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Volume 10, No. 2, 2017, 1438 H

 Arabic Articles

 

 

Dark Matter: Its Origins and Chapters

In this article, I present an extensive review of the hypothesis of dark matter, starting with the basic observations which provoked the assumption of invisible matter in galaxies and galaxy clusters. Then, I go through the development of the concept of dark matter in cosmology, where the analysis of the fluctuations of the Cosmic Microwave Background Radiation (CMBR) show the necessity of an excess of matter in the universe much more than the observed matter. Dark matter is thought to be non-baryonic, interacting only through gravitational effects which can be tested by gravitational lensing and other means. Investigating the motion of galaxies, specifically the rotation curves, showed that some sizable amount of dark matter might exist mostly in the galactic halo. For this reason, astrophysicists suggested that dark matter might be composed of invisible Massive Astrophysical Compact Halo Objects (MACHO) like black holes, neutron stars, white dwarfs and brown dwarfs. However, astronomical surveys of the sky showed less than 20% of the amount needed to cover the deficit in the mass of the universe. Cosmological observations of the accelerated expansion of the universe suggested that the missing mass in the composition of the universe might be subdivided into dark matter and dark energy. Analysis of the fluctuations of the cosmic microwave background radiation suggests that the amount of dark matter is about 26.8% of the mass of the whole universe and the dark energy should be about 68.3%. The remaining amount which is just about 4.9% is the observable matter.  ...

 

M. B. Altaie

JJP, 2017, 10(2) ,  59-83

Energy Analysis Power of the Nuclear Track Detector PM-355  for Alpha Particles

When a heavy charged particle passes through matter, it loses energy principally by scattering electrons within the matter it passes through it and will cause extensive ionization of the material through ionizing the atoms or molecules close to its path. Thus, the charged particle gradually loses its energy and is subjected to a gradual slowing down that could make it stop at the end of the path within the medium. The average energy loss of the particle per unit path length (dE/dx) is called the linear stopping power (S), which may be measured in units of MeV/cm or similar. The stopping power and hence, the density of ionization, usually increases toward the end of the range of the particle and reaches a maximum, the Bragg edge, shortly before the energy drops to zero. The curve that describes this is called the Bragg curve. The ionization processes can be treated statistically to derive the equation of stopping power, the best known being the Bethe formula. ...

 

S. H. S. Al-Nia'emi  and M. M. S. Al-Jobouri

JJP, 2017, 10(2) , 85-95

Bulk Etch Rate of CR-39 Detector Using NaOH/Ethanol Etchant

The science of solid-state nuclear track detectors was born in 1958.Operation of the solid-state nuclear track detector is based on the fact that a heavy charged particle will cause extensive ionization of the material when it passes through a medium. The bulk etch rate VB is the rate of removal of the undamaged surface of the detector. Due to the chemical reaction between the etching solution (etchant) and the detector material, some molecules of the detector material are removed. The final effect is the removal of the material from the detector surface. During etching, the material is removed layer by layer and the thickness of the detector becomes smaller and smaller.  The aqueous solutions of NaOH or KOH are the most frequently used chemical solutions in this regard. ...

 

Y. Y. Kasim

JJP, 2017, 10(2) , 97-103

Effect of Etching Solution Concentration on Track Diameter Development in CR-39 Nuclear Track Detector

In this work, two empirical relations related to the track diameter development of alpha particle tracks in CR-39 detectors and to the detector bulk etch rate  as a function of  concentration of etching solution are suggested and tested. The first empirical equation is a further extension of the equation suggested in reference [13] to accommodate the relation of the track diameter to both etching time and concentration effects. The second equation describes the bulk etch rate as a function of concentration of etching solution. The bulk etch rate is determined by the measurement of the removed layer method. In the process of developing these two equations, tracks formed on CR-39 track detector by 3 MeV alpha particles are etched at four NaOH etching solution concentrations of 4, 6, 8, and 10 N. The etching solution temperature is kept constant at 70 oC. Digital image processing method for diameter and detector thickness measurements is used. The study of track sensitivity measurements resulted is estimating that the optimum etching solution concentration is 6 N at 70 oC. ... 

 

Mushtaq Abed Dawood Al-Jubbori

 

JJP, 2017, 10(2) , 105-112