Of great benefit, but not limited to seafloor mineral exploration, is a technique that fairly rapidly determines the composition of a drilled vibracore (in a time comparable to the time involved in obtaining the core). The rapid assessment is desired to predict whether a given region warrants further exploration by coring. A proposed monitoring system, based on neutron capture gamma ray analysis, consists of a container tank filled with water and tubular extensions that house a Cf-252 neutron source and a detector positioned within the tank. The core sample is passed through the system in stop and count steps. The net count rates, due to "signature" capture gamma rays from neutron capture in elements in the core sample, are proportional to the amount of the element responsible for emitting the capture gamma ray. The proposed system was modeled and simulated by the Monte Carlo method to predict the relationship between the response of the detector and the elemental concentrations within the sample. Accurate and detailed treatment of neutron transport and gamma ray production and attenuation within the system were employed not only to predict the relationship of the photopeak responses with respect to elemental concentrations, but also to permit investigation of the design parameters and structural material changes in the system. The developed Monte Carlo code utilizes a variety of variance reduction techniques, such as implicit absorption with Russian Roulette and deterministic production of the gamma rays of interest, along with a form of correlated sampling to predict simultaneously the responses over a range of interest of the elemental concentrations. The predicted results were compared with predictions obtained from a well established general purpose Monte Carlo code (MCNP). / Graduation date: 1990

A Fortran IV language computer program has been written by the author for the analysis of gamma-gamma directional correlations obtained using radioactive sources. In this program the multipole-mixing ratio parameter, A, for the mixed multipole transition in the cascade is varied and the theoretical correlation is calculated for one hundred fifty-seven values of the mixing ratio for each trial spin sequence. The normalized chi-square test, Q2, is used to compare the theoretical and experimental results.The study of the effect of the multipole-mixing ratio and the attenuation factors on gamma-gamma directional correlation shapes has been investigated forsequence sets. The study has been separated into two parts: first, the effect of the attenuation factors when the multipole-mixing ratio is fixed; second, the effect of the multipole-mixing ratio for fixed attenuation factors.The results show the smoothing effect of the attenuation factors on the correlation function and it is illustrated graphically. The effect of the multipole-mixing ratio on the correlation function, with is a quadratic function in S, is also shown graphically.Ball State UniversityMuncie, IN 47306

A delayed-coincidence spectrometer system was developed to measure nuclear lifetimes in the picosecond region by the centroid-shift method. liming signals were derived from two plastic scintillators. A specially constructed NaI(Tl) detector was used to detect the gamma-rays which were Corrpton-scattered from one of the plastic scintillators. Energy identification was achieved by sumning the signals from the plastic detector and the NaI(Tl) detector to give the full energy photopeaks. In order to test the effectiveness of the system, the mean lives of the first excited states of Ni60 and Ba134 were measured. The 1.0-psec mean life in Ni60 could not be measured with the present system. The gamma-gamma and beta-gamma coincidence experiments gave the mean life of the first excited state of Ba134 as 6.1 ±0.8 psec and 4.8 ±0.6 psec, respectively. It is concluded that the shortest mean life that can reliably be measured by the present system is about 5 psec.Ball State UniversityMuncie, IN 47306

A delayed-coincidence timing spectrometer system was constructed to measure nuclear lifetimes in the picosecond region. The present investigation used the self-comparison method of delayed-coincidence timing. This method used two plastic detectors to obtain the timing information. Two sodium iodine (NaI) detectors were used in conjunction with the plastic detectors to provide energy identification. Significant changes were made to the geometrical detector arrangement to optimize collection of scattered gamma rays by the NaI detectors. The mean line for the first excited states of the sources Co-60 and Cs-134 were measured using the new spectrometer system. The mean life of the 1.33 MeV excited state of Co-60 was measured to by 0.34 + 1.32 psec. The mean life of the 0.605 MeV excited state of Cs-134 was measured to be 6.31 + 2.19 psec and agrees with two previously reported values.Ball State UniversityMuncie, IN 47306

