A new measurement of the weak magnetism term in the betaspectra of B and N

The betaspectra of ¹²B and ¹²N have been measured with a NaI crystal as spectrometer. Assuming a shape correction factor 1 + aW + bW² and b₋ = 1.106 × 10⁻⁴ MeV⁻², b₊ = −1.397 × 10⁻⁴ MeV⁻², the spectra yield a₋ = (+0.91 ± 0.11) × 10⁻² MeV⁻¹ and a₊ = (−0.07 ± 0.09) × 10⁻² MeV⁻. the a₋ − a₊ = (+0.98 ± 0.09) × 10⁻² MeV⁻¹ is in agreement with the weak magnetism prediction.     

On the luminescence of LiBaF3:Eu

From the temperature dependence of the line—band luminescence intensity ratio of LiBaF₃:Eu²⁺ a 4f−5d activation energy (Δ) of 800 cm⁻¹ is derived, being much higher than the value reported in the literature (100 cm⁻¹). The temperature dependence of the luminescence decay can be well described with Δ = 800 cm⁻¹ and with 4f−4f and 5d−4f radiative probabilities of 4×10²s⁻¹ and 6×10⁵s⁻¹, respectively.     

Study of cluster decay of Cm using SSNTD

Cluster decay of ²⁴²Cm with emission of ³⁴Si-particles was measured using track-recording phosphate glass detectors. The corresponding partial half-life is (1.4±0.3)×10²³ s. The branching ratio relative to decay is 1.0×10⁻¹⁶ and relative to spontaneous fission 1.6×10⁻⁹.     

Specific activity and derived intervention levels for Cesium-137 in Costa Rican export goods: Tuna fish, coffee and powdered milk

Cesium-137 is a fission product of ²³⁵U and ²³⁹Pu. After a major nuclear accident, it is released into the atmosphere and in the far field region it will produce radioactively contaminated food and drinking water. This paper will study the specific activity of ¹³⁷Cs in three Costa Rican export products: tuna fish, coffee and powdered milk. The average specific activities found are as follows: 0.89±0.41, 1.16±0.76 and 4.53±2.00 Bq kg⁻¹. They represent low values compared to their derived intervention levels: 1.25 × 10⁷, 1.25 × 10⁷ and 2.44 × 10⁵ Bq kg⁻¹, respectively.     

ENDOR of monovalent Cr in KMgF3 and the hyperfine constant of Cr as a function of covalency

Using ENDOR, the hyperfine constant of ⁵³Cr⁺ in KMgF₃ is found to be ⁵³A = (20.754 ± 0.003) × 10⁻⁴cm⁻¹. Taken with recent data for Cr⁺ in other environments, the result confirms that the dependence of ⁵³A on covalency is remarkably linear.     

Domain wall pinning in polycrystalline perovskite La0.7Sr0.3MnO3

Reversible and irreversible domain wall (DW) motions have been investigated in La_0.7Sr_0.3MnO₃ ceramic samples using frequency-response complex permeability with various amplitudes of AC field. We also examine the effects of temperature in the range from 293 to 368 K and transverse DC magnetic field with a maximum of 4.40×10⁵ A/m on the real part of permeability (μ′). Two relaxations corresponding to reversible wall motions and domain rotations occur in low and high frequency regions, respectively. The irreversible DW displacements can be activated as the amplitude larger than the pinning field of 3 A/m, leading to an increase in μ′. The μ′ obeys a Rayleigh law at the temperature below 343 K or under DC field of less than 4.22×10⁴ A/m. The Rayleigh constant η increases from 5.45×10⁻² to 1.54×10⁻¹ (A/m)⁻¹ as the temperature rises from 293 to 343 K, and η decreases from 5.58×10⁻² to 3.67×10⁻² (A/m)⁻¹ with increasing DC field from 1.99×10³ to 4.22×10⁴ A/m.     

Duree de vie et depolarisation par collisions avec l''helium des niveaux 5P3/2 Et 5P1/2 de l''ion Cd

The lifetimes of the Cd⁺ 5²P_3/2 and 5²P_1/2 states have been measured by the Hanle effect. The Cd⁺ ions are produced in a d.c. discharge in cadmium vapor, with helium as buffer gas. The results are: τ(5²P_3/2) = (2.60±0.20) ×10⁻⁹sec, and τ(5²P_1/2) = (3.05 ± 0.13) × 10⁻⁹sec.

We measured also the cross sections for the destruction of the orientation in the 5²P_1/2Cd⁺ state (<5Ų), of the orientation (18±10Ų) and of the alignment (46±10Ų) in the 5²P_3/2 state due to collisions with the helium atoms.     

