Electromagnetic contributions to proton- and neutron-4He scattering

A proper treatment of various electromagnetic contributions toN-⁴He scattering enables one to determinen(p)-⁴He observables fromp(n)-⁴He data. Several calculations ofn-⁴He observables considering different electromagnetic effects are presented. It is shown that the contribution of thep-⁴He Coulomb corrections ton-⁴He polarizations and differential cross sections dominates over other electromagnetic effects forθ _c.m.≧30°. For smaller scattering angles, neutron magnetic scattering is important and produces a divergingn-⁴He differential cross section atθ=0° and a large peak (Mott-Schwinger effect) in the polarization. The influence of thep- andn-⁴He vacuum polarizations on then-⁴He observables is found to be small.     

Tensor analyzing power T 20 of the dd → 3Hen and dd → 3Hp reactions at zero angle for energies 140, 200, and 270 MeV

RIKEN Accelerator Research Facility data on the tensor analyzing power T ₂₀ of the dd → ³Hen and dd → ³Hp reactions at zero angle for deuteron kinetic energies of 140, 200, and 270 MeV are reported. The observed positive sign of T ₂₀ clearly demonstrates the sensitivity to the D/S-wave ratio in the ³He and ³H wave functions in the energy range of the experiment. Data on T ₂₀ for the ³Hen channel are in agreement with those for the ³Hp channel within the experimental errors.     

A radiochemical study on the existence of dineutron

A radiochemical study has been made to search for dineutron² n produced in the simultaneous two-neutron emission of the excited⁶He nuclei,⁶He^*, induced in the reaction of⁹Be+n→-⁶He^*+α with fast neutrons in a reactor. It was attempted to detect the radio-activity of²⁸Mg as a product of the reaction² n+²⁷Al→²⁸Mg+p. The²⁸Mg radioactivity observed in heterogeneous samples composed of the² n-producing target Be and the² n-detecting target Al separately was not found to be more than that of a side reaction,²⁷Al{(n, p)(n _th, γ)+(n _th, γ)(n, p)}²⁸Mg, whereas it clearly exceeded that of the side reaction in alloy samples made of Be and Al metals. The former experiment gives an upper limit of the production rate of the dineutron in the bound state 1×10^?7 per event of the simultaneous two-neutron emission. A tentative explanation for the excessive²⁸Mg radioactivity observed in the latter experiment is the following two-step process,⁹Be+n→⁶He+α and²⁷Al+⁶He→+²⁸Mg+α+p, rather than the process induced by the dineutron in a virtual state.     

High spin states in103Rh

High spin states in¹⁰³Rh have been studied using the¹⁰⁰Mo(⁷Li, 4n) reaction. Standard in-beam measurements involving singlesγ-ray,γ-γ-t coincidences, angular distribution and linear polarization measurements have been performed. A perturbed band based on a 9/2⁺ state is interpreted as ag _9/2 coupled band. A sequence built on a 1/2^? state is related to thep _1/2 state. At higher excitation energy, in the range 2.2–3.7 MeV, the strongΔI=1 cascade observed, connecting negative parity levels, probably arises from states including three quasi-particle configurations.     

Exchange and nuclear symmetry interference in He+-He scattering

A method is described to determine the potential difference, V _g-V _u, that will accurately reproduce the exchange and nuclear symmetry oscillations observed by Aberth et al. in their experimental work on He⁺-He differential scattering. It is demonstrated that at higher energies and angles the experimental results for ⁴He⁺-⁴He, ⁴He⁺-³He and ³He⁺-³He appear incompatible with one another when investigated in terms of a two-state scattering theory. This is an indication that at these energies and angles the theory may require modification to include the effects of coupling to higher states.     

Determination of the coupling constants 3Hdn, 3Hπ and 3He3Heπ from data on the differential cross sections OF n3H and n3He elastic scattering

A determination of the coupling constants ³Hdn, ³H³H_π and ³He³He_π from existing differential cross section data for n³H and n³He elastic scattering has been carried out. The method is based on the extrapolation of dσ/dΩ to the deuteron and pion poles, exploiting conformal mapping techniques. Calculations result in a value of the ³Hdn coupling constant which is ≈ 20% smaller than dispersion relation predictions. A comparison of the value obtained with predictions based on nuclear models allows one to discriminate between different potentials. The residue at the pion pole turns out to be too weak and the conclusion is drawn that it is impossible to determine the coupling constants ³H³H_π and ³He³Heπ on the basis of existing data.     

