Production of exotic nuclei in peripheral nucleus-nucleus collisions below 10 A MeV

Experimental data from the literature concerning nucleus-nucleus collisions at beam energies of few A MeV above the Coulomb barrier are investigated in this work with emphasis on projectile-like fragment distributions. In peripheral collisions at beam energies below 10 A MeV, deep-inelastic transfer is shown to be the dominant reaction mechanism. In addition, the mechanism may involve an extension of the nuclear profile in the window (neck) region, observed primarily in reactions with very heavy target nuclei. Isoscaling observed at these energies can be used as a tool to predict the production rates of exotic nuclei in reactions induced by exotic secondary beams.     

Mass distribution in the bremsstrahlung-induced fission of Th,U and Pu

The yields of various fission products in the 10 MeV bremsstrahlung-induced fission of ²³²Th, ²³⁸U and ²⁴⁰Pu were determined using a recoil catcher and off-line γ-ray spectrometric techniques. From the yield data, mass yield distributions were obtained using charge distribution corrections. The higher yields of fission products around mass numbers 133–135, 138–140, 143–145 and their complementary products in the neutron and bremsstrahlung-induced fission of ²³²Th, ²³⁸U and ²⁴⁰Pu were interpreted based on nuclear structure effects. From the mass yield distribution, the peak-to-valley (P/V$P/V$) ratio was also obtained for the above fissioning systems. The present data, along with data from the literature on different bremsstrahlung- and mono-energetic neutron-induced fissions of ²³²Th and ²³⁸U are interpreted to examine the influence of excitation energy on the peak to valley ratio. For the same compound nucleus ²⁴⁰Pu^?, the data in the 10–30 MeV bremsstrahlung-induced fission of ²⁴⁰Pu were compared with similar data of thermal to 14 MeV neutron-induced fission of ²³⁹Pu and the spontaneous fission of ²⁴⁰Pu to examine the role of excitation energy due to bremsstrahlung radiation and mono-energetic neutrons.     

Wavelength-Dependent Photolysis of C3-C7 Aldehydes in the 280–330 nm Region

This article reviews the work over the past few years on the photolysis of propionaldehyde, n-butyraldehyde, n-pentanal, n-hexanal, and n-heptanal in the 280–330 nm region, obtained by combining laser photolysis with cavity ring-down spectroscopy. Absorption cross-sections of these aldehydes were measured. The HCO radical was observed as a photodissociation product. The HCO quantum yield was determined as a function of photolysis wavelength, aldehyde pressure, and nitrogen buffer-gas pressure. A scheme to group aldehydes according to similarity in photochemistry was proposed.     

MOLECULAR STRUCTURE AND PHOTOPHYSICS OF N-QUATERNARY DIARYLOXAZOLIUM SALTS

ABSTRACT

The concern of this work is to study molecular structure, electronic absorption and emission spectra of several N-quaternary salts of the well-known diaryloxazole scintillating compounds: 2,5-diphenyloxazole, para-, meta- and ortho- isomers of bis-2-(5-phenyl-oxazolyl)-benzene (POPOP). All of them were obtained from the initial aryloxazoles by their methylation with dimethylsulfate.

We found, that N-methylation manifests itself in arising of sterical hindrance in the molecules of diaryloxazolium salts, which results in distortion of their planarity. On the contrary to the ground state, the investigated molecules become more planar in their lowest singlet excited state. As a result of such an excited state flattening, fluorescence Stokes shifts values of the diaryloxazolium salts exceed 9000–10,000 cm^?1. The excited state flattening rate constants, estimated for the studied oxazolium compounds, are of the 10¹⁰ s^?1 range. No considerable increase of radiationless losses, induced by the excited state structural relaxation, was found. Owing to these facts, N-quaternary diaryloxazolium salts may be considered as effective abnormally high Stokes shift organic luminophores.     

Re-specification of Affine Term Structure Models: The Linkage to Empirical Investigations

Abstract

This paper specifies the dynamic and cross-sectional behaviour of bonds in the framework of the general affine term structure model (ATSM) of Duffie and Kan (1996, A yield-factor model of interest rate. Mathematical Finance, 6, 379–406). We present the calibrations of ATSM, with the numerics fitting in with the actual data under the physical probability measure. Without assumptions and restrictions on any specific physical process of the factors, we find theoretical loads by solving Riccati equations with parameters chosen for the solution to match those from the principal component models. The general condition on the boundary is satisfied; so, the Black-Scholes equation admits a unique solution, which supports the Condition of Duffie and Kan.     

飞秒激光中高能质子的产生与加速的研究

为了探索飞秒激光与固体靶相互作用中高能质子的产生和加速机制,在超短超强激光装置“SILEX-I”上进行了飞秒激光与平面固体薄膜Cu靶的相互作用中高能质子空间分布、能谱和产额的实验研究。实验采用固体核径迹探测器CR39和Thomson离子谱仪相结合的方式,在固体靶背表面法线方向测量了质子空间分布、能谱和产额。实验结果表明：质子沿着靶背法线方向发射,质子空间分布呈圆环状,存在一定的立体角;质子在一定能量处出现截断;截断能量的大小与靶厚度有关。经分析,高能离子的产生和加速是多种作用机制共同作用的结果,其中静电场中的TNSA加速机制则占主导地位。     

Annealing of radiation damage in graphite

Abstract

The electronic stopping of heavy ions with 7 ≤ Z, ≤ 54 in low-index directions of thin gold single crystals is measured in the energy range 200 keV ≤ E ≤ 1100 keV. Large oscillations in electronic stopping power are observed for constant ion velocity. The stopping powers of different low-index directions are compared.     

Mass Spectrum of Naturally Abundant Ethyldigermane

A complete mass spectral fragmentation pattern of naturally abundant ethyldigermane is presented. The base peak occurs at m/e 148 in the Ge₂H_×=0←5 ⁺ region and not in the parent region. Three metastable peaks are observed at m/e 52.70, m/e 59.36, and m/e 125.63 respectively.