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      Light Weight, Easy Formable and Non-Toxic Polymer-Based Composites for Hard X-ray Shielding: A Theoretical and Experimental Study

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          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          Composite lightweight materials for X-ray shielding applications were studied and developed with the goal of replacing traditional screens made of lead and steel, with innovative materials with similar shielding properties, but lighter, more easily formed and workable, with lower impact on the environment and reduced toxicity for human health. New epoxy based composites additivated with barium sulfate and bismuth oxide were designed through simulations performed with softwares based on Geant4. Then, they were prepared and characterized using different techniques starting from digital radiography in order to test the radiopacity of the composites, in comparison with traditional materials. The lower environmental impact and toxicity of these innovative screens were quantified by Life Cycle Assessment (LCA) calculation based on the ecoinvent database, within the openLCA framework. Optimized mixtures are (i) 20% epoxy/60% bismuth oxide/20% barite, which guarantees the best performance in X-ray shielding, largely overcoming steel, but higher in costs and a weight reduction of circa 60%; (ii) 20% epoxy/40% bismuth oxide/40% barite which has slightly lower performances in shielding, but it is lighter and cheaper than the first one and (iii) the 20% epoxy/20% bismuth oxide/60% barite which is the cheapest material, still maintaining the X-ray shielding of steel. Depending on cost/efficiency request of the specific application (industrial radiography, aerospace, medical analysis), the final user can choose among the proposed solutions.

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          Crystallography Open Database – an open-access collection of crystal structures

          1. Introduction The Crystallography Open Database (COD) is a recent tool offered to the scientific community on the Web at http://www.crystallography.net/. It was founded in February 2003 as a response to Michael Berndt’s letter published in the Structure Determination by Powder Diffractometry (SDPD) mailing list (http://tech.groups.yahoo.com/group/sdpd/message/1016). The historical fragmentation of structural data into three databases covering inorganic compounds (Inorganic Crystal Structure Database; Belsky et al., 2002 ▶), metals, alloys and intermetallics (Crystal Data for Metals Database, CRYSTMET; White et al., 2002 ▶), and organic and organometallic small molecules (Cambridge Structural Database; Allen, 2002 ▶) reflects the fact that in the past most public or private research laboratories concentrated their activity on one or the other of these very specialized topics. However, nowadays researchers at a given laboratory frequently extend their activities to all classes of compounds, focusing instead on materials with specific properties within more general classes of compounds, such as nanomaterials, hybrids or gas storage. Consequently, there is now a need to have access to all these databases simultaneously [together with powder data from the International Center for Diffraction Data (Kabekkodu et al., 2002 ▶) that are generally added for identification purposes]. Thus, a group of scientists (Armel Le Bail, Luca Lutterotti and Lachlan Cranswick) responded quickly to Michael Berndt’s letter and teamed up to create an open crystallography database. The group contacted Professor Robert T. Downs who generously offered strong support for the concept, including the data set from the American Mineralogist Crystal Structure Database (AMCSD; Downs & Hall-Wallace, 2003 ▶; Downs, 2008 ▶), along with MySQL/PHP scripts written by Hareesh Rajan. At the same time, Daniel Chateigner joined, and less than three weeks after the letter from Michael Berndt, the COD project was announced through various Internet media (newsgroups, various mailing lists and what’s new pages). This announcement introduced some new members to the effort (Brian Toby and Alexandre Yokochi) and, by the end of March 2003, the number of entries in the COD had increased to more than 5000. In order to ensure quality and standardization of uploaded files, the CIF2COD computer program was built by modifying CIF2SX with permission from Louis Farrugia. The first COD search page was coded in the PHP language. Uploads of crystallographic information files (CIFs) continued in April 2003 (1200 files from the Institut de Physique de la Matière Condensée, Grenoble) and after four months the number of entries in the COD surpassed 12 000 (Le Bail, 2003 ▶) as a result of uploads by individuals, laboratories and data shared by the AMCSD. In December 2003, a subset of