The Indiana silicon sphere 4π charged-particle detector array

A low threshold charged particle detector array for the study of fragmentation processes in light-ion-induced reactions has been constructed and successfully implemented at the IUCF and Saturne II accelerators. The array consists of 162-triple-element detector telescopes mounted in a spherical geometry and covering 74% of 4π in solid angle. Telescope elements are composed of (1) an axial-field gas ionization chamber operated with C₃F₈ gas; (2) a 0.5 mm thick passivated silicon detector, and (3) a 2.8 cm thick CsI(Tl) scintillation crystal with photodiode readout. Discrete element identification is obtained for ejectiles up to Z 16 over the dynamic range 0.7 ≤ E/A ≤ 95 MeV/nucleon. Isotopes are also distinguished for H, He, Li and Be ejectiles with 8 E/A 95 MeV. Custom-designed electronics are employed for bias supplies and linear signal processing. Data are acquired via a CAMAC/VME/Ethernet system.     

Performance of a three-element thin film detector

A nuclear charged particle detector has been designed and fabricated at the University of Florida for use in identifying the nuclear charge Z and mass number A of low energy (1 MeV/amu) heavy mass ions. The detector consists of a stack of three sequential thin film detectors (made from NE-102A plastic scintillator) for three successive measurements of the specific luminescence ΔL/Δx and velocity of a transiting ion and a terminal surface barrier detector for measuring the ion residual energy. This detector assembly was tested by measuring its response to various isotopes of germanium and selenium ions accelerated to selected energies between 53 and 169 MeV and then scattered from a thin gold target foil. The tests were performed to obtain quantitative information on the ability of the detector system to identify the nuclear Z of an impinging ion and to test the 0810 1076 V 3 advantage of having three successive measurements of ΔL/Δx from three sequential and independent thin film detectors. It was determined that below 2 MeV/amu the detector response was dependent on particle velocity but independent of particle mass and below about 0.9 MeV/amu the detector was not able to distinguish between ions having two units difference in Z, probably due to similarities in ionic charge state distributions. It was also determined that the use of three detectors reduced the FWHM of the TFD response by 54%.     

Measurement of continuous damage parameter

The present paper introduces several measuring methods of continuous damage parameter derived by the classical definition D = 1 − (A_e/A_a): (1) The measuring method on the basis of D = 1 − (E'/ E); (2) The measuring method on the basis of D = 1 − (ε₁/ε₂); (3) The measuring method on the basis of D = −Δρ_o/ρ_o, (4) The measuring method on the basis of D = A_d/A_a, and comments on these measuring methods.     

Mass resolution of recoil fragment detector telescopes for 0.05–0.5 A MeV heavy recoiling fragments

The factors governing the mass resolution for 0.05–0.5 A MeV recoil nuclei have been investigated for detector telescopes in which carbon-foil time zero detectors and ion-implanted silicon detectors are used to determine the time of flight and energy respectively. Experimentally determined second moments of the mass distribution have been compared with theoretical estimates based on literature data. The experimental mass resolution is in reasonably good absolute agreement with theoretical estimates. For low energy (< 0.3 A MeV) particles the mass resolution is dominated by the contribution from the silicon detector and thus largely independent of timed flight length. In fact for detection of very low energy (0.1 A MeV) recoil nuclei timed flight lengths of less than 0.22 m are sufficient.     

Driver age, car mass and accident exposure— A synthesis of available data

The tendency of younger drivers to be more likely than older drivers to drive smaller cars has been an important consideration in a number of prior investigations of the relation between car size and traffic safety. The purpose of the present study is to quantify this effect on a firmer basis than hitherto by fitting data from seven independent sources to a unified general model. More specifically, when the exposure measures “per unit distance of travel” or “per registered car” are used in studies of car mass effects on traffic safety, the exposure information often does not contain the variable driver age. This work develops a general procedure for disaggregating such exposure data into three driver (or owner) age categories; A₁: 16–24; A₂: 25–34; and A₃: 35 years. Data from the seven sources are fined to the equation

f(i,m) = H_i[1 + G _i(m/900 − 1)]

where m is the ear mass in kg, and f(i,m) is the fraction of cars of mass m which are driven (owned) by persons in the A_i, (i = 1, 2, 3) age category. The form of this equation permits easy comparison of 900 and 1800 kg cars. Those particular masses that have been chosen for illustrative comparisons in earlier work. The seven sets of data are used to derive overall average values of the parameters H₁ and G₁. The data from all seven sources show consistent effects which are summarized in one analytical expression which is well suited for use in future studies of car size effects because it reflects a synthesis of much prior data and it permits sensitivity analyses to be performed conveniently.     

