Fragmentation of gold projectiles: From evaporation to total disassembly

We have studied the fragmentation of Au projectiles interacting with targets of C, Al and Cu at an incident energy ofE/A=600 MeV. The employed inverse kinematics allowed a nearly complete detection of projectile fragments with chargeZ≧2. The recorded fragmentation events were sorted according to three observables, the multiplicityM _lp of light charged particles, the largest atomic numberZ _max within an event, and a new observable,Z _bound, representing the sum of the atomic numbersZ of all fragments withZ≧2. Using these observables, the impact parameter dependence of the fragmentation process was investigated. For all three targets, a maximum mean multiplicity of 3 to 4 intermediate mass fragments (IMFs) is observed. The corresponding impact parameters range from central collisions for theC target to increasingly peripheral collisions for the heavier targets. It is found that the correlation between the IMF multiplicity andZ _bound, extending from evaporation type processes (largeZ _bound) to the total disassembly of the projectile (smallZ _bound), is independent of the target nucleus. This universal behaviour may suggest an — at least partial — equilibration of the projectile fragment prior to its decay.     

Intermediate mass fragments emitted in the reaction Ag+14N at 100, 160 and 250 MeV bombarding energy

The fragments produced in the reaction between a ¹⁴N beam of various energies and a natural Ag target have been studied. The atomic numbers of the fragments have been identified up to Z = 17 by means of a E-ΔE counter telescope. The cross sections, the kinetic energy distributions as well as the angular distributions have been measured for each atomic number. The kinetic energy distributions show two components: a high-energy component (quasi-elastic), prevailing at angles close to the grazing angles and for atomic numbers close to Z = 7, and a low-energy component (relaxed), at energies close to the Coulomb repulsion energy, present at all angles and for all the Z. A detailed study of the relaxed components of the kinetic energy seems to account for both them means and the widths of these distributions on a purely statistical basis. The cross sections of the relaxed components appear to be quite large at low Z and to decrease rapidly to a fairly constant value in the region of 10 ≦ Z ≦ 17. A marked even-odd alternation in the cross sections is observed. The angular distributions are strongly forward peaked for Z < 7. For Z > 7 the forward peaking decreases rapidly until, for Z > 13, the limiting form 1/sinθ is attained. Evidence for the existence of a diffusion process along the mass asymmetry coordinate is discussed.     

Ab initio investigation of phonon spectra in GdLiF4 compound under hydrostatic pressure

Employing density functional theory (DFT) within the generalized gradient approximation, the GdLiF₄ structure has been studied for a pressure range from 0 to 12 GPa. The influence of pressure on the lattice vibrational spectrum of the scheelite phase (I4₁/a, Z = 4) has been evaluated by means the “direct” approach, i.e., using force constants calculated from atomic displacements. As a result the Raman and infrared modes have been identified and their dependencies on pressure have been investigated and compared with available experimental data. It has been found that instability of the crystal structure appears at pressures above 6 GPa.     

XPES studies of oxides of second- and third-row transition metals including rare earths

X-ray photoelectron spectroscopy has been employed to investigate oxides of second- and third-row transition metals, including those of rare earths. Systematics in the spin—orbit splittings and binding energies of core levels of the metals are described. In most of the cases studied, the dependence of the spin—orbit splittings on the atomic number Z is given by the relation ΔE = a(Z - Z₀)⁴, where a is the quantum defect parameter and Z₀ is the effective screening. Core-level binding energies are found to increase with the oxidation state of the metal. Most of the core-level binding energies are related to the atomic number Z by the expression E = x(Z - Z₀)², giving rise to linear plots of ln E versus ln Z. Specific features of individual oxides, with respect to satellites, multiplet structure, configuration mixing, and other properties are also discussed. The spectra of PrO₂, Pr₆O₁₁, TbO₂ and Tb₄O₇ are reported for the first time.     

