Nora L Maidana | Universidade de São Paulo (original) (raw)

Papers by Nora L Maidana

A calibration system composed of a 4pb-g gas-flow proportional counter coupled to a pair of NaI(T... more A calibration system composed of a 4pb-g gas-flow proportional counter coupled to a pair of NaI(Tl) crystals operating in coincidence was used for absolute measurement of Am sources activities. The samples were produced by irradiating dried aliquots of Am solution with epithermal neutrons in a research reactor. Efficiency tracing methodology using Co as tracer was applied. Thick external absorbers were used to change the Am beta detection efficiency and to avoid counting alpha particles from the dominating activity of Am. The resulting complex behavior of the beta detection efficiency curve was simulated by the Monte Carlo method, and the Am activity was obtained by least-squares method fitting. The activity was determined with an uncertainty of about 1%. r 2005 Elsevier B.V. All rights reserved. PACS: 27:90:þ b; 28.20.Fc; 28.50.Dr; 29.30. h

Disciplinas de mecanica frecuentemente abordan el estudio del movimiento del giroscopio por medio... more Disciplinas de mecanica frecuentemente abordan el estudio del movimiento del giroscopio por medio de recursos pedagogicos tipicamente demostrativos y/o explicaciones teoricas. Hemos desenvuelto material didactico para dar soporte a disciplinas introductorias de mecanica, aplicando nuevas tecnologias de la informacion y la comunicacion, mediante la filmacion experimentos reales y el procesado de esas imagenes. Los experimentos se realizaron en la Universidad de Sao Paulo y el material asi desenvuelto, alocado en la pagina de uso libre www.fisfoto.if.usp.br, es usado por los estudiantes de Licenciatura en Fisica de esa universidad. En este experimento se pueden medir posiciones angulares en momentos especificos de tiempo para determinar las velocidades de spin y precesion, ademas de encontrar la relacion entre el torque del peso del giroscopio y el momento angular. Entrevistamos 12 estudiantes que participaron en la actividad, con el fin de evaluar el material. Analizamos las entrevis...

La inclusion de laboratorios virtuales como actividad didactica en la ensenanza de la fisica en n... more La inclusion de laboratorios virtuales como actividad didactica en la ensenanza de la fisica en niveles basico y superior es una iniciativa que esta en expansion. Diversas experiencias fueron alocadas en la pagina de uso libre http://www.fisfoto.if.usp.br/, creadas a partir de la filmacion de experiencias reales, que son tratadas para obtener cuadros independientes de ese registro y permiten estudiar ciertos fenomenos con el auxilio de herramientas digitales. La experiencia de colisiones bidimensionales fue realizada con discos deslizando sobre una superficie con friccion despreciable e implementada por primera vez en la disciplina Laboratorio de Mecanica del tercer semestre del Profesorado en Fisica de la Universidad de Sao Paulo. Los informes de la experiencia, elaborados por los estudiantes, fueron analizados con intension de verificar la validad de la propuesta asi como para identificar errores o inconsistencias de la guia de la experiencia.

Hemos elaborado y aplicado en el aula una actividad experimental basada en una situacion real de ... more Hemos elaborado y aplicado en el aula una actividad experimental basada en una situacion real de lanzamiento de proyectil, con el objetivo de analizar su movimiento en diferentes sistemas de referencia. Para ello filmamos la locomotora de un tren en miniatura en movimiento horizontal, cuya chimenea posee un dispositivo capaz de lanzar verticalmente un objeto. Instantes antes que la locomotora atraviese un tunel, lanza una esfera hacia arriba – que realiza una trayectoria parabolica –y vuelve a caer en la chimenea. Este fenomeno, aparentemente inusitado, es el punto de partida para contextualizar los conceptos asociados a la transformacion de sistemas de referencia en movimiento relativo. La experiencia virtual esta disponible en el sitio http://www.fep.if.usp.br/~fisfoto y fue propuesta a los alumnos del curso Licenciatura en Fisica de la Univer-sidad de Sao Paulo. La descripcion de la experiencia, asi como los resultados de su aplicacion son narrados y discutidos aqui.

