Radiolysis of Nucleosides: Study of Sedimentary Microenvironment Models for the Protection of Bio-Organic Molecules on Early Earth

E Y AGUILAR-OVANDO1,2* AND A NEGRÓN-MENDOZA1

1 Instituto de Ciencias Nucleares (ICN), Universidad Nacional Autónoma de México (UNAM)

2 Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos (UAEM)

*Email: ellen.aguilar@nucleares.unam.mx

Abstract Nucleic acid bases and their derivatives are important compounds in biological systems. Many efforts have been made to demonstrate the possible prebiotic origin of these molecules, but the abiotic synthesis of these compounds has proved to be very difficult in that conditions. So, if their synthesis actually took place, a study of their stability in prebiotic conditions is quite relevant in chemical evolution studies. In this work, it has been examined and compared the influence of Sodium Montmorillonite on the chemical transformations undergone by two nucleosides (guanosine – purinic– and uridine, –pyrimidinic–) when subjected to conditions simulating the primitive Earth during the period of chemical evolution. The experiments prove the concentration capacity and protective role against external sources of ionizing radiation (specifically γ-ray) that clays can provide to these specific compounds adsorbed on them. By using X-ray diffraction, UVvis spectrophotometry and HPLC for the analysis, it was found that purinic nucleosides (more than pyrimidinic) are quickly adsorbed on clay at low pH values, and the temperature of mineral desiccation applied after adsorption promotes their decomposition into their corresponding nitrogenous bases. In both, purinic and pyrimidinic, desorption occurs in neutral or slightly basic aqueous solutions, and both are protected by clay. Pyrimidinic nucleosides show more resistance to heat, but less resistance towards ionizing radiation, even when adsorbed in clay.

DOI: https://doi.org/10.15415/jnp.2017.51010

LINK: http://dspace.chitkara.edu.in/jspui/bitstream/1/870/1/51010_JNP_Aguilar%20-%20Negron.pdf

Application of a CdTe Detector for Measurements of Mammographic X-ray Spectra

J C SANTOS 1*, A TOMAL2 AND P R COSTA1 .

1 Instituto de Física, Universidade de São Paulo, SP, Brazil

2 Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, SP, Brazil

*Email: josilene@usp.br

Abstract 
This work aims to characterize mammographic x-ray beams incident and transmitted by breast phantoms (from 0 to 45 mm) composed from known proportion of glandular and adipose tissue-equivalent materials. This study was performed for mammographic x-ray beams generated by a mammography equipment using different target/filter combinations (Mo/Mo, Mo/Rh and W/Rh). It was studied the modification of spectra shape of the beams transmitted through different thicknesses of these materials. It was also evaluated the penetrability of these transmitted beams by its correlations to the HVL, which were experimentally estimated and derived from the x-ray spectra measured using a spectrometry system with a CdTe detector. The x-ray spectra transmitted by the phantom with higher density presented lower intensity than those transmitted by those with lower density, as expected. The differences between the HVL values derived from the spectra and those estimated using air kerma measurements are lesser than 6% for about 88% of the spectra measured in this work. The expected spectra variations with phantom thickness, revealed by the measured transmitted x-ray spectra, were also confirmed by HVL measurements and agree with the estimated attenuation curves. The motivation of the study was related to the robustness of the spectra as a descriptor of radiation beams and the possibility of using these transmitted spectra for dose assessment related to mammographic procedures. We can conclude that developed method is able to characterize mammographic x-ray beams making it possible the use of this kind of data for dose assessment in mammography.

DOI: https://doi.org/10.15415/jnp.2017.51009

LINK: http://dspace.chitkara.edu.in/jspui/bitstream/1/869/1/51009_JNP_Josilene%20Santos%20-%20Brasil.pdf

Characterization Of Structures Of Equivalent Tissue With a Pixel Detector

M.C GRADOS LUYANDO* , B. DE CELIS ALONSO, E. MORENO BARBOSA, M.I. MARTÍNEZ HERNÁNDEZ, J.M. HERNÁNDEZ LÓPEZ AND G. TEJEDA MUÑOZ

1 Benemérita Universidad Autónoma de Puebla

*Email: carminagl87@gmail.com

Abstract 
Research using hybrid pixel detectors in medical physics is on the rise. Timepix detectors have arrays of 256 × 256 pixels with a resolution of 55 µm. Here, and by using Timepix counts instead of Hounsfield units, we present a calibration curve of a Timepix detector analog to those used for CT calibration. Experimentation consisted of the characterization of electron density in 10 different kinds of tissue equivalent samples from a CIRS 062M phantom (lung, 3 kinds of bones, fat, breast, muscle, water and air). Radiation of the detector was performed using an orthodontic X-ray machine at 70 KeV and .06 second of tube current with a purpose-built aluminum collimator. Data acquisition was performed at 1 frame per second and taking 3 frames per phantom. We were able to find a curve whose behavior was similar to others already published. This will lead to the verification of the usage of Timepix for identification of different tissues in an organ.

