Energy absorption buildup factors for thermoluminescent dosimetric materials and their tissue equivalence

Gamma ray energy-absorption buildup factors were computed using the five-parameter geometric progression (G-P) fitting formula for seven thermoluminescent dosimetric (TLD) materials in the energy range 0.015–15 MeV, and for penetration depths up to 40 mfp (mean free path). The generated energy-absorption buildup factor data have been studied as a function of penetration depth and incident photon energy. Buildup factors determined in the present work should be useful in radiation dosimetry, diagnostics and therapy. The tissue equivalence of TLD materials is also discussed.     

Simple Zeros of the Riemann Zeta-Function

Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26.     

Simultaneous presence of static and dynamic component in the fluorescence quenching of Bis-MSB by CCl4 and aniline

The fluorescence quenching of 1, 4-bis[2-(2-methylphenyl)ethenyl]-benzene (Bis-MSB) in toluene has been studied with carbon tetrachloride (CCl₄) and aniline by steady-state and transient methods. A positive deviation was observed in the Stern-Volmer (S-V) plot for both the quenchers. This indicates the presence of either static or transient quenching component in the overall dynamic quenching. The experimental data are analysed by sphere of action static quenching model. The value of radius of sphere of action determined from this model is greater than the sum of the radii of the Bis-MSB and respective quenchers. From the studies of temperature dependence of rate parameters and lifetime measurements, it could be explained that the positive deviation is due to the presence of a small static quenching component in the overall dynamic quenching. This fact suggests the simultaneous presence of static and dynamic component in the fluorescence quenching Bis-MSB by CCl₄ and aniline.     

Quantum Zeno and anti-Zeno paradoxes

Continuous observation of a time independent projection operator is known to prevent change of state (the quantum Zeno paradox). We discuss the recent result that generic continuous measurement of time dependent projection operators will in fact ensure change of state: an anti-Zeno paradox.     

粉粒体两相流的电容层析成象测量

粉粒体系统中的固相浓度分布的在线测量是十分困难的问题．电容层析成象技术是一种近年来发展起来的非侵入式快速浓度场测量技术．它不干扰流场，不受流动中颗粒浓度、加速度、不透明等因素的制约．本文讨论其测量原理、应用、近期进展、存在的主要问题及其解决的对策．     

An unique method of determining the excitation energy migration coefficient in organic liquid scintillators

An experimental method is described to determine the excitation energy migration coefficient Λ in an organic liquid scintillator by measuring the energy transfer rate parameterk ₃ and the quenching rate parameterk _7b as a function of temperature in the range of 20°C–70°C. In this experiment we have used toluene as donor, ethyl-1-n-butyl-2-methyl-5-hydroxyindole-3-carboxylate (EBMHC) as acceptor and bromobenzene as quencher. The values of Λ are found to be in good agreement with literature values. Hence this method can be used to determine the migration coefficient in organic liquid scintillators.     

ac Conductivity of mixed spinel NiAl0.7Cr0.7Fe0.6O4

ac Conductivity measurements are carried out across the metal to insulator transition in NiAl_0.7Cr_0.7Fe_0.6O₄. The low frequency data is analyzed using Summerfield scaling theory for hopping conductivity. The exponent of the scaling behavior has significantly different values in the conducting and insulating regimes. The hopping frequency and the zero frequency conductivity are found to increase with temperature, slowly in the metallic regime and rapidly in the insulating regime.