Bi Targets Research Articles

Expansion dynamics of Bi atoms produced by laser ablation of Bi and BGO targets

A comparative study of the expansion dynamics of the Bi species present in the plasma produced by laser ablation of Bi 12GeO 20 and Bi targets is carried out in vacuum by spatially-resolved real-time emission spectroscopy. The emission spectrum from the BGO target mainly shows the presence of neutral (Bi *) and single ionised (Bi +*) Bi species. Two populations of Bi * species are observed. The first one dominates the emission close to the target surface (0≤ d≤4 mm) at short times after the laser pulse; while the second population becomes dominant at distances d≥6 mm and lasts much longer ( t>5 μs). Such second population is not observed in the case of either the ionised species or any of the excited species present in the plasma generated by ablation of the Bi target. The existence of complex molecules in the plasma generated by ablation of BGO targets, which dissociate during the expansion, is proposed as the mechanism responsible for the appearance of the delayed Bi * population.

Measurement of the lifetime of heavy hypernuclei produced in the bombardment of Bi with protons

A very thin Bi target has been installed at the internal beam of COSY-Jülich and 1.0 and 1.9 GeV protons have been bumped onto it for determination of the background and production of hypernuclei, respectively. With the recoil-shadow method the position distribution of fission fragments was measured with two multi-wire proportional counters operated in coincidence. From the distribution recorded in the shadow region and the hypernucleus recoil momenta obtained through BUU calculations, a preliminary value of ∼ 145 ± 7 (stat) ± 23 (sys) ps was obtained for the lifetime of the heavy hypernuclei.

Effect of bismuth on the ferroelectric properties of SrBi2Ta2O9 thin films deposited on Pt/SiO2/Si by a modified radio-frequency magnetron sputtering technique

Bi-layered ferroelectric SrBi2Ta2O9 (SBT) films were successfully deposited on Pt/SiO2/Si substrates using a sintered SrBi2Ta2O9 ceramic target, and Bi and Ta metal targets by a modified rf magnetron sputtering technique. The ferroelectric properties of the films were greatly dependent on the bismuth sputtering power. The SBT films deposited under the conditions of rf power of 100 W, Bi dc power of 25 W, and Ta dc power of 10 W showed a dense and uniform microstructure. A remanent polarization, Pr, of 7.51 μC/cm2 and a coercive field Ec, of 28 kV/cm were obtained for an excitation voltage of 5 V. The SBT films show practically no polarization fatigue after 7×1010 switching cycles. Their retention characteristics look very promising up to 106 sec.

Investigation of production and fission decay of heavy hypernuclei at COSY Jülich

The production of very heavy hypernuclei has been investigated at COSY Jülich in the interaction of protons of 1.0 GeV, 1.5 GeV and 1.9 GeV with bismuth and uranium. Identification was based on the detection of fragments from Λ delayed fission using a recoil-shadow technique which yielded cross sections for production and fission decay of hypernuclei of about 5μb (Bi target) and 20±4(stat.) −8 +13(syst.)μb (U target). A lifetime of 240±45(stat.)±40(syst.) ps has been deduced for the uranium target from the position distribution of fission fragments.

Bi nanocrystals embedded in an amorphous Ge matrix grown by pulsed laser deposition

Bi nanoclusters embedded in an amorphous Ge matrix have been produced by alternate pulsed laser deposition in a vacuum. The resulting thin films have been analyzed by high resolution electron microscopy, and the images show that the Ge matrix is amorphous and that Bi nanocrystals are formed. The size of the nanoclusters was easily changed within the range 2 nm to 25 nm by varying the number of pulses on the Bi target. Both the dependence of the nanocrystal size on the number of laser pulses on the Bi target and the results of tilting experiments in the electron microscope show that the nanocrystals have an oblate ellipsoidal shape with a much shorter axis in the direction of the film normal. This particular shape is related to their growth mechanism after nucleation at the substrate.

Subbarrier cold fusion reactions leading to superheavy elements

The elements withZ ≥ 107 were synthesized in cold fusion reactions based on Pb and Bi targets. Heavy ions undergo fusion with these target nuclei deeply in the subbarrier region. The analysis of the potential energy surface of colliding nuclei shows that a cloud of paired nucleons or massive clusters may be transferred from the projectile to the target.

