WO2002055972A1 - Mossbauer spectrometer with piezo transducer technology and solid state detectors - Google Patents

Mossbauer spectrometer with piezo transducer technology and solid state detectors Download PDF

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Publication number
WO2002055972A1
WO2002055972A1 PCT/ES2002/000016 ES0200016W WO02055972A1 WO 2002055972 A1 WO2002055972 A1 WO 2002055972A1 ES 0200016 W ES0200016 W ES 0200016W WO 02055972 A1 WO02055972 A1 WO 02055972A1
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spectrometer
solid state
piezoelectric oscillator
radioactive source
spectrometer according
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PCT/ES2002/000016
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Spanish (es)
French (fr)
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Elies Molins Grau
Lluis Casas Duocastella
Anna Roig Serra
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Consejo Superior De Investigaciones Científicas
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Publication of WO2002055972A1 publication Critical patent/WO2002055972A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
    • G01N23/06—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and measuring the absorption

Definitions

  • M ⁇ ssbauer spectrometer with piezo-transducer technology and solid-state detectors M ⁇ ssbauer spectrometer with piezo-transducer technology and solid-state detectors.
  • the present invention consists in the introduction of the technology of piezoelectric transducers and solid state detectors in the design of Móssbauer spectrometers.
  • the application of such technology reports substantial improvements in the spectrometer's potential.
  • the Mossbauer effect a fundamental principle of homonymous spectroscopy, was discovered in 1958. Since its discovery, Mossbauer spectroscopy has developed as an ideal technique for structural and magnetic characterization of a wide variety of materials.
  • the technical area would therefore be the broad sector of natural and technological materials; including the most diverse application sectors: amorphous and nanocrystalline materials for magnetic applications, biochemical reactions, cancer diagnosis, catalysts, corrosion products, environmental studies, crystallographic and chemical characterization, metallurgy, materials science, mineralogy, geology and archeology to cite Only the most common.
  • a conventional Mossbauer spectrometer consists of:
  • a certain voltage applied to the device is equivalent to a certain vibrator speed, generally a triangular type signal with a frequency of 30 Hz is applied.
  • the Mossbauer spectrum consists of a graph of velocities (or radiation energies) vs. degree of radiation absorption, from it important data can be extracted about properties such as the oxidation state, the crystalline environment, the magnetic arrangement, the dynamic state of the atoms, etc. - a detection system comprising the detector, preamplifier, amplifier, discriminator and multichannel analyzer.
  • the most commonly used detectors are those consisting of a large crystal of sodium iodide attached to a photomultiplier or a gas detector (Ar, Xe or Kr).
  • the detected signal is amplified and conveniently selected [Viegers, MPA, Trooster, JM: Nucl. Instr. Meth. 118, 257 (1974)] until reaching the multichannel analyzer that manages the count in channels corresponding to speed intervals; then, therefore, its operation must be synchronized with the movement of the transducer or vibrator.
  • a very important accessory in a Mossbauer spectrometer is a cryostat for measurements at various temperatures, these are special designs due to the physical characteristics of the spectrometer [Cohen, RL, Wertheim, GK: Methods of Experimental Physics 11, 307 (1974)] .
  • the differences between the first spectrometers [Tomov, T.
  • the Móssbauer spectrometer has several limitations inherent to the use of traditional components: the electromagnetic transducer is usually a heavy cylinder 20 cm long and 10 cm in diameter, the detector is usually a large sodium iodide crystal attached to a photomultiplier in the case of high energy spectroscopy (ex. 28.3 keN 119 Sn) or more commonly (14.4 keN 57 Fe) a proportional gas detector also of decimetric dimensions.
  • cryostats For the measurements at pre-established temperatures and magnetic fields, expensive cryostats of specific design are used since the detector is always located outside and the transducer generally also so the cryostat must allow the entry and exit of gamma radiation.
  • the radioactive source is inside the cryostat so that the transmission of the vibration must be carried out by means of a long rod leading to a reduction in the reliability of such transmission.
  • Conventional outside detector and source
  • the loss of count due to the various mylar windows that radiation must pass through is considerable. Even at room temperature it is not possible to bring the source too close to the sample because, due to the amplitude of the vibration, the spectrum is distorted due to a geometric effect.
  • the basic components of the new design are:
  • a piezoelectric oscillator preferably of the "multilayer” type that can be controlled by a variable voltage synchronized with the opening and closing of the channels of the multichannel analyzer.
  • a radioactive source preferably 57 Co, rigidly attached to the piezoelectric oscillator.
  • a detection system consisting of one or several solid state detectors such as cadmium telluride (CZT) with a detection element of the order of 3x3x2 ram.
  • a system of amplification and management of the recorded data including the multichannel analyzer necessarily synchronized with the electrical function that controls the piezoelectric oscillator.
  • the two fundamental devices can operate at low temperatures
  • the design could be conceived as a MicroMóssbauer attached to the end of a rod as an "insert" for its introduction into conventional cryostats.
  • the new miniaturized device could be introduced in high magnetic fields, requiring in this case (except in exceptional cases) radioactive sources not susceptible to polarization.