Ion impact stopping cross sections for various media (Z = 3–100)

ABSTRACT

Stopping cross sections (SCS) for protons, alphas and Li ions are calculated with a modified form of our earlier work by incorporating a different electron density distribution of target materials; this involves four parameters – two projectile dependent and the rest two remain fixed. The prosed model has been tested for three stripped ion (H⁺, He^{2 +} and Li^{3 +}) projectiles and found that it describes quite satisfactorily the experimental SCS data from low energies with projectile velocities nearing v = Z₁v₀ (with Z₁ as the atomic number and v₀ the Bohr velocity) up to 100.0 MeV over a wide range of stopping media with atomic numbers Z₂ =3–100.     

Electromigration and permeation of hydrogen and deuterium in silver

A steady state flow technique was used to measure the effective charge number (Z*) and permeability (N) of hydrogen and deuterium in silver. Over the range of temperature (485–720°C) and pressure (220–750 torr) the effective charge number is a constant. The interstitial impurity migrates in the direction of the electron wind with Z_H* = ?6·8 and Z_D* = ? 18. The values of Z* are of the same order as self-electromigration but the size of the isotope effect is surprising. The quantum theories used to explain the isotope effect for hydrogen electromigration in Fe and Ni appear to fail here. In order to determine the effective charge number is was necessary to measure the permeability. For both H₂ and D₂, the permeability in silver follows the equation N = N_O exp(? Q/RT) where N_0D = 2·39 ± 0·40, Q_D = 14400 ± 300, N_OH = 2·86 ± 0·70 and Q_H = 14200 ± 500. Here Q is in units of cal/mol and N is in units of cc(ntp)/(sec - atm² - cm) The isotope effect ratio N_H/N_D = 1·25 was smaller than the classically expected value of (2)^1/2, but could be explained by the theory of Ebisuzaki, Kass and O'Keeffe.     

Radium ion: a candidate for measuring atomic parity violation

Parity Non Conservation (PNC) in atomic systems can be observed in experiments using a single trapped ion and intense laser fields. The original proposal is based on a single barium ion. Here, we study the feasibility for carrying out similar experiment with a single radium ion. Since the PNC effect in atomic system increases faster than the Z ³, where Z is the atomic number, radium is a natural choice. The advantages and disadvantages of measuring atomic parity violation in radium ion are discussed.     

Quasimolecular KX-ray excitation by bombarding La targets with La and Xe ions

The X-ray emission from 85 to 150 MeV Xe and 115 MeV La bombardments of thick natural La targets has been measured. The spectra and yields of X-ray emission are obtained. Continuous X-ray distributions have been found to lie beyond the target and projectile characteristic X-ray energies. The high-energy parts of these continua are interpreted as K-radiation of quasi-molecules with effective atomic numbers Z = 111 and Z = 114, respectively.     

Measurement of atomic number and amount of substance in objects using radioactive sources

The possibility of using radioactive sources to measure atomic number Z and the amount of substance nD of unknown objects is considered. An experiment is performed with test samples of different materials exposed to γ-rays from Cs-137 and Co-60 sources. The range of the method’s applicability in measuring atomic number Z and amount of substance nD is shown.     

Relativistic radiative transition rates and energies for the Li-like isoelectronic sequence: Electric and magnetic dipole and quadropole radiation

For Li-like ions in the isoelectronic sequence between the nuclear charges Z = 26 and 94, energies, oscillator strengths and probabilities of electric and magnetic dipole and quadropole transitions between the first 22 atomic levels were calculated by means of the multiconfigurational Dirac-Fock model. The effects of nonlocal Breit interaction, electron self-energy and vacuum polarization were included in calculating energy levels and radiative rates. The trends of transition energies and rates along the isoelectronic sequence, in particular, the enhancement of the forbidden transitions with increasing atomic number Z, are discussed.     

Practical method for experimental effective atomic number in the coherent to Compton scattering ratio

A practical method of calculating Z_eff was developed for the coherent to Compton scattering ratio and the method is applicable for any material with known weight percentages of different elements in the compound. The coherent to Compton scattering ratio depends only on the mixture under study and provides a measurement of certain complicated functions of the atomic number Z and Z_eff. In order to measure the effective atomic number of Sb₂O₃, BaO, La₂O₃, CeO₂ and Nd₂O₃, the linear differential scattering coefficients of 59.5 keV γ-rays have been studied using a high-resolution Si(Li) semi-conductor detector. The coherent to Compton scattering ratio R is taken from the linear differential scattering coefficients μ(E, q). The results obtained have been compared with relativistic (RT) and non-relativistic (NRT) theoretical values.     

