Resonance states of hydrogen nuclei 4H and 5H obtained in transfer reactions with exotic beams

To investigate ⁵H resonance states with a better instrumental resolution, we utilized the two-neutron transfer reaction ³H(t, p)⁵H accomplished with the use of a cryogenic liquid-tritium target and 57.5-MeV triton beam. As a result of this study, a valuable fraction of protons detected at ? _lab=18°–32° in ptn coincidence events was attributed to the states of the ⁵H nucleus. Two resonance states situated at 1.8±0.1 and 2.7±0.1 MeV above the t + n + n decay threshold were obtained in the missing mass energy spectrum of the ⁵H nucleus. The peak located close to E5_H was clearly seen in the ⁵H spectrum obtained from the energy distributions of ³H nuclei emitted in the reaction ²H(⁶He, ⁵H)³He at ? _lab=17°–32°. The width (Γ_obs≤0.5 MeV) obtained for the two ⁵H resonance states is surprisingly small. A state of ⁴H with E _res=3.3 MeV and γ ²=2.3 MeV was obtained in the reaction ²H(t, p)⁴H from the spectra of protons leaving the target at ? _lab=18°–32° and detected in coincidence with neutrons emitted in the decay of ⁴H nuclei.     

On the mechanism of the (n, 2n) reaction with 14MeV projectiles on127I and209Bi

The angular and spectral distributions of coincident neutrons from the reactions¹²⁷I(n, 2n)¹²⁶I and²⁰⁹Bi(n, 2n)²⁰⁸Bi have been measured with two time-of-flight detectors at the incident energy 14.1 MeV. Neutron emission has been studied for reaction anglesθ _lab between 10° and 150° (relative angles from 60° to 270°). Energy spectra, angular distributions and coincidence yields are compared with statistical model calculations including preequilibrium decay modes, and nuclear level density and spin cut off parameters are derived.     

Preparation and properties of the system CoPxS2−x

Lattice parameters were determined for members of the system CoP_xS_2?x (0 ≤ x ≥ 1). A cubic region was observed for 0 ≤ x ≤ 0·5 and a tetragonal region for 0·5 < x ≤ 1. Magnetization and susceptibility measurements were made on the sample CoP_xS_2?x (0 ≤ x ≤ 0·5) from 4·2 to 500°K and to 9·5 kOe. The ferromagnetic Curie temperature decreased almost linearly with composition from a value of 122(1)°K for x = 0 to 23(1)°K at x = 0·3. The saturation magnetization passed through a maximum at 41·5(2) e.m.u./g at x = 0·05, increasing from 40·0(2) e.m.u./g for x = 0, and then decreased to below 15 e.m.u./g for x = 0·3. The paramagnetic data gave a P²_eff/CO²⁺ that increased linearly with phosphorus substitution from 4·4(2)μ_B at x = 0 to 5·5(2)μ_B² at x = 0·5. The Weiss constant decreased almost linearly from 150(3)°K for x = 0 to 85(2)°K for x = 0·3. The magnetic properties of this system are compared with those of the system CoAs_xS_2?x and CoSe_xS_2?x. Changes, with composition, in the Curie and Weiss temperatures are almost identical in the three systems for x ≤ 0·25. As with CoAs_xS_2?x the ferromagnetic moment reaches a maximum at x = 0·05 and then decreases with increasing x, although the magnetic interactions remain ferromagnetic for all x ≤ 0·5.     

Crystalline and optical properties of Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>S (0.5 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 1) films doped with silver

The results from studying Cd _x Zn_1–x S (0.5 ≤ x ≤ 1) films fabricated via pyrolysis from thiourea coordination compounds of cadmium and zinc bromides doped with silver ions having impurity concentrations of 10^–7, 10^–6, 10^–5, 10^–4, and 10^–3 mol L^–1 in sputtered solutions are presented. Films prepared at 400°С have the wurtzite lattice. The bandgap of pure and doped films, determined from absorption spectra near the edge of fundamental absorption, varies linearly from 2.5 to 3.11 eV. An order of magnitude increase in the intensity of luminescence is observed after doping with silver.     