La historia de la astronomía de los rayos gammas en los últimos veinte años está marcada por el éxito que los telescopios Cherenkov han tenido en la exploración de la banda de muy altas energías. La ultima generación de telescopios Cherenkov, que incluye los telescopios HESS, VERITAS y MAGIC, ha logrado, en sólo siete años, aumentar el número total de fuentes conocidas de muy altas energías, desde unas pocas hasta más de un centenar. Esta populación de fuentes incluye objetos galácticos y extragalácticos. Los telescopios Cherenkov se han demostrado muy eficientes en el descubrimiento de nuevas emisoras de rayos gammas y también en el estudio detallado de la propiedades físicas de las fuentes bien conocidas, como por ejemplo, la Nebulosa del Cangrejo, el prototipo de los pleriones o Nebulosas de Viento de Púlsar ("pulsar wind nebulae"). Gracias a su brillo a todas las longitudes de onda, el Cangrejo es una fuente astrofísica de referencia. Su espectro ha sido medido en veinte ordenes de magnitud en energía, desde las frecuencias radio hasta las muy altas energías, pero nuevas medidas resultan aún esenciales para entender las contradicciones que surgen cuando se combinan los resultados de diferentes longitudes de onda. Finalizado del commissioning del segundo telescopio en el Otoño del 2009, y tras el comienzo de la toma de datos en modalidad estereoscopica, MAGIC ha mejorado significantivamente su rendimiento y alcanza el umbral en energía más bajo de todos los telescopios Cherenkov. Por lo tanto MAGIC es un instrumento ideal para medir el espectro de la Nebulosa del Cangrejo con una precisión sin precedentes a partir de 50 GeV. Este logro tiene una importancia extraordinaria para el astrofísica de muy altas energías y tiene el potencial de solucionar unos de los misterios aun no resueltos de esta fuente. Este es uno de los asuntos centrales de este trabajo de tesis. Por otro lado, MAGIC ha tenido también un impacto fundamental en el descubrimiento de nuevos objetos astrofísicos, y, con la mejora en sensibilidad del nuevo sistema de dos telescopios , este impacto será aún mas significativo. Entre las fuentes galacticas, los microcuásares constituyen unos de los mejores candidatos a emisores de rayos gammas. Su caracterización a muy alta energía aportaría información muy útil para entender la formación de chorros de partículas en objetos astronomicos. Aunque muchos modelos teóricos predicen esta emisión, aún no ha sido detectada. De hecho hay evidencias de que los tres sistemas binarios que se han detectado hasta la fecha por encima de 300 GeV son binarias de púlsares más que microcuásares. Sin embargo, el hecho que el microcuásar Cygnus X-3 haya sido detectado por encima de 100 MeV por los satélites AGILE y Fermi/LAT confirma que esta clase de objetos sigue siendo un objetivo interesente por la astrofísica de muy alta energía. En los últimos años, MAGIC ha dedicado un esfuerzo muy importante búsqueda de señales desde los microcuásares. Esta tesis presenta los resultados de las observaciones de dos de ellos: Cygnus X-3 y Scorpius X-1. Se han logrado extraer los limites superiores al flujo integral de estas dos fuentes más restrictivos hasta la fecha por encima de unos centenares de GeV. Para Cygnus X-3 en particular, se presentan además las primeras observaciones a estas energías totalmente simultáneas con la emisión detectada por los satélites. / of the Imaging Atmospheric Cherenkov Telescopes (IACTs) in the exploration of the Very- High-Energy (VHE) band. The last generation of IACTs have been capable to increase the total number of known VHE emitting sources from a few to almost one hundred in just seven years of operation. This population comprises galactic and extragalactic objects. IACTs have proved to be very effective in both the discovery of new emitters, as well as in the fine analysis of the physics properties of well established sources. Among them, the Crab Pulsar Wind Nebula is probably the best studied astrophysical object and the archetypal PWN. Due to its brightness at almost all wavelenghts, it is considered as an astrophysical candle. Despite the Crab Nebula broad-band spectrum has been thoroughly studied across twenty orders of magnitudes, from radio frequencies to VHE, further effort is needed to resolve the contradictions in the combination of all the multiwavelenght results. With the commissioning of the second MAGIC telescope in 2009 and the beginning of the operations in stereoscopic mode, the performance of the instrument improved dramatically, allowing MAGIC to reach the lowest ever energy threshold among all the existing IACTs, and describe the Crab Nebula spectrum with unprecedented precision down to 50 GeV. This achievement is of crucial importance for the VHE !-ray astrophysics in the pre-CTA era, since it can cast new light on some of the unsolved mysteries of one of its most established sources. On the other hand, MAGIC made a strong impact in the discovery of new VHE sources and, with the improved sensitivity of the stereoscopic mode, this will be even more so in the future. Among the galactic objects, Microquasars (MQs) constitute some of the best candidates for VHE emission, but despite several well accepted models predict such signal, it has not been detected. There are, in fact, evidences that the three binary systems which have been unambiguously detected at energies above few hundreds of GeV are binary pulsars rather than accreting microquasars. Nevertheless, the recent detection of the microquasar Cygnus X-3 above 100 MeV by both Agile and Fermi satellites, and the claim of short oneday flares from Cygnus X-1 reported by Agile confirmed that microquasars remain interesting targets for VHE telescopes. MAGIC made a strong effort in searching for VHE signals from microquasars, but found only a non-significant evidence of signal from Cygnus X-1 in 80 minutes of observation on September 24, 2006. MAGIC tried to detect similar flares in the following four years but the subsequent hundred more hours of observations were unsuccessful. Besides Cygnus X-1, MAGIC pointed at two other microquasar candidates, whose results are presented in this thesis: Cygnus X-3 and Scorpius X-1. The most constraining UL to the integral flux of these sources at the energy above few hundred GeV are provided. Further investigations are being planned to discover these sources at VHE in the next years.