Evaluation of neutron fundamental parameters from the total cross section data

Using experimental data from the neutron transmission measurements on enriched 206,207,208Pb, natural Pb and Bi targets, the potential scattering radii R' and the electric polarizability of the neutron αn were determined by general least squares fit at fixed neutron-electron bound scattering length values: bne = −1.32 × 10−3 fm (Garching) and bne = −1.59 × 10−3 fm (Dubna). The evaluations were performed in two versions: (1) The potential scattering radii R' were taken as fitted parameters; (2) R' values were deduced from optical model calculations. The obtained potential scattering radii values are in the range R' = 9.0 − 10.0 fm. The electric polarizability of the neutron in the first version resulted in αn = +(0.12 ± 0.44) × 10−3 fm3 with the Garching bne value and αn = −(0.97 ± 0.44) × 10−3 fm3 with the Dubna bne value, but in the second calculation version - in αn = −(0.14 ± 0.37) × 10−3 fm3 with both bne values. On the basis of obtained results we give preference to the Garching bne value.

In situ Growth of Fatigue-free SrBi2Ta2O9 Films by Pulsed Laser Ablation

In situ growth of SrBi2Ta2O9 (SBT) films as a function of Bi concentration in the target, substrate temperature, oxygen pressure, and the thickness of bottom Pt electrode by pulsed laser deposition was studied. The SBT phase initially formed at a temperature of 500–520 °C. The SBT films grown from the stoichiometric target generally showed Bi deficiency. A well-crystallized and stoichiometric SBT film could be grown at a temperature of 550–580 °C in 300 mTorr of O2 from the surplus Bi targets, which showed c-axis preferred orientation. The formation temperature of SrTa4O11 (ST) phase was above 600 °C, depending on the Bi concentration in the target. Higher oxygen pressure raised the formation temperatures of the SBT and ST phases and concomitantly enriched the Bi concentration of the SBT films. For the bottom Pt electrode 1200 Å thick, the voids were not observed in the SBT overlayer until the deposition temperatures were above 590 °C. Annealing at temperatures above 700 °C in an atmosphere of O2 was required to improve the contact between Pt electrode and the SBT film and hence the ferroelectric properties of the SBT film. In the present study, a smooth, stoichiometric, and c-axis oriented SBT film, about 350 nm thick, could be grown on Pt (1200 Å)/Ti/SiO2/Si at a temperature of 550–580 °C in 300 mTorr of O2 from the Bi surplus targets, which showed remnant polarization (Pr) of 3.0–3.5 μC/cm2 and coercive field (Ec) of 30–40 kV/cm at 4 V. No fatigue was observed up to 109. switching cycles

Angular distribution of oxide films deposited by multi- or single-component laser ablation

The angular distribution of Bi–Ge–O and Ge–O films prepared by pulsed laser deposition in an oxygen pressure has been studied for different target–substrate distances using two configurations: ablation of multi-component (Bi12GeO20 (BGO) and GeO2) and single-component (Bi and Ge) targets. The results show that the angular distribution of Bi–Ge–O films obtained by alternate ablation of single-component targets is narrower than the one obtained by ablation of the multi-component target. In the case of Ge–O films, in which the multi-component target contains only one cation (Ge), no significant dependence of the angular distribution on the ablation configuration was observed. The results are discussed in terms of the existence of intraplume effects which enhance the broadening effect due to the atmosphere when ablating multi-component targets with two or more cations.

Pion-induced fission in tin and bismuth observed with makrofol detectors

Pion is the field particle of nuclear force. Its interaction with the nucleons may lead to complete absorption resulting in the full deposition of the rest mass and kinetic energy within the nucleus. Consequently the nucleus can be excited to very high energies. This situation gives rise to binary decay even in those nuclei which are not normally prone to fission due to their high fission barriers. We have studied the occurrence of binary fission induced by pions of energies 500, 672, 1068 and 1665 MeV in the targets of Sn and Bi. The exposures have been made at the Brookhaven National Laboratory (USA). The experimental set-up was based on 2 π-geometry with targets in the form of thin foils placed in front of Makrofol detectors. The fission events were counted manually with an optical microscope. The incident beam was monitored with the help of a scintillator and local fluences were determined in-situ. The fission cross-sections were calculated by using the known values of target thickness and local frequencies of fission counts.