  • the dielectric nature of the piezoelectric oscillator necessarily produces a gap between the signal that governs the movement of the transducer and its movement. Due to this effect, displaced spectra are obtained that need modified software for analysis.
  • the direct relationship between the voltage and the position of the transducer makes a senosoidal signal (for its control) preferable to the triangular signal commonly used for conventional electromagnetic transducers.
  • the Móssbauer spectrometer object of the invention comprises (Fig. 1) a gamma ray source (1) rigidly connected to a piezoelectric oscillator (2) with a longitudinal vibration to the gamma ray path ( ⁇ ), an object absorbent (3) of study and a solid state radiation detector (4).
  • the detected signal is amplified in the preamp (5) and the amplifier (6), then the signal is sent to the analyzer (7), which comprises a discriminator (7a) that selects the correct energy, a multichannel analyzer (7b) whose Direction signal (channel opening and closing) is coordinated with the piezotransducer control system formed by the function generator (7c) and the power supply (8) of the transducer.
  • the detector and the Preamps have their own power supply (9), as well as the analyzer and amplifier (10).
  • the spectra recorded in the analyzer are sent to a computer (11) for viewing and processing by appropriate software.
  • the analyzer (7) could circumstantially be implemented as a card in the computer itself (11).
  • the assembly formed by the gamma ray source, the piezoelectric oscillator, the absorber and the detector (1,2,3 and 4) that constitute the core of the Móssbauer spectrometer could be located in a capsule of centimeter dimensions (12).
  • the spectrometer in a fixed spectrometer modality analogous to conventional ones but with the new components consists of a source of gamma rays of the type 57 Co: Rh with an activity of 10 mCi and dimensions of 5x5x2 mm 3 attached to the active part of a piezoelectric oscillator (or "actuator") of the "multilayer” type of a length of 70 mm and a diameter of 12 mm, with a modulable vibration frequency of the order of 90 Hz, a maximum operating voltage of 120N and a modular displacement in the range from 0 to 50 ⁇ m, achieving speeds of the radioactive source of the order of 0 to 15 mm / s.
  • the sample or absorbent consists of a small interlayer plate between the radioactive source and the detector.
  • the detector consists of a silicon plate (Si) of 2.5x3 mm 2 and a thickness of 300 ⁇ m that by photoelectric effect transforms the incident radiation into electrical pulses, these are transformed by a sensitivity preamplifier: lmN / keN, then a through B ⁇ C type connectors the pulses are sent to an amplifier that converts them into pulses suitable for the input of the multichannel analyzer (> 2 N). This usually consists of a minimum of 512 channels and channel advance times of the order of microsecond.
  • the central control unit consists of several electronic modules powered by a voltage of ⁇ 12 N and an intensity of 100 mA.
  • control unit there is also the function generator (senosoidal or triangular) that serves as input of the piezoelectric vibrator controller.
  • the main achievement of the control unit is the synchronization of the channel advance in the multichannel analyzer with the movement of the piezoelectric oscillator.
  • the signal that leaves the control unit to the piezo oscillator controller has a frequency of 90 Hz, and a voltage of about 6 V.
  • the piezoelectric controller amplifies this signal to about 85 N modulable maintaining the frequency and with a resulting current limited to the order of about 200 mA. This signal reaches the piezoelectric oscillator that responds by vibrating at the desired frequency and amplitude.
  • the spectrometer in an accessory mode designed to be inserted into a cryostat consists of a hollow cylinder 30 mm long and 10 mm in diameter. At one of the inner ends of it there is a piezoelectric transducer of multilayer type of 20mm in length and a diameter of 8mm with a modulable vibration frequency of the order of 1kHz. a maximum operating voltage of 120N and a modular displacement in the range 0 to 4 ⁇ m, attaining speeds of the attached radioactive source from 0 to 15mm / s.
  • the radioactive source is of the non-polarizable type under a magnetic field and with an activity of 10 mCi and dimensions of 2x2x1 mm 2 .
  • the absorbent consists of a small plate (containing a small 1 mg sample) insertable into the cylinder.
  • the detector consisting of a 3x3x2 mm 3 cadmium telluride (CZT) plate that by photoelectric effect transforms the radiation into electrical pulses.
  • the cylinder is attached to a steel rod of about 1.5 meters in length ready to be inserted in a conventional or ultra low temperature cryostat as well as in devices that create high magnetic fields.
  • the electronic part is analogous to that described in the previous example, with the particularity that the multichannel analyzer has a higher channel feed rate.
  • the control unit discriminator, multichannel analyzer and function generator

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  • General Health & Medical Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
  • Measurement Of Radiation (AREA)

Abstract

Mössbauer spectrometer (Figure 1) comprising the following basic components: a preferably multi-layered piezoelectric oscillator which can be controlled by means of a variable voltage and which is synchronised by opening and closing the channels of the multi-channel analyser; a radiation source, preferably 57Co, rigidly attached to the piezoelectric oscillator; a detection system comprising one or more solid state detectors such as silicon (Si) or cadmium telluride (CZT) detectors with a detection element of the order of 3x3x2 mm; a system for amplification and management of the data recorded, including the multi-channel analyser which must be synchronised with the electrical function that controls the piezoelectric oscillator.