The N=88 nuclei lie in a transitional region of the nuclear chart. Collective structure and nuclear deformation for this region is commonly occurring. Previously, some of the nuclei having 88 neutrons have been well studied, e.g., 148Nd, 150Sm, 152Gd, 154Dy; however, 156Er has not. To be able to understand the nuclei in this region one needs to extract all the systematics of these deformed nuclei and the relations between them. The structure of 156Er is the main focus in this thesis and the work seeks understanding of the N=88 nuclei and systematics among them. To accomplish this task, 156Tm to 156Er beta decay was studied. Many new levels and gamma transitions have been added to the existing scheme. The significance for detailed decay scheme studies far from stability is also discussed.

The radiological dispersal device (RDD) is a weapon of great concern to those agencies responsible for protecting the public from the modern age of terrorism. In order to effectively respond to an RDD event, these agencies need to possess the capability to rapidly identify the radiological agents involved in the incident and assess the uptake of each individual victim. Since medical treatment for internal radiation poisoning is radionuclide-specific, it is critical to identify and quantify the radiological uptake of each individual victim. This dissertation describes the development of automated analytical components that could be used to determine and quantify multiple radionuclides in human urine bioassays. This is accomplished through the use of extraction chromatography that is plumbed in-line with one of a variety of detection instruments. Flow scintillation analysis is used for ⁹⁰Sr and ²¹⁰Po determination, flow gamma analysis is used assess ⁶⁰Co and ¹³⁷Cs, and inductively coupled plasma mass spectrometry is used to determine actinides. Detection limits for these analytes were determined for the appropriate technique and related to their implications for health physics.

The IceCube Neutrino Observatory has reported the observation of 35 neutrino events above 30 TeV with evidence for an astrophysical neutrino flux using data collected from May 2010 to May 2013. These events provide the first high-energy astrophysical neutrino flux ever observed. The sources of these events are currently unknown. IceCube has looked for correlations between these events and a list of TeV photon sources including a catalog of 36 galactic sources and 42 extragalactic sources, correlations with the galactic plane and center, and spatial and temporal clustering. These searches have shown no significant correlations. The isotropic distribution of the event directions gives indications that the events could be extragalactic in nature and therefore may originate in the same processes that generate ultra-high-energy cosmic rays (UHECRs). The sources of these UHECRs are still unknown; however, gamma-ray bursts (GRBs) have been proposed as one possible source class. By determining the source of these high-energy neutrinos, it may be possible to determine the sources of UHECRs as well. This study is a search for directional and temporal correlation between 856 GRBs and the astrophysical neutrino flux observed by IceCube. Nearly 10,000 expanding time windows centered on the earliest reported time of the burst were examined. The time windows start at ±10 s and extend to ±15 days. We find no evidence of correlations for these time windows and set an upper limit on the fraction of the astrophysical flux that can be attributed to the observed GRBs as a function of the time window. GRBs can contribute at most 12% of the astrophysical neutrino flux if the neutrino-GRB correlation time is less than ≈20 hours, and no more than 38% of the astrophysical neutrino flux can be attributed to the known GRBs at time scales up to 15 days. We conclude that GRBs observable by satellites are not solely responsible for IceCube’s astrophysical neutrino flux, even if very long correlation time scales are assumed.

