Multiphoton Ionization of Uracil at 355 nm

E. PRIETO1 , A. GUERRERO1 , D. MARTÍNEZ1 , I. ÁLVAREZ1 , AND C. CISNEROS1*

1 Instituto de Ciencias Físicas-UNAM, Av. Universidad 1001, Chamilpa, 62210 Cuernavaca, Mor.

*Email: carmen@fis.unam.mx

Abstract We present the experimental results from ionization and dissociation by multiphoton absorption (MPI) of uracil and a mixture of uracil with Ar using a Reflectron time of flight spectrometer along with radiation from 355 nm at pulsed Nd:YAG laser . We focus on the light ions production. The MPI mass spectra show that the presence and intensity of the resulting ions depend on the density power of the laser. The resulting ions in the mass spectra are identified and found similar behavior in the case of H+ and C+ as when multiple charged ions are used. Different results were found in contrast with those, recently reported, when electrons or photons of other wavelength were used. The number of 355nm absorbed photons was calculated accordingly to Keldysh theory and similar results were fond using pure uracil or uracil-Ar mixture. Our results are compared with those obtained in other laboratories under different experimental conditions, some of them show only partial agreement and differences are discussed. 

DOI: https://doi.org/10.15415/jnp.2017.51004

LINK: http://dspace.chitkara.edu.in/jspui/bitstream/1/864/1/51004_JNP_Prieto%20-%20Cisneros.pdf

X-Ray Fluorescence Analysis of Ground Coffee

MARÍA CRISTINA HERNÁNDEZ1 , DARÍO ROMERO1 , HUMBERTO TORRES1 , JAVIER MIRANDA2,3*, AND A. ENRIQUE HERNÁNDEZ-LÓPEZ2

1 Facultad de Ciencias, Universidad Nacional Autónoma de México, Circuito Exterior, 04510, Coyoacán, Cd. Mx., MEXICO

2 Instituto de Física, Universidad Nacional Autónoma de México, Apartado Postal 20- 364, 01000 Álvaro Obregón, Cd. Mx., MEXICO 3 Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, Circuito Investigación Científica, 04510, Coyoacán, Cd. Mx., MEXICO

*Email: miranda@fisica.unam.mx

Abstract :

Coffee is becoming one of the most popular beverages in Mexico. In the present work, X-ray Fluorescence (XRF) was used to determine the contents of several elements (with atomic numbers between 11 and 38) in 11 samples of commercial ground coffee, comparing with another one of soluble coffee and two of used ground coffee. Samples were dried at room temperature and pelletized. XRF analyses were carried out using a spectrometer based on an Rh X-ray tube, registering the characteristic x-rays with a Silicon Drift Detector. The system detection calibration and accuracy check was performed through the analysis of NIST certified reference materials 1547 (peach leaves), 1570a (spinach leaves), 1573a (tomato leaves), and 1571 (orchid leaves). As a general rule, the elemental concentrations measured are similar in all samples of coffee, in values not exceeding toxic levels. However, the differences among the elemental concentrations are shown.

DOI: https://doi.org/10.15415/jnp.2017.51003

LINK: http://dspace.chitkara.edu.in/jspui/bitstream/1/863/1/51003_JNP_Miranda.pdf

Radiation Induced Oxidation Reactions of Ferrous Ions: An Agent-based Model

A.L. RIVERA1,2,*, A.S. RAMOS-BERNAL1 , A. NEGRÓN-MENDOZA

1 Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México. Circuito Exterior S/N, Ciudad Universitaria, Coyoacán, 04510 Ciudad de México, México.

2 Centro de Ciencias de la Complejidad, Universidad Nacional Autónoma de México.

*E-mail: ana.rivera@nucleares.unam.mx

Abstract:
Chemical Fricke dosimeter in the laboratory can be submitted to gamma radiation at low temperatures to study the evolution of oxidation reactions induced by radiation, a key process to understand the formation of complex molecules. Products generated by the interaction of the different elements under radiation can be determined through a mathematical model that considers chemical reactions as coupled nonlinear ordinary differential equations involving the mass balance of all the species in the reaction. In this paper is implemented an alternative way of solving this system of equations, species’ concentrations are calculated through an agent-based model implemented in Python. The model is a modified version of the prey-predator model where each chemical specie involved is considered as an agent that can interact with other specie with known reaction rates leading to production (source terms) and to destruction (sink terms). Here, the radiation is a factor that affects product formation while the bath temperature modifies the reaction speed. This model can reproduce experimental concentrations of products and the consumption of ferrous ions from a laboratory reaction of irradiation of iron salt solutions at 3 different temperatures (dry ice, liquid nitrogen, and room temperature).