Description

TITULOTITLE
Espectrómetro Mδssbauer con tecnología de piezotransductores y detectores de estado sólido.Mδssbauer spectrometer with piezo-transducer technology and solid-state detectors.
SECTOR DE LA TÉCNICASECTOR OF THE TECHNIQUE
La presente invención consiste en la introducción de la tecnología de transductores piezoeléctricos y detectores de estado sólido en el diseño de espectrómetros Móssbauer. La aplicación de dicha tecnología reporta sustanciales mejoras en el potencial del espectrómetro. El efecto Mossbauer, principio fundamental de la espectroscopia homónima, fue descubierto en 1958. Desde su descubrimiento, la espectroscopia Mossbauer se ha desarrollado como técnica idónea de caracterización estructural y magnética de gran variedad de materiales. El área de la técnica seria por lo tanto el amplio sector de los materiales naturales y tecnológicos; incluyendo los más diversos sectores de aplicación: materiales amorfos y nanocristalinos para aplicaciones magnéticas, reacciones bioquímicas, diagnosis de cáncer, catalizadores, productos de corrosión, estudios medioambientales, caracterización cristalográfica y química, metalurgia, ciencia de materiales, mineralogía, geología y arqueología por citar solamente los más comunes.The present invention consists in the introduction of the technology of piezoelectric transducers and solid state detectors in the design of Móssbauer spectrometers. The application of such technology reports substantial improvements in the spectrometer's potential. The Mossbauer effect, a fundamental principle of homonymous spectroscopy, was discovered in 1958. Since its discovery, Mossbauer spectroscopy has developed as an ideal technique for structural and magnetic characterization of a wide variety of materials. The technical area would therefore be the broad sector of natural and technological materials; including the most diverse application sectors: amorphous and nanocrystalline materials for magnetic applications, biochemical reactions, cancer diagnosis, catalysts, corrosion products, environmental studies, crystallographic and chemical characterization, metallurgy, materials science, mineralogy, geology and archeology to cite Only the most common.
ESTADO DE LA TÉCNICASTATE OF THE TECHNIQUE
Un espectrómetro Mossbauer convencional consiste en:A conventional Mossbauer spectrometer consists of:
- una fuente radiactiva de rayos gamma vibrando con el fin de cubrir un cierto rango de velocidades que se traducen en energías de la radiación por el denominado efecto Doppler. La vibración se transmite uniendo rígidamente la fuente a un dispositivo electromagnético [Kankeleit, E.: Rev. Sci. Instr. 35, 194- a radioactive source of gamma rays vibrating in order to cover a certain range of speeds that are translated into radiation energies by the so-called Doppler effect. The vibration is transmitted by rigidly joining the source to an electromagnetic device [Kankeleit, E .: Rev. Sci. Instr. 35, 194
(1964)] de funcionamiento análogo a un altavoz. Un determinado voltaje aplicado al dispositivo equivale a una determinada velocidad del vibrador, generalmente se aplica una señal de tipo triangular con una frecuencia de 30 Hz.(1964)] of operation analogous to a loudspeaker. A certain voltage applied to the device is equivalent to a certain vibrator speed, generally a triangular type signal with a frequency of 30 Hz is applied.
- la muestra de material a analizar (absorbente) que como requisito importante debe contener átomos capaces de reproducir el efecto Mossbauer (al menos 4 mg/cm2) de acuerdo con la energía de la radiación incidente. El espectro Mossbauer consiste en un gráfico de velocidades (o energías de radiación) vs. grado de absorción de la radiación, a partir del mismo pueden extraerse importantes datos acerca de propiedades tales como el estado de oxidación, el entorno cristalino, el ordenamiento magnético, el estado dinámico de los átomos, etc. - un sistema de detección que comprende el detector, preamplificador, amplificador, discriminador y analizador multicanal. Los detectores mas comúnmente utilizados son los consistentes en un gran cristal de yoduro sódico adosado a un fotomultiplicador o un detector de gas (Ar, Xe o Kr). La señal detectada se amplifica y selecciona convenientemente [Viegers, M. P. A., Trooster, J. M.:Nucl. Instr. Meth. 118, 257 (1974)] hasta llegar al analizador multicanal que administra el contaje en canales correspondientes a intervalos de velocidades; luego por tanto, su funcionamiento debe estar sincronizado con el movimiento del transductor o vibrador.- the sample of material to be analyzed (absorbent) which as an important requirement must contain atoms capable of reproducing the Mossbauer effect (at least 4 mg / cm 2 ) according to the energy of the incident radiation. The Mossbauer spectrum consists of a graph of velocities (or radiation energies) vs. degree of radiation absorption, from it important data can be extracted about properties such as the oxidation state, the crystalline environment, the magnetic arrangement, the dynamic state of the atoms, etc. - a detection system comprising the detector, preamplifier, amplifier, discriminator and multichannel analyzer. The most commonly used detectors are those consisting of a large crystal of sodium iodide attached to a photomultiplier or a gas detector (Ar, Xe or Kr). The detected signal is amplified and conveniently selected [Viegers, MPA, Trooster, JM: Nucl. Instr. Meth. 118, 257 (1974)] until reaching the multichannel analyzer that manages the count in channels corresponding to speed intervals; then, therefore, its operation must be synchronized with the movement of the transducer or vibrator.
