Search for the low lying transition in the 229Th Nucleus

This dissertation presents a search for the low lying transition in the 229Th nucleus. This nucleus is expected to have an exceptionally low energy and long-lived isomeric level just above the ground state which could be amenable to laser spectroscopy. We utilize 229Th doped LiSrAlF6 crystals to achieve high densities adequate for broadband synchrotron excitation. The charge state of the doped thorium atoms (4+) ensures a radiative decay upon de-excitation of the nucleus, necessary for fluorescence detection. Additionally; we built a pulsed VUV laser system, utilizing four wave difference frequency mixing in Xe, to continue interrogation of the 229Th:LiSrAlF6 crystals with improved sensitivities to longer lifetimes for the decay from the isomeric level. And finally, we utilize a 233U source along with superconducting single photon nanowire detectors (SNSPD's) in attempt to measure the internal conversion (IC) decay channel available to neutral 229Th. If successful, the experiment can provide the lifetime of the IC decay and can potentially provide energy bounds on the isomeric level

Search for the low lying transition in the 229Th Nucleus

This dissertation presents a search for the low lying transition in the 229Th nucleus. This nucleus is expected to have an exceptionally low energy and long-lived isomeric level just above the ground state which could be amenable to laser spectroscopy. We utilize 229Th doped LiSrAlF6 crystals to achieve high densities adequate for broadband synchrotron excitation. The charge state of the doped thorium atoms (4+) ensures a radiative decay upon de-excitation of the nucleus, necessary for fluorescence detection. Additionally; we built a pulsed VUV laser system, utilizing four wave difference frequency mixing in Xe, to continue interrogation of the 229Th:LiSrAlF6 crystals with improved sensitivities to longer lifetimes for the decay from the isomeric level. And finally, we utilize a 233U source along with superconducting single photon nanowire detectors (SNSPD's) in attempt to measure the internal conversion (IC) decay channel available to neutral 229Th. If successful, the experiment can provide the lifetime of the IC decay and can potentially provide energy bounds on the isomeric level

An entirely automated method to score DSS-induced colitis in mice by digital image analysis of pathology slides

SUMMARY The DSS (dextran sulfate sodium) model of colitis is a mouse model of inflammatory bowel disease. Microscopic symptoms include loss of crypt cells from the gut lining and infiltration of inflammatory cells into the colon. An experienced pathologist requires several hours per study to score histological changes in selected regions of the mouse gut. In order to increase the efficiency of scoring, Definiens Developer software was used to devise an entirely automated method to quantify histological changes in the whole H&E slide. When the algorithm was applied to slides from historical drug-discovery studies, automated scores classified 88% of drug candidates in the same way as pathologists’ scores. In addition, another automated image analysis method was developed to quantify colon-infiltrating macrophages, neutrophils, B cells and T cells in immunohistochemical stains of serial sections of the H&E slides. The timing of neutrophil and macrophage infiltration had the highest correlation to pathological changes, whereas T and B cell infiltration occurred later. Thus, automated image analysis enables quantitative comparisons between tissue morphology changes and cell-infiltration dynamics

The concept of laser-based conversion electron Mössbauer spectroscopy for a precise energy determination of 229m^{229m}Th

$^{229}$Th is the only nucleus currently under investigation for the development of a nuclear optical clock (NOC) of ultra-high accuracy. The insufficient knowledge of the first nuclear excitation energy of $^{229}$Th has so far hindered direct nuclear laser spectroscopy of thorium ions and thus the development of a NOC. Here, a nuclear laser excitation scheme is detailed, which makes use of thorium atoms instead of ions. This concept, besides potentially leading to the first nuclear laser spectroscopy, would determine the isomeric energy to 40 $\mu$eV resolution, corresponding to 10 GHz, which is a $10^4$ times improvement compared to the current best energy constraint. This would determine the nuclear isomeric energy to a sufficient accuracy to allow for nuclear laser spectroscopy of individual thorium ions in a Paul trap and thus the development of a single-ion nuclear optical clock

First on-line detection of radioactive fission isotopes produced by laser-accelerated protons

The on-going developments in laser acceleration of protons and light ions, as well as the production of strong bursts of neutrons and multi-[Formula: see text] photons by secondary processes now provide a basis for novel high-flux nuclear physics experiments. While the maximum energy of protons resulting from Target Normal Sheath Acceleration is presently still limited to around [Formula: see text], the generated proton peak flux within the short laser-accelerated bunches can already today exceed the values achievable at the most advanced conventional accelerators by orders of magnitude. This paper consists of two parts covering the scientific motivation and relevance of such experiments and a first proof-of-principle demonstration. In the presented experiment pulses of [Formula: see text] at [Formula: see text] duration from the PHELIX laser produced more than [Formula: see text] protons with energies above [Formula: see text] in a bunch of sub-nanosecond duration. They were used to induce fission in foil targets made of natural uranium. To make use of the nonpareil flux, these targets have to be very close to the laser acceleration source, since the particle density within the bunch is strongly affected by Coulomb explosion and the velocity differences between ions of different energy. The main challenge for nuclear detection with high-purity germanium detectors is given by the strong electromagnetic pulse caused by the laser-matter interaction close to the laser acceleration source. This was mitigated by utilizing fast transport of the fission products by a gas flow to a carbon filter, where the [Formula: see text]-rays were registered. The identified nuclides include those that have half-lives down to [Formula: see text]. These results demonstrate the capability to produce, extract, and detect short-lived reaction products under the demanding experimental condition imposed by the high-power laser interaction. The approach promotes research towards relevant nuclear astrophysical studies at conditions currently only accessible at nuclear high energy density laser facilities