K shell ionization cross sections of Au, Pb and Bi induced by low energy proton impact

K X-ray production cross sections induced by proton impact were measured on thick targets of Au, Pb and Bi in the energy range 0.5 < E 0 < 1.7 MeV. The yields of characteristic X-rays were normalised to the yields of backscattered protons. For proton energies E 0 > 0.8 MeV, the deduced K shell ionization cross sections are uncertain by 12%, these uncertainties being smaller than those of the data published before. Our experimental results are compared with the semiclassical cross sections calculated within the united atom binding procedure. Experimental values agree well with theoretical ones, their difference being generally smaller than our experimental errors. The ionization cross sections measured for E 0 < 0.8 MeV are too large to be explained by proton induced direct ionization. We showed that for thick targets and proton energies smaller than E 0 < 0.8 MeV, the K-shell ionization is produced notably by fluorescence on account of bremsstrahlung photons emitted in the collisions between protons and target nuclei.

Measurement of fusion cross section with neutron halo nuclei

Fusion cross sections of 11 Be, 10 Be and 9 Be have been measured on 209 Bi target at 30–70 MeV. Due to the neutron halo effect of 11 Be, a large enhancement or suppression of the fusion cross section around the Coulomb barrier was theoretically predicted. Comparing the excitation function of 11 Be with 10 Be at near the Coulomb barrier region, no significant difference has been observed.

Element 111 created by fusing nickel, bismuth

Scientists in Darmstadt, Germany, have added element 111 to the periodic table almost exactly one month after adding element 110. international team created three atoms of the new element by fusing atoms of nickel and bismuth. first of the three atoms was created on Dec. 8, 1994, after bombarding a rotating 209 Bi target with a high-energy beam of 64 Ni atoms for several days. new atoms have a half-life of around 1.5 milliseconds and a mass of 272. They form by fusion of nickel and bismuth nuclei, followed by emission of a neutron. scientists identified the element by examining the emission pattern of α-particles ( 4 He nuclei) of the atoms. They were able to follow the decay chain down to lawrencium (element 103): The most surprising thing is that although element 111 has a long a-decay chain, there is no spontaneous fission, says Peter Armbruster, head of the nuclear chemistry department at ...

Synthesis and characterization of Bi2Sr2Can−1CunOy(n=1–7) thin films grown by off-axis, three target magnetron sputtering

An alternate deposition method using three target magnetron sputtering and off-axis substrate geometry has been applied to control the number of CuO2 planes n in Bi2Sr2Can−1CunOy thin films. During alternate deposition, the substrate stayed sequentially at each target as Bi→Sr5Cu2O7→CaCuO2→Sr5Cu2O7→Bi. When the staying times at the Bi and Sr5Cu2O7 targets were fixed constant but varied for the CaCuO2 target, single phase films with n=1–7 were obtained. The x-ray diffraction patterns showed a systematic change in the relative line intensity with n in accordance with the calculated patterns, and all possible (00l) lines, including the (004_0_) line of the n=7 film, can be clearly observed below 2θ&amp;lt;60° region. The c dimension increases stepwise by 0.63 nm and approaches 6.27 nm for n=7, indicating a perovskite CaCuO2 plane is regularly inserted with n. The resistivity zero temperature, Tc zero, decreases systematically with n. For n=7, Tc decreased to onset 55 K and end 4 K. The systematic decrease in Tc zero with n can be accounted for by a combination effect of the hole concentration decrease and crystal defect increase with n.

Deposition and Properties of Yttria‐Stabilized Bi2 O 3 Thin Films Using Reactive Direct Current Magnetron Cosputtering

Yttria‐stabilized (YSB) thin films have been deposited using reactive direct current (d.c.) magnetron cosputtering from Y and Bi targets. The films were deposited in argon/oxygen sputtering gas mixtures onto silica glass, , and substrates. thin films with were obtained under metallic mode sputtering conditions, but were found to be ≈10% oxygen deficient. Post‐deposition annealing in air at led to fully stoichiometric films. X‐ray diffraction and transmission electron microscope (TEM) studies showed that the structure of the annealed films was cubic with lattice parameters following Vegard's law. The films were dense as judged by scanning electron microscope (SEM) and TEM. Complex impedance spectroscopy measurements were carried out in air on films with cermet electrodes. The temperature dependent ionic conductivity exhibited a knee point at , with activation energies of 1.2 eV below and 0.96 eV above , in good agreement with values for bulk YSB with the same composition. The interfacial resistance of the cermet with 30 volume percent (v/o) Ag on a YSB electrolyte thin film was ≈0.3 Ω cm2 at 750°C.