the COD was created and named PCOD (Predicted Crystallography Open Database) with the goal of gathering computationally predicted structures and with the expectation that the number of predicted entries could easily exceed the number of experimentally determined ones. In January 2004, the PCOD offered 200 entries. By October 2005, the COD contained 20 000 entries. The database also had 30 new volunteers along with three new COD Advisory Board members (Saulius Gražulis, Miguel Quirós Olozábal and Peter Moeck). With the help of these volunteers, the number of entries in the COD increased to 48 000 by December 2006, now including 10 000 structures from the AMCSD (Downs & Hall-Wallace, 2003 ▶; Downs, 2008 ▶). In February 2007, a massive PCOD update boosted the number of entries to more than 60 000, with the help of the GRINSP software (Le Bail, 2005 ▶) for crystal structure prediction. At the same time, using the PCOD data, the Predicted Powder Diffraction Database (P2D2; Le Bail, 2008 ▶) was created, which provides identification by a search–match procedure similar to that of the Powder Diffraction File (Kabekkodu et al., 2002 ▶). In September 2007, the IUCr Executive Committee decided that the CIFs associated with structural papers published in IUCr journals should be made freely available to all databases, including the COD, giving the COD permission to routinely download new files from the IUCr site. This very welcome decision brought about a reorganization of the COD with the center of operations being transferred from Le Mans (France) to Vilnius (Lithuania) in December 2007. Five years after its foundation, in 2008, the COD passed a major milestone by archiving the 50 000th entry, while PCOD climbed over the 100 000 structure limit in the same year. Our actions to date are but the start of this database, and the COD hopes that more crystallographers will upload their results in order to accelerate its completion. New developments at the COD including automation of data deposition, data validation and correction, a novel search interface, and mirror sites and their synchronization, as well as the calculation of powder diffraction patterns, are briefly described in this paper. 2. Methodology 2.1. COD and PCOD contents The COD and PCOD each consist of two major parts: an SQL database and a collection of structure data files. The structure files record crystallographic data that were published in peer-reviewed scientific journals, or that were determined or predicted and donated by established crystallographic laboratories. The master copy of the data is recorded in CIF format (Hall et al., 1991 ▶). From the master copy of the (P)COD data collection, data tables for the (P)COD SQL databases are generated. These tables abstract the most important crystallographic, chemical and bibliographic information and are used for online searches. Currently, the data tables contain cell constants (a, b, c, α, β, γ), cell volume, Hermann–Mauguin space-group symbol, a summary chemical formula, the number of distinct chemical elements, and a descriptive text that includes the chemical names of the substance and bibliographic references. A special field, coeditor code, is also included in the database, in order to generate URL links to the original papers for those journals that accept data sharing (currently, the IUCr journals). We check and, when possible, restore systematic and trivial names of the reported chemical compounds and their formulas (IUPAC, structural and summary), since this information is vital for identification of the material. Information about chemical and hydrogen bonds is preserved in the COD CIFs if present in the original data file, but is not otherwise inferred from the structure. Each structure deposited in the COD and the PCOD gets a unique seven-digit number, a (P)COD identifier. If a structure of a compound is redetermined, with higher precision or under different conditions, it will be deposited in the (P)COD under a new (P)COD number. Since the COD identifier of a structure, once assigned, remains unchanged, a problem might arise when a deposited COD file needs to be changed for some reason, say, a syntax or data error must be corrected after the deposition. Currently, we have adopted a version control system called Subversion (Collins-Sussman et al., 2008 ▶). Each change of any COD file is recorded in a central COD repository, and the new version of the file automatically gets a new revision number. These numbers, along with the COD repository address, are inserted by the software into the COD file header. There is a publicly accessible interface to the COD that allows older revisions of any file to be extracted and the COD change logs recorded by COD maintainers to be read. Having a COD number and the revision number of a file, it is always possible to restore a previous version of that file. Structures are accepted in two formats – standard CIF format (http://www.iucr.org/resources/cif/) and a very simple REF (http://www.crystallography.net/ref.html) format, devised by A. Le Bail. The REF format is intended to be used in those cases where old data, predating the CIF era, need to be keyed in by hand or converted from some other format. 