Study of the π+π+π-π- system centrally 0 produced by incident π+ andp beams at 85 GeV/c

The reactions π⁺ p→π⁺(π⁺π⁺π^-π^-)p andpp→p(π⁺π⁺π^-π^-)p, where the (π⁺ π⁺ π^- π^-) system is centrally produced have been studied at 85 GeV/c. The π⁺π⁺π^-π^- mass spectrum shows evidence for thef ₁ (1285) meson with a mass of 1278±2 MeV and width 41±12 MeV which decays mainly through ρ⁰(770)π⁺π^-. Thef ₁(1285) is also observed in the ηπ⁺π^- channel. There is no significant evidence for ηππ or 4π decay modes of thef ₁(1420). The ρ⁰ρ⁰ production is found to be small. A Dalitz plot analysis of the 3π system shows evidence fora ₂ (1320) production and for a large contribution of theJ ^PC=1⁺⁺ ρπ wave.     

Measurements of theP 3/2-S 1/2-intervals in then=4,n=5 andn=6 states of ionized helium

TheP _3/2-S _1/2-intervals in then=4,n=5 andn=6 states of ionized helium have been measured by a radio frequency method, which permits to determine the disturbing electric fields in the interaction region and to correct their influences. The experimental results for theP _3/2-S _1/2 intervals in then=4,n=5 andn=6 states were (20,180.6±0.8) MHz, (10,332.9±1.4) MHz and (5,979.1±1.2) MHz respectively. From these intervals, the following indirect values for theS _1/2-P _1/2-Lambshifts can be deduced: (1,768.5±0.8) MHz in then=4 state, (905.0±1.4) MHz in then=5 state and (524.3±1.2) MHz in then=6 state. The results agree with the theoretical predictions. The static electric fields in the interaction region, ranging from 2 to 6 V/cm, increased with increasing electron excitation current, but were independent of the helium pressure within the range of 10 to 26 mTorr. All uncertainties are expressed as 68% confidence values.     

Bestimmung derP 3/2 —D 3/2-Aufspaltimg und Nachweis von crossing-Signalen im Zustandn=3 von ionisiertem Helium

Radio frequency induced transitions between 3D _5/2- and 3P _3/2-Zeeman sublevels in He⁺ have been detected. From the position of the line center of theD _5/2 (m=?1/2)—P _3/2(m=1/2) transition, the splittings 3D _5/2—3P _3/2=(17259±13) MHz and 3P _3/2—3D _3/2=(81±13) MHz have been deduced. The theoretical values are 17254.9 and 85.4 MHz. Three crossings of Zeeman sublevels of the 3S-, 3P- and 3D-states of He⁺ have been detected both by a magnetic and an electric field modulation method. The crossing-field strengths are in good agreement with the calculated values.     

An experimental investigation of the onset of theL 2-L 3 M 4 andL 2-L 3 M 5 Coster-Kronig transitions forZ>90

L-M coincidence measurements were made on x rays from the radioactive decays of ₉₆ ²⁴⁴ Cm, ₉₄ ²³⁸ Pu, and ₉₂ ²³² U. The observation ofM x rays in coincidence with theL ₃ N _{4, 5} transition indicates that the onset of theL ₂-L ₃ M ₅ Coster-Kronig transition takes place atZ=91 or 92. The measured ratio of theM x-ray counting rates, coincident with theL ₃ N _{4, 5} andL ₂ M ₄ transitions, establishes that both theL ₂-L ₃ M ₄ and theL ₂-L ₃ M ₅ transitions are energetically possible forZ≧94, but the results do not rule out the possibility that these transitions begin as low asZ=92. The measurement ofL-M x-ray coincidences, together with relative Coster-Kronig electron intensities from theory or experiment, provides a new way to measure the totalL ₂-L ₃ Coster-Kronig transition probability,f ₂₃, at highZ for radioactive sources where the primary vacancies are created primarily in theL ₂ andL ₃ subshells. The present result atZ=94 indicates that the theoretical calculations of McGuire of the relative partial Coster-Kronig transition rates forL ₂-L ₃ M _4,5 are accurate to within 10 percent.     