Radiation Physics and Chemistry, 2020

Abstract Silicon PIN (p-type-intrinsic-n-type) photodiodes are well suited as particle detectors.... more Abstract Silicon PIN (p-type-intrinsic-n-type) photodiodes are well suited as particle detectors. Here the interest is on a low-cost solution by repurposing a commercial device meant to be used as a light sensor. The intended application is to measure the energy spectra of electrons scattered by thin metallic foils covering small angles close to the beam of the accelerator. The main requirements for a suitable device are: 1) a low-cost solution to allow frequent replacements; 2) a small size to avoid as much as possible an unused area that contributes with unnecessary capacitance; 3) a good energy resolution; and 4) an easy repurposing as a charged-particle detector. The photodiode type BPX 65 manufactured by Osram® fulfils well these requirements. Four samples of these commercial devices have been electrically characterised with respect to reverse current and depleted-region capacitance. At the selected working point of 18 V, comfortably below the maximum rating of 20 V recommended by the manufacturer for continuous operation, the total thickness of the depleted and intrinsic regions is estimated to be ( 60 ± 3 ) μm. For the four samples considered, the measured reverse currents for a reverse bias of 18 V are around 0.1 nA, well below the typical value specified by the manufacturer (1 nA). To evaluate the performance of the device as a detector, energy spectra have been acquired for γ-rays with energies from 10 to 140 keV using 241Am, 133Ba, and 57Co radioactive sources. The resolution of the BPX 65 encountered with the γ-rays emitted by 241Am at 59.5-keV is ≈ 2.5 keV (FWHM - Full Width at Half Maximum), which is close to the value obtained with a pulser, showing that its main limitation is the electronic chain employed in the setup. The response function to monoenergetic electrons in the same energy range is studied in the companion paper.

Physical Review A, 2019

The alignment parameter A 20 of 73 Ta, 74 W, and 79 Au ions after L 3 subshell ionization by elec... more The alignment parameter A 20 of 73 Ta, 74 W, and 79 Au ions after L 3 subshell ionization by electron impact has been determined experimentally and theoretically in the wide energy range (1.02-10.2)E L 3 , where E L 3 is the L 3 ionization threshold. The A 20 values have been deduced from measurements of the L (L 3 → M 1), Lα 2 (L 3 → M 4), and Lα 1 (L 3 → M 5) x-ray angular distributions using thin targets. The beam energies have been selected above the threshold energy of each L subshell in order to also investigate the influence of the Coster-Kronig transitions on the anisotropy of x-ray emission. The results provide a clear indication of alignment and agree with calculations carried out within the plane-wave Born approximation up to about 6E L 3 , but an unpredicted inversion in the sign of A 20 is observed above this energy.

Journal of Physics B: Atomic, Molecular and Optical Physics, 2017

We have used the low-energy beam line of the Sao Paulo Microtron accelerator to study the maximum... more We have used the low-energy beam line of the Sao Paulo Microtron accelerator to study the maximum energy transfer point (tip) of electron–atom bremsstrahlung spectra for C, Al, Te, Ta and Au. Absolute cross sections differential in energy and angle of the emitted photon were measured for various electron kinetic energies between 20 and 100 keV, and photon emission angles of 35◦, 90◦ and 131◦. The bremsstrahlung spectra were collected with three HPGe detectors and their response functions were evaluated analytically. Rutherford backscattering spectrometry allowed us to obtain the thicknesses of the targets with good accuracy. We propose a simple model for the tip region of the bremsstrahlung spectrum emitted at a given angle, whose adjustable parameters are the mean energy of the incident beam and its spread as well as an amplitude. The model was fitted simultaneously to the pulse-height distributions recorded at the three angles, determining the doubly differential cross sections from the corresponding amplitudes. The measured values have uncertainties between 3% and 13%. The agreement of the experimental results with the theoretical partial-wave calculations of Pratt and co-workers depends on the analyzed element and angle but is generally satisfactory. In the case of Al and Au, the uncertainty attributed to the theory is probably overestimated.

