1<Superscript>+</Superscript>(0<Superscript>+</Superscript>) state at 12.4 MeV in <Superscript>20</Superscript>Ne

Careful review of all the evidence makes it clear that at least three states are important at 12.4-MeV excitation in ²⁰Ne (four, if the broad (2⁺) at 12.5 MeV is included). The three states are 3 ^- , 0 ⁺ , and 1 ⁺ (0⁺). The latter, which is quite strong in ¹⁹F (³He, d) singles, is probably the state observed in coincidence with 6.13-MeV γ-rays in ¹⁹F(³He, dγ). Received: 19 August 2002 / Accepted: 28 October 2002 / Published online: 17 January 2003 RID="a" ID="a"e-mail: fortune@physics.upenn.edu Communicated by D. Guerreau     

Double-beta decay of <Superscript>150</Superscript>Nd to the first 0<Superscript>+</Superscript> excited state of <Superscript>150</Superscript> Sm: Current state

Two-neutrino double-beta decay of ¹⁵⁰Nd to the first 0⁺ excited state in ¹⁵⁰Sm is investigated with the 400-cm³ low-background HPGe detector. Preliminary data analysis for 6843 h shows an excess of events at 333.9 and 406.5 keV. If this excess is assigned to the investigated transition, then its half-life can be estimated at [1.2 _?0.3 ^+0.5 ±0.4(syst.)]×10²⁰ yr.     

Dynamical study of the Cs<Superscript>+</Superscript>(<Superscript>1</Superscript>S<Subscript>0</Subscript>)+Mg(3 <Superscript>1</Superscript>S<Subscript>0</Subscript>) non adiabatic collision system in the few keV energy range

The dynamics of collisional processes between Mg atoms and caesium ions is studied using the hemiquantal (HQ) approach with special attention to the collisional channels leading to Mg(3 ¹P) and Cs(6 ²P) states, for which the corresponding emission excitation functions have been previously measured in our laboratory. The radial and angular non-adiabatic couplings between the manifold of quasimolecular states have been determined using an ab initio configuration interaction calculation. The cross-sections for the different channels, as a function of the laboratory collisional energy, are compared with experimental values. The dynamical calculations indicate that, for the inelastic processes considered, the range of relevant impact parameters is small, active collisions being of the head-on type. .     

Double-beta decay of <Superscript>150</Superscript>Nd to the first 0<Superscript>+</Superscript> excited state of <Superscript>150</Superscript>Sm

Two-neutrino-double-beta decay of ¹⁵⁰Nd to the first 0⁺ excited state in ¹⁵⁰Sm is investigated with a 400-cm³ low-background HPGe detector. Data analysis for 11320.5 h shows an excess of events at 333.9 and 406.5 keV. This allows us to estimate the half-life of the investigated process as [1.4 _?0.2 ^+0.4 ±0.3(syst.)]×10²⁰ yr.     

On the unusual properties of the 282 keV state in <Superscript>135</Superscript>Sb

Recently the first excited state in ¹³⁵Sb has been observed at the unexpectedly low excitation energy of only 282keV and interpreted as mainly d _5/2 proton coupled to the ¹³⁴Sn core. Based on theoretical considerations it was suggested that its low excitation energy is related to a relative shift of the proton d _5/2 and g _7/2 orbits induced by the neutron excess. We have measured the lifetime of the 282keV state by the advanced time-delayed βγγ(t) method. The measured half-life, T _1/2 = 6.1(4)ns, yields exceptionally low limits of B(M1;5/2₁ ⁺→7/2₁ ⁺)≤3.0×10^-4 μ ² _N and B(E2;5/2₁ ⁺→7/2₁ ⁺)≤54e ² fm ⁴. These strongly hindered M1 and slow E2 transition rates are similar to those for the transition de-populating the first excited state at 405keV in ²¹¹Bi. Results of shell model calculations with realistic interactions are presented. The M1 decay rate was found to be extremely sensistive both to the wave function and to the M1 effective operator.     

Double beta decay of <Superscript>150</Superscript>Nd to the First 0<Superscript>+</Superscript> excited state of <Superscript>150</Superscript>Sm

Two neutrino double beta decay of ¹⁵⁰Nd to the first 0⁺ excited state in ¹⁵⁰Sm is investigated with the 400 cm³ low-background HPGe detector. Data analysis for 11320.5 h shows the excess of events at 333.9 and 406.5 keV. This makes it possible to estimate the half-life of the investigated process as [1.4 _?0.2 ^+.04 (stat)±0.3(syst)]×10²⁰yr.     

