A high resolution,low background fast neutron spectrometer

We discuss the possibility to create a spectrometer of full absorption based on liquid scintillator doped with enriched ${}^6$Li. Of specific interest, the spectrometer will have energy resolution estimated to lie in the range 5–10% for 14 MeV neutrons. It will be sensitive to fluxes from 10⁻⁴ to $\text{10}{}^6\text{cm}{}^{\mathrm{-2}}\text{s}{}^{\mathrm{-1}}$ above a threshold of 1 MeV in a γ-background of up to $\text{10}{}^4\text{s}{}^{\mathrm{-1}}$. The detector's efficiency will be determined by the volume of the scintillator only (∼3 l) and is estimated to be 0.2–10%. The main reason for the poor resolution of an organic scintillator based spectrometer of full absorption is a non-linear light-yield of the scintillator for recoil protons. The neutron energy is occasionally distributed among recoil protons, and due to non-linear light-yield the total amount of light from all recoil protons ambiguously determines the initial neutron energy. The high-energy resolution will be achieved by compensation of the non-linear light-yield of the scintillator through the use of optically separated sections. The applications of such a detector for low-background experiments in fundamental physics research, characterizations of neutron fluence in space, and the health physics community are discussed.     

The overall sink strength of an inhomogeneous lossy medium. Part I: self-consistent estimates

Steady-state diffusion in a medium containing a continuous distribution of sinks is considered. The medium comprises a matrix, with sink strength $\text{k}{}_2{}^2$, which contains a random array of identical spherical inclusions, with sink strength $\text{k}{}_1{}^2$. On a macroscopic scale, the medium appears homogeneous, with uniform sink strength $\text{k}\text{?}{}^2$. This work is devoted to the estimation of the overall sink strength $\text{k}\text{?}{}^2$, in terms of $\text{k}{}_1{}^2\text{, k}{}_2{}^2$ and the statistics of the distribution of the inclusions. Part I discusses three distinct schemes of self-consistent type. One is based upon a simple embedding procedure and makes no explicit allowance for spatial correlations. The other two make use, in different ways, of the quasicristalline approximation (QCA). Part II develops variational principles which yield bounds for $\text{k}\text{?}{}^2$. The self-consistent estimates are interpreted relative to the variational formulation and explicit numerical results are presented.     

Thermonuclear fusion neutrons under “Currentless plasmas” in Heliotron E

Thermonuclear fusion neutron emissions of up to 3 × 10⁹ neutrons/s have been observed in Heliotron E deuterium plasmas. “Currentless plasmas” were produced by electron cyclotron resonance (53 GHz, 150 kW) and further heated by hydrogen neutral beam injection (2.2 MW, H⁰→D⁺). It is found that all observed neutron emissions have thermonuclear origin due to the absence of hard X-ray background. Agreement between neutron and charge exchange ion temperature measurements (500 eV < T_i(0) × 900 eV) have been found at intermediate densities $\text{(1.5 ×}\text{n}{}_{\mathrm{<mtext>e</mtext>}}\text{× 3 × 10}{}^{13}\text{cm}{}^{\mathrm{?3}}\text{)}$. The neutrons reported in this paper are the first observations of pure thermonuclear fusion neutrons in a helical heliotron plasma confinement device.     

Formation and properties of metallic organotin films

Semiconductive and conductive films of metallic appearance are formed by glow discharge of appropriate organometallic compounds. Tetramethyltin is used as a starting compound for the film-forming experiments. The resulting films contain carbon, tin and hydrogen with a carbon-to-tin atomic ratio of 2.5 or less. These films are semiconductors with conductivities between 2 × 10^-1 and $\text{1 × 10}{}^{-2}\text{Ω}{}^{-1}\text{cm}{}^{-1}$. Transmission electron microscopy shows the films to be amorphous. Films of a certain composition are transformed to β-Sn on exposure to an electron beam. Thermal treatment increases the conductivity gradually to values of about $\text{1 × 10}{}^2\text{Ω}{}^{-1}\text{cm}{}^{-1}$.     

