Superheated drops of R114—as a neutron spectrometer

The basic principle that has been used in the application of superheated drops in neutron spectrometry is its dependence of threshold energy of nucleation on temperature. In the present work, superheated drops of R114 suspended in a visco-elastic gel were irradiated at different temperatures by neutrons obtained from an ²⁴¹Am–Be source. The temperature of the detector was converted to the energy of the incident neutrons following the method developed by us to unfold the neutron energy spectrum. The threshold energy obtained by us agrees well with other results obtained using monochromatic neutron sources, clearly demonstrating the validity of our principle of spectrometry.     

Study of the nuclear recoil response of a NaI(Tl) scintillator detector with a Cf neutron source

This paper describes the behavior of the scintillation pulses induced in a NaI(Tl) crystal scintillator under excitation of a ²⁵²Cf neutron source and a ¹³⁷Cs gamma source and the possible identification of the incident particle by the study of the pulse shape. Furthermore, the energy dependence of the mean decay time is presented.     

Structure and vibrational dynamics of isotopically labeled lithium borohydride using neutron diffraction and spectroscopy

The crystalline structure of a ⁷Li and ¹¹B labeled lithium borohydride has been investigated using neutron powder diffraction at 3.5, 360, and 400 K. The B-H bond lengths and H-B-H angles for the [BH₄]⁻ tetrahedra indicated that the tetrahedra maintained a nearly ideal configuration throughout the temperature range investigated. The atomic displacement parameters at 360 K suggest that the [BH₄]⁻ tetrahedra become increasingly disordered as a result of large amplitude librational and reorientational motions as the orthorhombic to hexagonal phase transition (T=384 K) is approached. In the high-temperature hexagonal phase, the [BH₄]⁻ tetrahedra displayed extreme disorder about the trigonal axis along which they are aligned. Neutron vibrational spectroscopy data were collected at 5 K over an energy range of 10-170 meV, and were found to be in good agreement with prior Raman and low-resolution neutron spectroscopy studies.     

Effect of the encapsulating material on the peak3/peak5 response ratio of TLD-300 irradiated with neutrons of various energy

The analysis of experimental data available in the literature shows that the neutron sensitivity ratio m=k₃/k₅ for the two main glow peaks P₃ and P₅ of TLD-300 (for ribbons of 3.2×3.2×0.9 mm³) is dependent upon the response ratio R₃/R₅ of these two peaks. This finding is in agreement with predictions from an equation derived from the two-peak method equations. The result implies that the peak response ratio R₃/R₅ for TLD-300 surrounded by Tissue Equivalent material is independent of the encapsulating material. This is also demonstrated experimentally.     

Specifications of a neutron exposure accelerator system for biological effects experiments (NASBEE) in NIRS

We developed a neutron irradiation facility, neutron exposure accelerator system for biological effect experiments (NASBEE) for biological studies in National Institute of Radiological Sciences, Japan. Irradiation field of 2 MeV average neutrons generated by a Be(d–n)B reaction is established. Dose uniformity of 240 mm in diameter irradiation field is producible within ±2.5% with a dose rate of 0.87 Gy/h at sample target distance of 1170 mm. Two irradiation rooms, a specific pathogen-free (SPF) conditioned one and a conventional, are now available. Irradiation protocols for in vitro experiments are now established and demonstrated by obtaining a relative biological effectiveness (RBE) of cell inactivation measured to be 3.54 with 10% survival dose (D₁₀).     

Study of a neutron radiography system using Cf neutron source

This paper presents a study about moderation and collimation of a neutron radiography system using ²⁵²Cf. A Monte Carlo Code, MCNP4B, has been used to obtain a maximum and more homogeneous thermal neutron flux in the collimator outlet next to the image plane. Among the various moderator materials investigated, high density polyethylene proved to be the most efficient, with a thermalization factor of 56 cm². Using a collimator design assembly it was possible to obtain a normalized thermal neutron flux, at the image plane of 6×10⁻⁶ n cm⁻² s⁻¹ at an effective collimator ratio of 7.5, or 3.2×10⁻⁷ n cm⁻² s⁻¹ at an effective collimator ratio of 50.     

A new type rechargeable lithium battery based on a Cu-cathode

In present work, we report a new type rechargeable lithium battery, in which a Cu-cathode in aqueous electrolyte and a Li-anode in non-aqueous electrolyte are united together by a lithium super-ionic conductor glass film (LISICON) through which only lithium-ions can pass. During the charge–discharge process, combining with the dissolution–deposition of metallic Cu (or Li) electrode, lithium ions transfer between aqueous electrolyte solution and non-aqueous electrolyte solution. In Li–Cu system, for the first time, the dissolution/deposition process of metallic Cu was used as cathode reaction to replace the Li-insertion/extraction reaction within conventional lithium-ion battery. The Cu-cathode is renewable, and displays a high capacity. The concept of Li–Cu system may provide a new direction for future lithium batteries study.     