Low-spin states in <Superscript>182</Superscript>Os and K<Superscript>π</Superscript> = 0<Superscript>+</Superscript>, 2<Superscript>+</Superscript> excited bands

Excited states in ¹⁸²Os were populated by the β⁺/EC decay of ¹⁸²Ir following mass separation. Gamma-ray and conversion electron spectroscopy techniques were employed. Monopole (E0) contributions were determined in transitions populating the ground-state band. A systematic study of the low-spin structures in the Os isotopes is presented and a detailed analysis in the framework of a microscopic configuration mixing approach is performed.     

The spin-quadrupole interaction and the 0<Superscript>+</Superscript> excitations in <Superscript>158</Superscript>Gd

In this work, the effect of spin-quadrupole forces on the 0⁺ sates in ¹⁵⁸Gd has been investigated. For this purpose, the model Hamiltonian including monopole pairing, quadrupole-quadrupole and spin-quadrupole forces has been diagonalized in one phonon basis. In conclusion, for the distribution of energies of the states and their collective properties, fairly good results have been obtained.     

Effect of high doses of N<Superscript>+</Superscript>, N<Superscript>+</Superscript> + Ni<Superscript>+</Superscript>, and Mo<Superscript>+</Superscript> + W<Superscript>+</Superscript> ions on the physicomechanical properties of TiNi

The surface layer of an equiatomic TiNi alloy, which exhibits the shape memory effect in the martensitic state, is modified with high-dose implantation of 65-keV N⁺ ions (the implantation dose is varied from 10¹⁷ to 10¹⁸ ions/cm²). TiNi samples are implanted by N⁺, Ni⁺-N⁺, and Mo⁺-W⁺ ions at a dose of 10¹⁷–10¹⁸ cm⁻² and studied by Rutherford backscattering, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction (glancing geometry), and by measuring the nanohardness and the elastic modulus. A Ni⁺ concentration peak is detected between two maxima in the depth profile of the N⁺ ion concentration. X-ray diffraction (glancing geometry) of TiNi samples implanted by Ni⁺ and N⁺ ions shows the formation of the TiNi (B2), TiN, and Ni₃N phases. In the initial state, the elastic modulus of the samples is E = 56 GPa at a hardness of H = 2.13 ± 0.30 GPa (at a depth of 150 nm). After double implantation by Ni⁺-N⁺ and W⁺-Mo⁺ ions, the hardness of the TiNi samples is ∼2.78 ± 0.95 GPa at a depth of 150 nm and 4.95 ± 2.25 GPa at a depth of 50 nm; the elastic modulus is 59 GPa. Annealing of the samples at 550°C leads to an increase in the hardness to 4.44 ± 1.45 GPa and a sharp increase in the elastic modulus to 236 ± 39 GPa. A correlation between the elemental composition, microstructure, shape memory effect, and mechanical properties of the near-surface layer in TiNi is found.     

Double-beta decay of <Superscript>100</Superscript>Mo to 0<Superscript>+</Superscript> excited states in <Superscript>100</Superscript>Ru

A brief review on the 2νββ decay of ¹⁰⁰Mo to the 0⁺ excited state in ¹⁰⁰Ru is performed. A weighted-average half-life value for the decay has been obtained, T_1/2 = (6.8 ± 1.2) × 10²⁰ yr. The corresponding average value for the nuclear matrix element was extracted, 0.095 ± 0.009.     

QED radiative corrections to the decay π<Superscript>0</Superscript>→e<Superscript>+</Superscript>e<Superscript>-</Superscript>

We reconsider QED radiative corrections (RC) to the π⁰→e⁺e^- decay width. One kind of RC investigated earlier has a renormalization group origin and can be associated with the final state interaction of electron and positron. It determines the distribution of lepton pair invariant masses in the whole kinematic region. The other type of RC has a double-logarithmic character and is related to almost on-mass-shell behavior of the lepton form factors. The total effect of RC for π⁰→e⁺e^- decay is estimated to be 3.2%, and for η→e⁺e^- decay it is 4.3%. PACS  13.25.Cq; 12.38.Lg; 12.38.-t     

Na<Superscript>+</Superscript>/K<Superscript>+</Superscript> selectivity in the formation of ion pairs in aqueous solutions

The integral equations of liquids (RISM) and molecular dynamics method were used to calculate the mean force potential for the SO₃ and COO hydrophilic groups and the CH₃ hydrophobic group in the acetate, methyl sulfonate, and hydrosulfate anions, which form ion pairs with sodium and potassium cations in water. The carboxyl group selectively binds sodium ions from solutions containing Na⁺ and K⁺ ions, in spite of their equal charges, because the potassium ion experiences stronger steric hindrances near this group compared with sodium. The biophysical consequences of the revealed selectivity are discussed.     

