Vol. 58 No. 3 (2012): Revista Mexicana de Física.

Published: 2012-01-01

Articles

  • Letter from the Editor

    Francisco Ramos-Gómez., Efraín R. Chávez L.
    2-2

  • Neutron spectra and H*(10) of photoneutrons inside the vault room of an 18 MV LINAC

    A. Bañuelos-Frías, C.G. Borja-Hernández, K.A. Guzmán-García, C. Valero-Luna, V.M. Hernández-Dávila, H.R. Vega-Carrillo.
    192-194
    Abstract:
    Neutron spectra and the ambient dose equivalent were estimated inside the radiotherapy hall with an 18 MV linac. Estimations were carried out using Monte Carlo methods where a realist hall was modeled including a phantom made of equivalent tissue. The source term for photoneutrons was calculated using the Tosi et al. function that account for evaporation and knock-on neutrons. The spectra were estimated using two different energy distributions. Detectors were located in several sites inside the hall including the maze and outside the hall door, all detectors were located at the plane were the isocenter is located. In the treatment hall, as the distance respect to the isocenter is increased, the amount of neutrons and the H*(10) are reduced, neutrons in the high-energy region are shifted to lower region peaking around 0.1 MeV, however the epithermal and thermal neutrons remain constant due to the room-return effect. In the maze the spectra are dominated by epithermal and thermal neutrons that contributes to produce activation and the production of prompt gamma-rays.
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  • Neutron absorbed dose in a pacemaker CMOS

    C.G. Borja-Hernández, K.A. Guzmán-García, C. Valero-Luna, A. Bañuelos-Frías, L. Paredes-Gutiérrez, V.M. Hernández-Dávila, H.R. Vega-Carrillo
    195-197
    Abstract:
    The neutron spectrum and the absorbed dose in a Complementary Metal Oxide Semiconductor, has been estimated using Monte Carlo methods. Eventually a person with a pacemaker becomes an oncology patient that must be treated in a linear accelerator. Pacemaker has integrated circuits as CMOS that are sensitive to intense and pulsed radiation fields. Above 7 MV therapeutic beam is contaminated with photoneutrons that could damage the CMOS. Here, the neutron spectrum and the absorbed dose in a CMOS cell was calculated, also the spectra were calculated in two point-like detectors in the room. Neutron spectrum in the CMOS cell shows a small peak between 0.1 to 1~MeV and a larger peak in the thermal region, joined by epithermal neutrons, same features were observed in the point-like detectors. The absorbed dose in the CMOS was $1.522\times10^{-17}$ Gy per neutron emitted by the source.
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  • Position sensitive detection system for charged particles

    E.A. Coello, F. Favela, Q. Curiel, E. Chávez, A. Huerta, A. Varela, D. Shapira
    198-204
    Abstract:
    The position sensitive detection system presented in this work employs the Anger logic algorithm to determine the position of the light spark produced by the passage of charged particles on a $170\times170\times10$ mm$^{3}$ scintillator material (PILOT-U). The detection system consists of a matrix of nine photomultipliers, covering a fraction of the back area of the scintillators. Tests made with a non-collimated alpha particle source together with a Monte Carlo simulation that reproduces the data, suggest an intrinsic position resolution of up to 6 mm is achieved.
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  • Relative intensities of gadolinium L X-Rays, induced by proton bombardment at energies between 200 keV to 750 keV

    C.E. Canto, O.G. de Lucio, J.G. Morales, J.C. Pineda
    205-210
    Abstract:
    Relative intensities of Gd characteristic L X-Ray, induced by proton impact have been measured for GdF$_{3}$ thin films, as a function of projectile energy and also as a function of a variable defined as the relative velocity of the incoming particle. Results are presented as intensity ratios for L sub-shells and intensity ratios for particular transitions both of them measured with respect to the total number of X-ray photons recorded; in all cases it is possible to show an energy dependence for these intensity ratios. Complementary microanalysis studies (AFM, SEM/EDS) were performed in order to have accurate information on the chemical composition and surface properties of the thin films.
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  • $^{40}$K measurement to determine the total potassium content

