P. Zélis | Universidad Nacional de La Plata (original) (raw)

Papers by P. Zélis

Long term gamma spectroscopy experiments involving singlechannel analyzer equipment depend upon t... more Long term gamma spectroscopy experiments involving singlechannel analyzer equipment depend upon thermal stability of the detector and its associated highvoltage supply. Assuming constant discrimination levels, a drift in the detector gain impacts the output rate, producing an effect on the output spectrum. In some cases (e.g. singleenergy resonant absorption experiments) data of interest can be completely lost. We present a digital selfadapting discrimination strategy that tracks emission line shifts using statistical measurements on a predefined regionofinterest of the spectrum. It is developed in the form of a synthesizable module that can be intercalated in the digital processing chain. It requires a moderate to small amount of digital resources and can be easily activated and deactivated.

Physica B: Condensed Matter, 2006

We have applied the transmission Mo¨ssbauer effect at a constant Doppler velocity technique, unde... more We have applied the transmission Mo¨ssbauer effect at a constant Doppler velocity technique, under 75 Oe external oscillating magnetic field in the frequency range 0-200 Hz, to determine the dynamics of the iron magnetic moments in nanocrystalline ribbons Fe 90 Zr 7 B 3 . The experiment was performed at a fixed Doppler velocity coincident with an absorption line of the absorbent. Since the dependence of the absorption on the angle between the gamma ray directions and the magnetic field at the nuclear probe is known, the change in the orientation of the iron atomic magnetic moments with the external field can be inferred. Due to the fact that in this case the absorption lines from the nanocrystalline phase are resolved from the amorphous one, performing the experiment at distinct absorption lines, we were able to determine the dynamics of the atomic moments of each phase independently. These results are complemented with Mo¨ssbauer Spectroscopy. r

Magnetic hydrophobic aerogels (MHA) in the form of nanocomposites of silica and maghemite (g-Fe 2... more Magnetic hydrophobic aerogels (MHA) in the form of nanocomposites of silica and maghemite (g-Fe 2 O 3 ) were prepared by one step sol-gel procedure followed by supercritical solvent extraction. Silica alcogels were obtained from TEOS, MTMS, methanol and H 2 O, and Fe(III) nitrate as magnetic precursor. The hydrophobic property was achieved using the methytrimethoxysilane (MTMS) as coprecursor for surface modification. The so produced nanocomposite aerogels are monolithic, hydrophobic and magnetic. The interconnected porous structure hosts $ 6 nm size g-Fe 2 O 3 particles, has a mean pore diameter of 5 nm, and a specific surface area (SSA) of 698 m 2 /g. Medium range structure of MHA is determined by SAXS, which displays the typical fractal power law behavior with primary particle radius of $ 1 nm. Magnetic properties of the nanoparticle ensembles hosted in them are studied by means of dc-magnetometry. .ar (M.B. Ferná ndez van Raap). Physica B 407 (2012) 3113-3116

Physics Letters A, 2002

Mössbauer thermal scans proved to be suitable to determining the magnetic hyperfine field tempera... more Mössbauer thermal scans proved to be suitable to determining the magnetic hyperfine field temperature dependence at the Fe site of the antiferromagnet FeSn 2 , if the Doppler energy is fixed at a value such that some of the nuclear transition energies cross that of the incident gamma ray when temperature is varied. 

Physica B: Condensed Matter, 2004

The alloy Fe 65 Ni 20 Nb 6 B 9 was obtained from the elemental constituents in a high-energy plan... more The alloy Fe 65 Ni 20 Nb 6 B 9 was obtained from the elemental constituents in a high-energy planetary ball mill and subsequently thermally treated at 873 and 900 K in order to obtain the equilibrium phases. The as-prepared nanocrystalline alloy consists primarily of metastable BCC a-Fe(Ni) nanocrystals while the treated ones consist of a mixture of BCC (ferromagnetic) and FCC (paramagnetic at room temperature) phases. Hysteresis loops at 5 and 300 K present low remanence and coercivity. As-prepared sample exhibits the best soft magnetic properties. In all samples, the susceptibility curves suggest magnetic collective (long-range order) behavior with a maximum between 70 and 90 K. This feature is caused by nanometric-sized magnetic particles. The huge difference between blocking and irreversibility temperatures in the field cooling and zero-field cooling scans indicates a wide grain-size distribution. r

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2014

Journal of Physics D: Applied Physics, 2008

Al coatings, with thickness (x) up to 20 µm, were deposited by dc sputtering on both sides of the... more Al coatings, with thickness (x) up to 20 µm, were deposited by dc sputtering on both sides of the Metglas 2605S2 precursor melt-spun ribbons. Spin reorientation, induced by the magnetoelastic effect, was clearly observed in the Al/Metglas 2605S2/Al trilayers by monitoring the 2 and 5 line intensities of the Mössbauer spectra obtained at different temperatures. The average spin orientation angles

Hyperfine Interactions, 2006

A prototype of a programmable constant-velocity scaler is presented. This instrument allows the a... more A prototype of a programmable constant-velocity scaler is presented. This instrument allows the acquisition of partial Mössbauer spectra in selected energy regions using standard drivers and transducers. It can be fully operated by a remote application, thus data acquisition can be automated. The instrument consists of a programmable counter and a constant-velocity reference. The reference waveform generator is amplitude modulated with 13-bit resolution, and is programmable in a wide range of frequencies and waveforms in order to optimize the performance of the transducer. The counter is compatible with most standard SCA, and is configured as a rate-meter that provides counts per selectable time slice at the programmed velocity. As a demonstration of the instrument applications, a partial Mössbauer spectrum of a natural iron foil was taken. Only positive energies were studied in 512 channels, accumulating 20 s per channel. A line width of 0.20 mm/s was achieved, performing with an efficiency of 80%.