Charged particle decays from the isoscalar giant quadrupole resonance in 28Si

The charged particle (c) decay from the isoscalar giant quadrupole resonance (GQ₀R) in ²⁸Si has been studied in a kinematically complete ²⁸Si(α, α'c) coincidence experiment at E_α = 155 MeV. The α'c coincidence spectra show α- as well as p-decay of the GQ₀R and indicate that different parts of the GQ₀R have strongly different decay branchings into individual decay channels c_i leading to low-lying final states. Coincidence spectra with c-particles detected in anti-quasifree kinematics show that quasifree scattering contributions can be minimized. Angular correlations have been obtained for c = p and α decays into low-lying states of ²⁷Al and ²⁴Mg, respectively. For the α₀ decay, interference phenomena have been observed in the angular correlations as well as in the fine structure of the α'-α₀ coincidence spectra, indicating contributions from fast direct α₀ decay. Direct and statistical decay features of the GQ₀R region are discussed on the basis of the measured spectra, angular correlations and deduced branching ratios which are compared to Hauser-Feshbach predictions.     

The decays of on-shell and off-shell polarized gauge bosons into massive quark pairs at NLO QCD

We discuss the polar angle decay distribution in the decay of on-shell and off-shell polarized (W, Z) gauge bosons into massive quark pairs. In particular for the off-shell decays in $H \to \left( {W,Z} \right) + \left( {W^* ,Z^* } \right)\left( { \to q_1 ,\vec q_2 } \right)$ it is important to keep the masses of the charm and bottom quarks at their finite values since the scale of the problem is not set by m _W,Z ² but by the offshellness of the gauge boson which varies in the range (m ₁ + m ₂)² ≤ q ² ≤ (m _H ? m _W,Z )².     

Correlations between the arrival directions of ultrahigh energy cosmic rays and the large-scale structure of the universe

We present the results of analyzing the arrival directions of cosmic rays with energies E ₀≥ 4×10¹⁷ eV and zenith angles θ≤45° detected at the Yakutsk setup during 1974–2000. It is shown that increased particle fluxes exceeding the anticipated random distribution levels by 4–5)σ arrive from the galactic plane at E ₀≈(2–4)×10¹⁸ eV and from the supergalactic plane at E ₀≥8×10¹⁸ eV.     

Search for resonant absorption of solar axions by atomic nuclei

Search for resonant absorption of solar axions by ⁵⁷Fe and ¹⁶⁹Tm nuclei, leading to the excitation of the first nuclear level: ⁵⁷Fe: A + ⁵⁷Fe → ⁵⁷Fe* → ⁵⁷Fe + γ and A + ¹⁶⁹Tm → ¹⁶⁹Tm* → ¹⁶⁹Tm + γ, has been performed. To this end, the energy spectra of the Si(Li) detector with ⁵⁷Fe and ¹⁶⁹Tm targets have been measured. The detector and targets were located in a low-background setup equipped with passive and active shields. A new upper limit on the axion mass: m _A ≤ 330 eV (90% confidence level) has been established from the spectrum of ⁵⁷Fe (30 days). Measurements with a ¹⁶⁹Tm target during 8 days gave a new upper limit on the product of the axion-photon coupling constant and the axion mass: g _Aγ (GeV^?1) × m _A (eV) ≤ 2.9 × 10^?4 (90% confidence level).     

Correlation between raman spectra and structural properties of Zn<Subscript>2 − 2<Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>x</Subscript>In<Subscript>x</Subscript>Se<Subscript>2</Subscript> films

The Raman spectra of Zn_{2 ? 2x} Cu_xIn_xSe₂ (ZCIS) semiconductor films designed for use as optically active layers in thin-film solar cells have been investigated. The Raman spectra of ZCIS films are characterized by the presence of the dominant mode A ₁, which is observed in A^IB^IIIC ₂ ^VI compounds with chalcopyrite structure. The spectra of CuInSe₂ films (x = 1) obtained at low temperatures (T ≤ 400°C) contain and additional mode at 258 cm^?1, which is due to the presence of the impurity Cu_xSe phase. All modes observed in the spectra of ZCIS films with a Zn concentration ≤20 at % obtained under optimal conditions (520–540°C) correspond to the symmetry of vibrations in the chalcopyrite structure. The broadening and blue shift of the A ₁ mode occurring with an increase in the Zn concentration are indicative of degradation of the chalcopyrite crystal structure and the chalcopyrite → sphalerite phase transition at Zn concentrations exceeding 20 at %.     