Un accesorio muy importante en un espectrómetro Mossbauer es un criostato para realizar medidas a diversas temperaturas, se trata de diseños especiales debido a las características físicas del espectrómetro [Cohén, R. L., Wertheim, G. K.: Methods of Experimental Physics 11, 307 (1974)]. Las diferencias entre los primeros espectrómetros [Tomov, T. et al.: Pribory i teknika eksperimenta 5, 133 (1967)] y los actuales son escasas y conciernen básicamente a la mejora del control electrónico del transductor: minimización de errores e implementación en computadoras, así mismo se han desarrollado diseños específicos para realizar medidas a bajas temperaturas y en presencia de campo magnético o para aplicaciones concretas [Klingelhofer, G.: Móssbauer Spectroscopy in Materials Science, M.Miglierini and D. Petridis (eds), Kluwer Academic Publishers, 413 (1999)].A very important accessory in a Mossbauer spectrometer is a cryostat for measurements at various temperatures, these are special designs due to the physical characteristics of the spectrometer [Cohen, RL, Wertheim, GK: Methods of Experimental Physics 11, 307 (1974)] . The differences between the first spectrometers [Tomov, T. et al .: Pribory i teknika eksperimenta 5, 133 (1967)] and the current ones are scarce and basically concern the improvement of the electronic transducer control: minimization of errors and implementation in computers Likewise, specific designs have been developed for measurements at low temperatures and in the presence of a magnetic field or for specific applications [Klingelhofer, G .: Móssbauer Spectroscopy in Materials Science, M.Miglierini and D. Petridis (eds), Kluwer Academic Publishers , 413 (1999)].
A pesar de los múltiples diseños existentes, la tecnología que se usa en todos es prácticamente la misma que en el diseño estándar: oscilador electromagnético y detector proporcional de gas. La presente patente responde a la introducción de componentes radicalmente distintos a los clásicos. Tales cambios introducen como ventaja principal la posibilidad de miniaturizar a niveles inéditos el espectrómetro. Dicha miniaturización ha sido ya optimizada para el diseño convencional [Klingelhófer, G.: Móssbauer Spectroscopy in Materials Science, M.Miglierini and D. Petridis (eds), Kluwer Academic Publishers, 413 (1999)], el diseño objeto de la presente invención rebasa sobradamente dicha optimización.Despite the many existing designs, the technology used in all is practically the same as in the standard design: electromagnetic oscillator and proportional gas detector. The present patent responds to the introduction of radically different components to the classic ones. Such changes introduce as a main advantage the possibility of miniaturizing the spectrometer at unprecedented levels. This miniaturization has already been optimized for conventional design [Klingelhófer, G .: Móssbauer Spectroscopy in Materials Science, M.Miglierini and D. Petridis (eds), Kluwer Academic Publishers, 413 (1999)], the design object of the present invention exceeds this optimization.
Diversas patentes han sido registradas a propósito de la espectroscopia Mossbauer, en su mayoría, se refieren a adaptaciones especificas del dispositivo estándar, ninguna de ellas entra en conflicto con la presente invención [patente JP 09049809 A "Instrument and method for mossbauer spectroscopy", Hiroshi, M.; Takuichi, M.; Shigeyuki, M. (4 agosto 1995); patente GB 2205395 A "Mossbauer gamma-ray spectrometer", Irkaev, S.M.; Kupriyanov, V.N.; Semenkin, N.A.; Vakhonin, M.E. (2 junio 1987); patente SU 945761 B 'Object defect detection", Kvasov, Ν.T.; Polonin, A.K. (17 noviembre 1980); patente CΝ 85102591 B "Mossbauer spectrometer with single board microcomputer", Jiying, S.; Jianwei, EL; Qisheng, L.; Guohuan, D. (1 abril 1985); patente SU 01402878 Al "Mossbauer spectrometer", Fedorov, Ν.P.; Tselikov, IN. (15 junio 88); patente US 05327733 "Substantially vibration-free shroud and mounting system for sample cooling and low temperature spectroscopy ", Boolchand; P.; Lemon; G.H.; Bresser; W. J.; Enzweiler; R. Ν. (12 julio 94)].Various patents have been registered with regard to Mossbauer spectroscopy, mostly, they refer to specific adaptations of the standard device, none of them conflicts with the present invention [JP 09049809 A "Instrument and method for mossbauer spectroscopy", Hiroshi , M .; Takuichi, M .; Shigeyuki, M. (August 4, 1995); patent GB 2205395 A "Mossbauer gamma-ray spectrometer", Irkaev, S.M .; Kupriyanov, V.N .; Semenkin, N.A .; Vakhonin, M.E. (June 2, 1987); SU 945761 B 'Object defect detection ", Kvasov, Ν.T .; Polonin, AK (November 17, 1980); CΝ 85102591 B" Mossbauer spectrometer with single board microcomputer ", Jiying, S .; Jianwei, EL; Qisheng, L .; Guohuan, D. (April 1, 1985); SU 01402878 patent to "Mossbauer spectrometer", Fedorov, Ν.P .; Tselikov, IN. (June 15, 88); US patent 05327733 "Substantially vibration-free shroud and mounting system for sample cooling and low temperature spectroscopy ", Boolchand; P .; Lemon; GH; Bresser; WJ; Enzweiler; R. Ν. (July 12, 94)].