2.2. COD deposition procedure and validation Data in REF format, or occasionally in some other formats, are converted into the CIF format and then enter the same validation and deposition procedure as CIFs (Fig. 1 ▶). Each CIF is checked for syntax errors, using both the publicly available ‘vcif’ tool from the IUCr (McMahon, 1998 ▶) and our own CIF parser written in Perl (http://www.perl.com/; Wall et al., 2000 ▶). Syntactic errors, if any, must be corrected manually; this task is currently performed by a COD maintainer responsible for deposition. When the syntax is correct, structures are assigned a new range of sequential COD numbers. Bibliographic information is taken either from the data sections of the CIFs, from the data_global sections, or from auxiliary files in BibTeX (Patashnik, 2003 ▶) or PubMed XML format (http://www.ncbi.nlm.nih.gov/entrez/query/static/overview.html). As a last resort, the bibliographic information may be taken from the names of the directories containing CIFs, which are then chosen to reflect journal, year and journal issue, or the name of the donating person and laboratory. Each separate CIF is given a full copy of available bibliographic information, so that it can be further processed and stored independently. The CIFs now can be validated to check whether all necessary data items such as cell parameters, symmetry or bibliography are present. When all quality checks are passed, the existing COD database is scanned for duplicates. Duplicate structures are as a rule not deposited into the COD. A structure is considered a potential duplicate if its cell constants are within 0.5 Å and cell angles within 1.2° of any existing entry, the summary chemical formulas match, and both structures have been published in the same paper. If pressure and temperature are specified, these are also checked, and structures are considered duplicates only if they were measured under identical conditions. All potential duplicates are flagged and reviewed manually. The final step involves insertion of the CIFs into the Subversion repository and insertion of the data dump into the COD SQL table. The checked CIFs are presented to the CIF2COD program, which computes some derived data and creates a data dump that can be loaded into the COD MySQL table. The new structures become available on the Web immediately after deposition. Automated procedures have been developed to simplify the submission of data for users. For several years now, the MAUD software (Lutterotti et al., 1999 ▶) has included algorithms for submission. Such functionality makes it simple to submit data to the COD; submission does not even require a visit to the COD Internet page. The ‘Submit Structure to COD’ submenu lists the CIF of one of the actual phases of a given analysis. The corresponding window allows manual modification of the file, if necessary, before the submission is completed by simply clicking the ‘Submit to COD’ button. After submission, the uploaded CIF is treated identically to other ‘regular’ submissions from the Internet. 3. Discussion 3.1. Current status of COD and PCOD Currently, the COD stores over 80 000 structures of small organic and metal–organic molecules, inorganics, and minerals. The PCOD contains over 100 000 predicted inorganic crystal structures in CIF format, generated by the GRINSP programs (Le Bail, 2005). The number of different structure types is close to 30 000, the total number being attained by adding series of isostructural virtual compounds. For instance, there are ∼6400 different (Al/P)O4 compounds, and three other series of isostructural compounds with formulations SiO2, (Al/Si)O4 and (Al/S)O4. Besides the possibility of searching through the PCOD web interface, in a similar way to the COD, 48 complete series of compounds (characterized by the presence of the same chemical elements) are downloadable for prospective research. For anybody who wishes to use the COD and the PCOD databases, the collected files are presented using standard open protocols and formats. The database can be searched online on the COD server using a simple web-based search form, and the structural results can be downloaded either one by one or in a compressed .zip file. Alternatively, the whole collection of the COD files and database tables can be downloaded from the COD web site (using the http protocol) as a compressed .zip, .tar.gz or .tar.bz2 file, or updated via an rsync protocol (http://samba.anu.edu.au/rsync/) from rsync://www.crystallography.net/cod-cif