نتایج جستجو برای: kidney shielding

تعداد نتایج: 230231  

1998
James C. Liu Tony T. Ng

The shielding for 14-MeV neutrons from a D-T generator at SLAC needs to be optimized in terms of shield thickness and cost. Shielding calculations were made using the MCNP4B Monte Carlo code and the ENDF/B-VI cross section set. A few materials were studied: iron, borated polyethylene, three types of normal and heavy concrete, and mixtures of iron and borated polyethylene. The effects of shieldi...

2014
Paula Duarte Correia Cristiano Roberto Fabri Granzotti Yago da Silva Santos Marco Aurelio Corte Brochi Paulo Mazzoncini de Azevedo-Marques

OBJECTIVE Several studies have been published regarding the use of bismuth shielding to protect the breast in computed tomography (CT) scans and, up to the writing of this article, only one publication about barium shielding was found. The present study was aimed at characterizing, for the first time, a lead breast shielding. MATERIALS AND METHODS The percentage dose reduction and the influen...

Journal: :Physical chemistry chemical physics : PCCP 2015
Iann C Gerber Franck Jolibois

Chemical shift requires the knowledge of both the sample and a reference magnetic shielding. In few cases as nitrogen (15N), the standard experimental reference corresponds to its liquid phase. Theoretical estimate of NMR magnetic shielding parameters of compounds in their liquid phase is then mandatory but usually replaced by an easily-get gas phase value, forbidding direct comparisons with ex...

Journal: :journal of physical & theoretical chemistry 2005
h. aghaie m. monajjemi gh. ghassemi m. kia

we have evaluated the nmr shielding tensors for a:t,g:c,a:u in watson-crick, and u-quartet. we have computed nmr shielding tensors at b31yp level by using 6-31g(d) basis set. we have compute anisotropy and asymmetry in a:t,g:c,a:u and u-quartet. the nmr shielding tensors were calculated using the giao method. the natural bonding orbital analysis (nbo) were performed. nbo calculation have been ...

Journal: :Orthopedics 2017
Mark C Lee Jessica Lloyd Matthew J Solomito

Plain pelvic radiographs are commonly used for a variety of pediatric orthopedic disorders. Lead shielding is typically placed over the gonads to minimize radiation exposure to these sensitive tissues. However, misplaced shielding can sabotage efforts to protect patients from excessive radiation exposure either by not covering radiosensitive tissues or by obscuring anatomic areas of interest, p...

Journal: :Physical chemistry chemical physics : PCCP 2010
Anu M Kantola Perttu Lantto Juha Vaara Jukka Jokisaari

The series of methyl halides, CH(3)X (X = F, Cl, Br, and I), is prototypic for demonstrating the s.c. normal halogen dependence of light-atom nuclear magnetic resonance shielding constants in the presence of halogen atoms of varying electronegativity. We report a systematic experimental and first-principles theoretical study of the (13)C and (1)H shielding tensors in this series. The experiment...

Journal: :Physics in medicine and biology 2007
J Fan W Luo E Fourkal T Lin J Li I Veltchev C-M Ma

In this paper, we present the shielding analysis to determine the necessary neutron and photon shielding for a laser-accelerated proton therapy system. Laser-accelerated protons coming out of a solid high-density target have broad energy and angular spectra leading to dose distributions that cannot be directly used for therapeutic applications. A special particle selection and collimation devic...

Journal: :Journal of the American Chemical Society 2002
Jonathan Boyd Nikolai R Skrynnikov

Ring currents can exert a large effect upon the chemical shielding of NMR resonances. The analytical expression developed by Waugh and Fessenden (Waugh, J. S.; Fessenden, R. W. J. Am. Chem. Soc. 1957, 79, 846) and Johnson and Bovey (Johnson, C. E.; Bovey, F. A. J. Chem. Phys. 1957, 29, 1012) only quantifies the contribution of ring currents to the isotropic component of the shielding tensor. In...

2002
Sungsool Wi Stephen Wimperis Lucio Frydman

We investigate the nature of higher-order effects arising in solid-state nuclear magnetic resonance ~NMR! when quadrupolar nuclei are subject to significant chemical shift anisotropies. It is shown that the quadrupole interaction can give rise to shielding-derived terms that are not entirely averaged away by conventional magic-angle spinning ~MAS!. These terms are proportional to the square of ...

Journal: :Physical chemistry chemical physics : PCCP 2015
Sarah Reimann Ulf Ekström Stella Stopkowicz Andrew M Teale Alex Borgoo Trygve Helgaker

The sources of error in the calculation of nuclear-magnetic-resonance shielding constants determined by density-functional theory are examined. Highly accurate Kohn-Sham wave functions are obtained from coupled-cluster electron density functions and used to define accurate-but current independent-density-functional shielding constants. These new reference values, in tandem with high-accuracy co...

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