Physics Education, 2016

The Virtual Laboratory was created as a complementary educational activity, with the aim of worki... more The Virtual Laboratory was created as a complementary educational activity, with the aim of working abstract concepts from an experimental point of view. In this work, the motion of a ring rolling and slipping in front of a grid printed panel was recorded. The frames separated from this video received a time code, and the resulting set of images can be visually inspected to determine the object angular and center-of-mass positions at known moments. From the positions versus time table, it is possible to analyse the dynamical evolution of the system and the ensuing physical interpretation of the ring rotation and translation. It is also shown here how this hands-on activity has been assigned to university students, that access the material from the website www.fep.if.usp.br/~fisfoto.

Radiation Physics and Chemistry, 2016

Type 2 diabetes still remains a major challenge to human health management. Protein tyrosine phos... more Type 2 diabetes still remains a major challenge to human health management. Protein tyrosine phosphate 1B has been continuously explored for its therapeutic potential to treat type 2 diabetes as it is linked with negative regulation of insu signal transduction. QSAR studies were performed on derivatives of 2 and SVM aided linear and non-linear models were obtained which were further evaluated to identify descriptors revealing underlying structure-activity relationship. QSAR models were validated through a series of validation techniques like Y randomization and descriptor sensitivity in addition to internal validation parameters. Information content index (IC1) of neighbourhood symmetry of order-1 has bee activity relationship of 2-arylsulphonylaminobenzothiazoles derivatives. Geary auto polarizability are also actively correlated to biological respo

Applied Radiation and Isotopes, 2004

The procedure to determine the statistical correlations between gray intensities is described her... more The procedure to determine the statistical correlations between gray intensities is described here, as well as that required to take these correlations into account. The advantages of using branching-ratios and feeding fractions instead of gray intensities in the gray standards are discussed.

Ionizing radiation produces both singly and multiply damaged DNA sites. One of the dilemmas encou... more Ionizing radiation produces both singly and multiply damaged DNA sites. One of the dilemmas encountered in radiation biology is that the dependence of relative biological effectiveness (RBE) on linear energy transfer (LET) for double-strand break (DSB) induction in DNA ...

Journal of synchrotron radiation, 2018

Dead-time effects in X-ray spectra taken with a digital pulse processor and a silicon drift detec... more Dead-time effects in X-ray spectra taken with a digital pulse processor and a silicon drift detector were investigated when the number of events at the low-energy end of the spectrum was more than half of the total, at counting rates up to 56 kHz. It was found that dead-time losses in the spectra are energy dependent and an analytical correction for this effect, which takes into account pulse pile-up, is proposed. This and the usual models have been applied to experimental measurements, evaluating the dead-time fraction either from the calculations or using the value given by the detector acquisition system. The energy-dependent dead-time model proposed fits accurately the experimental energy spectra in the range of counting rates explored in this work. A selection chart of the simplest mathematical model able to correct the pulse-height distribution according to counting rate and energy spectrum characteristics is included.

Journal of Physics B: Atomic, Molecular and Optical Physics

Radiation Physics and Chemistry

Nuclear Instruments Methods in Physics Research Section a Accelerators Spectrometers Detectors and Associated Equipment, 2005

The 232Th(n,Γ)233Th thermal neutron-capture reaction cross section was measured using targets of ... more The 232Th(n,Γ)233Th thermal neutron-capture reaction cross section was measured using targets of ∼ 1.5 mg of high-purity metallic thorium irradiated in the IPEN IEA-R1m 5 MW pool research reactor. The 197Au(n,Γ)198Au reaction was used to monitor the thermal and epithermal neutron fluxes in the irradiation position, which was found using the Westcott formalism. The residual gamma-ray activity was followed with an HPGe detector. The detector efficiency curve was fitted by the least-squares method applying covariance analysis to all uncertainties involved. The experimental result is σ0 =7.20±0.20 b, in agreement with previous published values.