Observation of two-photon emission in nuclear pion capture

The emission of two photons above 25 MeV energy was observed in the capture of stopped pions by beryllium and carbon with a rate of (1.0 ± 0.1) × 10⁻⁵, respectively (1.4 ± 0.2) × 10⁻⁵ per capture. These rates are about two to four times greater than various free-nucleon estimates based on the π⁻+π⁺→γγ annihilation mechanism alone.     

Hadronic production by ee collisions at the energy 990 MeV with the Orsay storage ring

Data were taken at the energy 2E = 990 MeV to search for multibody events, with the same large solid angle detector which has been used for the measurement of the , ω andφ production by e⁺e⁻ annilations. Assuming a π⁺π⁻π⁰π⁰ production by the quasi two-body process e⁺e⁻ → → ωπ⁰ we give the correspondi ng cross section σ(e⁺e⁻ → π⁺π⁻π⁰π⁰) = (1.1 ± 0.5) 10⁻³² cm². Since no events with 3 and 4 charged pions have been observed σ(e⁺e⁻ → π⁺π⁻π⁰π⁻) 1.5 × 10⁻³³ cm².     

Defect versus nanocrystal luminescence emitted from room temperature and hot-implanted SiO2 layers

Silicon nanocrystals have been synthesized in SiO₂ matrix using Si ion implantation. Si ions were implanted into 300-nm-thick SiO₂ films grown on crystalline Si at energies of 30–55 keV, and with doses of 5×10¹⁵, 3×10¹⁶, and 1×10¹⁷ cm⁻². Implanted samples were subsequently annealed in an N₂ ambient at 500–1100°C during various periods. Photoluminescence spectra for the sample implanted with 1×10¹⁷ cm⁻² at 55 keV show that red luminescence (750 nm) related to Si-nanocrystals clearly increases with annealing temperature and time in intensity, and that weak orange luminescence (600 nm) is observed after annealing at low temperatures of 500°C and 800°C. The luminescence around 600 nm becomes very intense when a thin SiO₂ sample is implanted at a substrate temperature of 400°C with an energy of 30 keV and a low dose of 5×10¹⁵ cm⁻². It vanishes after annealing at 800°C for 30 min. We conclude that this luminescence observed around 600 nm is caused by some radiative defects formed in Si-implanted SiO₂.     

Chemical effects of Ne bombardment on the MoS2(0001) surface studied by high-resolution photoelectron spectroscopy

The effect of 1 keV Ne⁺ bombardment on the clean MoS₂(0001)-1 × 1 surface with fluences between 4 × 10¹⁴ and 4 × 10¹⁶ Ne⁺/cm² was studied using high-resolution photoelectron spectroscopy excited with synchrotron radiation. Spectra of the Mo 3d and S 2p core levels were measured with photon energies that ensured that the kinetic energy of the photoelectrons was the same, resulting in the same depth being probed for both core levels. For lower fluences (i.e., 2 × 10¹⁵ Ne⁺/cm²), S vacancy defect formation occurs in the MoS₂ lattice, with the concurrent formation of a small amount (< 10%) of dispersed elemental molybdenum [Mo(0)]. For fluences greater than l × 10¹⁶ Ne⁺/cm², the Mo(0) is the predominant species in the surface region, while the remaining species consist of amorphous MoS_2−x and polysulfide species. Valence band spectra taken with photon energies of 152 and 225 eV were consistent with the core level results. The movement of the valence band maximum toward the Fermi level indicated the formation of a metallic surface region. Annealing the sample to temperatures up to 1000 K resulted in the formation of metallic Mo coexisting, in approximately equal amounts, with reformed MoS₂ in a surface with no long-range order as determined by LEED. Finally, a qualitative depth distribution of the chemical species present after Ne⁺ bombardment was determined by varying the photon energies used for the core level spectra. The results indicate that the preferential sputtering of sulfur over molybdenum occurs predominantly through a mechanism involving chemical bonding effects, specifically, through the preferential emission of polysulfide ions over other species in the bombarded region.     

The axial isoscalar neutral current from inelastic electron-nuclear scattering

Parity violating effects due to neutral currents in isoscalar 0⁺→1⁺ nuclear transitions induced by electron scattering are enhanced owing to the small isoscalar magnetic dipole strength. A polarization asymmetry of the order 10⁻⁴ is expected at q 100 MeV for the ¹²C transition to the 1⁺(T = 0) state at 12.71 MeV. It would allow to single out the (electron vector current) × (hardonic axial isoscalar current) quantum numbers and couplings of the neutral current interaction.     

Cross section of the charged current reaction C(ve, e)Ng.s.

The charged current nuclear transition ¹²C(v_e, e⁻)¹²N_g.s. has been observed in the KARMEN experiment. The flux average cross section for v_e from μ⁺ decay at rest is determined to be σ = [8.1±0.9(stat.)±0.75 (syst.)]×10⁻⁴²cm². For the first time also the energy dependence of the cross section has been measured for neutrino energies up to 50 MeV.     

