Gimenez-Alventosa, V., Gimenez, V., Ballester, F., Vijande, J., & Andreo, P. (2020). Monte Carlo calculation of beam quality correction factors for PTW cylindrical ionization chambers in photon beams. Phys. Med. Biol., 65(20), 205005–11pp.
Abstract: The beam quality correction factork(Q)for megavoltage photon beams has been calculated for eight PTW (Freiburg, Germany) ionization chambers (Farmer chambers PTW30010, PTW30011, PTW30012, and PTW30013, Semiflex 3D chambers PTW31021, PTW31010, and PTW31013, and the PinPoint 3D chamber PTW31016). Simulations performed on the widely used NE-2571 ionization chamber have been used to benchmark the results. The Monte Carlo code PENELOPE/penEasy was used to calculate the absorbed dose to a point in water and the absorbed dose to the active air volume of the chambers for photon beams in the range 4 to 24 MV. Of the nine ionization chambers analysed, only five are included in the current version of the International Code of Practice for dosimetry based on standards of absorbed dose to water (IAEA TRS 398). The values reported in this work agree with those in the literature within the uncertainty estimates and are to be included in the average values of the data obtained by different working groups for the forthcoming update of TRS 398.
|
Richard, J. M., Valcarce, A., & Vijande, J. (2020). Very Heavy Flavored Dibaryons. Phys. Rev. Lett., 124(21), 212001–4pp.
Abstract: We explore the possibility of very heavy dibaryons with three charm quarks and three beauty quarks, bbbccc, using a constituent model which should lead to the correct solution in the limit of hadrons made of heavy quarks. The six-body problem is treated rigorously, in particular taking into account the orbital, color, and spin mixed-symmetry components of the wave function. Unlike a recent claim based on lattice QCD, no bound state is found below the lowest dissociation threshold.
|
Valdes-Cortez, C., Ballester, F., Vijande, J., Gimenez, V., Gimenez-Alventosa, V., Perez-Calatayud, J., et al. (2020). Depth-dose measurement corrections for the surface electronic brachytherapy beams of an Esteya(R) unit: a Monte Carlo study. Phys. Med. Biol., 65(24), 245026–12pp.
Abstract: Three different correction factors for measurements with the parallel-plate ionization chamber PTW T34013 on the Esteya electronic brachytherapy unit have been investigated. This chamber type is recommended by AAPM TG-253 for depth-dose measurements in the 69.5 kV x-ray beam generated by the Esteya unit. Monte Carlo simulations using the PENELOPE-2018 system were performed to determine the absorbed dose deposited in water and in the chamber sensitive volume at different depths with a Type A uncertainty smaller than 0.1%. Chamber-to-chamber differences have been explored performing measurements using three different chambers. The range of conical applicators available, from 10 to 30 mm in diameter, has been explored. Using a depth-independent global chamber perturbation correction factor without a shift of the effective point of measurement yielded differences between the absorbed dose to water and the corrected absorbed dose in the sensitive volume of the chamber of up to 1% and 0.6% for the 10 mm and 30 mm applicators, respectively. Calculations using a depth-dependent perturbation factor, including or excluding a shift of the effective point of measurement, resulted in depth-dose differences of about +/- 0.5% or less for both applicators. The smallest depth-dose differences were obtained when a shift of the effective point of measurement was implemented, being displaced 0.4 mm towards the center of the sensitive volume of the chamber. The correction factors were obtained with combined uncertainties of 0.4% (k = 2). Uncertainties due to chamber-to-chamber differences are found to be lower than 2%. The results emphasize the relevance of carrying out detailed Monte Carlo studies for each electronic brachytherapy device and ionization chamber used for its dosimetry.
|
Vijande, J., Valcarce, A., & Richard, J. M. (2013). Adiabaticity and color mixing in tetraquark spectroscopy. Phys. Rev. D, 87(3), 034040–5pp.
Abstract: We revisit the role of color mixing in the quark model calculation of tetraquark states, and compare simple pairwise potentials to more elaborate string models with three-and four-body forces. We attempt to disentangle the improved dynamics of confinement from the approximations made in the treatment of the internal color degrees of freedom.
|
Vijande, J., Valcarce, A., Richard, J. M., & Sorba, P. (2016). Search for doubly-heavy dibaryons in a quark model. Phys. Rev. D, 94(3), 034038–6pp.
Abstract: We study the stability of hexaquark systems containing two heavy quarks and four light quarks within a simple quark model. No bound or metastable state is found. The reason stems from a delicate interplay between chromoelectric and chromomagnetic effects. Our calculation also provides information about anticharmed pentaquarks that are seemingly unbound in simple quark models.
|