A calibration system composed of a 4pb-g gas-flow proportional counter coupled to a pair of NaI(T... more A calibration system composed of a 4pb-g gas-flow proportional counter coupled to a pair of NaI(Tl) crystals operating in coincidence was used for absolute measurement of Am sources activities. The samples were produced by irradiating dried aliquots of Am solution with epithermal neutrons in a research reactor. Efficiency tracing methodology using Co as tracer was applied. Thick external absorbers were used to change the Am beta detection efficiency and to avoid counting alpha particles from the dominating activity of Am. The resulting complex behavior of the beta detection efficiency curve was simulated by the Monte Carlo method, and the Am activity was obtained by least-squares method fitting. The activity was determined with an uncertainty of about 1%. r 2005 Elsevier B.V. All rights reserved. PACS: 27:90:þ b; 28.20.Fc; 28.50.Dr; 29.30. h

Disciplinas de mecanica frecuentemente abordan el estudio del movimiento del giroscopio por medio... more Disciplinas de mecanica frecuentemente abordan el estudio del movimiento del giroscopio por medio de recursos pedagogicos tipicamente demostrativos y/o explicaciones teoricas. Hemos desenvuelto material didactico para dar soporte a disciplinas introductorias de mecanica, aplicando nuevas tecnologias de la informacion y la comunicacion, mediante la filmacion experimentos reales y el procesado de esas imagenes. Los experimentos se realizaron en la Universidad de Sao Paulo y el material asi desenvuelto, alocado en la pagina de uso libre www.fisfoto.if.usp.br, es usado por los estudiantes de Licenciatura en Fisica de esa universidad. En este experimento se pueden medir posiciones angulares en momentos especificos de tiempo para determinar las velocidades de spin y precesion, ademas de encontrar la relacion entre el torque del peso del giroscopio y el momento angular. Entrevistamos 12 estudiantes que participaron en la actividad, con el fin de evaluar el material. Analizamos las entrevis...

La inclusion de laboratorios virtuales como actividad didactica en la ensenanza de la fisica en n... more La inclusion de laboratorios virtuales como actividad didactica en la ensenanza de la fisica en niveles basico y superior es una iniciativa que esta en expansion. Diversas experiencias fueron alocadas en la pagina de uso libre http://www.fisfoto.if.usp.br/, creadas a partir de la filmacion de experiencias reales, que son tratadas para obtener cuadros independientes de ese registro y permiten estudiar ciertos fenomenos con el auxilio de herramientas digitales. La experiencia de colisiones bidimensionales fue realizada con discos deslizando sobre una superficie con friccion despreciable e implementada por primera vez en la disciplina Laboratorio de Mecanica del tercer semestre del Profesorado en Fisica de la Universidad de Sao Paulo. Los informes de la experiencia, elaborados por los estudiantes, fueron analizados con intension de verificar la validad de la propuesta asi como para identificar errores o inconsistencias de la guia de la experiencia.

Hemos elaborado y aplicado en el aula una actividad experimental basada en una situacion real de ... more Hemos elaborado y aplicado en el aula una actividad experimental basada en una situacion real de lanzamiento de proyectil, con el objetivo de analizar su movimiento en diferentes sistemas de referencia. Para ello filmamos la locomotora de un tren en miniatura en movimiento horizontal, cuya chimenea posee un dispositivo capaz de lanzar verticalmente un objeto. Instantes antes que la locomotora atraviese un tunel, lanza una esfera hacia arriba – que realiza una trayectoria parabolica –y vuelve a caer en la chimenea. Este fenomeno, aparentemente inusitado, es el punto de partida para contextualizar los conceptos asociados a la transformacion de sistemas de referencia en movimiento relativo. La experiencia virtual esta disponible en el sitio http://www.fep.if.usp.br/~fisfoto y fue propuesta a los alumnos del curso Licenciatura en Fisica de la Univer-sidad de Sao Paulo. La descripcion de la experiencia, asi como los resultados de su aplicacion son narrados y discutidos aqui.