DOI: https://doi.org/10.15415/jnp.2017.51002

LINK: http://dspace.chitkara.edu.in/jspui/bitstream/1/862/1/51002_JNP_%20RIVERA%20-%20NEGRON.pdf

Atomic Multiplet and Charge Transfer Effects in the Resonant Inelastic X-Ray Scattering (RIXS) Spectra at the Nickel L2,3 Edge of NiF2

J JIMÉNEZ-MIER,1,* P OLALDE-VELASCO,2 P DE LA MORA,3 W-L YANG,4 AND J DENLINGER4

1 Instituto de Ciencias Nucleares, UNAM, 04510 Ciudad de México, México
2 Instituto de Física, Benemérita Universidad Autónoma de Puebla, Puebla, A. Postal J-48 Puebla,         Puebla 72750, Mexico
3 Facultad de Ciencias, UNAM, 04510 Ciudad de México, México
4 The Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA

 *Email: jimenez@nucleares.unam.mx

Abstract Resonant inelastic x-ray scattering (RIXS) is used to study the electronic structure of NiF2 , which is the most ionic of the nickel compounds. RIXS can be viewed as a coherent two-steps process involving the absorption and the emission of x-rays. The soft x-ray absorption spectrum (XAS) at the metal L2,3 edge indicate the importance of atomic multiplet effects. RIXS spectra at L2,3 contain clearly defined emission peaks corresponding to d-excited states of Ni2+ at energies few eV below the elastic emission, which is strongly suppressed. These results are confirmed by atomic multiplet calculations using the Kramers-Heisenberg formula for RIXS processes. For larger energy losses, the emission spectra have a broad charge-transfer peak that results from the decay of hybridized Ni(3d)-F(2p) valence states. This is confirmed by comparison of the absorption and emission spectra recorded at the nickel L and fluorine K edges with F p and Ni d partial density of states using LDA + U calculations. Keywords: Core-level spectroscopies. RIXS, Nickel difluoride, Electronic structure

To read full paper please click here;
http://dspace.chitkara.edu.in/jspui/bitstream/1/861/1/51001_JNP_JIMENEZ.pdf

The Indoor Radon Concentration within the Tunnels of the Cholula Pyramid Through a Nuclear Tracks Methodology

DOI

10.15415/jnp.2016.41008

AUTHORS

A. Lima Flores, R. Palomino-Merino, E. Espinosa, V. M. Casta ño, E. Merlo Juárez, M. Cruz Sanchez, G. Espinosa

ABSTRACT

Global organizations, including the World Health Organization (WHO), the Environmental Protection Agency of the United States (US-EPA) and the European Atomic Energy Community (EURATOM) recognize that radon gas as one of the main contributors to environmental radiation exposure for humans. Accordingly, a study and analysis of the indoors radon concentrate in the Cholula Pyramid contributes to understand the Radon dynamic inside of the Pyramid tunnels and to evaluate the radiological health risk to visitors, archaeologists, anthropologists and persons who spend extended periods inside the Pyramid. In this paper, the radon measurements along the Pyramid tunnels are presented. The Nuclear Track Methodology (NTM) was chosen for the measurements, using a close end-cup device developed at the Dosimetry Application Project (DAP) of the Physics Institute UNAM, following very well established protocols for the chemical etching and reading with the Counting Analysis Digital Imaging System (CADIS). The Cholula Pyramid consists of eight stages of constructions, each built in different periods of time. Cholula Pyramid is recognized as the pyramid with the largest base in the World, with 400 meters per side and 65 meters high. The tunnels of the pyramid were built in 1931 by architect Ignacio Marquina, with the aim of exploring and studying the structure. The results show an important indoor radon concentration in the measured tunnels, several times higher than levels recommended by United States Environmental Protection Agency (US-EPA). The recommendation will be to mitigate the radon concentration levels, in order to avoid unnecessary exposition to the people.

KEYWORDS

Indoor radon, radon concentration, Nuclear Track Methodology, Cholula pyramid

LINK: http://jnp.chitkara.edu.in/abstract.php?id=476#exactabstracts

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A Scaling Law for L-Shell X-Ray Production Cross Sections Induced by Impact of 4He+, 9Be2+, and N2+ Ions

DOI

10.15415/jnp.2016.41007

AUTHORS

Javier Miranda

ABSTRACT

Experimental results of L-subshell X-ray production cross sections induced by the impact of several ions heavier than protons were compiled in order to propose possible scaling laws. The ions of interest in this work are ⁴He+, ⁹Be²+, and ¹⁴N²+. A feasible universal scaling for the x-ray production cross sections of the Lα (L₃M₄ + L₃M₅) line is based on a reduced velocity parameter ξ R L. In this scheme, the experimental data follow well resolved curves for each ion. A similar scaling for the Lγ line (L₂N₄ + L₁N₂ + L₁N₃ + L₁O₃ + L₁O₂ + L₂N₁ + L₂O₄) is also recommended, based on a different reduced velocity parameter ξ R L1,2. These results appear to be useful for all the studied projectile-target combinations covered in this work, supporting the idea that more theoretical studies in this direction should be done. However, the behavior of the fitting does not seem to follow the previously observed one.

