Browsing by Subject "heavy ions"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Dependence of cross sections for multi-electron loss by 6 mev/amu xe18+ ions on target atomic number(Texas A&M University, 2004-09-30) Peng, YongIt has been proposed to use heavy ion beams with energies around 10 MeV/amu, masses around 200, and average charges of 1+ as a driver for inertial fusion reactor. Current designs require the beams to travel through a region where the background gas pressure is several milli-torr. Thus, it is important to assess the rate at which the charge state of an incident beam evolves while passing through the background gas. The first objective of this project is to study the dependence of cross sections for multi-electron loss on target atomic number by using 6 MeV/amu Xe18+ ions and to compare the results with the n-body Classical Trajectory Monte Carlo calculations. A secondary objective of this project is to determine the extent to which the cross sections for molecular targets can be represented as sum of the cross sections for their atomic constituents. Cross sections for loss of one through eight electrons from 6 MeV/amu Xe18+ in single collisions have been measured with noble gas targets. The target Z-dependence of the total loss cross section was found to be well represented by two straight line segments. The cross section for He and Ne define one straight line segment and those for Ar, Kr and Xe define the other, where exhibits a smaller slope. The predictions of n-CTMC calculations are in good agreement with the measured total electron loss cross sections. A semiempirical fitting procedure based on the independent electron approximation provided a reasonably good representation of the individual cross sections for all of the noble gas targets. Additional measurements performed with a variety of molecular targets provided a rigorous test of cross section additivity and showed that the additivity rule works well for electron loss from heavy ions in the present energy and charge regime. A semiempirical calculation based the IEA shows that the average most probable impact parameter for electron loss is much smaller than the target molecular bond length. This result is believed to account for the finding of the insensitivity of the electron loss cross section to molecular structure.Item THE EVOLUTION OF OXYGEN AND IRON FLUENCE DURING SOLAR PARTICLE EVENTS AND THEIR CONTRIBUTION TO SKIN DOSE FOR EVENTS FROM OCTOBER 1997 TO DECEMBER 2005(2010-01-16) Hill, MarcusOne of the primary concerns with space travel is the protection of astronauts from potentially lethal radiation. A major source of potentially lethal radiation is our own sun. During Solar Cycle 23 there were 97 detected Solar Particle Events (SPEs). In order to develop radiation protection guidelines and establish methods to protect astronauts the spectrum of particles emitted during a SPE must be understood. Data for oxygen and iron particle fluence was taken from the Solar Isotope Spectrometer. The fluence was sorted and formatted for each solar particle event. After determining the contribution to skin dose for oxygen, the time evolution of each event was analyzed. After analyzing the raw count data, a threshold was set that could be applied to each event. Using this threshold count rate as the starting point, each event was plotted and fitted with a smoothing polynomial function. The slope calculated from this function was then plotted against the previously calculated skin dose and a Weibull function was fitted to the data. The resulting plot provides a method to predict the cumulative dose due to the oxygen fluence over the first 24 hours of an event and thereby provide a warning of future high dose rate in time to achieve significant dose sparing for most events. For the ten events that delivered the highest oxygen dose, the dose sparing that could be achieved by taking shelter when the high dose rate was predicted was greater than 70 percent for all but one event. The one outlier achieved a dose paring of only 57 percent.