Based on data from the Fermi Gamma-ray Space Telescope, we have discovered two gigantic gamma-ray emitting bubble structures in our Milky Way (known as the Fermi bubbles), extending \(\sim 50\) degrees above and below the Galactic center with a width of \(\sim 40\) degrees in longitude. The gamma-ray emission associated with these bubbles has a significantly harder spectrum \((dN/dE \sim E^{-2})\) than the inverse Compton emission from known cosmic ray electrons in the Galactic disk, or the gamma-rays produced by decay of pions from proton-ISM collisions. There is no significant difference in the spectrum or gamma-ray luminosity between the north and south bubbles. The bubbles are spatially correlated with the hard-spectrum microwave excess known as the WMAP haze; we also found features in the ROSAT soft X-ray maps at \(1.5 - 2 keV\) which line up with the edges of the bubbles. The Fermi bubbles are most likely created by some large episode of energy injection in the Galactic center, such as past accretion events onto the central massive black hole, or a nuclear starburst in the last \(\sim 10 Myr\). Study of the origin and evolution of the bubbles also has the potential to improve our understanding of recent energetic events in the inner Galaxy and the high-latitude cosmic ray population. Furthermore, we have recently identified a gamma-ray cocoon feature within the southern bubble, with a jet-like feature along the cocoon's axis of symmetry, and another directly opposite the Galactic center in the north. If confirmed, these jets are the first resolved gamma-ray jets ever seen. / Astronomy

The BAT Slew Survey (BATSS) is the first wide-field survey of the hard X-ray sky (15–150 keV) with a slewing coded aperture imaging telescope. Its fine time resolution, high sensitivity and large sky coverage make it particularly well-suited for detections of transient sources with variability timescales in the \(\sim 1 sec–1 hour\) range, such as Gamma-Ray Bursts (GRBs), flaring stars and Blazars. As implemented, BATSS observations are found to be consistently more sensitive than their BAT pointing-mode counterparts, by an average of 20% over the 10 sec–3 ksec exposure range, due to intrinsic systematic differences between them. The survey’s motivation, development and implementation are presented, including a description of the software and hardware infrastructure that made this effort possible. The analysis of BATSS science data concentrates on the results of the 4.8-year BATSS GRB survey, beginning with the discovery of GRB 070326 during its preliminary testing phase. A total of nineteen (19) GRBs were detected exclusively in BATSS slews over this period, making it the largest contribution to the Swift GRB catalog from all ground-based analysis. The timing and spectral properties of prompt emission from BATSS GRBs reveal their consistency with Swift long GRBs (L-GRBs), though with instances of GRBs with unusually soft spectra or X-Ray Flashes (XRFs), GRBs near the faint end of the fluence distribution accessible to Swift-BAT, and a probable short GRB with extended emission, all uncommon traits within the general Swift GRB population. In addition, the BATSS overall detection rate of 0.49 GRBs/day of instrument time is a significant increase (45%) above the BAT pointing detection rate. This result was confirmed by a GRB detection simulation model, which further showed the increased sky coverage of slews to be the dominant effect in enhancing GRB detection probabilities. A review of lessons learned is included, with specific proposals to broaden both the number and range of astrophysical sources found in future enhancements. The BATSS survey results provide solid empirical evidence in support of an all-slewing hard X-ray survey mission, a prospect that may be realized with the launch of the proposed MIRAX-HXI mission in 2017. / Physics