Study of the (p,pn) reaction in light nuclei

The (p, pn) reaction on ²H, ⁶Li, ⁷Li, ⁹Be has been studied at 47 MeV bombarding energy. Excitation energy spectra and energy sharing spectra are presented. Fragmentary information on ¹⁰B, ¹¹B and ¹²C was also obtained. Sequential decay contributions to the ⁶Li(p, pn)⁵Li¹ reaction suggest an admixture of parentage $\text{(α)π(}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)π(}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)}$ for the (3^?), 23 MeV excited state of ⁶Be. A possible 15.5 MeV excited state in ⁶Be is reported. An extensive study of the ⁹Be (p, pn)⁸Be reaction for 45 MeV protons was made. Results for θ_p = θ_n = 25°, 30°, 35°, 40°, 45°, 55°, 65°; θ_n = 40°, θ_p = 25°, 30°, 35°, 40°, 45°, 55°, 65°; θ_p/θ_n = 40°/45°, 38.5° are reported and compared to DWIA calculations. Agreement is good when the lower momentum components of the wave function are sampled, and deteriorates as higher momenta are required. Results are in agreement with the Cohen and Kurath spectroscopic factors for ⁹Be.     

Temperature-dependent light scattering from magnetic excitons in TlCoF3

Raman spectra of antiferromagnetic thallium cobaltous fluoride have been obtained with 4579A argon ion laser excitation at temperatures from 4°K to T_N = 94 ± 2°K. The features observed consist of six Co²⁺ excitons ranging in energy from 325 to 1070 cm^-1, at two-magnon peak with low-temperature energy of 315 cm^-1, and a one-magnon feature whose 4°K energy is 37 cm^-1. The energy and linewidth of the one-magnon scattering has been measured from 4°K to about 0.8 T_N; it is found that the magnon becomes critically damped at about 0.8 T_N, in good agreement with our previous observations on RbCoF₃. The Co²⁺ excitons observed at 325, 380, 410, 730 (weak), 960, and 1070 cm^-1 agree in energy quite well with the KCoF₃ levels calculated by Buyers, Holden et al. as 340, 400, 467, 767, 967 and 1050 cm^-1.     

Low-lying states of the 16F nucleus

Low-lying proton-emitting states of ¹⁶F have been investigated through the sequential particle decay reactions ¹⁴N(³He, n)¹⁶F(p)¹⁵O. Excitation energies were determined by measuring outgoing proton energies. Estimations of proton decay widths and spin limitations were made from proton spectra and angular correlation data which were obtained by detecting the protons in time coincidence with the associated neutrons at θ_n = 0°. To date, the ground-state spin of ¹⁶F has been considered to be J = 0; however, the present work suggests J = 1 to be preferable.     

810.6–863.6 keV γγ-directional correlation in58Fe

The 810.6–863.6 keV γγ-directional correlation has been measured with an NaI(Tl)-Ge(Li) detector system. The NaI window was set on the 810.6+863.6 keV composite peak. From the (810.6 NaI gate) (863.6 Ge spectrum) data at 90 °, 135 °, and 180 °, we deducedA ₂=+0.51±0.03 andA ₄=+0.09±0.04. These results disagree with the values previously obtained from⁵⁸Co decay (with Nal-NaI detector systems) but agree with the values from γγ(θ) studies following thermal neutron capture by⁵⁷Fe.     

Pi-mesic decays of A = 4 hypernuclei

Angular distributions and energy spectra for the decay modes _Λ⁴He→π^?p³He, _Λ⁴H → π^?p³H, _Λ⁴H → π^?n³He are calculated and compared with experiment. Final state nuclear interactions have been adjusted to fit the corresponding scattering data. With S-, P- and D-wave interactions we were able to obtain reasonably good agreement with the experimental decay spectra. It is suggested that the _Λ⁴H → π^?n³He decay spectra may be decisive in selecting the right set of p³H complex phase shifts from several possible solutions.     

The decays of the Tz = 32 β-delayed proton precursors 83Zr, 87Mo and 91mRu

The decays of the nuclides ⁸³Zr,⁸⁷Mo and ^91mRu have been studied with singles proton counting as well as with pX and pγ coincidences. The half-lives for the three nuclides were measured to be 37.8 ± 1.1 s, 13.3 ± 0.4 s and 7.6 ± 0.8 s, respectively. The proton branch in the decay of ⁸³Zr that populates the first excited state in ⁸²Sr was measured to be (6 ± 4) % of the total delayed proton decay. The corresponding branch in the decay of ⁸⁷Mo, populating the first excited state in ⁸⁶Zr was measured to be (15 ± 8) %. Restrictions to the possible spin and parity assignments of ⁸³Zr and ⁸⁷Mo were deduced from comparisons between the experimental excited-state branches, and those predicted from a statistical model of delayed particle decay. Fits to the endpoints of the delayed proton spectra from ⁸³Zr and ⁸⁷Mo yielded values of the energy available for delayed proton decay (Q_e.c.?B_p) of 2.75 ± 0.10 MeV and 3.7 ± 0.3 MeV, respectively. Comparison between calculated and experimental proton spectra was used as an argument that the source of ⁹¹Ru activity is actually a $\text{1}\text{2}{}^{\mathrm{?}}$ isomer.     