En diciembre del 1998 presentamos la solicitud de patente de la que denominamos MicroMóssbauer, el avance en la construcción del prototipo, así como modificaciones en el diseño del mismo nos llevan a reformular la solicitud atendiendo a la mayor cobertura de la presente invención.In December 1998 we presented the patent application of what we call MicroMóssbauer, the progress in the construction of the prototype, as well as modifications in the design of the same lead us to reformulate the application according to the greater coverage of the present invention.
El espectrómetro Móssbauer presenta diversas limitaciones inherentes al uso de los componentes tradicionales: el transductor electromagnético suele ser un pesado cilindro de 20 cm de longitud y 10 cm de diámetro, el detector suele ser un gran cristal de yoduro sódico adosado a un fotomultiplicador en el caso de la espectroscopia de alta energía (ex. 28.3 keN 119Sn) o más comúnmente (14.4 keN 57Fe) un detector proporcional de gas también de dimensiones decimétricas.The Móssbauer spectrometer has several limitations inherent to the use of traditional components: the electromagnetic transducer is usually a heavy cylinder 20 cm long and 10 cm in diameter, the detector is usually a large sodium iodide crystal attached to a photomultiplier in the case of high energy spectroscopy (ex. 28.3 keN 119 Sn) or more commonly (14.4 keN 57 Fe) a proportional gas detector also of decimetric dimensions.
Para las medidas a temperaturas y campos magnéticos preestablecidos se utilizan caros criostatos de diseño especifico ya que el detector siempre se sitúa en el exterior y el transductor generalmente también por lo que el criostato debe permitir la entrada y salida de radiación gamma. En algunos diseños, la fuente radiactiva se halla dentro del criostato con lo que la transmisión de la vibración debe realizarse mediante un largo vastago conllevando una reducción de la fiabilidad de tal transmisión. En los diseños convencionales (detector y fuente exteriores), la perdida de contaje debido a las diversas ventanas de mylar que debe traspasar la radiación es considerable. Incluso a temperatura ambiente no es posible acercar demasiado la fuente a la muestra ya que debido a la amplitud de la vibración, el espectro se distorsiona a causa de un efecto geométrico.For the measurements at pre-established temperatures and magnetic fields, expensive cryostats of specific design are used since the detector is always located outside and the transducer generally also so the cryostat must allow the entry and exit of gamma radiation. In some designs, the radioactive source is inside the cryostat so that the transmission of the vibration must be carried out by means of a long rod leading to a reduction in the reliability of such transmission. In the designs Conventional (outdoor detector and source), the loss of count due to the various mylar windows that radiation must pass through is considerable. Even at room temperature it is not possible to bring the source too close to the sample because, due to the amplitude of the vibration, the spectrum is distorted due to a geometric effect.
DESCRIPCIÓN DE LA INVENCIÓNDESCRIPTION OF THE INVENTION
La introducción de un transductor piezoeléctrico sustituyendo al de tipo electromagnético y un detector de estado sólido sustituyendo al de Nal o de gas, minimiza todos los inconvenientes apuntados sobre el diseño estándar. Las dimensiones pueden reducirse en mas de un 90% en volumen. El aumento de la frecuencia de vibración del transductor combinado con el uso de fuentes puntuales elimina completamente el efecto geométrico. Los componentes transductor, absorbente, y detector pueden estar mucho más cerca ganando en contaje y actividad aparente de la fuente. Los requisitos de cantidad de muestra dejan de ser tan exigentes (~1 mg sería suficiente). El sistema transductor-absorbente-detector podría someterse a muy bajas temperaturas (~1 mK). Ambas novedades abren la posibilidad de realizar medidas hasta el momento absolutamente inabordables. Con el novedoso diseño de espectrómetro Mossbauer que presentamos aquí se obtienen espectros un tanto diferentes a los convencionales pero no por eso menos útiles para la caracterización de materiales y con las ya citadas ventajas en lo que respecta al dispositivo experimental: dimensiones reducidas, capacidad de trabajo a muy bajas temperaturas, optimización del aprovechamiento de la fuente radioactiva, menor cantidad de muestra requerida, portabilidad del espectrómetro.The introduction of a piezoelectric transducer replacing the electromagnetic type and a solid state detector replacing that of Nal or gas, minimizes all the inconveniences noted on the standard design. The dimensions can be reduced by more than 90% by volume. Increasing the frequency of vibration of the transducer combined with the use of point sources completely eliminates the geometric effect. The transducer, absorber, and detector components can be much closer to gain in counting and apparent activity of the source. Sample quantity requirements are no longer as demanding (~ 1 mg would be sufficient). The transducer-absorber-detector system could be subjected to very low temperatures (~ 1 mK). Both novelties open the possibility of making measures so far absolutely unapproachable. With the innovative design of Mossbauer spectrometer that we present here are obtained spectra somewhat different from the conventional ones but not less useful for the characterization of materials and with the aforementioned advantages in regard to the experimental device: reduced dimensions, work capacity at very low temperatures, optimization of the use of the radioactive source, lower amount of sample required, portability of the spectrometer.