An analysis of a two-cell coupled nonlinear chemical oscillator

A two-cell chemical oscillator, based on cubic autocatalysis, is considered, with the reaction in each identical cell being P → A; A + 2B → 3B; B → C. The coupling between the cells is assumed to take place by a linear exchange of either reactant A or autocatalyst B. In the former case, five possible stationary states are found with there being a range of parameter values over which non-symmetric stable stationary states can exist. In the latter case, the only possible stationary state is the same as for the uncoupled system. In both cases, Hopf bifurcations are found, leading to sequences of complex dynamical behaviour     

Cyclodextrin inclusion complexes of the central analgesic drug nefopam

Inclusion complexes of nefopam base (NEF) with various β-cyclodextrins (βCDs) were investigated. All tested βCDs increased the apparent solubility of NEF according to a Higuchi A_L type plot (except βCD: A_N type plot), which indicates the formation of 1:1 stoichiometry inclusion complexes. ¹H-NMR and ¹³C-NMR experiments showed that complexation by CDs allowed an easy separation of the R and S enantiomers. Based on spectral data obtained from the two-dimensional rotating frame nuclear Overhauser effect spectroscopy (2D-ROESY), a reasonable geometry for the complexes could be proposed implicating the insertion of the benzoxazocine ring into the wide end of the torus cavity.     

The electric and dielectric properties of a coal tar epoxy coating

The dielectric properties of a coal tar epoxy coating on a steel surface in a dry dielectric layer, metal/organic coating/metal (MOCM) structures, as well as in electrochemical systems, metal/organic coating/electrolyte (MOCE), have been investigated by means of impedance spectroscopy. The influence of temperature and chemically-different contacting electrolytes on the electrical properties of the organic coating are discussed on the basis of the frequency-dependent impedance modulus ωZ(ω)ω and the phase angle Θ(ω) which are both accessible through measurements. The results are presented in the form of Bode plots. It was possible to model the measured values of the modulus by the linear relation lnωZ(ω)ω = K−n ln ω and in terms of Kramers-Kronig (KK) relations. It was shown that the poles and residues of the KK integrand [lnωZ(ω)ω/(ω²−ω²_c)] suffice to establish Θ(ω) uniquely. This means that if the modulus in the Bode plot can be represented by a linear relation with a slope -n, the phase angle is frequency-independent. The experimental results for Θ(ω) are in good agreement with this prediction for a dry (MOCM) and an electrochemical system (MOCE).     

CHICSi—a compact ultra-high vacuum compatible detector system for nuclear reaction experiments at storage rings. II. Detectors

We describe the detectors for identification of charged particles and fragments in CHICSi, a large solid angle multi-telescope system mounted inside an ultra-high vacuum (UHV), cluster-jet target chamber. CHICSi performs nuclear reaction experiments at storage rings. The telescopes consist of a first very thin, 10–14 μm Si detector, a second 300 μm (or possibly 500 μm) ion implanted Si detector supplemented by a 6 mm GSO(Ce) scintillator read out by a photodiode (PD) or by a third 300 μm Si detector. The telescopes provide full charge separation up to Z=17 and mass resolution up to A=9 in the energy range 0.7–60A MeV. The thin p-i-n diode detector, etched out from a 280 μm Si wafer, and the GSO/PD detector, both exclusively developed for CHICSi, provide an energy resolution 8%, while the standard 300 μm detectors have 2% energy resolution. Radiation stability of the Si detectors is confirmed up to an integrated flux of 10¹⁰ alpha particles. The GSO detector has 70% light collection efficiency with the optical coupling to the PD a simple open, 0.2 mm, gap. A new method, developed to perform absolute energy calibration for the GSO/PD detector is presented.     