Ferrielectric phase transition in ammonium sulphate: A study of two-sublattice model by EPR of polar VO2+ probes

EPR spectra from VO²⁺ -doped (NH₄)₂SO₄ crystals were studied in the range between ?40 and ?150°C. VO²⁺ impurities substituted fog NK₄⁺ ions are accompanied with lattice defects, forming complexes oriented in crystals. Below the transition temperature (?50°C) the spectra exhibited splittings into two branches with unequal intensities, as previously observed in ferroelectric TGS. In ferrielectrie (NH₄)₂SO₄, however, the temperature dependence of the spectra was markedly different from the TGS case. While the internal field determined from the dipolar energies of VO²⁺-probes was consistent with anomalous polarization observed by Unruh[1], the displacement in VO²⁺-directions showed a monotonie increase when the temperature was lowered. We consider that the local order in the molecular arrangement is reflected in the VO²⁺-displacement. The two-sublattice model for the ferrielectrie (NH₄)₂SO₄ is reviewed on the basis of the present EPR results, and the validity of the concept of sublattice polarization is discussed.     

3.508 μ-HeXe-laser line absorption by CH3COOCH3, CH3, and NO2 and infrared emission at 6.89 μ by CH3COOCH3 and CH3 at elevated temperatures

Shock-tube HeXe-laser absorption data at ω_L=2850.633 cm^-1 for CH₃COOCH₃ at 757≤T, °K≤1344, NO₂at 412≤T, °K≤1859, andCH₃at 1283≤T, °K≤1562 are presented. Approximate models are used for the effective spectral absorption coefficient of vibration-rotation lines for analytical representations of the results around atmospheric pressures. For CH₃COOCH₃, an equivalent Voigt-profile for an isolated line was adopted in order to account for a dependence on total pressure of the laser absorption coefficient. Shock-tube emission data at λ=6.890 μ(Δλ=0.197μ) forCH₃COOCH₃at 814≤T, °K≤1651 and for CH₃at 1377≤T, °K≤1562 in the v₄-fundamental of the H-bond bending mode of the CH₃-group are well described at atmospheric pressures by approximations of just-overlapping-line models for polyatomic molecules. The adopted models are useful for concentration-time history measurements of methyl acetate, nitrogen dioxide, and methyl radicals behind shock waves.     

Alpha-heavy-ion angular correlations from 28Si + 12C

Alpha particles have been measured in coincidence with heavy recoil nuclei from the ²⁸Si + ¹²C reaction. At E_lab = 87 MeV angular correlations for alphas between 15° and 55° and heavy ions at angles ?9°, ?12° and ?15° have been taken. An excitation function of coincidence events with θ_α = 30° and θ_HI = ?12° has been measured for 84 MeV < E_lab < 91.5 MeV. The results are well described by a statistical-model calculation for compound nucleus decay. No evidence is found for additional processes.     

Alpha decay of the new isotope172Au

The first observation of the extremely neutrondeficient nucleus¹⁷²Au is reported, produced using the fusion evaporation reaction⁷⁰Ge+¹⁰⁶Cd→¹⁷⁶Hg^* (E_x?64 MeV). Mass separated evaporation residues were implanted into a double-sided silicon strip detector, and the energy and time of subsequent decay events were recorded. The alpha decay of¹⁷²Au was measured with an energy =6860±10 KeV, corresponding to =7020±10 Kev, and a half-life of 4±1 ms. No evidence was seen for a proton decay branch, implying a limit ofb _p ≤ 2 %.     

Intense green-emitting Sr2LiSiO4F:Eu2+ phosphor for n-UV white LEDs

Eu²⁺-activated Sr₂LiSiO₄F phosphors were synthesized at 900°C by solid-state reaction in reducing atmosphere, and their photoluminescence (PL) properties were systematically investigated by diffuse reflection spectra, PL excitation and emission spectra, and by the fluorescence decay curve. Sr₂LiSiO₄F:Eu²⁺ emits intense green light at 520 nm originating from the 5d¹4f⁶−4f⁷ transition of Eu²⁺ under 365 nm n-UV excitation. The PL excitation spectrum matches the emission from n-UV chips. These materials could be promising green phosphors for use in generating white light in phosphor-converted white light-emitting-diodes (LEDs).