DOI: https://doi.org/10.15415/jnp.2017.51008

LINK: http://dspace.chitkara.edu.in/jspui/bitstream/1/868/1/51008_JNP_Grados%20-%20Buap.pdf

Analysis and characterization of neutron scattering of a Linear Accelerator (LINAC) on medical applications.

A. LIMA FLORES1 , R. PALOMINO-MERINO1 , E. ESPINOSA1 , V.M. CASTAÑO2 , L. GUZMÁN-GATICA3 AND G. ESPINOSA4

1 Facultad de Ciencias Físico Matemáticas, Benemérita Universidad Autónoma de Puebla, Avenida San Claudio y 18 Sur, Colonia San Manuel, Ciudad Universitaria, Puebla C.P.72570, México

2 Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México, Boulevard Juriquilla 3001, Santiago de Querétaro, Querétaro C.P.76230, México

3 Servicios de Salud del Estado de Puebla, Antiguo Camino a Guadalupe Hidalgo 11350, Puebla C.P. 72490, México

4 Instituto de Física, Universidad Nacional Autónoma de México, Circuito de la Investigación Científica, Ciudad Universitaria, México D.F. C.P.04510, México

*Email: jaflores8630@gmail.com

Abstract 

In several theoretical and experimental studies, the topic of the undesirable generation of photoneutrons in rooms where a linear accelerator (LINAC) operates has been discussed. When energies above 10 MeV are used to produce X-rays and give radiotherapy treatment to patients resulting in additional radiation to patients. Accordingly, an analysis and characterization of the neutron scattering distribution on different zones in a treatment room contributes to evaluate the radiological health risk to patients, technical and other workers involved in treatment. For the evaluation, a device developed at the PAD-IFUNAM formed by a CR-39 detector enclosed by two 3mm thick acrylic plates was employed. To avoid environmental contamination, the CR-39 and the acrylics plates are enclosed in a round plastic box. Sixteen of these devices were settled in different places inside the treatment room, where a linear accelerator is used. The results show a significant concentration of neutron scattering in areas near the head of irradiation. The recommendation will be to evaluate the neutron scattering concentration in all rooms that’s operates a LINAC in order to verify the radiological health risk and to mitigate the neutron scattering when concentration levels are to high like those in our case, in order to avoid unnecessary exposition to patients and personnel in general. 

DOI: https://doi.org/10.15415/jnp.2017.51007

LINK: http://dspace.chitkara.edu.in/jspui/bitstream/1/867/1/51007_JNP_Lima-Flores%20Buap.pdf

Study of H2/N2Mixture Plasma Treatment on the AISI 1045

E. PARDO L.1*, J.G. GONZÁLEZ- RODRÍGUEZ1 , B CAMPILLO2 , F. CASTILLO2 , O. FLORES2 AND H. MARTINEZ2

1 Center of Research in Engineering and Applied Science, FCQeI UAEM., Av. Univ. 1001 Col., Chamilpa 62209, Cuernavaca Mor., Mexico

2 Institute of Physical Sciences, Autonomous National University of Mexico, P.O. Box 48-3, Av. Universidad s/n, Col. Chamilpa 62210, Cuernavaca Mor., Mexico

*Email: esteban.pardo@uaem.mx

Abstract:
 In the present work, we analyzed the effect of the plasma treatment of 80% H2 /20% N2 mixture plasma over the AISI 1045 steel. To produce the plasma, an AC discharge of 0.1 A at 350 V was produced at a total pressure of 3.0 Torr. The mixture plasma was analyzed using optical emission spectroscopy (OES), in the wavelength range of 200 to 1100 nm. The principal species observed in the plasma were NH, N2 , N2 +, H2 , and Hα. The electron temperature and ion density have been measured using a double Langmuir probe. The samples of steel were treated by plasma at different discharge times, between 3 and 12 h, at the same pressure and AC parameters (0.1 A and 350 V). The treated samples were characterized using X-ray analysis, finding the phases gamma and epsilon of iron nitride. The thickness of the nitrided layers was measured using a scanning electron microscope (SEM). From the images obtained, it is possible to appreciate the interphase between the nitrided layer and the steel matrix. The relationship between the morphology of the surface of nitrided steel and the wetting was analyzed by measuring the contact angle between the surface and a drop of 5 µL of distilled water. The contact angle of the drop increased with the increase of plasma treatment time. The control sample without treatment presented a smaller angle, and after the treatment the surfaces of the steel became hydrophobic. This may be related to the morphology change of the steel surface produced by plasma treatment.

DOI: https://doi.org/10.15415/jnp.2017.51006

LINK: http://dspace.chitkara.edu.in/jspui/bitstream/1/866/1/51006_JNP_Pardo%20-%20Fermin.pdf