    E. Escareño-Juárez, H.R. Vega-Carrillo
    211-214
    Abstract:
    Total potassium concentration has been determined measuring the 1461 keV gamma-rays emitted during the $^{40}$K decay. Using KCl salt set of $^{40}$K sources were prepared as standards and were used to characterize a NaI(Tl) $\gamma $-ray spectrometer. To test the procedure two unknown sources were used, for these $^{40}$K mass were determined as well as the specific activity. The rate of change between the mass of K and the net count rate under the 1461 keV photopeak is constant, allowing determining the mass of K measuring the $\gamma $-ray emitted during $^{40}$K decay. Specific activity was approximately 31 Bq/g being consistent with values reported in literature.
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  • Ageing effects on polymeric track detectors: studies of etched tracks at nanosize scale using atomic force microscope

    G. Espinosa, J.I. Golzarri, R. Fragoso, C.Vazquez-Lopez., A.F. Saad, A.A. El-Namrout, M. Fujii, .
    215-219
    Abstract:
    Among several different techniques to analyze material surface, the use of Atomic Force Microscope (AFM) is one of the finest method. As we know, the sensitivity to detect energetic ions is extremely affected during the storage time and conditions of the polymeric material used as a nuclear track detector. On the basis of the surface analysis of several track detector materials, we examined the detection sensitivity of these detectors exposed to alpha particles. The preliminary results revealed that the ageing effect on its sensitivity is very strong, that need to be considered on the routine applications or research experiments. The results are consistent with the experimental data in the literature.
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  • Passive neutron area monitor with TLD pairs

    K.A. Guzmán-García, C.G. Borja-Hernández, C. Valero-Luna, V.M. Hernández-Dávila, H.R. Vega-Carrillo
    220-223
    Abstract:
    The response of a passive neutron area monitor with pairs of thermoluminescent dosimeters has been calculated using the Monte Carlo code MCNP5. The response was calculated for one TLD 600 located at the center of a polyethylene moderator. The response was calculated for 47 monoenergetic neutron sources ranging from 1E(-9) to 20 MeV. Response was calculated using two irradiation geometries, one with an upper source and another with a lateral source. For both irradiation schemes the response was calculated with the TLD in two positions, one parallel to the source and another perpendicular to the source. The advantage of this passive neutron monitor area is that can be used in locations with intense, pulsed and mixed radiation fields like those in radiotherapy vault rooms with linear accelerators.
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  • Determination of uranium and polonium in Sparus aurata by alpha spectrometry

    M. Luna Porres, G. Manjón Collado, I. Díaz, M. Rentería, M.E. Montero Cabrera
    224-227
    Abstract:
    The aim of this study was optimizing conditions for the specific activities determination of some uranium-series radionuclides present in Sparus aurata by alpha spectrometry. Determinations of specific activities were conducted varying the type of digestion: acid attack on hot plate, controlled microwave digestion and acid attack after calcination of the sample. The latter procedure was applied only to the case of uranium isotopes determination. The variation in the isotope extraction method consisted of applying the techniques of liquid-liquid extraction using Tributyl phosphate (TBP) or chromatographic UTEVA resin. Results depending on the type of treatment given to the samples were compared based on obtained chemical yields. The results reveal a higher bioaccumulation of polonium in the liver sample, with activities of 0.809, 2.495 and 2.439 Bq kg$^{ - 1}$ fresh wt compared with the fillet. The best chemical yields for polonium were close to 60% for samples that were digested by microwave. In the case of uranium the best chemical yields, close to 80% for fillet, were obtained with a previous calcination of the sample and using the UTEVA resin.
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  • Thermoluminescence characteristics of the irradiated minerals extracted from red pepper (Capsicum annuum L.) spice