A neutron diffraction study of the d and d lithium garnets Li3Nd3W2O12 and Li5La3Sb2O12

The garnets Li₃Nd₃W₂O₁₂ and Li₅La₃Sb₂O₁₂ have been prepared by heating the component oxides and hydroxides in air at temperatures up to 950 °C. Neutron powder diffraction has been used to examine the lithium distribution in these phases. Both compounds crystallise in the space group with lattice parameters a=12.46869(9) Å (Li₃Nd₃W₂O₁₂) and a=12.8518(3) Å (Li₅La₃Sb₂O₁₂). Li₃Nd₃W₂O₁₂ contains lithium on a filled, tetrahedrally coordinated 24d site that is occupied in the conventional garnet structure. Li₅La₃Sb₂O₁₂ contains partial occupation of lithium over two crystallographic sites. The conventional tetrahedrally coordinated 24d site is 79.3(8)% occupied. The remaining lithium is found in oxide octahedra which are linked via a shared face to the tetrahedron. This lithium shows positional disorder and is split over two positions within the octahedron and occupies 43.6(4)% of the octahedra. Comparison of these compounds with related d⁰ and d¹⁰ phases shows that replacement of a d⁰ cation with d¹⁰ cation of the same charge leads to an increase in the lattice parameter due to polarisation effects.     

MOSFET with a boron-loaded gate as a low-energy neutron dosimeter

A MOSFET-based low-energy neutron dosimeter has been fabricated using a ¹⁰B loaded gate electrode as (n,α) converter. The response to thermal neutrons has been studied.     

Simulating the introduction of a sapphire crystal into an epithermal neutron beamline

The epithermal beamline at the Portuguese Research Reactor is being optimized for Prompt Gamma Neutron Activation Analysis (PGNAA). One of the major changes is to thermalise the beam by the introduction of a sapphire crystal into the beamline. Placing the sapphire at the exit of the beamline would greatly reduce the alterations and work necessary to the port and make the crystal easily removable. However, the scattered neutrons from the sapphire would increase both the neutron-induced detector damage and the background radiation. MCNPX was used to simulate the crystal in the beam port and at the exit of the port.     

Uses of neutron and X-ray beams to investigate magnetism

Experimental techniques using beams of neutrons and X-ray have more than proved their worth in studies of magnetism. Their similarities and differences will be discussed, and illustrated with reference to recent experimental studies of surface and bulk magnetism.     

Monitoring of gamma emission and neutron transmission during boron neutron capture treatment delivery

The ability to map boron and hydrogen distributions in the body is paramount to the success of boron neutron capture therapy (BNCT). We investigated treatment-time quantitative mapping of these distributions by detecting (i) 0.48 MeV de-excitation photons from neutron capture by boron-10; (ii) 2.22 MeV photons from neutron capture by hydrogen; and (iii) transmitted neutrons. Monte Carlo simulations reported no detectable difference when ¹⁰B in tumour was varied from 0 to 50 ppm, and when the tumour size was varied from 0.0 to 9.5 cm³.     

A neutron inelastic scattering investigation of the diffusion kinetics of H2O molecules and hydration complexes in concentrated ionic solutions

Intermolecular frequencies of H₂O's and the diffusion kinetics have been investigated by neutron inelastic scattering for concentrated ionic solutions containing small and/or multiply charged cations (e.g., Cr⁺³, Mg⁺², Ca⁺², and Li⁺¹). As higher concentrations are approached such that the majority of H₂O's are in hydration layers, their exchange time can exceed the neutron interaction time. Then the diffusion kinetics depart functionally from activated reorientations of individual H₂O's characteristic of lower concentrations and evolve to continuous diffusion processes of hydration complexes characterized by small self-diffusion coefficients. The general features of the observed evolution in the functionality of the diffusion kinetics are found to be functionally consistent with an approximate model which includes contributions from the delayed diffusional exchange of individual H₂O's as well as the continuous diffusion of hydrated ions. At a given concentration, the temperature interval over which this evolution in functionality occurs increases both with increasing strength of the primary cation-H₂O coordination and with anion basicity. Further, as the temperature decreases, frequencies of defined cation-water hydration complexes gradually sharpen in a continuous manner, showing no abrupt variations at glass transitions. Anions of increasing basicity decrease the self-diffusion coefficients of the ion-water complexes and perturbed frequencies characteristic of cation-water hydration complexes. Such anion effects, at high concentrations, correspond to an increasing degree of time-average indirect or direct ion pairing with increasing anion basicity. This results, in turn, both in a distortion or partial disruption of the cation hydration sheaths and in a degree of coupling and/or bridging between anions and hydrated cations so as to increase the effective masses and friction coefficients associated with their diffusional motions.     

Development of a threshold positron spectrometer

We introduce a new positron spectroscopy experimental technique that we call threshold positron spectroscopy, by analogy with its similar threshold photoelectron spectroscopy. An apparatus that is being developed to explore this technique is described in this work.     

