Oscillatory flows of second grade fluid in a porous space

The exact analytical solutions are developed for the magnetohydrodynamic (MHD) flows of the second grade fluid in a porous medium. The analysis is performed using modified Darcy’s law and takes into account the effect of the Hall current. Closed form solutions are given for three problems using the Fourier sine transform. Comparison has been made with the existing results and are found to be in excellent agreement. The graphs are plotted for various emerging parameters and discussed.     

Thermal neutron induced α-particle reaction on64, 65, 67Zn and77Se

The (_n th,α) reaction spectroscopy was done on^{64, 65, 67}zn and⁷⁷Se at the 87 m curved thermal neutron guide of the Grenoble high flux reactor. In each of the⁶⁴Zn(n, α)⁶¹ Ni and⁶⁷ Ni(n, α) ⁶⁴Ni reactions, one line showed up corresponding to anα-particle transition to the first excited state in⁶¹Ni and⁶⁴Ni withσ _α1=11±3 μb and 159±20 μb respectively. In the case of the radioactive⁶⁵Zn(T _1/2=244d) nucleus, two lines showed up corresponding to the ground state and the first excited state transitions in⁶²Ni with large values ofσ _α0=1.0±0.1b andσ _α1=1.0±0.1b. For the⁷⁷Se(n, α)⁷⁴Ge reaction, the ground state and first excited transitions were present withσ _α0=940±20 μb andσ _α1 = 30±5 μb respectively. The spin-parity (J ^π) of the neutron resonance contributing at thermal energy are discussed.     

Hawking radiation and strong gravity black holes

We show that the strong gravity theory of Salam et al. places severe restrictions on black hole evaporation. Two major implications are that: mini black holes (down to masses ～ 10^?16 kg) would be stable in the present epoch; and that some suggested mini black hole mechanisms to explain certain astrophysical phenomena would not work. The first result implies that f-gravity appears to make black holes much safer by removing the possibility of extremely violent black hole explosions suggested by Hawking.     

Observation of proton emission following thermal neutron capture in 34.5 d 84Rb

Using a target prepared by on-line isotope separation, thermal neutron capture in ⁸⁴Rb (I^π = 2^?) has been shown to induce proton emission to the ground state (0⁺) and first excited state (2⁺) of ⁸⁴Kr. The branching ratio was measured as $\text{Γ}{}_{\mathrm{<mtext>p</mtext>}}\text{(0}{}^{\mathrm{+}}\text{)}\text{Γ}{}_{\mathrm{<mtext>p</mtext>}}\text{(2}{}^{\mathrm{+}}\text{)}\text{= 4.7 ± 0.7}$, favouring a $\text{3}\text{2}{}^{\mathrm{?}}$ assignment of the capturing state without excluding $\text{5}\text{2}{}^{\mathrm{?}}$, and the (n_th, p) cross section as 12 ± 2 b. The energy available for the process was determined to be 3.45 ± 0.01 MeV, in agreement with other mass data in the region.     

The thermal neutron induced fission cross section of 232Th

The thermal neutron induced fission cross section of ²³²Th was measured using the highly pure thermal neutron beam from the 87 m curved neutron guide at the High Flux Reactor of the ILL (Grenoble). An upper limit of 4 μb was obtained for the fission cross section, which is an order of magnitude smaller than previous results. This result is discussed in terms of the double-humped fission barrier theory.     

The Pn values of the 235U(nth, f) produced precursors in the mass chains 90, 91, 93–95, 99, 134 and 137–139

The first results are reported on the P_n values obtained with the recoil focussing parabolatype mass separator for unslowed fission products Lohengrin installed at the Grenoble high flux reactor. The mass chains studied were 90, 91, 93, 94, 95, 99, 134, 137, 138 and 139. Both the neutron and the β activities were measured simultaneously. The technique used to measure the neutron and the β activities and the method of analyzing the experimental data are discussed in detail. The present work led to: (i) three new periods corresponding to the new isotopes of selenium (${}^{91}\text{Se}\text{, T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 0.27±0.05}\text{sec}$), strontium (⁹⁹Sr, 0.6±0.2 sec) and telurium (¹³⁸Te, 1.3±0.3 sec); (ii) accurate periods of ${}^{99}\text{Y}\text{(T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 1.45±0.22}\text{sec}\text{)}\text{and}{}^{134}\text{Sn}\text{(0.7±0.2}\text{sec}\text{)}$; (iii) four new delayed neutron precursors consisting of ⁹¹Se, ⁹⁴Kr, ⁹⁹Sr and ¹³⁸Te; (iv) six new P_n values corresponding to the precursors ${}^{91}\text{Se}\text{(P}{}_{\mathrm{<mtext>n</mtext>}}\text{= (21±10)\%),}{}^{94}\text{Kr}\text{((5.7±2.2)\%),}{}^{99}\text{Sr}\text{((3.4±2.4)\%),}{}^{99}\text{Y}\text{((1.2±0.8)\%),}{}^{134}\text{Sn}\text{((17±13)\%)}\text{and}{}^{138}\text{Te}\text{((6.3±2.1)\%)}$; (v) a precise P_n value of the precursor ¹³⁷Te ((2.5±0.5)%); (vi) a redetermination of the P_n values of the precursors ^{90, 91}Br, ⁹³Kr, ^{93, 94, 95}Rb and ^{137, 138, 139}I. The results of this work are discussed and compared with the existing data. The low level sensitivity of the present detection system is determined to be $\text{P}{}_{\mathrm{<mtext>n</mtext>}}\text{(m)Y}{}_{\mathrm{q}}\text{(m) ? 0.4 × 10}{}^{\mathrm{?6}}\text{n}\text{/}\text{f}$ (where Y_q(m) is the cumulative yield for the mass m and the ionic charge q).     

Fission fragment yield distributions as a function of their excitation energies for 235U(nth, f)

The recent ²³⁵U(n_th, f) data taken at the Grenoble high flux reactor have been reanalysed to determine the fragment mass distributions as a function of their excitation energies $\text{E}{}^1$. The mass distributions for low $\text{E}{}^1$ values show the known fine structures. However, the distributions for $\text{E}{}^1\text{> 30}\text{MeV}$ do not show the fine structure reported by Newson. Beyond $\text{E}{}^1\text{≈ 35}\text{MeV}$, the most probable masses of distributions decrease monotonously as $\text{E}{}^1$ goes up.