    J. Marcazzó, E. Cruz-Zaragoza, L. Montiel, V. Chernov, T. Calderón
    228-233
    Abstract:
    The inorganic polymineral content in the foodstuffs allows to analyze the main thermoluminescence (TL) characteristics that may be useful in the identification of irradiated food. The mineral fraction was separated from commercial Mexican red pepper (Capsicum annuum L.). X-ray diffraction shows that the mineral composition of the samples was mainly quartz. From the mineral fraction of different grain sizes, samples of 149 $\mu $m were selected for this study because of the high TL signals. The samples were irradiated from 1 to 500 Gy by using a $^{60}$Co irradiator. The TL characteristics like glow curve shape, dose-response, UV and sunlight bleaching and fading were analyzed. The glow curves show an intense TL peak at 82 $^\circ$C followed by others with less intensity at 130, 170 and 340 $^\circ$C. The T$_{M}$-T$_{STOP }$method shows six TL glow peaks that was taken into account for calculation the activation energies values. Because the complex structure of the glow curves, the kinetics parameters were determined by using a computerized deconvolution program assuming the general order kinetics model.
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  • Application of the alpha spectrometry for the study of core sediment extracted in the San Marcos dam in Chihuahua

    C. Méndez García, R.García-Tenorio., M. Rentería Villalobos, María Elena Montero Cabrera.
    234-237
    Abstract:
    The determination of the specific activities of $^{210}$Po and isotopic uranium by alpha spectrometry was performed in a sediment core from San Marcos Dam. The objective of this work was to analyze the vertical distribution of isotopic uranium and $^{210}$Po and the behavior of these radionuclides along sediment core collected from the San Marcos Dam. Sample was divided into 11 sections, in which $^{210}$Po and Isotopic Uranium were determined using liquid-liquid extraction with tributyl phosphate (TBP). Furthermore, it was made a comparison between the TBP technique and the technique of extraction chromatography using UTEVA resins for uranium. The results of specific activities for $^{210}$Po show a trend to decrease along the core, whereas the uranium isotopic does not show a pointed trend. The results of isotopic ratios between the $^{234}$U and $^{238}$U show that they are close to secular equilibrium in each of the core sections. The comparison between the two uranium extraction techniques indicates that chemical yield is better using the UTEVA technique than TBP extraction.
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  • Measurement of L X-ray production cross sections by impact of protons with energies between 2.5 MeV and 5.0 MeV in selected lanthanoids

    J. Mir, a., G. Murillo, B. Méndez, J. López-Monro, J. Aspiazu, P. Villaseñor, .
    238-240
    Abstract:
    Accurate quantitative analysis with particle induced X-ray emission (PIXE) requires an accurate knowledge of the X-ray production cross sections, in particular the L lines. While there are a lot of experimental results, recent reviews have found a disagreement between several previously published papers and also by the use of different atomic parameters databases (fluorescence yields and Coster-Kronig transition probabilities). Therefore, it is very convenient to redo some of these cross sections measurements and to extend to other proton energy ranges. Thus, this paper presents results with lanthanoid elements (Ce, Nd, Sm, Eu, Gd, Dy, Ho) irradiated with protons in the energy range 2.5 MeV to 5.0 MeV. The results are compared also with predictions of the ECPSSR theory with the United Atom modification and experimental data of other authors.
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  • Radioactive hydrogeochemical processes in the Chihuahua-Sacramento Basin, Mexico

    J.C. Burillo, M. Re, es Cortés., M.E. Montero Cabrera, I. Re, es., M.S. Espino, M. Rentería-Villalobos, E.F. Herrera Peraza
    241-248
    Abstract:
    The Chihuahua Basin is divided by its morphology into three main subbasins: Chihuahua-Sacramento subbasin, Chihuahua Dam subbasin and Chuviscar River subbasin. In the aquifers at the Sacramento subbasin, specific concentrations of uranium in groundwater range from 460 to 1260 Bq / m$^{3}$. The presence of strata and sandy clay lenses with radiometric anomalies in the NW of Chihuahua Valley was confirmed by a litostatigraphic study and gamma spectrometry measurements of drill cuttings. High uranium activity values found in the water of some deep wells may correspond to the presence of fine material bodies of carbonaceous material, possible forming paleo-sediment of flooding or paleo-soils. It is suggested that these clay horizons are uranyl ion collectors. Uranyl may suffer a reduction process by organic material. Furthermore the groundwater, depending on its pH and Eh, oxidizes and re-dissolves uranium. The hydrogeochemical behavior of San Marcos dam and the NW Valley area is the subject of studies that should help to clarify the origin of the radioactive elements and their relationships with other pollutants in the watershed.
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  • Particle induced X-ray emission of lake sediment