Production characteristics of charmed particles in neutrino interactions

Using a hybrid emulsion spectrometer installed in the Fermilab wide-band neutrino beam, we located a total of 3855 neutrino interactions in the fiducial volume of our target. For 122 charmed-particle decays found in these interactions, we present distributions of x,y, charm-muon angular projection, Feynman-X, and the fragmentation Z. We find that the number of strange quarks in the nucleon sea is 4.2±2.1±2.6% of the number of down quarks.     

Systematic trends in the transport mean free path with electron energy and atomic number

The inelastic mean free path, λ_i, and the transport mean free path, λ_tr, hold the key to understanding the effects of elastic scattering of electrons in electron spectroscopy techniques such as Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). Systematic trends in the variation of λ_tr and χ=λ_i/λ_tr with atomic number, Z, and electron energy, E, are explored using the differential elastic scattering cross-section data of Czyzewski et al. (J. Appl. Phys., 68 (1990) 3066). At low Z, λ_tr increases with energy in accord with the predictions of the Born approximation, but at higher Z, a more complex behaviour is revealed. In the first and second transition metal series, χ varies little with energy over much of the kinetic energy range probed in XPS in accord with the energy scaling ideas from the semi-classical scattering theory of Tilinin (Soviet Physics JETP, 67 (1992) 1570). In the third transition series, a pronounced minimum is found at around 200 eV, with χ for Au lower than for the corresponding transition metals. The results identify regions of the periodic table where elastic scattering effects are particularly pronounced.     

Z2 oscillation of mean charge states of fast Si and Cl ions after passage through thin foils

Z₂ (target atomic number) oscillation of equilibrium charge states has been observed for 30–110 MeV Si and 70 and 110 MeV Cl ions after the passage through 22 different Z₂ foils. This oscillation may be related to the Z₂ oscillation of electron capture cross sections into the projectile K vacancy.     

Experimental measurement of effective atomic number of composite materials for Compton effect in the <Emphasis Type="Italic">γ</Emphasis>-ray region 280–1115 keV by a new method

In this paper, we report a new method to determine the effective atomic number, Z _eff, of composite materials for Compton effect in the γ-ray region 280–1115 keV based on the theoretically obtained Klein–Nishina scattering cross-sections in the angular range 50°–100° as well as a method to experimentally measure differential incoherent (Compton) scattering cross-sections in this angular range. The method was employed to evaluate Z _eff for different inorganic compounds containing elements in the range Z = 1–56, at three scattering angles 60°, 80° and 100° at three incident gamma energies 279.1 keV, 661.6 keV and 1115.5 keV and we have verified this method to be an appropriate method. Interestingly, the Z _eff values so obtained for the inorganic compounds were found to be equal to the total number of electrons present in the sample as given by the atomic number of the elements constituting the sample in accordance with the chemical formula of the sample. This was the case at all the three energies.     

Formation of relief on a metallic target surface under the action of compression-plasma flows

The results of experimental and theoretical investigations of relief formation on the surface of a steel target (grade St 3 steel, GOST (State Standard) 380) during treatment by compression-plasma flows are represented. The density of energy absorbed by the target varied in the range from 15 to 25 J/cm², the pulse duration was 100 μs, and the pulse number was N = 1, 3, 5, 7. The experiment revealed the expansion of boundaries of the central area (the area on which the plasma flow is incident normally to the surface) with increasing pulse number. This is explained by the more uniform surface treatment at a greater pulse number. It is shown that to describe relief formation in the central area there is a need to take into account the pressure of the plasma flow on the target surface, apart from surface tension forces and energy dissipation due to viscosity.     

