Browsing by Subject "Ar"
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Item Explosion dynamics of van der Waals clusters using 38 nm XUV laser pulses(2016-08) Helal, Ahmed Mohammed; Ditmire, Todd; Keto, John W.; Bengtson, Roger D; Downer, Michael; Ben-Yakar, AdelaThe interaction of intense XUV laser pulses with matter and rare gas cluster has been the focus of the scientific c community for decades. This focus has been sparked by the ongoing efforts to reach microscopy with atomic resolution, leading to a time resolved image on the scale of the atomic motion. The interest in van der Waals clusters appears due to it's similarity with the small bio-molecules, studying the behavior of these cluster will shed some light on how the biomolecules behavior under intense laser pulse. We have conducted a major upgrade to the UT THOR laser system, that enables us to achieve 17.7 nJ of XUV energy, produced by high harmonic generation, which is used to conduct multiple cluster experiments. We investigated the dynamics of rare-gas clusters produced by Ar and Xe gases, the ion time of flight, kinetic energy and electron energy have been measured, the generation of ion kinetic energy of two di different temperatures (6 and 55 eV) due to hydrodynamic expansion was observed. viii For Xe clusters, we observed the generation of unexplained high charge states up to Xe^9+, that could be due to the effect of continuum lowering and inner ionization of the giant resonance 4d-level. We also investigated the dynamics of small molecule clusters. Stating with nitrogen clusters, we noticed a dependence of the ionization ratio between N+ 2 and N+on the cluster size has been noticed. In addition to that nitrogen clusters shows the highest ion kinetic energy generated between all the clusters investigated in this dissertation. The interaction of XUV laser pulses with Methane cluster is studied, we could not detect any high charges of methane fragments such as (CH2+ 4 ). However, we noticed that we generated multiple fragments by breaking C-H bonds (CH+3 ;CH+ 2 ;CH+) in addition to bare carbon with high cluster sizes. The generation of CH+5 , H+ and H+2 was also observed. Studying the partial yield of each of these reveals that the correlation between CH+ 5 and H+ is opposite to what is expected, which might be due to the change of the cluster properties or the expansion dynamic itself (towards more hydrodynamics).Item Radioargon production at The University of Texas at Austin(2012-08) Egnatuk, Christine Marie; Biegalski, Steven R.; Landsberger, Sheldon; Biegalski, Kendra M.; Friese, Judah; Schneider, ErichThe interest in the detection of radioargon isotopes--³⁷Ar, ³⁹Ar, and ⁴²Ar--is increasing important for on-site inspections within the Comprehensive Nuclear-Test-Ban Treaty verification regime. In an underground nuclear explosion ³⁷Ar is produced by ⁴⁰Ca(n,[alpha])³⁷Ar reaction in surrounding soil and rock. With a half-life of 35 days, ³⁷Ar provides a signal useful for confirming the location of an underground nuclear event. The development of detector systems is underway. This work produced radioargon isotopes by three methods for the development and testing of radioargon detection systems. The irradiation of argon gas at natural enrichment in the 3L facility within the Mark II TRIGA reactor facility at The University of Texas at Austin provides a source of ³⁷Ar for the calibration of the ULBPC in development at PNNL. The ⁴¹Ar activity is measured by the gamma activity using an HPGe detector after the sample is removed from the core. Using the ⁴¹Ar/³⁷Ar production ratio and the ⁴¹Ar activity, the amount of ³⁷Ar created is calculated. The ⁴¹Ar decays quickly (half-life of 109.34 minutes) leaving a radioactive sample of high purity ³⁷Ar and only trace levels of ³⁹Ar. The second method was the irradiation of a calcium-containing compound. This option is not the best match for the TRIGA reactor type due to the thermal neutron flux. Therefore, the use of the Cd-lined 3L irradiation canister minimized the thermal activation of impurities while still allowing the majority of the ⁴⁰Ca(n,[alpha])³⁷Ar reactions occur. The third and last irradiation technique was a large volume, in-core gas facility developed at The University of Texas at Austin MARK II TRIGA reactor to produce a sample of ⁴²Ar with an activity above 1 mBq. The method requires a large volume, 1.4 L, of natural argon gas (99.6003% ⁴⁰Ar) at about 1 atm and three-12 hour irradiation periods. The production of ⁴²Ar requires a double capture to be produced from the stable 40Ar isotope. This method produced 940 kBq of ³⁹Ar, 3.08 MBq ³⁷Ar, 114 GBq ⁴¹Ar, and 0.311 Bq ⁴²Ar at the end of the final irradiation period.