Long term gamma spectroscopy experiments involving singlechannel analyzer equipment depend upon t... more Long term gamma spectroscopy experiments involving singlechannel analyzer equipment depend upon thermal stability of the detector and its associated highvoltage supply. Assuming constant discrimination levels, a drift in the detector gain impacts the output rate, producing an effect on the output spectrum. In some cases (e.g. singleenergy resonant absorption experiments) data of interest can be completely lost. We present a digital selfadapting discrimination strategy that tracks emission line shifts using statistical measurements on a predefined regionofinterest of the spectrum. It is developed in the form of a synthesizable module that can be intercalated in the digital processing chain. It requires a moderate to small amount of digital resources and can be easily activated and deactivated.

Physica B: Condensed Matter, 2006

We have applied the transmission Mo¨ssbauer effect at a constant Doppler velocity technique, unde... more We have applied the transmission Mo¨ssbauer effect at a constant Doppler velocity technique, under 75 Oe external oscillating magnetic field in the frequency range 0-200 Hz, to determine the dynamics of the iron magnetic moments in nanocrystalline ribbons Fe 90 Zr 7 B 3 . The experiment was performed at a fixed Doppler velocity coincident with an absorption line of the absorbent. Since the dependence of the absorption on the angle between the gamma ray directions and the magnetic field at the nuclear probe is known, the change in the orientation of the iron atomic magnetic moments with the external field can be inferred. Due to the fact that in this case the absorption lines from the nanocrystalline phase are resolved from the amorphous one, performing the experiment at distinct absorption lines, we were able to determine the dynamics of the atomic moments of each phase independently. These results are complemented with Mo¨ssbauer Spectroscopy. r

Magnetic hydrophobic aerogels (MHA) in the form of nanocomposites of silica and maghemite (g-Fe 2... more Magnetic hydrophobic aerogels (MHA) in the form of nanocomposites of silica and maghemite (g-Fe 2 O 3 ) were prepared by one step sol-gel procedure followed by supercritical solvent extraction. Silica alcogels were obtained from TEOS, MTMS, methanol and H 2 O, and Fe(III) nitrate as magnetic precursor. The hydrophobic property was achieved using the methytrimethoxysilane (MTMS) as coprecursor for surface modification. The so produced nanocomposite aerogels are monolithic, hydrophobic and magnetic. The interconnected porous structure hosts $ 6 nm size g-Fe 2 O 3 particles, has a mean pore diameter of 5 nm, and a specific surface area (SSA) of 698 m 2 /g. Medium range structure of MHA is determined by SAXS, which displays the typical fractal power law behavior with primary particle radius of $ 1 nm. Magnetic properties of the nanoparticle ensembles hosted in them are studied by means of dc-magnetometry. .ar (M.B. Ferná ndez van Raap). Physica B 407 (2012) 3113-3116

Physics Letters A, 2002

Mössbauer thermal scans proved to be suitable to determining the magnetic hyperfine field tempera... more Mössbauer thermal scans proved to be suitable to determining the magnetic hyperfine field temperature dependence at the Fe site of the antiferromagnet FeSn 2 , if the Doppler energy is fixed at a value such that some of the nuclear transition energies cross that of the incident gamma ray when temperature is varied. 

Physica B: Condensed Matter, 2004

The alloy Fe 65 Ni 20 Nb 6 B 9 was obtained from the elemental constituents in a high-energy plan... more The alloy Fe 65 Ni 20 Nb 6 B 9 was obtained from the elemental constituents in a high-energy planetary ball mill and subsequently thermally treated at 873 and 900 K in order to obtain the equilibrium phases. The as-prepared nanocrystalline alloy consists primarily of metastable BCC a-Fe(Ni) nanocrystals while the treated ones consist of a mixture of BCC (ferromagnetic) and FCC (paramagnetic at room temperature) phases. Hysteresis loops at 5 and 300 K present low remanence and coercivity. As-prepared sample exhibits the best soft magnetic properties. In all samples, the susceptibility curves suggest magnetic collective (long-range order) behavior with a maximum between 70 and 90 K. This feature is caused by nanometric-sized magnetic particles. The huge difference between blocking and irreversibility temperatures in the field cooling and zero-field cooling scans indicates a wide grain-size distribution. r

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2014

Journal of Physics D: Applied Physics, 2008

Al coatings, with thickness (x) up to 20 µm, were deposited by dc sputtering on both sides of the... more Al coatings, with thickness (x) up to 20 µm, were deposited by dc sputtering on both sides of the Metglas 2605S2 precursor melt-spun ribbons. Spin reorientation, induced by the magnetoelastic effect, was clearly observed in the Al/Metglas 2605S2/Al trilayers by monitoring the 2 and 5 line intensities of the Mössbauer spectra obtained at different temperatures. The average spin orientation angles

Hyperfine Interactions, 2006

A prototype of a programmable constant-velocity scaler is presented. This instrument allows the a... more A prototype of a programmable constant-velocity scaler is presented. This instrument allows the acquisition of partial Mössbauer spectra in selected energy regions using standard drivers and transducers. It can be fully operated by a remote application, thus data acquisition can be automated. The instrument consists of a programmable counter and a constant-velocity reference. The reference waveform generator is amplitude modulated with 13-bit resolution, and is programmable in a wide range of frequencies and waveforms in order to optimize the performance of the transducer. The counter is compatible with most standard SCA, and is configured as a rate-meter that provides counts per selectable time slice at the programmed velocity. As a demonstration of the instrument applications, a partial Mössbauer spectrum of a natural iron foil was taken. Only positive energies were studied in 512 channels, accumulating 20 s per channel. A line width of 0.20 mm/s was achieved, performing with an efficiency of 80%.