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The direction of arrival estimation and the estimation of energy pulses in x-ray spectroscopy are based on the same parameter, the phase shift of measured signals relative to a reference. This work demonstrates the possibility of applying well-established direction-of-arrival estimation techniques to the problem of spectroscopy. The two themes are correlated in an introductory part and, then, they are discussed separately giving emphasis on the intrinsic characteristics of each topic. In the problem of direction of arrival estimation, the signal model for the sensor array is presented as well as some maximum likelihood-based methods. It consists of a uniform linear array of half-wavelength spaced sensors, which produce phase-shifted copies of a reference signal in each circuit. The time lag is closely related to the direction of arrival of a planar wave. The spatial domain shows complex exponentials whose frequencies should be estimated. The main estimation methods are MODE, MODEX, modified MODEX, and SEAD. They are discussed along this work, but special attention lies on the SEAD method, which is based on the eigenvalue decomposition of the modified spatial correlation matrix. The di˙erence between the two largest eigenvalues constitute an interesting measure, it provides an initial guess for the estimates by presenting prominent peaks near the true direction of arrival positions. By sweeping the entire angular interval with a test angle and calculating the eigenvalues the di˙erential spectrum can be traced. A mathematical analysis of the di˙erential spectrum has shown that it is basically a matrix norm calculation, leading to the definition of the total di˙erential spectrum. Therefore, a matrix-based approach is proposed to estimate the arriving angles. This procedure allows to express the angular spectrum in terms of the true angles, a test angle, the correlation between the signals, the number of sources, and the number of sensors. This mathematical formulation is general and demonstrates the principles of operation of the SEAD method, it is one of the main contributions of the present work. The use of the norm-based approach avoided the need of performing the eigenvalue-decomposition, consequently reducing the overall runtime while enhancing the performance for widely-spaced sources. SEAD method based on matrix norms outperformed the MODE method and its derivatives regarding the root mean square error. However, for a number of sources less than 4, the execution time of SEAD-based method is more time consuming than MODEX and modified MODEX. The estimation of energy pulses in x-ray spectroscopy is not a new topic, however, the microwave SQUID multiplexer is a relatively new approach and it is currently a thriving research subject. The objective of the system is to simultaneously read out the energy of energetic particles that fall into detectors for a large amount of resonators. The detectors may be a transition edge sensor or a metallic magnetic calorimeter. Metallic calorimeters are paramagnetic sensors that are situated in a weak magnetic field. They translate temperature variation into magnetic flux variation. To readout the magnetic flux variations due to charged particles, a superconducting quantum interference device is used. The SQUID is an extremely sensitive interferometer and behaves as a variable inductor. The SQUID is coupled to a termination of a superconducting transmission line and produces changes in the resonant frequency of the circuit. Therefore, particle energy can be readout electronically by demodulating a radio frequency that travels through the resonator. Modulation occurs at the amplitude and phase of the complex carrier. After the discard of intermediate frequencies, mixing down the carrier, a complex low frequency carrier is obtained. The signal can be recovered by demodulating the carrier phase. Due to the similarity with the direction of arrival estimation problem, it is proposed a sensor array-based approach, which profits from the spatial correlation matrix decomposition into its eigenvalues. In this way, an analogy is established between the two problems. For obtaining the correlation matrix, a virtual reference vector is considered, whose phase does not depend on the incidence of particles, i.e. when the system is idle. This reference vector is compared by means of the correlation function with the received data sample by sample. A convenient data vector length is defined, so that a snapshot matrix with two sensors is obtained and, consequently, a 2 × 2 dimension correlation matrix is set. The eigenvalue decomposition