Authors: Lacy, Jeffrey L. | Athanasiades, Athanasios | Martin, Christopher S. | Nguyen, Richard | Davenport, Stephen | Lyons, Tom | Liu, Yangwei
Article Type: Research Article
Abstract: Modified boron-coated straw (BCS) detector configurations are introduced, in order to improve detection efficiency, and reduce the number of layers required to match the response of high-pressure 3 He tubes, in large-scale neutron science instruments. A new 7-straw design employing thin-walled aluminum tubes facilitates operation in vacuum, and substantially reduces the scattering material by a factor of 5 compared with the flow-through design of the Multi-Grid detector. Another design introduces 18 radial walls inside each straw, coated on both sides with enriched boron carbide, to increase the coated wall perimeter 4.3 times. The so-called Pie straw offers a significant benefit …in detection efficiency compared with round straws used in LoKI. An example of such a straw having 18 septa is explored in modeling and experimental studies, that can potentially reduce the number of layers needed in large-scale instruments like LoKI by a factor of 2.8. In a parallel development, a totally new configuration of boron-coated detectors is introduced, aimed to address the need for high spatial resolution, and high-rate capability in single crystal diffractometers, like MaNDi and TOPAZ at the SNS, and in neutron reflectometers. The proposed structure is a close-packed array of rectangular cells, each fabricated by wrapping copper foil having a coating of 10 B4 C on one side and electroplated tin on the other side, around precisely machined rectangular bars. The array is pressed together and then vacuum brazed together. The resulting structure is quite strong and precise in geometry. This so-called Microcell Straw Array can be configured with channel dimensions as small as 0.5 mm × 2.5 mm. Due to its ultra thin walls (25 μ m) secondary scattering of neutrons is minimized. It is sealed inside a fully welded thin aluminum containment vessel that allows convenient operation in vacuum. A mature low power readout system capable of an estimated count rate of 22 MHz in a 15 × 15 cm2 detector is also proposed. The improvements are the result of recent advances in BCS design, spurred by the development of compact, high-sensitivity monitors for homeland security and military applications. Show more
Keywords: Neutron detectors, boron-coated straws, neutron diffractometers, neutron reflectometers
DOI: 10.3233/JNR-190138
Citation: Journal of Neutron Research, vol. 22, no. 2-3, pp. 353-369, 2020
Authors: Smith, Mark A. | Bowen, Richard L. | Nguyen, Richard Q. | Perry, George | Atwood, Craig S. | Rimm, Alfred A.
Article Type: Research Article
Abstract: Background: Estrogen and hormone replacement therapies to reduce Alzheimer’s disease (AD) have yielded conflicting results. However, this study proposes that the well-characterized increase in serum gonadotropins following menopause or andropause are accountable for the increased risk of developing AD among the elderly population. Objective: To determine the role of gonadotropins in the development of AD and investigate gonadotropin-releasing hormone (GnRH) agonist therapy as a potential preventative and/or disease-modifying approach to AD management. Methods: Male Medicare beneficiaries aged 67 to 75 and hospitalized with prostate cancer (n = 115,789) were compared to three control groups: men of the same demographics undergoing a …cholecystectomy (n = 97,267), herniorrhaphy (n = 68,778), or transurethral prostatectomy (n = 267,691). A proportion of the patients hospitalized with prostate cancer were assumed to have low concentrations of serum gonadotropins and sex steroids as a result of GnRH agonist therapy, while those in the control groups were assumed to have elevated gonadotropin but lowered sex steroid levels that are associated with andropause in this age group. Results: The rates of development of select diagnoses of dementia, including AD, over a twelve-year follow-up period following surgery. When compared to control patients, men hospitalized with prostate cancer have a protection against dementia after twelve years of follow-up, with relative risks ranging from 0.48 to 0.83. Conclusion: Patients with prostate cancer are treated with the GnRH analogue leuprolide acetate, our data suggest that leuprolide acetate may be therapeutic for AD via its downregulation of serum gonadotropins. Show more
Keywords: Alzheimer’s disease, cancer, castration, epidemiology, gonadotropin receptors, hormone replacement therapy, leuprolide, Medicare Part A, testosterone
DOI: 10.3233/JAD-170847
Citation: Journal of Alzheimer's Disease, vol. 63, no. 4, pp. 1269-1277, 2018