Radiation Physics and Chemistry, 2020

Abstract Silicon PIN (p-type-intrinsic-n-type) photodiodes are well suited as particle detectors.... more Abstract Silicon PIN (p-type-intrinsic-n-type) photodiodes are well suited as particle detectors. Here the interest is on a low-cost solution by repurposing a commercial device meant to be used as a light sensor. The intended application is to measure the energy spectra of electrons scattered by thin metallic foils covering small angles close to the beam of the accelerator. The main requirements for a suitable device are: 1) a low-cost solution to allow frequent replacements; 2) a small size to avoid as much as possible an unused area that contributes with unnecessary capacitance; 3) a good energy resolution; and 4) an easy repurposing as a charged-particle detector. The photodiode type BPX 65 manufactured by Osram® fulfils well these requirements. Four samples of these commercial devices have been electrically characterised with respect to reverse current and depleted-region capacitance. At the selected working point of 18 V, comfortably below the maximum rating of 20 V recommended by the manufacturer for continuous operation, the total thickness of the depleted and intrinsic regions is estimated to be ( 60 ± 3 ) μm. For the four samples considered, the measured reverse currents for a reverse bias of 18 V are around 0.1 nA, well below the typical value specified by the manufacturer (1 nA). To evaluate the performance of the device as a detector, energy spectra have been acquired for γ-rays with energies from 10 to 140 keV using 241Am, 133Ba, and 57Co radioactive sources. The resolution of the BPX 65 encountered with the γ-rays emitted by 241Am at 59.5-keV is ≈ 2.5 keV (FWHM - Full Width at Half Maximum), which is close to the value obtained with a pulser, showing that its main limitation is the electronic chain employed in the setup. The response function to monoenergetic electrons in the same energy range is studied in the companion paper.

Physical Review A, 2019

The alignment parameter A 20 of 73 Ta, 74 W, and 79 Au ions after L 3 subshell ionization by elec... more The alignment parameter A 20 of 73 Ta, 74 W, and 79 Au ions after L 3 subshell ionization by electron impact has been determined experimentally and theoretically in the wide energy range (1.02-10.2)E L 3 , where E L 3 is the L 3 ionization threshold. The A 20 values have been deduced from measurements of the L (L 3 → M 1), Lα 2 (L 3 → M 4), and Lα 1 (L 3 → M 5) x-ray angular distributions using thin targets. The beam energies have been selected above the threshold energy of each L subshell in order to also investigate the influence of the Coster-Kronig transitions on the anisotropy of x-ray emission. The results provide a clear indication of alignment and agree with calculations carried out within the plane-wave Born approximation up to about 6E L 3 , but an unpredicted inversion in the sign of A 20 is observed above this energy.

Journal of Physics B: Atomic, Molecular and Optical Physics, 2017

We have used the low-energy beam line of the Sao Paulo Microtron accelerator to study the maximum... more We have used the low-energy beam line of the Sao Paulo Microtron accelerator to study the maximum energy transfer point (tip) of electron–atom bremsstrahlung spectra for C, Al, Te, Ta and Au. Absolute cross sections differential in energy and angle of the emitted photon were measured for various electron kinetic energies between 20 and 100 keV, and photon emission angles of 35◦, 90◦ and 131◦. The bremsstrahlung spectra were collected with three HPGe detectors and their response functions were evaluated analytically. Rutherford backscattering spectrometry allowed us to obtain the thicknesses of the targets with good accuracy. We propose a simple model for the tip region of the bremsstrahlung spectrum emitted at a given angle, whose adjustable parameters are the mean energy of the incident beam and its spread as well as an amplitude. The model was fitted simultaneously to the pulse-height distributions recorded at the three angles, determining the doubly differential cross sections from the corresponding amplitudes. The measured values have uncertainties between 3% and 13%. The agreement of the experimental results with the theoretical partial-wave calculations of Pratt and co-workers depends on the analyzed element and angle but is generally satisfactory. In the case of Al and Au, the uncertainty attributed to the theory is probably overestimated.

