning     

Photodesorption of O<Subscript>2</Subscript> from Ag<Subscript>2</Subscript><Superscript>-</Superscript>: A time-resolved study of Ag<Subscript>2</Subscript>O<Subscript>2</Subscript><Superscript>-</Superscript>

We present time-resolved photoelectron spectra of mass-selected Ag₂O₂ anions. The anions are photoexcited by photons with an energy of 3.1 eV, and photoelectron spectra of the excited species Ag₂O₂ ^{- *} and the subsequently appearing fragments are recorded using a probe laser pulse with a photon energy of 1.5 eV. The excited state of Ag₂O₂ ^- has a short lifetime of 130 fs±70 fs only and decays by direct photodesorption of O₂. The data demonstrate the ability of time-resolved photoelectron spectroscopy (TR-PES) to observe the breaking of chemical bonds if the decay process of the excited state is direct (non-thermal desorption). The data are compared to recent results of a NeNePo experiment [1] on the same system. PACS 68.43.Tj; 78.47.+p; 33.80.Eh; 36.40.-c     

Structure and total strength of the magnetic dipole resonance in <Superscript>35</Superscript>Cl nuclei

The γ-decay of the resonance-like structure observed in the ³⁴S(pγ)³⁵Cl reaction in the energy range E _p = 1.0–3.0 MeV of accelerated protons was investigated. The M1 resonance on the ground and excited states of ³⁵Cl with E* = 1219 and 1763 keV was identified. The position of the center of gravity and total strength of the M1 resonance on ground state ³⁵Cl nucleus are determined. The position and total strength of the M1 resonance on the ground state in ³⁵Cl are explained taking into account pairing forces.     

Neutron single-particle structure of <Superscript>48</Superscript>Ca, <Superscript>50</Superscript>Ti, <Superscript>52</Superscript>Cr, <Superscript>54</Superscript>Fe,and <Superscript>56</Superscript>Ni nuclei

The change in the neutron single-particle structure of (1f?2p)-shell magic nuclei near the Fermi energy with an increase in the number of protons in the 1f _7/2 subshell from 0 for ⁴⁸Ca to 8 for ⁵⁶Ni has been investigated. Good agreement of the experimental and estimated values of the single-particle energies E _nlj of the bound states of neutrons in these nuclei with the results of calculations within the dispersive optical model is obtained.     

New double-magic nucleus <Superscript>96</Superscript>Zr and conditions for existence of new magic nuclei

New information about energies and occupation probabilities of neutron and proton single-particle (hole) subshells in even—even nuclei was obtained in previous studies applying the method of putting into correspondence all available data on one-nucleon pickup and stripping reactions. The most important and interesting resultwas identification of several nuclei as new magic ones. Namely, itwas found that a filling of the neutron 2d _5/2 subshell in ⁹⁶Zr makes this nuclide a magic one. Moreover, changes in proton subshell energies with increasing neutron number N are accompanied by an increasing energy gap between closed 2p _1/2 and empty 1g _9/2 subshells. Thus, the neutron number N = 56 appears to be a magic one if the proton number Z is equal to 40. The proton number Z = 40 manifests properties of the magic number in ⁹⁶Zr. Therefore, ⁹⁶Zr was identified as a new double-magic nucleus. Further investigations revealed that the energy of the first 2⁺ state E(2 ₁ ⁺ ) in ⁹⁶Zr is much higher than that in the neighboring isotopes and isotones, whereas the ratio E(4 ₁ ⁺ )/E(2 ₁ ⁺ ) and the quadrupole deformation parameter β2 are, vice versa, clearly lower. Moreover, the A dependence of the neutron separation energy B(n) in Zr isotopes has an irregularity at N = 56 which is typical of magic nuclei. As a result of these investigations, it was found that, near the Fermi energy, there are two closed subshells with the same (and large) angular momentum j = 5/2 (viz. π1f _5/2 and ν2d _5/2). We call this situation the jj connection. The magic numbers under discussion (Z = 40 and N = 56) are achieved at the points where both subshells are closed, and in addition, the closed subshell with j = 1/2, π2p _1/2, occurs above the proton π1f _5/2 subshell. This looks like a result of some additional attractive proton-neutron interaction. It was found that application of this scheme (jj connection) to other subshells reveals several other new magic nuclei: ⁵⁴Ca (closed π1d _3/2 and ν2p _3/2 together with closed ν2p _1/2), ³⁰S and ³⁰Si (closed π1d _5/2 and ν1d _5/2 together with closed (π/ν)2s _1/2), and ¹⁴O and ¹⁴C (closed π1p _3/2 and ν1p _3/2 together with closed ν2p _1/2). The text was submitted by the authors in English.     

On the magnetism of Ln<Subscript>2/3</Subscript>Cu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> (Ln = lanthanide)

The magnetic and thermodynamic properties of the complete Ln_2/3Cu₃Ti₄O₁₂ series were investigated. Here Ln stands for the lanthanides La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb. All the samples investigated crystallize in the space group Im[`3]Im\bar{3} with lattice constants that follow the lanthanide contraction. The lattice constant of the Ce compound reveals the presence of Ce⁴⁺ leading to the composition Ce_1/2Cu₃Ti₄O₁₂. From magnetic susceptibility and electron-spin resonance experiments it can be concluded that the copper ions always carry a spin S = 1/2 and order antiferromagnetically close to 25 K. The Curie-Weiss temperatures can approximately be calculated assuming a two-sublattice model corresponding to the copper and lanthanide ions, respectively. It seems that the magnetic moments of the heavy rare earths are weakly coupled to the copper spins, while for the light lanthanides no such coupling was found. The 4f moments remain paramagnetic down to the lowest temperatures, with the exception of the Tm compound, which indicates enhanced Van-Vleck magnetism due to a non-magnetic singlet ground state of the crystal-field split 4f manifold. From specific-heat measurements we accurately determined the antiferromagnetic ordering temperature and obtained information on the crystal-field states of the rare-earth ions.     

O<Subscript>2</Subscript> photodesorption from a Ag<Subscript>8</Subscript>O<Stack><Subscript>2</Subscript><Superscript>-</Superscript></Stack> cluster

The decay path of an Ag₈(O₂)^- cluster photoexcited by a 3.1 eV photon is elucidated using time-resolved photoelectron spectroscopy. Photoabsorption results in the formation of an excited state giving rise to a peak in the photoelectron spectra with well-resolved vibrational finestructure. With a lifetime of about 100 fs this bound state decays into an anti-bonding state which dissociates into O₂ and Ag₈^- on a timescale of 10 ps. In the photoelectron spectra, this corresponds to a broad maximum shifting gradually towards higher binding energy while the O₂ and Ag₈^- separate. Finally, the spectrum of bare Ag₈^- appears. This process is unique to small clusters, because on metal surfaces excited state lifetimes are too short to allow for direct dissociation.