Parameter of local cyclic strain distribution

The local cyclic strain distribution near the crack tip was investigated by the Computer Aided Fine Grid Method. This method makes it possible to measure continuously every in-plane component of local cyclic strain distribution. It was found that the magnitude of the local cyclic strain distribution near the crack tip was varied by the applied cyclic load level and the material, but the shape of the local cyclic strain distribution near the crack tip was experimentally scarcely altered.

The local cyclic strain field near the crack tip could be written as the following equation. Δε_eq(r, θ) = ΔA · f(θ) · r⁻¹ A single parameter ΔA, which characterizes the local cyclic strain field near the crack tip, was newly proposed by authors.     

Resolution of complex γ spectra from triple-coincidence data: Ba–Mo split in Cf spontaneous fission

Using triple-coincidence events of prompt fission γ rays from spontaneous fission of ²⁵²Cf, we made a new analysis of the yield matrix of coincident pairs of barium (Z=56) and molybdenum (Z=42) fission fragments. Branching from γ-bands (K=2) and octupole-bands (K=0) were also measured. From this reanalysis the previously proposed “extra-hot-fission mode” (8–10 neutrons evaporated) is much weaker than first reported. In this paper, we discuss in detail the methodology, including background subtraction for triple-coincidence data. The importance of minimal compression spectra allowing least-squares peak-fitting analysis is emphasized.     

An energy based mode III fracture criterion for composites

In this work, a new fracture hypothesis referred to as the Z-criterion is developed for mode III cracks in orthotropic composite materials. The new theory predicts critical crack propagation conditions and the crack propagation direction. The Z-criterion (Zhang et al., Engng Fracture Mech. 34, 749–769 (1989) (S-criterion) (Sih, Proc. 10th SES Annual Meeting, 221–234, Boston (1975)) removes certain deficiencies by considering separately the dilatational and distortional strain energy density factors. It suggests that under mode I conditions, crack initiation is controlled by the dilatational strain energy density factor and for mode II and mode III conditions, crack initiation is controlled by the distortional strain energy density factor (Zhang et al. A new Z-criterion… submitted to Engng Fracture Mech.). These controlling parameters allow extension to mixed mode and three dimension crack analysis. Eleven different composite materials are used to test and verify the proposed Z-criterion.     

Systematic analysis of neutron yields from thick targets bombarded by heavy ions and protons with moving source model

A simple phenomenological analysis using the moving source model has been performed on the neutron energy spectra produced by bombarding thick targets with high energy heavy ions which have been systematically measured at the Heavy-Ion Medical Accelerator (HIMAC) facility (located in Chiba, Japan) of the National Institute of Radiological Sciences (NIRS). For the bombardment of both heavy ions and protons in the energy region of 100–500 MeV per nucleon, the moving source model incorporating the knock-on process could be generally successful in reproducing the measured neutron spectra within a factor of two margin of accuracy. This phenomenological analytical equation is expressed having several parameters as functions of atomic number Z_p, mass number A_p, energy per nucleon E_p for projectile, and atomic number Z_T, mass number A_T for target. By inputting these basic data for projectile and target into this equation we can easily estimate the secondary neutron energy spectra at an emission angle of 0–90° for bombardment with heavy ions and protons in the aforementioned energy region. This method will be quite useful to estimate the neutron source term in the neutron shielding design of high energy proton and heavy ion accelerators.     

Stage II fatigue crack growth

The linear part of the fatigue crack growth diagram is found to be divided into Stages IIa and IIb by the point O whose coordinates K^* and A are dependent on the physical and structural characteristics of the material. In Stage IIa K_eff remains constant as the microcrack advances in increments corresponding to the dislocation cell structure size, λ, pausing for (dN−1) cycles to accumulate the elastic energy required for the crack opening. During Stage IIb K_op remains constant and the microcrack opens during each cycle and advances irrespective of the substructure but in accordance with an increasing value of K_eff. The effects of temperature and vacuum on K^* are considered; the A values correspond to those of λ and are independent of the above effects.     

