Nonlinear dynamical magnetosonic wave interactions and collisions in magnetized plasma

The one-dimensional nonlinear dynamical wave interactions in a system of quasineutral two-fluid plasma in a constant magnetic field are investigated.The existence of the travelling wave solutions is discussed.The modulation stability of linear waves and the modulation instability of weakly nonlinear waves are presented.Both suggest that the Korteweg-de Vries(KdV)system is modulationally stable.Besides,the wave interactions including the periodic wave interaction and the solitary wave interaction are captured and presented.It is shown that these interacting waves alternately exchange their energy during propagation.The Fourier spectrum analysis is used to depict the energy transformation between the primary and harmonic waves.It is known that the wave interactions in magnetized plasma play an important role in various processes of heating and energy transportation in space and astrophysical plasma.However,few researchers have considered such magnetohydrodynamic(MHD)wave interactions in plasma.It is expected that this work can provide additional insight into understanding of behaviors of MHD wave interactions.

Optimization of Am-Be millicuries neutron source in a small volume cylindrical water tank for NAA

Background The neutron activation analysis(NAA)is a very powerful method for multi-element analysis of samples.NAA technique needs to be developed for low neutron flux in millicuries using the 241Am-Be neutron source.Aims To optimize sample and neutron source geometry for maximumγ-ray yield for neutron activation analysis.Method Gamma ray neutron activation analysis(NAA)has been set up where a 50-millicurie Am-Be neutron source is available.In this experimental setup,the neutron source is placed at the center of a cylindrical water tank of 40 x 40 cm in xyz plan,and thermal neutrons are produced at a distance of 1.2 cm from the source.The system is used for the activation analysis of sodium carbonate,sodium chloride and copper with the gamma ray emissions of 1.37,1.73,2.25 and 2.76 MeV for 24Na and 0.511 MeV for 64Cu having half lives of 15 hrs and 12.9 hrs,respectively.The thermal neutron activation analysis has been demonstrated by placing the samples at about 1.2 cm from the neutron source.HPGe and 3x3 inch NaI(Tl)gamma ray spectrometers have been used for the gamma ray spectrometry of these activated samples with the use of a Marinelli beaker.The geometry of the sample with respect to the neutron source has been optimized for the maximumγ-ray yield in NAA.Conclusion The geometry of the sample with respect to the neutron source has been optimized for the maximumγ-ray yield in NAA.The increase in gamma ray flux distribution in the medium of water,due to the neutron source inside the tank,has been observed by a GM detector which is due to the production of short-lived 16N on activation of 16O in water.This system can also be used for promptγ-ray analysis.