can be explicitly solved as a function of the matrix entries, such that a general formulation for the method is presented. In addition, simplifications were imposed that allows its implementation on dedicated hardware. The estimation error is analyzed for the proposed method and the maximum likelihood method. The eigenvalue-based method presented greater robustness against the e˙ects of noise. In some specific cases, in which the maximum likelihood method was not able to properly estimate the energy pulse, the proposed method proved to be quite eÿcient. A estimação da direção de chegada e a estimação de pulsos de energia na espectroscopia de raios-x são baseadas no mesmo parâmetro, o deslocamento de fase de sinais em relação a uma referência. Neste trabalho é demonstrada a possibilidade de aplicar técnicas já estabelecidas para a estimação da direção de chegada ao problema de espectroscopia. Os dois temas são correlacionados em uma parte introdutória e em seguida eles são discutidos separadamente dando ênfase nas características intrínsecas de cada um. No problema de estimação da direção de chegada, inicialmente apresenta-se o modelo de sinal para o arranjo de sensores e alguns métodos baseados no estimador de máxima verossimilhança. Considerando um arranjo de sensores linearmente distribuídos e com espaçamento uniforme entre os elementos, os sinais induzidos em cada circuito serão cópias defasadas de um sinal de referência. O defasamento está intimamente relacionado com a direção de chegada. No domínio espacial, as direções de chegada representam frequências de funções exponenciais complexas, as quais deverão ser estimadas. Os principais métodos de estimação são o MODE, MODEX, o MODEX modificado, e o SEAD. Atenção especial é dispensada ao método SEAD que é baseado na decomposição em autovalores da matriz de correlação espacial modificada. A diferença entre os dois maiores autovalores gera uma curva com picos proeminentes indicando as direções de chegada de ondas planas. A esta curva dá-se o nome de espectro diferencial. Uma análise matemática do espectro diferencial, denominada de espectro diferencial total, é desenvolvida e demonstra-se que a norma matricial induzida pela norma-2 vetorial é a principal componente do cálculo. Portanto, propõe-se uma abordagem baseada em normas matriciais para a estimação das direções de chegada. Uma descrição matemática geral foi desenvolvida, a qual explicita a relação entre os verdadeiros ângulos de chegada e um ângulo sintético usado para varrer todo o espectro, a correlação entre as fontes, o número de fontes e o número de sensores. Demonstra-se que a diferença entre os ângulos determina a amplitude do pico gerado. A formulação matemática do espectro angular constitui em uma das principais contribuições deste trabalho, porém, outros aprimoramentos foram alcançados através da proposta de uso de normas matriciais. A utilização da abordagem baseada em normas evita a necessidade de realização da decomposição da matriz em autovalores e, consequentemente, o tempo de execução total do método é reduzido e o erro quadrático médio é reduzido para situação de fontes afastadas. Comparando as propostas com os métodos estabelecidos na literatura, a abordagem de normas supera o método MODE e seus derivados com relação ao erro quadrático médio. Porém, com relação ao tempo de execução os métodos baseados no SEAD são mais custosos computacionalmente para um número de fontes menor do que 4. A estimação de pulsos de energia na espectroscopia de raios-x não é um tema novo, porém, o multiplexador SQUID de micro-ondas é uma abordagem relativamente nova e, atualmente, ele consiste em um tema de pesquisa pujante. O objetivo do sistema é estimar a energia de partículas energéticas que incidem em detectores, os quais podem ser do tipo transition edge sensor ou metallic magnetic calorimeters. Os calorímetros metálicos são sensores paramagnéticos que estão situados em um campo magnético fraco, eles traduzem variação de temperatura em variação de fluxo magnético. Para realizar a leitura das variação de fluxo magnético decorrente da incidência de partículas emprega-se um componente supercondutor denominado de superconducting quantum interference device (SQUID). O SQUID é um interferômetro de extrema sensibilidade e se comporta como um indutor variável. O SQUID é acoplado a uma terminação de uma linha de transmissão supercondutora e produz alterações na frequência de ressonância do circuito. Portanto, a energia de partículas pode ser lida eletronicamente através da demodulação de uma onda de rádio que percorre o ressonador. A modulação ocorre na amplitude e fase de uma portadora complexa. Após