The electronic structure of colossal magnetoresistive manganites

The ferromagnetic manganites A_{1 − x}B_xMnO₃ (A a trivalent element and B divalent) have been the subject of intensive study in the past few years. These manganites exhibit colossal magnetoresistance (CMR), i.e. their resistance can drop several orders of magnitude under influence of an external magnetic field. Electronic structure calculations show that these manganites are half-metallic: they are conducting for one spin direction exclusively. The possible relation between half-metallic magnetism and colossal magnetoresistance is discussed.     

Structure quantitative map in application for AB2X4 system

Structure maps are constructed for AB₂X₄ (A = metal, B = three-valency element and X = O, S, Se, Te) system (>490 compounds). A way to improve the resolution of the maps is proposed. Crystal structure characteristic (symmetry) is represented on a quantitative scale (coordinate axe Z). The 3D structure diagram with approximating integral plane is constructed and a field of high symmetry compounds is specified with ion radii ratio R(A)/R(X) ≈ 0.60–0.85 and R(B)/R(X) ≈ 0.55–0.70.     

Two-Cell coupled cubic autocatalator: the effect of the uncatalysed reaction

A two-cell coupled chemical oscillator based on the cubic autocatalator: P→AA + 2B→ 3BB → C is considered with the inclusion of the extra uncatalysed reaction A→ B. Two cases are considered. In each the cells are assumed to be identical, with the coupling between them taking place by a linear exchange of either reactant A or autocatalyst B. In the former case parameter ranges are found over which it is possible to have one, three or five stationary states; these are discussed in detail, as well as the points of Hopf bifurcation on the various branches of solution. In the latter case, it is shown that the only stationary state possible is the same as for the uncoupled system with Hopf bifurcations also at the same parameter values as for the uncoupled system for all values of the non-dimensional constant describing the coupling between the cells.

Asymptotic solutions are derived for large values of the coupling constants in both cases. With coupling through the autocatalyst the system is shown to reduce to the uncoupled system, whilst for coupling through A the former asymmetric solutions are still found, with Hopf bifurcations on these solution branches     

Bulk Si1−xGex single- and poly-crystals: a new prospective material for electronics

Si_1−xGe_x is a prospective material for electronics. This is mostly because Si_1−xGe_x-based technology is close to silicon-based technology, which is advanced, widely applicable, and cheap. The majority of work on this material is devoted to Si_1−xGe_x-based heteroepitaxy, and in particular to the Si_1−xGe_x/Si system; few publications are devoted to bulk single-crystal. Here we focus on some interesting properties of bulk Si_1−xGe_x solid solutions. First, under heat treatment and alpha- and beta-irradiation the efficiency of defect introduction decreases with the increase of Ge composition of the Si_1−xGe_x single-crystal. This is because Ge atoms in a crystal lattice are annihilation centers for primary defects. Hence, this material is more resistant to temperature and radiation than silicon. Second, it is known that, since Z(Ge)Z(Si), the sensitivity of the material to irradiation should increase with the concentration of Ge. We show that Si_1−xGe_x nuclear detectors have efficiency three times higher than silicon detectors. Finally, we note that one of the major problems in materials based on solid solutions is the composition uniformity. Our investigations on the influence of composition fluctuations on material properties have shown that the material has a sufficient uniformity at x<0.1. Such an alloy is a prospective material for electronics.     

A measurement of the beta asymmetry in neutron decay with PERKEO II

The recent measurement of the electron asymmetry in neutron decay using the spectrometer PERKEO II is presented. In a preliminary analysis we arrive at the following result: A=−0.1189(8), implying λ=−1.2740(21).     

The momentum-loss achromat — A new method for the isotopical separation of relativistic heavy ions

The application of the slowing-down process of relativistic heavy ions in a layer of matter in ion-optical devices is theoretically investigated. The modifications of the phase space of the ion beam due to the dissipative forces and the straggling phenomena are discussed. Methods are developed to study the properties of the momentum-loss achromat, an isotope separator consisting of an achromatic magnetic system with an energy degrader located in the intermediate dispersive focal plane. This device separates projectile fragments with respect to A and Z up to uranium over a wide energy range with an efficiency of the order of 50% and with separation times of several hundred nanoseconds.