Physics Education, 2016

The Virtual Laboratory was created as a complementary educational activity, with the aim of worki... more The Virtual Laboratory was created as a complementary educational activity, with the aim of working abstract concepts from an experimental point of view. In this work, the motion of a ring rolling and slipping in front of a grid printed panel was recorded. The frames separated from this video received a time code, and the resulting set of images can be visually inspected to determine the object angular and center-of-mass positions at known moments. From the positions versus time table, it is possible to analyse the dynamical evolution of the system and the ensuing physical interpretation of the ring rotation and translation. It is also shown here how this hands-on activity has been assigned to university students, that access the material from the website www.fep.if.usp.br/~fisfoto.

Radiation Physics and Chemistry, 2016

Type 2 diabetes still remains a major challenge to human health management. Protein tyrosine phos... more Type 2 diabetes still remains a major challenge to human health management. Protein tyrosine phosphate 1B has been continuously explored for its therapeutic potential to treat type 2 diabetes as it is linked with negative regulation of insu signal transduction. QSAR studies were performed on derivatives of 2 and SVM aided linear and non-linear models were obtained which were further evaluated to identify descriptors revealing underlying structure-activity relationship. QSAR models were validated through a series of validation techniques like Y randomization and descriptor sensitivity in addition to internal validation parameters. Information content index (IC1) of neighbourhood symmetry of order-1 has bee activity relationship of 2-arylsulphonylaminobenzothiazoles derivatives. Geary auto polarizability are also actively correlated to biological respo

Applied Radiation and Isotopes, 2004

The procedure to determine the statistical correlations between gray intensities is described her... more The procedure to determine the statistical correlations between gray intensities is described here, as well as that required to take these correlations into account. The advantages of using branching-ratios and feeding fractions instead of gray intensities in the gray standards are discussed.

Ionizing radiation produces both singly and multiply damaged DNA sites. One of the dilemmas encou... more Ionizing radiation produces both singly and multiply damaged DNA sites. One of the dilemmas encountered in radiation biology is that the dependence of relative biological effectiveness (RBE) on linear energy transfer (LET) for double-strand break (DSB) induction in DNA ...

Journal of synchrotron radiation, 2018

Dead-time effects in X-ray spectra taken with a digital pulse processor and a silicon drift detec... more Dead-time effects in X-ray spectra taken with a digital pulse processor and a silicon drift detector were investigated when the number of events at the low-energy end of the spectrum was more than half of the total, at counting rates up to 56 kHz. It was found that dead-time losses in the spectra are energy dependent and an analytical correction for this effect, which takes into account pulse pile-up, is proposed. This and the usual models have been applied to experimental measurements, evaluating the dead-time fraction either from the calculations or using the value given by the detector acquisition system. The energy-dependent dead-time model proposed fits accurately the experimental energy spectra in the range of counting rates explored in this work. A selection chart of the simplest mathematical model able to correct the pulse-height distribution according to counting rate and energy spectrum characteristics is included.

Journal of Physics B: Atomic, Molecular and Optical Physics

Radiation Physics and Chemistry

Nuclear Instruments Methods in Physics Research Section a Accelerators Spectrometers Detectors and Associated Equipment, 2005

The 232Th(n,Γ)233Th thermal neutron-capture reaction cross section was measured using targets of ... more The 232Th(n,Γ)233Th thermal neutron-capture reaction cross section was measured using targets of ∼ 1.5 mg of high-purity metallic thorium irradiated in the IPEN IEA-R1m 5 MW pool research reactor. The 197Au(n,Γ)198Au reaction was used to monitor the thermal and epithermal neutron fluxes in the irradiation position, which was found using the Westcott formalism. The residual gamma-ray activity was followed with an HPGe detector. The detector efficiency curve was fitted by the least-squares method applying covariance analysis to all uncertainties involved. The experimental result is σ0 =7.20±0.20 b, in agreement with previous published values.