X-ray spectroscopy of multiply-charged ions from laser plasmas

Original results are reported on the observation and identification of spectra of multiply-charged ions in the range of λ ≈ 1.5–15 Å, which corresponds to transitions with a range of principal quantum number n. The main part of the review consists of tables with about a thousand spectral lines, which have been mainly observed in laser-plasma radiation, as well as in the solar corona and other laboratory sources at an electron temperature T_e≈10⁷°K. The accuracy for the wavelengths (Δλ) is the following: Δλ is equal to ≈ 0.0005 Å for λ ≈ 2.5 Å and it is equal to ≈ 0.003 Å for λ ≈ 15 Å. The spectral lines are considered for the following transitions: 1-n type for [H]-like ions (Z = 11–16)and [He]-like ions (Z = 11–26); 2-n type for [Li]-like ions (Z = 19–26), [Be]-like ions (Z = 22–34) and [Ne]-like ions (Z = 26–42); 3-n type [Co]- and [Ni]-like ions (Z = 73). The line-list contains about four hundred wavelengths for multiply-charged iron L-ions (Fe(XVII)-Fe(XXIV)) and is presented with identification of some of the transitions. The wavelengths and intensities of satellites of the [H]-like ions and [He]-like ions, which are caused by transitions from the doubly-excited autoionization states 2l2l′ and 1s2l2L′ of [He]-like ions (Z = 11–16) and [Li]-like ions (Z = 11–26), respectively, are also considered.     

Dependence of the Compton to Rayleigh intensity ratio on the scatterer atomic number in the range of 4(Be) to 31(Ga)

Compton to Rayleigh scattering intensity ratios (I_C/I_R) have been measured using X-rays with energy 17.44 keV for single-component materials with atomic number Z from 4 (Be) to 31 (Ga) and binary compounds of stoichiometric composition. The measurements have been performed using two optical schemes: an energy-dispersive X-ray fluorescence scheme with a molybdenum secondary target and wavelength-dispersive X-ray fluorescence one. The processing of the spectra was carried out by fitting with Pearson VII functions. For single-component and binary standards, the experimental dependence of the scattering intensity ratio on the atomic number was found to be the same. This confirms the additivity of the contribution of different atoms to the scattering. The dependence has a complex shape but is well described by the theoretical relationship for I_C/I_R with correction on the difference between Compton and Rayleigh radiation absorption coefficients. Two ranges of atomic number values are defined, in which the effective atomic number Z_eff can be determined by the calibration method using this dependence: for Z from 4 to 7 with low error of ΔZ_eff =±0.15 and for Z_eff from 10 to 18 with low error of ΔZ_eff =±0.69. A change in the shape of the Compton peak and an overestimated value of the of the Compton and Rayleigh peak intensity ratio when passing from a single-component scatterer (Al or Si) to their oxides Al₂O₃ or SiO₂, respectively, have been revealed.     

Effect of ambient conditions on laser-induced breakdown spectra

The role of different ambient conditions on LIBS signal intensity was investigated for better understanding and performance of LIBS as a quantitative and qualitative analytical technique. For this purpose, the relative LIBS signal intensities were measured for a standard Cr line (520.8 nm) at different gas pressures of Ar, He, and air. The plasma was generated using a Q-switched pulsed Nd:YAG laser having wavelength of 1064 nm and pulse duration of 8 ns. The analysis revealed that the intensities of the spectral atomic Cr line (520.8 nm) were strongly enhanced under the argon environment in 10?C40 mbar range. The electron excitation temperature (T _e ) and number density (n _e ) were estimated by using a Boltzmann plot and a Stark broadening profile, respectively. For optimum dependence of LIBS, laser energy and pressure dependence was also studied. The electron temperature and number density showed an increase with increase in ambient gas pressure.     

Improved Thomas-Fermi interaction potential for atoms with very dissimilar nuclear charges

The interaction potential,U(R), for atoms with nuclear chargesZ ₁ andZ ₂ (Z ₁?Z ₂) is discussed. It is shown that within the linear approximation inZ ₂/Z ₁ this potential is determined by the atomic screening function,?(R;Z), alone. On the basis of the Thomas-Fermi model allowing for quantum corrections, several universal expressions for?(R; Z) are suggested. They permit reliable estimates ofU(R) up toR～2 a.u. and forZ ₂/Z ₁?1/5.