Development of electromagnetic cascades in the atmosphere including the Landau-Pomeranchuk-Migdal effect

Numerical solutions have been obtained for the one-dimensional atmospheric electromagnetic cascade diffusion equations, including the Landau-Pomeranchuk-Migdal and screening effects. Spectra produced by primary gamma rays of various energies are given at a number of deths in the atmosphere

Raising Her Voice: African-American Women Journalists Who Changed History

Each chapter is a biographical sketch of an influential black woman who has written for American newspapers or television news, including Maria W. Stewart, Mary Ann Shadd Cary, Gertrude Bustill Mossell, Ida B. Wells-Barnett, Josephine St.Pierre Ruffin, Delilah L. Beasley, Marvel Cooke, Charlotta A. Bass, Alice Allison Dunnigan, Ethel L. Payne, and Charlayne Hunter-Gault. Little research exists on African-American women journalists, even in studies of the black press. To address this gap, Streitmatter presents eleven biographies of journalists from the early nineteenth century to the present. -- Journal of Women\u27s History [Streitmatter] finds that their attraction to journalism cam from their desire to be advocates of racial reform, that they were courageous in the face of sexism and financial discrimination, and that they used education as their entry into journalism and subsequently received support from African-American male editors. -- Journal of Women\u27s History An historical chronology of eleven interesting and determined black female journalists. -- Washington Timeshttps://uknowledge.uky.edu/upk_african_american_studies/1006/thumbnail.jp

Doctor of Philosophy

dissertationThe concept of relative biological effectiveness (RBE) in radiation therapy and diagnostic imaging for a particular radiation type is defined by the ratio of absorbed dose of a reference radiation, typically a low linear energy transfer (LET) radiation to the absorbed dose of a test radiation of typically higher LET that achieves the same biological effect. It is used to quantify and compare expected outcomes (therapy) and deterministic and stochastic risk (imaging, radiation protection) from different types of ionizing radiation. Numerical modeling of RBE and other metrics related to the biological response to ionizing radiation in radiation therapy, diagnostic X-ray imaging, and other related fields is becoming increasingly important as hadron therapy becomes more prevalent and as the concerns associated with diagnostic X-ray dose increase. This dissertation develops and tests a multiscale biophysical model to aid in both estimating clinically relevant biological metrics and to further understand the underlying mechanisms in the special cases examined. The investigation of these special, asymptotic cases in clinical applications of ionizing radiation are used to further refine and improve the multiscale model. On the therapy side, the high-LET binary radiation therapy of boron neutron capture therapy (BNCT) is used to test the multiscale model. In this therapy modality, there is both dependence on the primary neutron source and biodistribution of the boron with respect to the targeted cells. The radiobiology of these densely ionizing, short range particles are much different than that of sparsely ionizing photons. On the diagnostic imaging side, the RBE and dosimetric characteristics of computed tomography (CT) are examined with the multiscale model, looking specifically at effects of iodine enhancement. Recent experimental data showing that kV X-rays and electrons have an RBE greater than unity are in line with predictions from the multiscale model. Furthermore, the reported studies also provide strong support for the hypothesis that the RBE for DSB induction is within a few percent of the RBE for cell survival over a wide range of photon and electron energies. The final part of this research focuses on the further integration and expansion of the multiscale model

SU(2) x U(1) vacuum and the Centauro events

It is proposed that the fireballs invoked to explain the Centauro events are bubbles of a metastable superdense state of nuclear matter, created in high energy (E is approximately 10 to the 15th power eV) cosmic ray collisions at the top of the atmosphere. If these bubbles are created with a Lorentz factor gamma approximately = 10 at their CM frame, the objections against the origin of these events in cosmic ray interactions are overcome. Assuming further, that the Centauro events are to the explosive decay of these metastable bubbles, a relationship between their lifetime, tau, and the threshold energy for bubble formation, E sub th, is derived. The minimum lifetime consistent with such an interpretation in tau is approximately 10 to the -8th power sec, while the E sub th appears to be insensitive to the value of tau and always close to E sub th is approximately 10 to the 15th power eV. Finally it is speculated that if the available CM energy is thermalized in such collisions, these bubbles might be manifestations of excitations of the SU(2) x U(1) false vacuum. The absence of neutral pions in the Centauro events is then explained by the decay of these excitations

Cosmic ray nuclei of energy 50 GeV/NUC

Preliminary results from the High Energy Gas Cerenkov Spectrometer indicate that the sub-iron to iron ratio increases beyond 100 GeV/nucleon. This surprising finding is examined in light of various models for the origin and propagation of galactic cosmic rays

Antiprotons in cosmic rays

Recent experimental observations and results are discussed. It was found that the approximately 50 antiprotons collected in balloon experiments to date have generated considerable theoretical interest. Clearly, confirmatory experiments and measurements over an extended energy range are required before definite conclusions are drawn. Antiproton measurements have a bearing on astrophysical problems ranging from cosmic ray propagation to issues of cosmological import. The next generation of balloon experiments and the Particle Astrophysics Magnet Facility being discussed for operation on NASA's space station should provide data and insights of highest interest

Simulation Studies of Delta-ray Backgrounds in a Compton-Scatter Transition Radiation Detector

In order to evaluate the response to cosmic-ray nuclei of a Compton-Scatter Transition Radiation Detector in the proposed ACCESS space-based mission, a hybrid Monte Carlo simulation using GEANT3 and an external transition radiation (TR) generator routine was constructed. This simulation was employed to study the effects of delta-ray production induced by high-energy nuclei and to maximize the ratio of TR to delta-ray background. The results demonstrate the ability of a Compton-Scatter Transition Radiation Detector to measure nuclei from boron to iron up to Lorentz factors ~ 10^5 taking into account the steeply falling power-law cosmic ray spectra.Comment: Presented at TRDs for the 3rd millennium: Third Workshop on advanced Transition Radiation Detectors for accelerator and space applications, Ostuni, Italy, September 2005, 4 pages, 2 figure