    G.F. Peaslee, P.A. DeYoung
    249-252
    Abstract:
    Three recent ion beam analysis research projects are described that have been undertaken by the Hope College Nuclear Group. Success in the routine ion beam analysis of lake sediment as well as the elemental analysis of lake sediment for environmental fingerprinting is reported. In addition, a novel ion beam analysis detection method for organohalogen flame retardants in polyurethane foam is proposed, and in each of these research projects significant student training has occurred. Building on the success of prior research published in both nuclear physics and applied physics, these projects involve undergraduate students in every aspect of the sample collection, data acquisition and data analysis. The combination of publishable scientific inquiry and undergraduate training using ion beam analysis is suggested as a model that could be done wherever there are appropriate accelerator facilities.
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  • Synthesis of Potassium and Calcium Uranovanadates, analogues of Carnotite and Metatyuyamunite Minerals

    J.L. Requena Yáñez, M. Re, es Cortés., E. Torres Mo, e., D. Lardizabal, H. Riveros, M.E. Montero Cabrera
    253-257
    Abstract:
    The aim of this study was to develop a synthesis of metatyuyamunite (Ca(VUO$_{6})_{2}\cdot$3-5H$_{2}$O) and carnotite (KVUO$_{6}\cdot$1-3H$_{2}$O) under hydrothermal conditions. Also, crystals obtained from this synthesis were compared with crystals from melting method. The analyses of synthesis products were performed by X-Ray techniques. X-Ray Diffraction was used for both species identification, whereas Scanning Electron Microscopy was used to analyze their morphology and elemental composition. Both uranovanadates were positive synthesized under hydrothermal conditions; besides, their morphology presents particles agglomerates. Calcium uranovanadate agglomerates contain well-defined crystals, whereas potassium uranovanadate agglomerates consist in fine powder particles.
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  • Capture of air particulate matter and gaseous Hg$^{0}$ by ionic liquids analyzed by PIXE

    M.A. Martínez-Carrillo, C. Solís, E. Andrade, M.A. Mondagón G, B. Méndez.
    258-261
    Abstract:
    Particle induced X-ray emission (PIXE) has been extensively employed to study the elements associated to air particulate matter (PM). However, the atmosphere is a very complex system and inorganic pollutants may be also in gaseous phases. Aerosol monitoring does not allow the determination of all the volatile inorganic compounds, since they are not retained in the filters, or if they are trapped, the analysis under vacuum results in a partial or total loss of them. In order to extend the applications of PIXE there is a need to develop new methods to simultaneously capture particulate matter and volatile substances. Ionic liquids (IL) result from combinations of organic cations and anions that may be liquid at room temperature. The physicochemical characteristics of ILs allow them to absorb atmospheric trace metals present in solid and gaseous phases, a task normally performed with independent sampling methods. In this work we explored this capability of ILs as monitors of chemical species which can be found in the gas phase and as particulate matter. The tested ILs included 1-Butyl-3-Methyl-Imidazolium-Hexafluorophosphate [BMIM][PF$_{6}$] for PM and Hg capture; and 1-Butyl-3-methylimidazolium thiocyanate [BMIM][SCN] only for Hg capture. Elemental analysis of both experiments was performed by Particle Induced X-ray emission (PIXE). Changes in the molecular structure on BMIM PF$_{6}$ due to the Hg binding were followed by infrared (IR) spectroscopy. [BMIM][PF$_{6}$] proved to be successful as passive collector of PM. However when both were used for Hg capture, [BMIM][SCN] showed better selectivity. These preliminary results showed the potential of IL's for simultaneous uptake of PM and volatile inorganic compounds.
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  • Neutron area monitor with passive detector