a exclusão de frequências intermediárias, resultado do processo de mixagem da portadora, obtem-se uma portadora complexa de frequência baixa sobre a qual métodos de estimação de fase são aplicados. Pela semelhança com o problema de estimação da direção de chegada, propõe-se uma abordagem baseada em arranjo de sensores e decomposição da matriz de correlação espacial em autovalores. Desta forma, estabelece-se uma analogia entre os dois problemas. Para a obtenção da matriz de correlação, considera-se a existência de um vetor de referência cuja fase não depende da incidência de partículas, i.e., quando o sistema está em repouso. Este vetor de referência é comparado por meio da função de correlação com os dados que são recebidos a cada instante. Define-se um comprimento do vetor de dados que seja conveniente e, desta forma, obtem-se uma matriz de snapshots com dois sensores e uma matriz de correlação de dimensões 2 × 2. A decomposição em autovalores pode ser resolvida explicitamente em função das entradas da matriz, de tal maneira, que uma formulação geral para o método é apresentada. Além disso, simplificações podem ser impostas com o objetivo de implementação em hardware dedicado. O erro de estimação é analisado para o método proposto e o método de máxima verossimilhança. O método de autovalores apresentou maior robustez ao ruído e em algumas circunstâncias consegue resolver o problema de estimação sem artifícios externos, algo que não ocorre para o método de máxima verossimilhança. Die Schätzung der Ankunftsrichtung und die Energieimpulsschätzung in der Röntgenspek-troskopie basieren auf demselben Parameter, der Phasenverschiebung von Signalen relativ zu einer Referenz. Diese Arbeit demonstriert die Möglichkeit, bereits etablierte Techni-ken zur Abschätzung der Ankunftsrichtung auf das Spektroskopie Problem anzuwenden. Die beiden Themen werden in einem einleitenden Teil miteinander korreliert und dann separat diskutiert, wobei die spezifischen Merkmale der einzelnen Themen hervorgehoben werden. In dem Problem der Abschätzung der Ankunftsrichtung präsentieren wir zunächst das Signalmodell für die Sensoranordnung und einige Methoden, die auf dem Maximum-Likelihood-Schätzer basieren. Betrachtet man eine Anordnung linear verteilter Sensoren mit gleichmäßigem Abstand zwischen den Elementen, so sind die induzierten Signale in jeder Schaltung Kopien eines Referenzsignals mit Verzögerung. Die Verzögerung ist eng mit der Ankunftsrichtung verbunden. In der räumlichen Domäne stellen Ankunftsrich-tungen Frequenzen komplexer Exponentialfunktionen dar, die geschätzt werden sollten. Die wichtigsten Schätzmethoden sind MODE, MODEX, Modifiziert MODEX und SEAD. Besonderes Augenmerk wird auf die SEAD-Methode gelegt, die auf der Eigenwertzerlegung der modifizierten räumlichen Korrelationsmatrix basiert. Die Di˙erenz zwischen den beiden größten Eigenwerten erzeugt eine Kurve mit markanten Spitzenwert, die die Ankunftsrich-tungen flacher Wellen angeben. Diese Kurve wird als Di˙erenzspektrum bezeichnet. Eine mathematische Analyse des Di˙erentialspektrums, das als Gesamtdi˙erentialspektrum bezeichnet wird, wird entwickelt und es wird gezeigt, dass die durch die euklidische Vek-tornorm induzierte Matrixnorm die Hauptkomponente der Berechnung ist. Daher schlagen wir einen Ansatz vor, der auf Matrixnormen für die Schätzung der Ankunftsrichtungen basiert. Es wurde eine allgemeine mathematische Beschreibung entwickelt, die die Bezie-hung zwischen tatsächlichen Einfallswinkeln und einem synthetischen Winkel erläutert, der zum Abtasten des gesamten Spektrums, der Korrelation zwischen Quellen, der An-zahl von Quellen und der Anzahl von Sensoren verwendet wird. Die Di˙erenz zwischen den Winkeln wird angezeigt, um die Amplitude des erzeugten Peaks zu bestimmen. Die mathematische Formulierung des Winkelspektrums ist einer der Hauptbeiträge dieser Arbeit, aber andere Verbesserungen wurden durch die vorgeschlagene Verwendung von Matrixnormen erreicht. Die Verwendung des auf Standards basierenden Ansatzes vermeidet die Notwendigkeit, eine Matrixzerlegung in Eigenwerten durchzuführen, und folglich wird die Gesamtzeit der Ausführung der Methode reduziert und der mittlere quadratische Fehler für Situationen mit entfernten Quellen reduziert. Vergleicht man die Vorschläge mit den in der Literatur etablierten Methoden, übertri˙t der Standardansatz die MODE-Methode und ihre Ableitungen in Bezug auf den mittleren quadratischen Fehler. In Bezug auf die Laufzeit sind SEAD-basierte Methoden für eine Reihe von Quellen unter 4 jedoch rechenintensiver. Die Schätzung von Energieimpulsen in der Röntgenspektroskopie ist kein neues Thema, der Mikrowellen-SQUID-Multiplexer