and rsync://www.crystallography.net/pcod-cif so that the files can be used and examined on a user’s local machine. Finally, the COD and PCOD CIFs, database dumps and web scripts are available for anonymous checkouts from the COD Subversion server (svn://www.crystallography.net/cod and svn://www.crystallography.net/pcod). From this server an interested user can reconstitute locally the whole COD database and the web site for local searches, and also browse COD deposition logs and retrieve older revisions, should they be necessary. To facilitate the use of the COD as a reference database, it is planned that all data published in the COD will be assigned persistent URLs. Thus, any structure deposited in the COD should be available as http://www.crystallography.net/cif/〈COD number〉, e.g. http://www.crystallography.net/cif/1000000.cif. The open-access nature of the COD and the PCOD permits the creation of numerous mirrors of the COD and the PCOD. At present, three mirrors are available at http://cod.ibt.lt/, http://cod.ensicaen.fr/ and http://nanocrystallography.org/. Currently, one centralized repository is kept as an authoritative source of data, but with the growth of the databases a decentralized implementation is possible. 3.2. Future directions of COD and PCOD development A current challenge for all crystallographic databases, including the COD, is an exponential increase in the number of determined structural data entries. Fortunately, there is plenty of room to improve the efficiency of the COD deposition procedure. The current procedure involves a step in which a COD number is assigned by COD coordinator, and a step where the structures are checked by human depositors for possible errors. Both steps can be automated and parallelized. Finally, the structures still requiring human attention can be checked and edited in parallel by numerous COD reviewers all over the world, provided there is adequate software and enough volunteers participate in COD maintenance. Currently, the number of people contributing or willing to contribute to the development of the COD amounts to several dozen, apparently enough to provide qualified peer-review for the incoming structures. The development of the automatic data submission, annotation and CIF correction software is under way. Calculation of powder patterns is implemented for the PCOD data in the Match! software (http://www.crystalimpact.com/match/match18.htm). For researchers who wish to publish their structure-related work, most journals require the deposition of structures with a crystallographic database and ask for the database accession number as proof of deposition. For such structures, a special deposition status, ‘on hold until publication’, will be introduced. The structures submitted to the COD with the ‘on hold’ flag will be included in the COD SQL database where their cell constants, composition, symmetry and authorship will be indicated. A COD number will be assigned to the structure and returned to the author, and will be visible through the search interface of the COD. The atomic coordinates themselves, however, will not be released to the public until either the publication describing them appears, the authors inform the COD team that the coordinates should be released, or one year elapses from the original deposition of the CIFs. If the structure is not published within one year, an e-mail will be sent to the depositing author asking whether the structure should be released or withdrawn. At present, one of the main limitations of the functionality of the COD is the absence of a substructure search engine. In organic and metal–organic chemistry, the best way of defining such similarity is generally the presence of a common group of atoms chemically linked in the same way: this is what we call a ‘substructure’. For performing this task with COD data, we need to represent the chemical connectivity of the structures included in the COD in a suitable format, provide a tool for the user to input into the COD the definition of the substructure and finally employ a search–match engine that compares the user input against the COD data. A specialized chemical format such as CML (http://en.wikipedia.org/wiki/Chemical_Markup_Language) or SMILES (http://www.opensmiles.org/) with molecules already ‘grown’ across any possible crystallographic symmetry elements and simplifying the possible presence of chemically identical but crystallographically different moieties could be used for encoding the necessary information. The tools for user-friendly structure input and search are available under both free and commercial licenses (http://xdrawchem.sourceforge.net/, http://www.cambridgesoft.com/software/ChemOffice/, http://sourceforge.net/projects/joelib/, http://sourceforge.net/projects/cdk/). The remaining task is the integration of these tools with the COD.