Development of the AASHTO fracture-toughness requirements for bridge steels

This paper describes the effects of temperature and strain rate on the fracture-toughness behavior of bridge steels. The test results showed the existence of a fracture-toughness transition that is an inherent material property rather than a behavior caused only by a change in the stress state. The effect of a slow loading rate, compared with impact loading rates, is to shift the fracture-toughness transition to lower temperatures. The magnitude of the temperature shift between stow loading ($\text{?≈ 10}{}^{\mathrm{?5}}\text{sec}{}^{\mathrm{?1}}$)and impact loading ($\text{/.? ≈ 10 sec}{}^{\mathrm{?1}}$) decreased with increased yield strength of the steel. The fracture-toughness behavior of bridge steels under strain rates that are encountered in actual bridge ($\text{/.? t~ 10}{}^{\mathrm{?3}}\text{sec}{}^{\mathrm{?1}}$) is closer to slow loading than to impact loading.Relationships are presented among fracture-toughness values determined by testing fracture-mechanics-type specimens, Charpy $\text{V-}\text{notch}$ (CVN) specimens, and nil-ductility-transition (NDT) specimens. Moreover, procedures are presented for using CVN impact-test results to predict $\text{K}{}_{\mathrm{IC}}$ values at slow or at moderate loading rates such as occur in actual bridges. The predicted $\text{K}{}_{\mathrm{IC}}$ values are shown to be close to those experimentally determined by testing $\text{K}{}_{\mathrm{IC}}$ specimens at various strain rates.The test results were used to develop fracture-toughness requirements for bridge steels. These toughness requirements have been approved by the Federal Highway Administration (FHWA) and by the American Association of State Highway and Transportation Officials (AASHTO) and are mandatory requirements on all Federal-aid highway programs in the United States.     

Theorems of zaremba type for thermoelastic solid

It was shown in [2] that any solution of the equation of coupled dynamic thermoelasticity (a) $\text{[(?}{}^2\text{??}{}_{\mathrm{t}}{}^2\text{)(?}{}^2\text{??}{}_{\mathrm{t}}\text{)?∈?}{}_{\mathrm{t}}\text{?}{}^2\text{]phi = 0, (?}{}_{\mathrm{t}}\text{= ?/?t)}$, subject to homogeneous initial conditions admits the representation $\text{phi = phi}{}_1\text{+ phi}{}_2$, where (b) $\text{(?}{}^2\text{??}{}_{\mathrm{t}}{}^2\text{?∈?}{}_{\mathrm{t}}\text{?∈?∈K 1)phi}{}_1\text{= 0}$, and (c) $\text{?}{}^2\text{??}{}_{\mathrm{t}}\text{+∈+teK (s)phi}{}_2\text{= 0}$. Here $\text{K = K(t, epsi)}$ is a given function and ¹ denotes the operation of convolution with respect to time $\text{t}$. In the present paper three uniqueness theorems associated with (a), (b) and (c) are given, and a domain of influence theorem for (b) is established. Next, these theorems are used to show that there exist such couplings between the external mechanical and thermal fields applied to the boundary of a thermoelastic solid that inside the body the temperature is either of a wave type or of a diffusive type, but not of both types.     