ist jedoch ein relativ neuer Ansatz und derzeit ein florierendes Forschungsthema. Das Ziel des Systems ist es, die Energie von energetischen Partikeln zu schätzen, die in Detektoren fallen. Die Detektoren können die transition edge sensor oder metallische magnetische Kalorimeter sein. Metallische ma-gnetische Kalorimeter sind energiedispersive Teilchendetektoren, deren Detektionsprinzip auf dem ersten Hauptsatz der Thermodynamik beruht. Sie sind paramagnetische Senso-ren, die sich in einem schwachen Magnetfeld befinden und Temperaturschwankungen in Schwankungen der magnetische Flusses umsetzen. Um die Magnetflussvariation aufgrund des Teilcheneinfalls zu lesen, wird eine supraleitende Komponente, die als supraleitende Quanteninterferenzvorrichtung bezeichnet wird, verwendet. Das SQUID ist ein äußerst empfindliches Interferometer und verhält sich wie ein variabler Induktor. Der SQUID ist mit einem Abschluss einer supraleitenden Übertragungsleitung verbunden und erzeugt Änderungen in der Resonanzfrequenz des Schaltkreises. Daher kann die Teilchenenergie elektronisch gelesen werden, indem eine Funkwelle, die sich durch den Resonator ausbreitet, demoduliert wird. Die Modulation erfolgt an der Amplitude und Phase eines komplexen Trägers. Nach dem Ausschluss von Zwischenfrequenzen infolge des Trägermischprozesses wird ein komplexer Niederfrequenzträger erhalten, auf den Phasenschätzungsverfahren angewendet werden. Aufgrund der Ähnlichkeit mit dem Ankunftsrichtungsschätzungspro-blem schlagen wir einen Ansatz vor, der auf der Sensoranordnung und der räumlichen Korrelationsmatrix in Eigenwertezerlegung basiert. Auf diese Weise wird eine Analogie zwischen den beiden Problemen hergestellt. Um die Korrelationsmatrix zu erhalten, wird angenommen, dass ein Referenzvektor existiert, dessen Phase nicht vom Einfall von Parti-keln abhängt, d.h., wenn das System in Ruhe ist. Dieser Referenzvektor wird mittels der Korrelationsfunktion mit den zu jedem Zeitpunkt empfangenen Daten verglichen. Eine geeignete Datenvektorlänge wird definiert und somit eine Zwei-Sensor-Matrix (snapshots) und eine 2 × 2-Korrelationsmatrix erhalten. Die Eigenwertzerlegung kann explizit in Ab-hängigkeit von den Eingaben gelöst werden, so dass eine allgemeine Formulierung für die Methode vorgestellt wird. Darüber hinaus können Vereinfachungen zum Zweck der Implementierung auf dedizierter Hardware eingeführt werden. Der Schätzfehler wird für die vorgeschlagene Methode und die Maximum-Likelihood-Methode analysiert. Die Eigenwert-methode zeigte eine größere Robustheit gegenüber Rauschen und kann unter Umständen das Schätzproblem ohne externe Geräte lösen, was bei der Maximum-Likelihood-Methode nicht der Fall ist. La estimación de la dirección de llegada y la estimación del pulso de energía en la espectroscopia de rayos X se basan en el mismo parámetro, el desplazamiento de fase de las señales en relación con una referencia. Este trabajo demuestra la posibilidad de aplicar técnicas ya establecidas para la estimación de la dirección de llegada al problema de espectroscopia. Los dos temas se relacionan en una parte introductoria y luego se discuten por separado con énfasis en las características intrínsecas de cada uno. En el problema de estimación de la dirección de llegada, inicialmente presentamos el modelo de señal para la disposición del sensor y anlgunos métodos basados en el estimador de máxima verosimilitud. Considerando un conjunto de sensores distribuidos linealmente con espaciado uniforme entre los elementos, las señales inducidas en cada circuito serán copias rezagadas de una señal de referencia. El retraso está estrechamente relacionado con la dirección de llegada. En el dominio espacial, las direcciones de llegada representan frecuencias de funciones exponenciales complejas, que deben estimarse. Los principales métodos de estimación son MODE, MODEX, MODEX modificado y SEAD. Se presta especial atención al método SEAD que se basa en la descomposición del valor propio de la matriz de correlación espacial modificada. La diferencia entre los dos valores propios más grandes genera una curva con picos prominentes que indican las direcciones de llegada de las ondas planas. Esta curva se llama espectro diferencial. Se desarrolla un análisis matemático del espectro diferencial, llamado espectro diferencial total, y se muestra que la norma de la matriz inducida por el vector norma-2 es el componente principal del cálculo. Por lo tanto, proponemos un enfoque basado en reglas de matriz para la estimación de las direcciones de llegada. Se ha desarrollado una descripción matemática general que explica la relación entre los ángulos de llegada