    C. Valero-Luna, K.A. Guzmán-García, C.G. Borja-Hernández, V.M. Hernández-Dávila, H.R. Vega-Carrillo
    262-264
    Abstract:
    Using Monte Carlo methods the responses of a passive neutron monitor area has been calculated. To detect thermal neutrons the monitor has a gold foil that is located at the center of a polyethylene cylinder. Impinging neutrons are moderated by polyethylene nuclei reaching the gold foil with the energy to induce activation through the reaction $^{197}$Au(n, $\gamma)\;\;^{198}$Au. The $^{198}$Au decays emitting 0.411 MeV gamma rays with a half life of 2.7 days. The induced activity is intended to be measured with a gamma-ray spectrometer with a 3'' ${\O} \times$ 3'' NaI(Tl) scintillator and the saturation activity is correlated to the ambient dose equivalent. The response was calculated for 47 monoenergetic neutron sources ranging from 1$\times10^{-9}$ to 20 MeV. Calculated fluence response was compared with the response of neutron monitor area LB 6411.
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  • Paraxial theory of sum-frequency generation by sideways alignment and phase-matching in uniaxial crystals

    S. Hac, an.
    265-269
    Abstract:
    A formalism in terms of Hertz potentials is presented describing sum-frequency generation in a uniaxial non-linear crystal. A scheme is proposed consisting in aligning the sideways propagation of extraordinary waves in combination with phase-matching. Simplified paraxial equations describing this situation are obtained. Particular attention is paid to the generation of second harmonics.
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  • Modulation of coherence and polarization using nematic 90$^{\circ}$-twist liquid-crystal spatial light modulators

    C. Rickenstorff, E. Flores, M.A. Olvera-Santamaría, A.S. Ostrovsk, .
    270-273
    Abstract:
    A technique for modulating the coherence and polarization of the electromagnetic field using 90$^{\circ}$-twist liquid-crystal spatial light modulators (LC-SLMs) is proposed. The controlled change of the statistical properties of light is achieved through computer generated random signals applied to a pair of 90$^{\circ}$-twist LC-SLMs arranged in an interferometric setup. Experimental results obtained using Holoeye LC2002 modulators show the efficiency of the proposed technique.
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  • On maximizing positive Lyapunov exponents in a chaotic oscillator with heuristics

    L.G. de la Fraga, E. Tlelo-Cuautle, V.H. Carbajal-Gómez, J.M. Muñoz-Pacheco
    274-281
    Abstract:
    A positive Lyapunov exponent indicates the presence of chaos in a dynamical system. In this manner, computing its maximum value guarantees the unpredictability grade of a chaotic system. In this investigation we present the application and comparison of two heuristics: Differential Evolution (DE) and Particle Swarm Optimization (PSO), to maximize the positive Lyapunov exponent in a multi-scroll chaotic oscillator based on saturated nonlinear function series. The computed results show that DE and PSO algorithms are suitable to maximize the positive Lyapunov exponent of truncated coefficients over the continuous spaces. In addition, the phase diagrams show that for a small positive Lyapunov exponent the attractors are well defined, while for its maximum value, the attractors are not well appreciated because the unpredictability grade of the chaotic oscillator is increased.
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  • On the scope and importance of the Revista Mexicana de Física in the Mexican and Latin American Physical Science Community

    F. Ramos-Gómez, Raúl Espejel-Morales.
    282-288
    Abstract:
    We analyze the scope and importance that the Revista Mexicana de Física (RMF) has had in the Mexican and Latin American physical science community, from two points of view: the author(s) institution and the different fields within physics of the published papers over a five years period (2007--2011). We find that almost every Mexican scientific institution that does research in physical science has published in RMF over the mentioned period. The presence of other Latin American institutions is also illustrated. We also show the great diversity of fields (according to the declared PACS$^{\textregistered}$ codes) covered in the RMF papers, which confirms the general physics nature of our journal.
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