Distribution coefficients in (YSmLuCa)3(FeGe)5O12 film growth

The composition of bubble garnet films has been analyzed by Inductively Coupled Plasma Emission Spectroscopy (ICP) to determine the distribution coefficients for different growth conditions. Under typical growth conditions, the distribution coefficients, k, of each element are as follows: k^Y = 2.15, k^Sm = 1.56, k^Lu = 1.32, k^Ca = 0.45, k^Fe = 0.98, k^Ge = 1.10. As the supercooling temperature (growth rate) increases, k^Ca, which is the smallest and deviates most from 1.0, changes in the direction approaching 1.0. For charge compensation, k^Ge also increases, consequently, k^Fe must decrease. Also k^Y, which is the largest, $\text{k}{}^{\mathrm{Sm}}\text{k}{}^{\mathrm{Y}}$ and $\text{k}{}^{\mathrm{Lu}}\text{k}{}^{\mathrm{Y}}$ change in the direction approaching 1.0. On the other hand, as the melt parameter R₁ (≡ $\text{Fe}{}_2\text{O}{}_3\text{Σ}\text{Ln}{}_2\text{O}{}_3$) increases, k^Fe decreases, and k^Y, k^Sm and k^Lu increase, whereas $\text{k}{}^{\mathrm{Sm}}\text{k}{}^{\mathrm{Y}}$ and $\text{k}{}^{\mathrm{Lu}}\text{k}{}^{\mathrm{Y}}$ remain constant at 0.73 and 0.61, respectively.     

Studies in convergence of stochastic models in rough-surface hydrodynamic lubrication theory

The stochastic Reynolds equation for hydrodynamic lubrication with random homogeneous roughness of the lubricated surface is studied using series expansions. In the case in which the roughness function $\text{δ ? C}{}^0\text{(}\text{}\text{?}\text{gW)}$, we show convergence of the series for pressure and its expectation in the Sobolev space $\text{H}{}^1\text{(Ω)}$, whereas in the case in which $\text{δ ? C}{}^1\text{(}\text{}\text{?}\text{gW)}$, the series converge in $\text{C}{}^2\text{(Ω)}$ provided ▽δ is uniformly bounded.     

Photoelectrochemical study of TiS3 in aqueous solution

TiS₃ single crystals have been grown by chemical vapor transport. They were characterized by X-ray diffraction and measurement of their electronic transport properties. A photoelectrochemical study shows both anodic and cathodic dark currents and anodic photocurrents. Flat band potentials and anodic corrosion p$\text{o}$te$\text{n}$tials in acidic and basic solutions and in the presence of an $\text{I}{}^{\mathrm{?}}{}_3\text{I}{}^{\mathrm{?}}$ redox couple have been determined from the onset of photocurrent and from the Schottky-Mott plot of capacitance. The flat band potential ex$\text{h}$ibits a pH dependence but is almost independent of the presenc$\text{e}$ o$\text{f}$ I^? in solution. The stability of this material in a 1N H₂SO₄+ 1N $\text{I}{}^{\mathrm{?}}{}_3\text{I}{}^{\mathrm{?}}$ solution has been observed for a period of fourteen days with a photocurrent of approximately $\text{1}\text{mA}\text{cm}{}^2$. A particular photocorrosion mechanism is reported. The reaction starts at the edges of the layer and proceeds toward the interior. These mechanisms are discussed in relation to the existence of two types of S atoms in the structure: sulfur dimers and S^2? ions.     

The elastic field around an elliptical crack in an anisotropic medium under an applied stress of polynomial forms

A general form is presented for the stress disturbance caused by an elliptical crack in an anisotropic medium under an arbitrary stress field in the form of polynomials. Somigliana's dislocation method is employed for analysis as Willis [4] did, but a different integral process is taken. The results are expressed in the integral forms defined on the subspace of the surface of a unit sphere. The following theorem is proved: If the displacement discontinuity of the elliptical Somigliana's dislocation has the form where is a homogeneous polynomial of degree $\text{N}$ in the coordinates $\text{x′}{}_1$ and $\text{x′}{}_2$ and $\text{a}{}_1$ and $\text{a}{}_2$ are the semi-axes of the elliptical Somigliana's dislocation, the stresses on the plane of the Somigliana's dislocation are inhomogeneous polynomials in the coordinates, whose terms are of degree $\text{N, (N ? 2}$), $\text{(N ? 4),4.}$     

Liquid phase epitaxial growth of gallium arsenide on an etched substrate

A method is described for etching the surface of GaAs substrates with a Ga solution $\text{in}$$\text{situ}$ immediately prior to epitaxial layer growth from the liquid phase. Layers grown by this procedure show excellent surface morphologies and electrical properties ($\text{μ～5100}\text{cm}{}^2\text{v-sec}$ at 300°K for $\text{n～ 7.8×10}{}^{16}\text{cm}{}^3$). Advantages of the method and its applicability to epitaxial growth of other III-V compounds are discussed.     