Structures and Electrical Properties of Bi12SiO20 Thin Films Prepared by ECR Plasma Sputtering

Bismuth‐silicon‐oxide (BSO) thin films have been prepared on glass substrates by ECR plasma sputtering with Bi and Si multi targets systems. The polycrystalline thin films of δ‐phase BSO have been obtained without any substrate heating, ≦ 150°C, and these films can be transformed into γ‐phase BSO by heat‐treatment above 400°C in air. Some γ‐phase BSO thin films show a large photoconductivity in the range of 380–460 nm. This large photoconductivity of BSO thin films deposited on glass substrates is the first experimental result to our knowledge. The details of the preparation, structure, and some electrical properties of the BSO thin films are described in this paper.

On-line measurements of target properties in experiments for the investigation of the heaviest known elements

The progress in investigations of the heaviest known elements in the recent years was only possible with an elaborate target technology. Large area thin and homogeneous targets of Pb and Bi, mounted on a rotating wheel to allow high projectile currents, were used in the experiments performed at the velocity filter SHIP at GSI Darmstadt. Various techniques for the on-line monitoring of the targets will be described and their importance for the experiments will be discussed. The experimental results from the investigations of the heaviest elements will be summarized briefly.

Strong convoy electron yield dependence on surface properties

Velocity spectra of electrons ejected in the forward direction as a result of ion-solid collisions, are characterized by a cusp shaped structure, the convoy electron peak, if the velocity u p of the projectile matches that of the electron, ν e ∼- ν p. production models assume either volume-multiple step processes or surface-last-layer processes. To probe these models convoy electrons from sputter-cleaned surfaces of C, Al, Ni, Cu, Pd, Ag, Sm, Gd, Au and Bi targets have been studied for the first time under UHV-conditions by proton or krypton ion impact (0.8 and 2.0 MeV respectively), it is found that the convoy electron yield depends strongly on the surface coverage B of adsorbed substances, on the target material and, for Kr + ions, on the work function of the investigated elements. For C targets both yield and convoy electron energy are affected by the hydrogen content.

Synthesis and study of atomic nuclei with Z > 100

The studies of atomic nuclei with Z > 100 are closely related to the synthesis of new chemical elements and to the investigation of stability limits for the heaviest nuclides. From the mid-50s these studies have been carried out using intense heavy-ion beams and highly sensitive techniques designed for the physical and chemical identification of rare short-lived nuclei. The studies proceeded in two stages, the first one being characterized by the use of hot-fusion reactions between the U, Pu, Am, Cm and Cf target nuclei and the C, N, O, and Ne projectiles and the second being based on the use of the cold-fusion reactions induced by Cr, Mn, and Fe projectiles on Pb and Bi target nuclei. As a result, the chemical elements with atomic numbers from 102 to 109 have first been synthesized. The radioactive properties of over 40 isotopes of these elements have been investigated and unambiguous evidence has been obtained that shell effects play a decisive role for the stability of the Z ≳ 104 nuclei against spontaneous fission. This provides an experimental substantiation for the known hypothesis that the island of nuclear stability should lie around Z ⋍ 114 and N ⋍ 178 or 184. It has been proposed to synthesize elements with Z ≥ 110 by the complete fusion reactions of uranium and adjacent element nuclei with projectile nuclei such as Ar and Ca. The spontaneous fission of a product nucleus (a total of 26 events) has been observed in Dubna experiments with the 232Th + 44Ca and 236U + 40Ar reactions. The authors of those studies tentatively assigned this activity to the decay of the nuclei of element 110.

Fission and particle evaporation following stopped-negative-pion absorption in 209Bi

Fission and particle evaporation following stopped- π − absorption were measured for 209Bi. The fission probability per captured π − was obtained as W f = (3.01 ± 0.34) × 10 −3 from the number of fission tracks observed in the mica track detector and that of π − stopped in the Bi target. The latter was derived from the observed absolute intensities of pionic Bi X-rays. The isotopic yield distributions for the ( π −, xn) and ( π −, pxn) reactions were also determined by in-beam and activation γ-ray measurements. From the analysis of the fission probability and the product-yield distribution, it was concluded that the thermally equilibrated nuclear states have a wide energy distribution and rather low excitation energies (∼50 MeV) compared to the initially involved energy of 140 MeV. A model was proposed for the formation and decay of 209Bi nuclei excited by the capture of the stopped π −. The model well reproduces the experimental results.