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            TOPAS and TOPAS-Academic: an optimization program integrating computer algebra and crystallographic objects written in C++

             Alan Coelho (2018)
            TOPAS and its academic variant TOPAS-Academic are nonlinear least-squares optimization programs written in the C++ programming language. This paper describes their functionality and architecture. The latter is of benefit to developers seeking to reduce development time. TOPAS allows linear and nonlinear constraints through the use of computer algebra, with parameter dependencies, required for parameter derivatives, automatically determined. In addition, the objective function can include restraints and penalties, which again are defined using computer algebra. Of importance is a conjugate gradient solution routine with bounding constraints which guide refinements to convergence. Much of the functionality of TOPAS is achieved through the use of generic functionality; for example, flexible peak-shape generation allows neutron time-of-flight (TOF) peak shapes to be described using generic functions. The kernel of TOPAS can be run from the command line for batch mode operation or from a closely integrated graphical user interface. The functionality of TOPAS includes peak fitting, Pawley and Le Bail refinement, Rietveld refinement, single-crystal refinement, pair distribution function refinement, magnetic structures, constant wavelength neutron refinement, TOF refinement, stacking-fault analysis, Laue refinement, indexing, charge flipping, and structure solution through simulated annealing.
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              Radiation attenuation by lead and nonlead materials used in radiation shielding garments.

              The attenuating properties of several types of lead (Pb)-based and non-Pb radiation shielding materials were studied and a correlation was made of radiation attenuation, materials properties, calculated spectra and ambient dose equivalent. Utilizing the well-characterized x-ray and gamma ray beams at the National Research Council of Canada, air kerma measurements were used to compare a variety of commercial and pre-commercial radiation shielding materials over mean energy ranges from 39 to 205 keV. The EGSnrc Monte Carlo user code cavity. cpp was extended to provide computed spectra for a variety of elements that have been used as a replacement for Pb in radiation shielding garments. Computed air kerma values were compared with experimental values and with the SRS-30 catalogue of diagnostic spectra available through the Institute of Physics and Engineering in Medicine Report 78. In addition to garment materials, measurements also included pure Pb sheets, allowing direct comparisons to the common industry standards of 0.25 and 0.5 mm "lead equivalent." The parameter "lead equivalent" is misleading, since photon attenuation properties for all materials (including Pb) vary significantly over the energy spectrum, with the largest variations occurring in the diagnostic imaging range. Furthermore, air kerma measurements are typically made to determine attenuation properties without reference to the measures of biological damage such as ambient dose equivalent, which also vary significantly with air kerma over the diagnostic imaging energy range. A single material or combination cannot provide optimum shielding for all energy ranges. However, appropriate choice of materials for a particular energy range can offer significantly improved shielding per unit mass over traditional Pb-based materials.
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                Author and article information

                Journal
                Int J Mol Sci
                Int J Mol Sci
                ijms
                International Journal of Molecular Sciences
                MDPI
                1422-0067
                28 January 2020
                February 2020
                : 21
                : 3
                Affiliations
                [1 ]Dipartimento di Scienze e Innovazione Tecnologica, Università degli Studi del Piemonte Orientale, viale T. Michel, 11-15121 Alessandria, Italy; mattia.lopresti@ 123456uniupo.it (M.L.); simone.cantamessa@ 123456uniupo.it (S.C.); giorgio.cantino@ 123456uniupo.it (G.C.); eleonora.conterosito@ 123456uniupo.it (E.C.); luca.palin@ 123456uniupo.it (L.P.)
                [2 ]Bytest s.r.l.-TÜV SÜD Group, Research Center, via Pisa 12, 10088 Volpiano, Italy; gabriele.alberto@ 123456tuv.it
                Author notes
                Article
                ijms-21-00833
                10.3390/ijms21030833
                7037949
                32012889
                © 2020 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

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