KEYWORDS

X-rays, cross sections, heavy ion impact, PIXE.

LINK: http://jnp.chitkara.edu.in/abstract.php?id=475#exactabstracts

REFERENCES

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Theoretical Model to Estimate the Distribution of Radon in Alveolar Membrane Neighborhood

DOI

110.15415/jnp.2016.41006

AUTHORS

J. C. Corona, F. Zaldívar, L. A. Mandujan o-Rosas, F. Méndez, J. Mulia, D. Osorio-González

ABSTRACT

Radon is a naturally occurring radioactive gas which tends to concentrate indoors, easily emanates from the ground into the air, where it disintegrates and emits radioactive particles. It can enter the human body through breathing or ingesting mostly water. When radon inhaled, travels through the respiratory tract to alveoli where the majority is expelled into the environment. Moreover, when ingested in water, it passes into the intestine where it is absorbed and driven from the bloodstream to the lungs; in these organs, due to differences in partial pressures, it is transported to alveoli by simple diffusion process. When radon is not removed, it decays in short-lived solid disintegration products (218Po and 214Po) with high probability of being deposited in biological tissues, causing DNA damage because of the densely ionizing alpha radiation emitted. We propose a semi-empirical, smooth, and continuous pair potential function in order to model the molecular interactions between radon and lung alveolar walls; we use Molecular Dynamics (MD) to determine the gas distribution in an alveolar neighborhood wall, and estimate the quantity thereof it diffuses through the alveolar membrane as a concentration function.

KEYWORDS

Radon distribution; alveolar membrane; molecular dynamics; radon in alveoli

LINK:http://jnp.chitkara.edu.in/abstract.php?id=474#exactabstracts 

REFERENCES

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Using Green Fluorescent Protein to Correlate Temperature and Fluorescence Intensity into Bacterial Systems

DOI

10.15415/jnp.2016.41005

AUTHORS

K. Beltrán, J. M. de Jesús-Miranda, J. A. Castro, L. A. Mandujano-Rosas, J. M. Paulin-Fuentes, D. Osorio-González

ABSTRACT

The unique and stunning spectroscopic properties of Green Fluorescent Protein (GFP) from the jellyfish Aequorea victoria, not to mention of its remarkable structural stability, have made it one of the most widely studied and used molecular tool in medicine, biochemistry, and cell biology. Its high fluorescent quantum yield is due to its chromophore, structure responsible of emitting green visible light when excited at 395 nm. Although it is noteworthy that there is enormous available information of the wonderful luminescent properties of GFP, the fact is that there are features and properties unexplored yet, particulary about its capabilities as molecular reporter in several biological processes. In this work, we used recombinant DNA technology to express the protein in bacteria; prepared the bacterial system both in liquid and solid media, and assembled an experimental set to expose those media to a laser beam; thereby we excited the protein chromophore and used emission spectroscopy in order to observe variations in fluorescence when the bacterial system is exposed to different temperatures.

KEYWORDS

green fluorescent protein; bacterial systems; bacterial temperature; spectroscopic properties

REFERENCES

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On the Equivalent Sources and Geometric Factor Calculation for a Circular Detection

DOI

10.15415/jnp.2016.41004

AUTHORS

Tony Viloria A., Luis Montiel, Laszlo Sajo-Bohus, Daniel Palacios

ABSTRACT

In all absolute measurements of the intensity of the radioactive materials and calibration of the detectors, it is essential the knowledge of the geometric efficiency. This work describes how to obtain the sources with different geometries and equal geometric efficiency (equivalent sources for geometric factor), corresponding to a linear, circumferential and circular homogeneous sources parallel to a circular detector. It is estimated the geometric factor of them by the Monte Carlo method. The results are compared with the published in the literature, thus confirming the validity of this method.

KEYWORDS

geometric factor, Monte Carlo method, equivalent source.

LINK:http://jnp.chitkara.edu.in/abstract.php?id=472#exactabstracts

REFERENCES

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X-Ray Fluorescence Analysis of Fine Atmospheric Aerosols from a Site in Mexico City

DOI

10.15415/jnp.2016.41003

AUTHORS

A. E. Hernández-López, J. Miranda, J. C. Pineda

ABSTRACT

A study was performed in the Winter of the year 2015 in a Southwestern site in the MAMC (Ciudad Universitaria), collecting PM2.5 samples with a MiniVol. As a part of wider study focused to fully characterize aerosols at this site, an X-ray Fluorescence (XRF) spectrometer (based on an Rh X-ray tube) built to analyze environmental samples, was used to characterize the sample set. A total of 16 elements (Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, and Pb) were detected in most samples and mean concentrations were calculated. Cluster analysis was also applied to the elemental concentrations to find possible correlations among the elements.

KEYWORDS

XRF, atmospheric aerosols

REFERENCES

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