Structural and dynamic single chain behaviour in a binary blend of low molecular mass poly(siloxanes) as studied by small angle neutron scattering and neutron spin echo spectroscopy

Elastic and quasi elastic neutron scattering investigations, using the small angle neutron scattering (SANS) and neutron spin echo (NSE) techniques, respectively, were performed in order to study the static and dynamic single chain behaviour in a binary blend of low molecular mass deuterated poly(dimethylsiloxane) (d-PDMS) and protonated poly(ethylmethylsiloxane) (p-PEMS) at the critical composition _c. Since the single chain observation requires that only a small amount of one of both components is labelled, the d-PDMS/p-PEMS system was modified in such a way that the major part of the protonated PEMS component was replaced by the corresponding deuterated material. Although the de-mixing of the PEMS isotopes occurs far below the de-mixing of the PDMS/PEMS system the resulting chemically binary d-PDMS/d-PEMS/p-PEMS blend with the volume composition 0.5/0.425/0.075 is strictly speaking a ternary system. This complication had to be taken into account, in particular with respect to the correct evaluation of the SANS data.The careful analysis of the SANS curves allows one to determine all three thermodynamic interaction parameters with reasonable reliability and gives evidence that the radii of gyration agree with those, which were determined in corresponding isotopic PDMS and PEMS blends. This is in contrast to the observation on real binary PDMS/PEMS blends at _c, where the collective conformational properties exhibit a considerable chain expansion. The NSE data of the ternary system follow completely the predictions of the Rouse model, which describes the dynamics of a dense low molecular mass polymeric system in a single chain approximation. The experimental observations are also in contrast to the results of former NSE measurements on binary PDMS/PEMS blends, where a transition from Rouse behaviour at short times to a much weaker relaxation at longer times became obvious.The results of the static and dynamic single chain behaviour presented here confirm the results of a computer simulation on a low molecular mass binary blend at the critical concentration, where explicitly the pure single chain behaviour was probed and no indications for chain expansion and deviations from the Rouse dynamics were found.Dedicated to Prof. Dr. Erhard W. Fischer on the occasion of the 75th anniversary of his birthday.     

Synthesis, structural characterization and Li ion conductivity of a new vanado-molybdate phase, LiMg3VMo2O12

A new vanado-molybdate LiMg₃VMo₂O₁₂ has been synthesized, the crystal structure determined an ionic conductivity measured. The solid solution Li_2−zMg_2+zV_zMo_3−zO₁₂ was investigated and the structures of the z=0.5 and 1.0 compositions were refined by Rietveld analysis of powder X-ray (XRD) and powder neutron diffraction (ND) data. The structures were refined in the orthorhombic space group Pnma with a∼5.10, b∼10.4 and c∼17.6 Å, and are isostructural with the previously reported double molybdates Li₂M₂(MoO₄)₃ (M=M²⁺, z=0). The structures comprise of two unique (Li/Mg)O₆ octahedra, (Li/Mg)O₆ trigonal prisms and two unique (Mo/V)O₄ tetrahedra. A well-defined 1:3 ratio of Li⁺:Mg²⁺ is observed in octahedral chains for LiMg₃VMo₂O₁₂. Li⁺ preferentially occupies trigonal prisms and Mg²⁺ favours octahedral sheets. Excess V⁵⁺ adjacent to the octahedral sheets may indicate short-range order. Ionic conductivity measured by impedance spectroscopy (IS) and differential scanning calorimetry (DSC) measurements show the presence of a phase transition, at 500-600 °C, depending on x. A decrease in activation energy for Li⁺ ion conductivity occurs at the phase transition and the high temperature structure is a good Li⁺ ion conductor, with σ=1×10⁻³-4×10⁻² S cm⁻¹ and E_a=0.6 to 0.8 eV.     

Development of a miniature simultaneous MPT spectrometer

An unique miniature simultaneous microwave plasma torch (MPT) atomic emission spectrometer employing linear UV intensified charge-coupled device (ICCD) array detector has been developed and studied preliminarily. The detection limits and precisions of the spectrometer for Ag, Al, Ba, Ca, Cr, Cu, Fe, Mg, Mn, Sr and V by using different CCD exposure times have been determined. An analysis of a practical sample has been carried out. The preliminary results demonstrate that such simultaneous spectrometer has advantages of saving sample and time, especially suitable for use as detector for chromatography and in combination with flow injection systems. Taking analytical figures of merit and portability into accounts, the miniature simultaneous MPT system will have extended application areas and greater competition potential as compared with commercialized scanning MPT spectrometers.     

Development of a palm portable mass spectrometer

A palm portable mass spectrometer (PPMS) has been developed with a weight of 1. 48 kg (3 lb) and a size of 1.54 L (8.2 × 7.7 × 24.5 cm³) that can be operated with an average battery power of 5 W. A miniaturized ion trap has been used as a mass analyzer that consists of four parallel disks with coaxial holes. A rf voltage of 1500 V _p-p at 3.9 MHz has been used for scanning ion mass of up to m/z 300. An ion-getter pump serves for high vacuum of the PPMS. Sample gas was introduced in pulse mode. An embedded microcomputer has been developed for system control. Detection of organic gases diluted in the air has been demonstrated up to 6 ppm for toluene and 22 ppm for dimethyl methylphosphonate (DMMP). Performance results suggest usefulness of the PPMS as a personal mobile device for detection/identification of chemical warfare agents in the field.