Collective excitations in145Ba

High-spin levels in¹²⁵Ba have been produced in the¹¹⁶Sn(¹² C, 3n) reaction and studied by in-beam spectroscopic methods. Two strongly populated band structures are observed. The odd-parity one is based on a 7/2^? state and can be explained as the result of the coupling between anh _11/2 neutron-hole and a prolate type triaxial core. The even-parity band, built on a 7/2⁺ state, corresponds to collective excitations associated with a neutron-hole in theg _7/2 shell. Comparisons with heavier odd-A Ba isotopes and discussions are made in the frame work of the triaxial core model. Nuclear Reactions¹¹⁶Sn(¹²C, 3nγ), E=45–55 MeV; measuredσ(E;E _γ,θ),γγ-coinc,γ-γ delay. Enriched target, Ge(Li) detectors.¹²⁵Ba deduced levels,J,π,γ-mixing.     

Die2H+d-Reaktion bei niedrigen Energien

It is shown that in the angular distributions of the²H(d, p)³H (using polarized and unpolarized deuterons) and likewise in the neutron polarization of the mirror reaction²H(d, n)³He the resonance found atE _d ≈105 keV can be understood as a threshold resonance. From the experimental dataJ)^π=2⁽⁺⁾,T=0 is derived for spin, parity and isospin of the resonance. Additionally it is found, that the resonant part of the reaction has a small coupling matrix element, linking the²H+d channel with the³H+p and³He+n channels.     

Search for dibaryon production in 4Hep interactions at intermediate energies

With the aid of the 2-m liquid-hydrogen bubble chamber constructed at the Institute of Theoretical and Experimental Physics (ITEP, Moscow), ⁴Hep interactions are studied at primary alpha-particle momenta of 2.7 and 5 GeV/c (the respective kinetic energies of primary protons in the ⁴He rest frame are T _p=220 and 620 MeV). The effective-mass spectra of two nucleons from the reactions ⁴Hep → dppn and ⁴Hep → pppnn are analyzed. The effective-mass spectrum of the two-proton system produced in the quasielastic-charge-exchange reaction p ⁴He → n _F(pp)d at T _p=620 MeV (here, n _F stands for the fast neutron in the ⁴He rest frame) shows a narrow peak, which is indicative of the existence of a dibaryon whose mass and width are M _2p =2008±13 MeV and Γ _2p =0±5 MeV, respectively. In the mass spectra of the two-proton system from the reactions p ⁴He → n _F(pp)d and p ⁴He → p _F(pp)(nn), narrow threshold peaks are also found at a mass of M _2p ?1878–1879 MeV.     

Specific features of the excitation spectrum of helium II in a plasma initiated by an electron beam

The emission of a low-pressure helium plasma (P≤2 Torr) initiated by a monochromatic electron beam is investigated. It is found that an increase in the current leads to a drastic increase in the rate of charge exchange of doubly charged helium ions. The assumption is made that inelastic collisions of He⁺⁺ ions with metastable helium atoms provide the main channel of charge exchange of these ions due to the reaction He⁺⁺+Hem→ He⁺*+He ₀ ⁺ .     

The decaysK S 0 →γγ andK L 0 →γγ in the chiral approach

We calculate theK _S ^Emphasis>0 →γγ decay within the approach of non-linear realization of chiralS U(3)×S U(3). The branching ratio with respect to theπ ⁺ π ^- channel turns out to be 3.5×10^?6 and therefore similar to the result gotten previously by dispersion relation techniques in a non-chiral model. We also discuss theK _L ⁰ →γγ decay by taking into account new results onη ₁-η ₈ mixing from recent measurements of the η→γγ decay.     