verdaderos y un ángulo sintético utilizado para escanear todo el espectro, la correlación entre las fuentes, la cantidad de fuentes y la cantidad de sensores. La diferencia entre los ángulos se muestra para determinar la amplitud del pico generado. La formulación matemática del espectro angular es una de las principales contribuciones de este trabajo, pero se lograron otras mejoras mediante el uso propuesto de reglas de matriz. El uso del enfoque basado en estándares evita la necesidad de realizar la descomposición de la matriz en valores propios y, en consecuencia, el tiempo total de ejecución del método se reduce y el error cuadrado medio se reduce para la situación de fuentes remotas. Comparando las propuestas con los métodos establecidos en la literatura, el enfoque estándar supera el método MODE y sus derivados en relación con el error cuadrático medio. Sin embargo, con respecto al tiempo de ejecución, los métodos basados en SEAD son más costosos desde el punto de vista informático para varias fuentes de menos de 4. La estimación de los pulsos de energía en la espectroscopia de rayos X no es un tema nuevo, sin embargo, el multiplexor SQUID de microondas es un enfoque relativamente nuevo y actualmente es un tema de investigación próspero. El objetivo del sistema es estimar la energía de las partículas energéticas que caen en los detectores, que pueden ser de tipo transition edge sensor o metallic magnetic calorimeters. Los calorímetros metálicos son sensores para-magnéticos que se encuentran en un campo magnético débil, traducen la variación de temperatura en variación de flujo magnético. Para leer las variaciones del flujo magnético debido a la incidencia de partículas, se utiliza un componente superconductor llamado superconducting quantum interference device. El SQUID es un interferómetro extremadamente sensible y se comporta como un inductor variable. El SQUID está acoplado a una terminación de una línea de transmisión superconductora y produce cambios en la frecuencia de resonancia del circuito. Por lo tanto, la energía de las partículas puede leerse electrónicamente demodulando una onda de radio que viaja a través del resonador. La modulación ocurre en la amplitud y fase de un portador complejo. Después de la exclusión de frecuencias intermedias como resultado del proceso de mezcla de portadora, se obtiene una portadora compleja de baja frecuencia sobre la cual se aplican los métodos de estimación de fase. Debido a la similitud con el problema de estimación de la dirección de llegada, proponemos un enfoque basado en la disposición del sensor y la descomposición de la matriz de correlación espacial en valores propios. De esta manera, se establece una analogía entre los dos problemas. Para obtener la matriz de correlación, se considera que existe un vector de referencia cuya fase no depende de la incidencia de partículas, es decir, cuando el sistema está en reposo. Este vector de referencia se compara mediante la función de correlación con los datos que se reciben en cada momento. Se define una longitud de vector de datos conveniente, por lo que obtiene una matriz de instantáneas con dos sensores y una matriz de correlación de dimensiones 2 × 2. La descomposición del valor propio se puede resolver explícitamente en función de las entradas de la matriz, de modo que se presente una formulación general para el método. Además, se pueden imponer simplificaciones con el fin de implementarlas en hardware dedicado. El error de estimación se analiza para el método propuesto y el método de máxima verosimilitud. El método de valores propios presentó una mayor robustez al ruido y, en algunas circunstancias, puede resolver el problema de estimación sin dispositivos externos, algo que no ocurre con el método de máxima verosimilitud. Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES

The specific heat of dilute alloys of holmium in gold and in silver plays a major role in the optimization of low temperature microcalorimeters with enclosed $^{163}\textrm{Ho}$, such as the ones developed for the neutrino mass experiment ECHo. We investigate alloys with atomic concentrations of $x_\textrm{Ho}=0.01\,\% - 4\,\%$ at temperatures between $10\,\textrm{mK}$ and $800\,\textrm{mK}$. Due to the large total angular momentum $J=8$ and nuclear spin $I=7/2$ of $\textrm{Ho}^{3+}$ ions, the specific heat of $\underline{\textrm{Au}}\textrm{:Ho}$ and $\underline{\textrm{Ag}}\textrm{:Ho}$ depends on the detailed interplay of various interactions, including contributions from the localized 4f electrons and nuclear contributions via hyperfine splitting. This makes it difficult to accurately determine the specific heat of these