Heat transfer analysis study for the design of the New Polychromatic Beam Neutron Reflectometer CANDOR (Chromatic Analysis Neutron Diffractometer Or Reflectometer)

A newly developed polychromatic beam neutron reflectometer CANDOR (Chromatic Analysis Neutron Diffractometer Or Reflectometer) on NG-1 at the NIST Center for Neutron research (NCNR) utilizes a wavelength-sensitive neutron detector consisting of 324 analyzing highly-oriented pyrolytic graphite (HOPG) crystals positioned sequentially in rows. Known for having a small thermal diffuse scattering cross section, HOPG crystals can lead to low signal-to-noise ratios in wavelength-sensitive detectors such as CANDOR. Even though it is possible to mathematically separate the desired signal from thermal diffuse scattering; by cooling the detector array of HOPG crystals in order to minimize the Debye Waller effect generates a better solution to this problem. In this heat transfer analysis study we show, within the instrument design constrains and thermodynamic considerations, technical feasibility and test results for the development of the New Polychromatic Beam Neutron Reflectometer CANDOR (Chromatic Analysis Neutron Diffractometer Or Reflectometer) at the NIST Center for Neutron Research.

Light scattering from cells: the contribution of the nucleus and the effects of proliferative status

As part of our ongoing efforts to understand the fundamental nature of light scattering from cells and tissues, we present data on elastic light scattering from isolated mammalian tumor cells and nuclei. The contribution of scattering from internal structures and in particular from the nuclei was compared to scattering from whole cells. Roughly 55% of the elastic light scattering at high-angles (> 40 degrees) comes from intracellular structures. An upper limit of 40% on the fractional contribution of nuclei to scattering from cells in tissue was determined. Using cell suspensions isolated from monolayer cultures at different stages of growth, we have also found that scattering at angles greater than about 110 degrees was correlated with the DNA content of the cells. Based on model calculations and the relative size difference of nuclei from cells in different stages of growth, we argue that this difference in scattering results from changes in the internal structures of the nucleus. This interpretation is consistent with our estimate of 0.2 micron as the mean size of the scattering centers in cells. Additionally, we find that while scattering from the nucleus accounts for a majority of internal scattering, a significant portion must result from scattering off of cytoplasmic structures such as mitochondria.