Los componentes básicos del nuevo diseño son:The basic components of the new design are:
Un oscilador piezoeléctrico preferentemente de tipo "multilayer" que puede ser controlado mediante un voltaje variable sincronizado con la apertura y cierre de los canales del analizador multicanal. - Una fuente radioactiva, preferentemente de 57Co, unida rígidamente al oscilador piezoeléctrico. - Un sistema de detección formado por uno o varios detectores de estado sólido tales como los de telururo de cadmio (CZT) con un elemento de detección del orden de 3x3x2 ram.A piezoelectric oscillator preferably of the "multilayer" type that can be controlled by a variable voltage synchronized with the opening and closing of the channels of the multichannel analyzer. - A radioactive source, preferably 57 Co, rigidly attached to the piezoelectric oscillator. - A detection system consisting of one or several solid state detectors such as cadmium telluride (CZT) with a detection element of the order of 3x3x2 ram.
- Un sistema de amplificación y gestión de los datos registrados incluyendo el analizador multicanal necesariamente sincronizado con la función eléctrica que controla el oscilador piezoeléctrico.- A system of amplification and management of the recorded data including the multichannel analyzer necessarily synchronized with the electrical function that controls the piezoelectric oscillator.
Los dos dispositivos fundamentales (vibrador piezoeléctrico y detector de estado sólido) pueden operar a bajas temperaturas, el diseño podría concebirse como un MicroMóssbauer adosado al extremo de una caña a modo de "inserí" para su introducción en criostatos convencionales. De forma similar, el nuevo dispositivo miniaturizado podría introducirse en elevados campos magnéticos requiriéndose en este caso (excepto en casos excepcionales) fuentes radiactivas no susceptibles de polarización. La naturaleza dieléctrica del oscilador piezoeléctrico produce necesariamente un desfase entre la señal que rige el movimiento del tranductor y el movimiento del mismo. Debido a este efecto, se obtienen espectros desplazados que necesitan de software modificado para su análisis. Por otra parte, la relación directa existente entre el voltaje y la posición del transductor hace preferible una señal senosoidal (para su control) a la señal triangular utilizada comúnmente para los tranductores electromagnéticos convencionales.The two fundamental devices (piezoelectric vibrator and solid state detector) can operate at low temperatures, the design could be conceived as a MicroMóssbauer attached to the end of a rod as an "insert" for its introduction into conventional cryostats. Similarly, the new miniaturized device could be introduced in high magnetic fields, requiring in this case (except in exceptional cases) radioactive sources not susceptible to polarization. The dielectric nature of the piezoelectric oscillator necessarily produces a gap between the signal that governs the movement of the transducer and its movement. Due to this effect, displaced spectra are obtained that need modified software for analysis. On the other hand, the direct relationship between the voltage and the position of the transducer makes a senosoidal signal (for its control) preferable to the triangular signal commonly used for conventional electromagnetic transducers.
DESCRIPCIÓN DETALLADA DE LA FIGURADETAILED DESCRIPTION OF THE FIGURE
El espectrómetro Móssbauer objeto de invención comprende (Fig.l) una fuente de rayos gamma (1) unido rígidamente a un oscilador piezoeléctrico (2) con una vibración longitudinal a la trayectoria de los rayos gamma (γ), un absorbente (3) objeto de estudio y un detector de radiación de estado sólido (4). La señal detectada se amplifica en el preamplificador (5) y el amplificador (6), a continuación la señal se envía al analizador (7), que comprende un discriminador (7a) que selecciona la energía correcta, un analizador multicanal (7b) cuya señal de dirección (apertura y cierre de canal) esta coordinada con el sistema de control del piezotransductor formado por el generador de funciones (7c) y la fuente de alimentación (8) del transductor. El detector y el preamplificador tienen su propia fuente de alimentación (9), así como el analizador y amplificador (10). Los espectros registrados en el analizador son enviados hacia una computadora (11) para su visualización y tratamiento mediante software apropiado. El analizador (7) podría circunstancialmente implementarse como tarjeta en la propia computadora (11). El conjunto formado por la fuente de rayos gamma, el oscilador piezoeléctrico, el absorbente y el detector (1,2,3 y 4) que constituyen el núcleo del espectrómetro Móssbauer podrían estar situados en una cápsula de dimensiones centimétricas (12).The Móssbauer spectrometer object of the invention comprises (Fig. 1) a gamma ray source (1) rigidly connected to a piezoelectric oscillator (2) with a longitudinal vibration to the gamma ray path (γ), an object absorbent (3) of study and a solid state radiation detector (4). The detected signal is amplified in the preamp (5) and the amplifier (6), then the signal is sent to the analyzer (7), which comprises a discriminator (7a) that selects the correct energy, a multichannel analyzer (7b) whose Direction signal (channel opening and closing) is coordinated with the piezotransducer control system formed by the function generator (7c) and the power supply (8) of the transducer. The detector and the Preamps have their own power supply (9), as well as the analyzer and amplifier (10). The spectra recorded in the analyzer are sent to a computer (11) for viewing and processing by appropriate software. The analyzer (7) could circumstantially be implemented as a card in the computer itself (11). The assembly formed by the gamma ray source, the piezoelectric oscillator, the absorber and the detector (1,2,3 and 4) that constitute the core of the Móssbauer spectrometer could be located in a capsule of centimeter dimensions (12).