materials numerically. Instead, we measure their specific heat by using three experimental set-ups optimized for different concentration and temperature ranges. The results from measurements on six holmium alloys demonstrate that the specific heat of these materials is dominated by a large Schottky anomaly with its maximum at $T\approx 250\,\textrm{mK}$, which we attribute to hyperfine splitting and crystal field interactions. RKKY and dipole-dipole interactions between the holmium atoms cause additional, concentration-dependent effects. With regard to ECHo, we conclude that for typical operating temperatures of $T\leq 20\,\textrm{mK}$, silver holmium alloys with $x_\textrm{Ho}\gtrsim 1\,\%$ are suited best., 15 pages, 4 figures. Replacement with small modifications after peer-review, no change to scientific content

Accurate decay data of radionuclides are necessary for many fields of science and technology, ranging from medicine and particle physics to metrology. However, data that are in use today are mostly based on measurements or theoretical calculation methods that are rather old. Recent measurements with cryogenic detectors and other methods show significant discrepancies to both older experimental data and theory in some cases. Moreover, the old results often suffer from large or underestimated uncertainties. This is in particular the case for electron-capture (EC) decays, where only a few selected radionuclides have ever been measured. To systematically address these shortcomings, the European metrology project MetroMMC aims at investigating six radionuclides decaying by EC. The nuclides are chosen to cover a wide range of atomic numbers Z, which results in a wide range of decay energies and includes different decay modes, such as pure EC or EC accompanied by $$\gamma $$γ- and/or $$\beta ^{+}$$β+-transitions. These will be measured using metallic magnetic calorimeters (MMCs), cryogenic energy-dispersive detectors with high-energy resolution, low-energy threshold and high, adjustable stopping power that are well suited for measurements of the total decay energy and X-ray spectrometry. Within the MetroMMC project, these detectors are used to obtain X-ray emission intensities of external sources as well as fractional EC probabilities of sources embedded in a $$4\pi $$4π absorber. Experimentally determined nuclear and atomic data will be compared to state-of-the-art theoretical calculations which will be further developed within the project. This contribution introduces the MetroMMC project and in particular its experimental approach. The challenges in EC spectrometry are to adapt the detectors and the source preparation to the different decay channels and the wide energy range involved, while keeping the good resolution and especially the low-energy threshold to measure the EC from outer shells.

Proceedings of the 21st International Conference on Radionuclide Metrology and its Applications (ICRM), 15-19 May 2017, Buenos Aires, Argentina. Organizer: Argentinian Comis Nacl Energia Atomica; International audience; The ratios of the electron capture probabilities P-K, P-L and P-M of Fe-55 have been measured with a metallic magnetic calorimeter, a specific type of cryogenic detector. The Fe-55 source was enclosed in the detector absorber, whose dimensions were chosen such that the detection efficiency for Mn K X-rays was larger than 99.99%. Since all electrons and photons emitted by the source are absorbed in the detector, the detection efficiency is virtually 100% for K, L and M captures. The energy threshold was low enough to allow for clear separation of the M captures (similar to 80 eV) from noise. The capture probability ratios were translated to capture probabilities using the recommended value for the probability of the undetected N captures. The resulting values are in agreement both with the recommended values of P-K, P-L and P-M and with the experimental data of Pengra and coworkers.

International audience; Metallic magnetic calorimeters have been used for several years for the determination of the shapes of beta spectra. Experimental spectra of the beta decays of $^{63}$Ni and $^{241}$Pu exhibit, at very low energy, strong deviations from standard theoretical calculations including corrections for screening, radiative, and nuclear size effects. These discrepancies can be attributed to the atomic exchange effect. In particular the spectrum of $^{63}$Ni measured with an electroplated $^{63}$Ni source is in excellent agreement with theory including the exchange effect. This underlines the quality of the experimental spectrum as well as the correctness of the calculation of the exchange effect.