Oscillator strengths of Rb quadrupole lines

The oscillator strengths of the forbidden lines of Rb (5²S_1/2-n²D_5/2 and 5²S_1/2-n²D_3/2, 4≤ n ≤9) have been measured in absorption. The dependence of the oscillator strength on the principal quantum number is qualitatively the same as calculated by Warner.⁽¹⁾ It was found that the values for the second quadrupole doublet are extremely small.     

Phosphor-converted light-emitting diode based on ZnO-based heterojunction

A phosphor-converted light-emitting diode (LED) was realized by coating BaMg₂Al₁₆O₂₇:Eu²⁺·Mn²⁺ and (SrCaPO₄)·B₂O₃:Eu²⁺·Na⁺ phosphors onto an n-ZnO/i-MgO/p-GaN heterojunction diode. Two emission bands at around 450 and 520 nm were observed in the phosphor-converted LED under the injection of continuous current. By analyzing the optical properties of the heterojunction diode and phosphors, it is concluded that the emission at 450 nm comes from (SrCaPO₄)·B₂O₃:Eu²⁺·Na⁺ phosphor, while the one at 520 nm comes from BaMg₂Al₁₆O₂₇:Eu²⁺·Mn²⁺ phosphor under the excitation of the light emitted from the n-ZnO/i-MgO/p-GaN heterojunction diode. The results reported in this paper may provide a route to ZnO-based phosphor-converted LEDs for future lighting or displaying purpose.     

High spin states in153Er

High spin states in¹⁵³Er have been populated in the¹⁴⁴Sm(¹²C, 3n)¹³³Er reaction. Excitation functions, lifetimes, angular distributions,γ-γ coincidences and internal conversion coefficients were measured. Three isomeric states at 2.75 MeV (T _1/2=400 ns), 2.95 MeV (T _1/2～10 ns) and 5.2 MeV (T _1/2=200 ns) have been observed. A fourth isomer seems to be weakly excited above 6.8 MeV. The level scheme proposed is discussed in term of the nuclear shell model.     

Spin-label HF-EPR of lipid ordering in cholesterol-containing membranes

Conventional oxazolidine spin-labelled lipids have the axial¹⁴N-hyperfine tensorz-axis directed along the long axis of the lipid chain. Investigation of lateral ordering of the lipids in membranes requires measurement of thex-y Zeeman anisotropy of the nonaxialg-tensor at high fields. Both the lateral and transverse ordering of the lipid chains in membranes of dimyristoyl phosphatidylcholine containing 40 mol% cholesterol in the liquid-ordered phase have been studied with 94 GHz electron paramagnetic resonance spectroscopy. This has been done by using probe amounts of phosphatidylcholine systematically spin-labelled at positionsn along the length of thesn- 2 chain [n-PCSL, 1-acyl-2-(n-(4,4-dimethyloxazolidine-N-oxyl) stearoyl)-sn-glycero-3-phosphocholine]. Nonaxial (g_xx?g_yy) anisotropy of the spin-labelled lipid chains is detected over a wide range of temperature throughout the liquid-ordered phase. The transverse profile of lateral ordering with position,n, of chain labelling follows the profile of the rigid steroid nucleus of cholesterol. It becomes progressively averaged towards the terminal methyl group of thesn- 2 chain, in the region of the flexible hydrocarbon chain of cholesterol. The nonaxial lipid ordering may be related to lipid domain formation in membranes containing cholesterol and saturated-chain lipids.     

Investigation of two resonances in the18O(p,n)18F reaction

Excitation functions for the¹⁸O(p,n)¹⁸F reaction were measured at bombarding energiesE _p=4.6 to 6.6 MeV. In and near two resonances of the yield curves atE _p=5.622 and 6.061 MeV, angular distributions were measured with neutron time-of-flight techniques. The strong neutron decay to theT=1 state in¹⁸F and the similarity of the¹⁸O(p,n) and¹⁸O(n,n) yield curves give good evidence that the structures in the¹⁸O(p,n) yield curve arise from the formation ofT=3/2 states in¹⁹F. A two-level-analysis does not give satisfactory fits to the strongly asymmetric angular distributions.