EXPERIMENTAL EVALUATION OF NEUTRON SHIELDING MATERIALS
A new proposed design of neutron shielding material-based on the commercial material Borotron UH050 with an addition of Al(OH)3-is evaluated in order to determine if its neutron and gamma shielding properties match those of a reference material, NS4FR. Neutron and gamma dosimetry measurements are performed, as well as neutron spectrometry measurements and Monte Carlo simulations. Negligible differences are found between the materials for neutron shielding, while significant differences are found for gamma shielding. The effect of Al(OH)3 addition to Borotron UH050 is to reduce neutron shielding properties while increasing gamma shielding properties. The resulting material is as efficient as NS4FR for neutron shielding but less efficient for gamma shielding-thicknesses 20% higher are required to match gamma shielding properties of NS4FR. Monte Carlo models of the materials are validated based on the performed measurements of neutron spectra and neutron and gamma ambient dose equivalent.
Least squares for different experimental cases
Ve discuss the problem of fitting an experimental data sel into a linear curve when experimental uncertainties can not be overlooked. Difficulties with the standard least-squares method are pointed out. An alternative weighted least-squared method, depending on knowledge about the uncertainties ror fouT different cases.is prc. sented, and we use it to tl.nalyzc the data from a particular cxperiment. From this application it is shown that we get better results using the proper ra.se. \Ve want to point out a widespread error in the use of linear regrcssion analysis when, in experimental situations, the experimentalist wants to determine the functional relationship betwccn tIJe experimental data. The hroad use of pockct programmable ca1culators and statistical software for microcompllters makes easicr the hcavy work neccssary to obtain such relationship bet\\'cen the experimental data. Unfortunatcly, the most common analysis tcchnique available in lhe least square fitting of a line is not always lhe most proper. Experiments in physics made to determine pararneters through lhe functional relationship between valucs of x and y involvc a series of experimental Illcasurements of x and lhe corresponding y. In several cases there are not only measuremen:; errors in Yi, bul also there are measurcrnenl eTrors in Xj. Many experimentalists apply lhe slandard Ica.sl-squares mclhod, which implicitly assumes errors neilber in Xi ilOr in yi. Accordingly, this procedure affects the llnknown parameters to be obtained from the functionaI rclationship, and it givcs estimalcs of errors that are smaller than the truc errors. This paper presents a review of standard least-squarcs rnethod as applied to a slraight line, and the weighted least-squarcs method, ",here the weighting factor is related to the experimental data precision. This gives place to four different experimental cases; cach one of thcse cases are applied to the same experimental data sel and the resulls of this weighlcd lcast-square fitting method oC a straight Iine are discussed as wcll.
An anionic shell shields a cationic core allowing for uptake and release of polyelectrolytes within core-shell responsive microgels.
To realize carriers for drug delivery, cationic containers are required for anionic guests. Nevertheless, the toxicity of cationic carriers limits their practical use. In this study, we investigate a model system of polyampholyte N-isopropylacrylamide (NIPAM)-based microgels with a cationic core and an anionic shell to study whether the presence of a negative shell allows the cationic core to be shielded while still enabling the uptake and release of the anionic guest polyelectrolytes. These microgels are loaded with polystyrene sulfonate of different molecular weights to investigate the influence of their chain length on the uptake and release process. By means of small-angle neutron scattering, we evaluate the spatial distribution of polystyrene sulfonate within the microgels. The guest molecules are located in different parts of the core-shell microgels depending on their size. By combining these scattering results with UV-vis spectroscopy, electrophoretic mobility and potentiometric titrations we gain complementary results to investigate the uptake and release process of polyelectrolytes in polyampholyte core-shell microgels. Moreover, Brownian molecular dynamic simulations are performed to compare the experimental and theoretical results of this model. Our findings demonstrate that the presence of a shell still enables efficient uptake of guest molecules into the cationic core. These anionic guest molecules can be released through an anionic shell. Furthermore, the presence of a shell enhances the stability of the microgel-polyelectrolyte complexes with respect to the cationic precursor microgel alone.