Magnetohydrodynamic stratified flow past a sphere

This paper considers the uniform, steady, horizontal flow of a vertically stratified, electrically conducting, non-diffusive fluid over a non-conducting sphere in the presence of a uniform magnetic field. The force exerted on the sphere is investigated on the basis of the method of matched asymptotic expansions, for small values of a stratification parameter α, $\text{R}{}_{\mathrm{e}}\text{? ¦α¦}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$, $\text{F}{}_{\mathrm{r}}{}^2\text{? ¦α¦}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>3</mtext>}}$ and for $\text{M}{}^2\text{= 0(α}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$. Up to the first order of calculations the drag is computed for a few typical values of magnetic interaction parameter when, (a) The applied magnetic field lies in the vertical plane and inclined with the ambient flow direction. (b) The applied magnetic field lies in the horizontal plane and perpendicular to the flow direction. Further it is shown that the sphere has no tendency to rotate nor it experiences a lift force upto the order of calculations which we have made. The drag experienced by the sphere is found to be increased due to the combined effects of stratification and magnetic field.     

Fiber-optic lightguides in scintillator telescopes for charged particle detection

The use of flexible fiber-optic bundles as lightguides for thin scintillators in a telescope is described. The telescopes will be used in the pion induced fission experiment $\text{π}{}^{\mathrm{+}}{}^6\text{Li}\text{→ 2}{}^3\text{He}$. The fiber-optic lightguide detector was tested, under identical condi against a conventional lightguide-detector arrangement and for α-particles of 5.5 MeV. An efficiency > 99% was obtained with a relative transmission efficiency of ～ 45% compared to the conventional lightguide arrangement.     

Carburization and decarburization kinetics of iron in CH4 — H2 mixtures between 1000 – 1100 °C

In this study the rate constants of the methane decomposition reaction on iron surfaces were determined in the 1000–1100°C temperature range, by grav? metric methods. Earlier works showed that the reaction velocity was given by The results indicate that the constant values vary from 2.72 × 10^?6 to $\text{16.74 × 10}{}^{\mathrm{?6}}\text{mol C/cm}{}^2\text{/sec/atm}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for k and 2.61 × 10^?8 to $\text{8.62 × 10}{}^{\mathrm{?8}}\text{mol C/cm}{}^2\text{/sec/atm}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ for k′ between 1000 and 1100°C.     

A cooled photoresistor based on n-type germanium alloyed with copper

A photoresistor cooled with liquid nitrogen is described based on n-type Ge alloyed with Cu with a detection sensitivity of $\text{10}{}^{14}\text{cmHz}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{W}{}^{\mathrm{?1}}$ in the spectral range from 0.8 to 1.7 μm.     

Vaporization reactions of manganese gallium sulfide

The vaporization of manganese gallium sulfide was investigated in the temperature range 500–975°. Manganese gallium sulfide was found to vaporize incongruently by the reaction:

$\text{3}\text{MnGa}{}^2\text{S}{}^4\text{(s) =}\text{Mn}{}^3\text{Ga}{}^2\text{S}{}^6\text{(s) + 2}\text{Ga}{}^2\text{S}\text{(g) + 2}\text{S}{}^2\text{(g)}$

and

$\text{Mn}{}^3\text{Ga}{}^2\text{S}{}^6\text{(s) = 3}\text{MnS(s)}\text{+}\text{Ga}{}^2\text{S}\text{(g) +}\text{S}{}^2\text{(g)}$

Approximate vapor pressures were measured by the Knudsen effusion technique. Lattice parameters, density, and chemical analysis of the new ternary compound Mn₃Ga₂S₆ are reported.     