Defects in H implanted GaAs studied by ion-beam and low-energy positron techniques

Ion-beam and low-energy positron-beam techniques have been used to study damage and implanted ion distributions and their annealing behavior in semi-insulating GaAs after the room temperature implantation of 3 × 10¹⁵−1 × 10¹⁷ 60 keV H⁺ cm^-2. The redistribution of the implanted H during annealing was observed to be connected to the migration of implantation-induced defect-complexes. A huge increase in the displaced atom concentration in the region of the H concentration was observed after annealings. A monovacancy overlayer, dissociation of H-vacancy complexes, and formation of stable vacancy-H agglomerates were observed in the different parts of the slowing-down region of the implanted H.     

Observation and study of latent tracks on the surface of HOPG induced by H ions

The topography and size of damage on the surface of HOPG (Highly Oriented Pyrolitic Graphite) bombarded by high fluence (1×10¹⁶ ions/cm²) of H⁺ ions were observed and studied. In this work, 457 STM images of each one with 9×9 nm² area were obtained. From 163 of these pictures visible damage was found. In these 163 STM images the diameter of most damage is from 0.2 to 0.8 nm. In this study the number density of visible damage is much less than the ion fluence. The probability of damage is only about 1.8×10⁻⁴. The possible mechanism of damage formation is also analyzed and discussed.     

A new upper limit for the decay μ→eee

A search for the decay μ⁺→e⁺e⁺e⁻, in which no candidate was found, yields a new upper limit for the branching ratio R_μ→3e<1.6×10⁻¹⁰ (90% confidence). A total of 16 decays were observed, in agreement both in number and momentum distribution with V - A theory.     

Optical pumping of the 2p3sP0 State of Ne (I = 3/2): g factor and metastability exchange cross section

A C.W. multi-mode dye laser is used to obtain by optical pumping an orientation of the 2p⁵ 3s³P₀ (F = 3/2) state of ²¹Ne. A magnetic resonance experiment leads to the measurement of the g factor g (³P₀) = 3.027 (8) × 10⁻⁴ to be compared with the theoretical prediction (3.025(6) × 10⁻⁴). One obtains also the metastability exchange cross section σ(³P₀) = 18.4 ± 4 Ų for collisions between metastable (³P₀) Ne atoms and ground state Ne atoms. This result is compared with other measurements and theoretical evaluation.     

The ratio of K-capture to positon emission in the decay of P

The ratio of K-capture to positon emission in the 2.5 min decay of ³⁰P has been measured by a proportional counter-flow technique. The experimental value of the K/β⁺ was found to be (1.24 ± 0.04) × 10⁻³ in agreement with the conventional theoretical ratio i.e. apparently supporting the view that exchange and overlap effects are small.     

Escape of charged particles at stopping annihilation of antiprotons in the heavy nuclei of nuclear photoemulsion

“Rare” annihilation channels for antiprotons stopping on heavy (Ag, Br) nuclei of photoemulsion, have been sought; 4872 stops of antiprotons on photoemulsion nuclei are analysed. Events of formation and decay of the hyperfragment _Λ⁴H, escape of ⁸He and ⁸Li nuclei, one-prong stars with the mean range 79.5±5.1 μm of secondary slow “b” particles are found among the annihilation stars at capture on nuclei (Ag, Br). The lower limits for the production probability of _Λ⁴H and ⁸He, ⁸Li nuclei per antiproton stopping in the nuclei (Ag, Br) are

W_Λ⁴H2×10⁻⁴ and W_⁸He,⁸Li=(1.3±0.6)×10⁻³.

The branching ratio for the production of one-prong stars with the secondary “b” particles is at least (1.3±0.6)×10⁻³. Possible mechanisms for a production of these events in annihilation processes are considered.     

Enhanced performances of ZnO-TFT by improving surface properties of channel layer

Top-contact thin film transistors with ZnO as the channel layer and thermally grown SiO₂ as the gate dielectric were fabricated by using rf sputtering. The performances of ZnO-TFTs with different thicknesses of the active layer were investigated and the optimized condition was obtained. With the active layer thickness from 25 to 70 nm, the leakage current of devices increased from 10⁻¹⁰ to 10⁻⁸ A, and the on/off ratio decreased from 1.2×10⁷ to 2×10⁴. Atomic force microscope research indicated that with the thickness increased, the surface morphology of the active layer improved noticeably at first and then deteriorated. The 25-nm-thick ZnO TFT had the best surface morphology, and showed the best performance with a field effect mobility of 5.1 cm²/V S, on/off ratio of 1.2×10⁷ and threshold voltage of 20 V. This indicates that the surface properties of the channel layer have crucial affects on the performances of ZnO-TFTs.