Electron impact dissociation of ND<Superscript>+</Superscript>: formation of D<Superscript>+</Superscript>

Absolute cross sections for electron impact dissociation of ND⁺ leading to the formation of D⁺ have been measured by applying the animated electron-ion beam method in the energy range from the reaction threshold up to 2.5 keV. The maximum inclusive cross section is observed to be (16.8 ± 0.8) × 10⁻¹⁷ cm² at the electron energy of 65.1 eV. The appearance energy for the D⁺ production is measured to be (4.0 ± 0.5) eV. Collected data are analyzed in details by means of an original procedure in order to determine separately the contributions of dissociative channels. A specific Monte Carlo modeling has been developed, which is proven to reconstruct adequately the dissociative ionization cross section. The present energy thresholds provide information about the ground and excited states of the molecular ion, as well as about the possible population of the vibrational levels. The reaction D₂(v) + N⁺ (or H₂(v) + N⁺) is a probable source for that population and it constitutes the first step of the molecular activated processes, so the corresponding chain of reactions has to be considered to study the chemistry of plasma sources.     

Frequency measurements in the b <Superscript>3</Superscript>Π(0<Subscript>u</Subscript><Superscript>+</Superscript>) - X <Superscript>1</Superscript>Σ<Subscript>g</Subscript><Superscript>+</Superscript> system of K<Subscript>2</Subscript>

Absolute transition frequencies of the b ³Π(0_u ⁺) - X ¹Σ_g ⁺ system of K₂ were measured in a molecular beam with Lamb dip absorption spectroscopy applying a frequency comb from a femtosecond pulsed laser. Both, K atoms and K₂ molecules are present in the beam and are expected to interact by collisions. The atoms can be deflected optically out of the beam, and thus the collision rate between K atoms and K₂ molecules is changed by about an order of magnitude. The molecular transition frequencies for low collisional rate are compared with those for high one. Limits for the collisional frequency shift within the beam are determined.     

Graviton resonances in e<Superscript>+</Superscript>e<Superscript>-</Superscript>→μ<Superscript>+</Superscript>μ<Superscript>-</Superscript> at linear colliders with beamstrahlung and ISR effects

The electromagnetic radiation emitted by colliding beams is expected to play an important role at the next generation of high energy e⁺e^- linear colliders. Focussing on the simplest process, e⁺e^-→μ⁺μ^-, we show that, for suitable machine parameters and luminosity, radiative effects like initial state radiation (ISR) and beamstrahlung can be used to search for resonant graviton modes of the Randall–Sundrum model in an efficient manner.     

Diffractive production of two ρ<Superscript>0</Superscript><Subscript>L</Subscript> mesons in e<Superscript>+</Superscript>e<Superscript>-</Superscript> collisions

We present an estimate of the cross-section for the exclusive production of a ρ_L ⁰-meson pair in e⁺e^- scattering, which will be studied in the future high-energy International Linear Collider. For this aim, we complete calculations of the Born order approximation of the amplitudes γ^* _L,T(Q₁ ²)γ^* _L,T(Q₂ ²)→ρ_L ⁰ρ_L ⁰, for arbitrary polarization of virtual photons and longitudinally polarized mesons, in the kinematical region s≫-t,Q₁ ²,Q₂ ². These processes are completely calculable in the hard region Q₁ ²,Q₂ ²≫Λ² _QCD, and we perform most of the calculations in an analytical way. The resulting cross-section turns out to be large enough for this process to be measurable with foreseen luminosity and energy, for Q₁ ² and Q₂ ² in the range of a few GeV².     

Isotopomer selective optimization of <Superscript>39</Superscript>K<Superscript>85</Superscript>Rb<Superscript>+</Superscript> and <Superscript>41</Superscript>K<Superscript>87</Superscript>Rb<Superscript>+</Superscript> using optimal control

We report on isotope selective three-photon ionization of two isotopomers of KRb by applying evolution strategies. The particularity of this experiment is based on the high resolution phase and amplitude modulation of the fs-laser pulses provided by a 2 × 640 pixel pulse shaper. The optimization in a closed feedback loop performed with spectrally broad pulses centered at 840 nm shows high enhancements of one isotopomer at the expense of the other isotopomer and vice versa. From the optimal laser field we aim to gain details about the selective ionization sequence and the wavepacket evolution on the involved vibrational states.