EJEMPLO 1EXAMPLE 1
El espectrómetro en una modalidad de espectrómetro fijo análogo a los convencionales pero con los novedosos componentes consiste de una fuente de rayos gamma del tipo 57Co:Rh con una actividad de 10 mCi y unas dimensiones de 5x5x2 mm3 adosada a la parte activa de un oscilador piezoeléctrico (o "actuator") cilindrico de tipo "multilayer" de una longitud de 70 mm y un diámetro de 12mm, con una frecuencia de vibración modulable del orden de 90 Hz, un voltaje máximo de funcionamiento de 120N y un desplazamiento modulable en el rango de 0 a 50 μm, consigμiéndose velocidades de la fuente radioactiva del orden de 0 a 15 mm/s. La muestra o absorbente consiste en una pequeña placa intercalable entre la fuente radiactiva y el detector. El detector consiste en una placa de silicio (Si) de 2.5x3 mm2 y un espesor de 300 μm que por efecto fotoeléctrico transforma la radiación incidente en pulsos eléctricos, estos son transformados mediante un preamplificador de sensibilidad: lmN/keN, a continuación a través de conectores de tipo BΝC los pulsos son enviados a un amplificador que los convertirte en pulsos adecuados para el input del analizador multicanal (>2 N). Éste, suele constar de un mínimo de 512 canales y tiempos de avance de canal del orden de microsegundo. La unidad central de control consiste en varios módulo electrónicos alimentado por un voltaje de ±12 N y una intensidad de 100 mA. En la unidad de control se encuentra también el generador de funciones (senosoidal o triangular) que sirve de input del controlador del vibrador piezoeléctrico. El principal logro de la unidad de control es la sincronización del avance de canal en el analizador multicanal con el movimiento del oscilador piezoeléctrico. La señal que sale de la unidad de control hacia el controlador del oscilador piezoeléctrico tiene una frecuencia de 90 Hz, y un voltaje de unos 6 V. El controlador piezoeléctrico amplifica esta señal a unos 85 N modulables manteniendo la frecuencia y con una corriente resultante limitable del orden de unos 200 mA. Esta señal llega al oscilador piezoeléctrico que responde vibrando a la frecuencia y amplitud deseadas.The spectrometer in a fixed spectrometer modality analogous to conventional ones but with the new components consists of a source of gamma rays of the type 57 Co: Rh with an activity of 10 mCi and dimensions of 5x5x2 mm 3 attached to the active part of a piezoelectric oscillator (or "actuator") of the "multilayer" type of a length of 70 mm and a diameter of 12 mm, with a modulable vibration frequency of the order of 90 Hz, a maximum operating voltage of 120N and a modular displacement in the range from 0 to 50 μm, achieving speeds of the radioactive source of the order of 0 to 15 mm / s. The sample or absorbent consists of a small interlayer plate between the radioactive source and the detector. The detector consists of a silicon plate (Si) of 2.5x3 mm 2 and a thickness of 300 μm that by photoelectric effect transforms the incident radiation into electrical pulses, these are transformed by a sensitivity preamplifier: lmN / keN, then a through BΝC type connectors the pulses are sent to an amplifier that converts them into pulses suitable for the input of the multichannel analyzer (> 2 N). This usually consists of a minimum of 512 channels and channel advance times of the order of microsecond. The central control unit consists of several electronic modules powered by a voltage of ± 12 N and an intensity of 100 mA. In the control unit there is also the function generator (senosoidal or triangular) that serves as input of the piezoelectric vibrator controller. The main achievement of the control unit is the synchronization of the channel advance in the multichannel analyzer with the movement of the piezoelectric oscillator. The signal that leaves the control unit to the piezo oscillator controller has a frequency of 90 Hz, and a voltage of about 6 V. The piezoelectric controller amplifies this signal to about 85 N modulable maintaining the frequency and with a resulting current limited to the order of about 200 mA. This signal reaches the piezoelectric oscillator that responds by vibrating at the desired frequency and amplitude.