Electronic and spin configurations of Co3+ and Ni3+ ions in oxides of K2NiF4 structure: A magnetic susceptibility study

In La₄LiCoO₈, Li⁺ and Co³⁺ ions are ordered in two dimensions and Co³⁺ ions undergo transitions from the low-spin to the intermediate as well as the high-spin states. Both Sr₄TaCoO₈ and Sr₄NbCoO₈ exhibit low to intermediate-spin state transitions of Co³⁺ ions. In the system LaSr_1?xBa_xNiO₄, the e_g electrons are essentially in extended states forming a band. With increase in x, the band width decreases accompanying an increase in unit cell volume; high-spin Ni³⁺ ions are formed to a small extent with increasing x, but there is no spin-state transition. In LaSrAl_1?xNi_xO₄, at small x, there is a small proportion of high-spin Ni³⁺; when x ≈ 0.6, there is an abrupt decrease in the $\text{c}$/$\text{a}$ ratio, signalling the formation of the band. In LnSrNiO₄, the $\text{c}$/$\text{a}$ ratio decreases sharply between Ln = La and Nd; this is likely to be accompanied by a broadening of the band.     

Nouveaux conducteurs ioniques caracterises par une structure a tunnels entrecroises

The ionic conductivity of pyrochlores A_1+α(Ta_1+αW_1?α)O₆ was investigated for A = Na and T1. The thallium compounds are rather good conductors (0.34 ≤ ΔE ≤ 0.40 eV and $\text{5 10}{}^{\mathrm{?8}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{25°}\text{C}\text{≤ 5.5 10}{}^{\mathrm{?5}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$); the sodium oxides are poor conductors (0.76 eV ≤ ΔE ≤ 1.48 eV and $\text{10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{500}\text{K}\text{≤ 10}{}^{\mathrm{?5}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$). The differences between these two classes of pyrochlores are explained in terms of structure. New non-stoechiometric oxides T1_12+x(M_30+xW_3?x)O₉₀, with M = Ta, Nb, and 0 ≤ x ≤ 3, were isolated. They are, like pyrochlores, characterized by an intersecting tunnel structure, which is an intergrowth of pyrochlore and A₂M₇O₁₈ structures. These oxides show ionic conduction properties which are very close to those of pyrochlores: the tantalum oxides are better conductors (0.30 eV ≤ ΔE ≤ 0.37 eV ; $\text{3.6 10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{25°}\text{C}\text{≤ 1.4 10}{}^{\mathrm{?6}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$) than the niobium oxides (0.36 eV ≤ ΔE ≤ 0.42 eV ; $\text{10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{25°}\text{C}\text{≤ 3.8 10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$). The evolution ofionic conduction properties of all these compounds is discussed.     

Concentration quenching of Nd3+ fluorescence in ordered perovskite oxides and fluorides

New ordered perovskite-type fluorides, Rb₂KNdF₆ and Cs₂KNdF₆, have been synthesized and their luminescence properties investigated. Their neodymium emission shows weak self-quenching. This results both from the isolation of the neodymium in discrete NdF₆ octahedra and from the weak absorption associated with the ${}^4\text{I}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{→}{}^4\text{I}{}_{\mathrm{<mtext>15</mtext><mtext>2</mtext>}}$ transitions in the region of the ${}^4\text{F}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{→}{}^4\text{I}{}_{\mathrm{<mtext>15</mtext><mtext>2</mtext>}}$ emission, which restricts cross-relaxation via the intermediate ${}^4\text{I}{}_{\mathrm{<mtext>15</mtext><mtext>2</mtext>}}$ levels. In contrast the emission of neodymium, substituted for lanthanum in the homologous Ba₂LaNbO₆ oxide, shows a strong concentration self-quenching.