EJEMPLO 2EXAMPLE 2
El espectrómetro en una modalidad de accesorio diseñado para ser introducido en un criostato consiste en un cilindro hueco de 30 mm de longitud y lOmm de diámetro. En uno de los extremos interiores del mismo se sitúa un transductor piezoeléctrico de tipo multilayer de 20mm de longitud y un diámetro de 8mm con una frecuencia de vibración modulable del orden de 1kHz. un voltaje máximo de funcionamiento de 120N y un desplazamiento modulable en el rango 0 a 4 μm consiguiéndose velocidades de la fuente radioactiva adosada de 0 a 15mm/s. La fuente radiactiva es del tipo no polarizable bajo campo magnético y con una actividad de 10 mCi y unas dimensiones de 2x2x1 mm2. El absorbente consiste en una pequeña placa (conteniendo 1 mg escaso de muestra) insertable en el cilindro. En el otro extremo interior del cilindro se sitúa el detector consistente en una placa de 3x3x2 mm3 de telururo de cadmio (CZT) que por efecto fotoeléctrico transforma la radiación en pulsos eléctricos. El cilindro esta unido a una caña de acero de unos 1.5 metros de longitud lista para ser insertada en un criostato convencional o de ultra baja temperatura así como en dispositivos que crean elevados campos magnéticos. La parte electrónica es análoga a la descrita en el ejemplo anterior, con la particularidad de que el analizador multicanal tiene una velocidad de avance de canal mayor. La unidad de control (discriminador, analizador multicanal y generador de funciones) está implementados en una computadora para mayor portabilidad del espectrómetro. The spectrometer in an accessory mode designed to be inserted into a cryostat consists of a hollow cylinder 30 mm long and 10 mm in diameter. At one of the inner ends of it there is a piezoelectric transducer of multilayer type of 20mm in length and a diameter of 8mm with a modulable vibration frequency of the order of 1kHz. a maximum operating voltage of 120N and a modular displacement in the range 0 to 4 μm, attaining speeds of the attached radioactive source from 0 to 15mm / s. The radioactive source is of the non-polarizable type under a magnetic field and with an activity of 10 mCi and dimensions of 2x2x1 mm 2 . The absorbent consists of a small plate (containing a small 1 mg sample) insertable into the cylinder. At the other inner end of the cylinder is the detector consisting of a 3x3x2 mm 3 cadmium telluride (CZT) plate that by photoelectric effect transforms the radiation into electrical pulses. The cylinder is attached to a steel rod of about 1.5 meters in length ready to be inserted in a conventional or ultra low temperature cryostat as well as in devices that create high magnetic fields. The electronic part is analogous to that described in the previous example, with the particularity that the multichannel analyzer has a higher channel feed rate. The control unit (discriminator, multichannel analyzer and function generator) is implemented in a computer for greater spectrometer portability.

Claims

REIVINDICACIONES
1. Espectrómetro Móssbauer caracterizado porque el oscilador es de tipo piezoeléctrico y el detector es de estado sólido.1. Móssbauer spectrometer characterized in that the oscillator is piezoelectric and the detector is solid state.
2. Espectrómetro Móssbauer según reivindicación 1 caracterizado por contiene los siguientes componentes básicos:2. Móssbauer spectrometer according to claim 1 characterized in that it contains the following basic components:
Un oscilador piezoeléctrico preferentemente de tipo "multilayer" que puede ser controlado mediante un voltaje variable sincronizado con la apertura y cierre de los canales del analizador multicanal.A piezoelectric oscillator preferably of the "multilayer" type that can be controlled by a variable voltage synchronized with the opening and closing of the channels of the multichannel analyzer.
- Una fuente radioactiva, preferentemente de 57Co, unida rígidamente al oscilador piezoeléctrico.- A radioactive source, preferably 57 Co, rigidly attached to the piezoelectric oscillator.
Un sistema de detección formado por uno o varios detectores de estado sólido tales como los de telururo de cadmio (CZT) o de silicio (Si) con un elemento de detección del orden de 3x3x2 mm.A detection system consisting of one or more solid state detectors such as cadmium telluride (CZT) or silicon (Si) with a detection element of the order of 3x3x2 mm.
- Un sistema de amplificación y gestión de los datos registrados incluyendo el analizador multicanal necesariamente sincronizado con la función eléctrica que controla el oscilador piezoeléctrico.- A system of amplification and management of the recorded data including the multichannel analyzer necessarily synchronized with the electrical function that controls the piezoelectric oscillator.
3. Espectrómetro según reivindicaciones 1 y 2 caracterizado porque tiene unas dimensiones de orden decimétrico o inferior.3. Spectrometer according to claims 1 and 2 characterized in that it has dimensions of decimetric or lower order.
4. Espectrómetro según reivindicación 3 caracterizado porque se adosa a una caña, diseñado a modo de "insert", para ser introducido en un criostato, y/o en un campo magnético.4. Spectrometer according to claim 3 characterized in that it is attached to a rod, designed as an "insert", to be introduced in a cryostat, and / or in a magnetic field.
5. Espectrómetro según reivindicación 4 caracterizado porque la fuente radioactiva es de tipo puntual.5. Spectrometer according to claim 4 characterized in that the radioactive source is of the punctual type.
6. Espectrómetro según reivindicación 4 caracterizado porque la fuente radiactiva es una fuente radiactiva no polarizable bajo campo magnético. 6. Spectrometer according to claim 4 characterized in that the radioactive source is a non-polarizable radioactive source under a magnetic field.
PCT/ES2002/000016 2001-01-15 2002-01-15 Mossbauer spectrometer with piezo transducer technology and solid state detectors WO2002055972A1 (en)

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