International audience; The beta spectra of $^{241}$Pu and $^{63}$Ni have been recently measured using metallic magnetic calorimeters. This powerful experimental technique allows theoretical beta spectra calculations to be tested at low energy with an accuracy never before achievable. Their comparison with classical beta calculations exhibits a significant deviation below 4 keV for $^{241}$Pu and 8 keV for $^{63}$Ni. The atomic exchange effect explains the main part of this deviation in the $^{63}$Ni beta spectrum. This effect has a significant contribution, equivalent to the magnitude of the screening, in the $^{241}$Pu beta spectrum.

International audience; Metallic magnetic calorimeters are a specific type of cryogenic detectors that have been shown to enable precise measurement of the shape of low energy beta spectra. The aim of their use at LNHB is the determination of the shape factors of beta spectra. The beta source is enclosed in the detector absorber, allowing for very high detection efficiency. It has turned out that the type of source is of crucial importance for the correctness of the measured spectrum. Spectra of 63Ni measured with several sources prepared by drying a NiCl2 solution differ from one another and from theory, whereas spectra measured with electroplated sources are reproducible and agree with theory. With these latter measurements we could confirm the atomic exchange effect down to very low energy (200 eV).

International audience; Following an increased demand from users for a precise knowledge of beta spectra coupled with well-established uncertainties, LNHB is leading a study of beta spectral shapes at the metrological level. The evaluation of these beta spectra, especially to reach metrological uncertainties, requires new measurements and new calculations with high precision. The first part of this contribution will describe a new experimental setup for the measurement of beta energy spectra based on a silicon detector with a very thin entrance window and operating at liquid nitrogen temperatures under high-vacuum. Monte Carlo simulations were performed to optimize the detection chamber and source holder. Some preliminary results are included. The second part summarizes the calculations already implemented. These complex calculations are compared to some measurements of beta spectra obtained by using metallic magnetic calorimeters, and highlight the major contribution of the atomic screening and exchange effects at low energy.

International audience; We are developing metallic magnetic calorimeters for beta spectrometry with the aim of determining the shape factors of beta spectra. The beta emitter is enclosed inside the detector absorber and the absorber size is chosen such that the detection efficiency is close to 100% for the entire spectrum.The nature of the deposit of the beta emitter is critical for precise measurement. A dependence of the shape of the spectrum on the quality of the source has been observed, supposedly due to interactions between the electrons and the deposit itself. We chose for this comparative study a nuclide with an allowed transition whose theoretical spectrum is relatively well-known, $^{63}$Ni, a pure beta emitter with an endpoint energy of 66.98 keV.Results of measurements of $^{63}$Ni deposited with different techniques are presented and compared to each other and to the theoretical spectrum.

Proceedings of the 17th International Conference on Radionuclide Metrology and its Applications (ICRM 2009)7-11 September 2009 • Bratislava, Slovak Republic; International audience; The LNE-LNHB is developing metallic magnetic calorimeters, a specific type of cryogenic detectors, for beta spectrometry. The aim is the determination of the shape factors of beta spectra. Our latest detector has been designed to measure the spectrum of 241Pu, a pure beta emitter with an endpoint energy of 20.8 keV. In this paper, the detection principle of metallic magnetic calorimeters is explained and a detailed description is given of the realization of the detector enclosing a 241Pu source inside the detector absorber. A spectrum resulting from our first measurement is shown and compared with a theoretical spectrum.

ISBN: 978-0-7354-0751-0 - Conference date: 20–24 July 2009Location: Stanford (California), USA; International audience; We are developing metallic magnetic calorimeters for beta spectrometry in the context of ionizing radiation metrology. The aim is the determination of the shape factors of beta spectra. Our latest detector has been designed to measure the spectrum of $^{241}$Pu, a pure beta emitter with an endpoint energy of 20.8 keV. We present the spectrum resulting from our first measurement and compare it with theoretical spectra.

International audience; We present a prototype of metallic magnetic calorimeters that we are developing for absolute activity measurements of low energy emitting radionuclides. We give a detailed description of the realization of the prototype, containing an $^{55}$Fe source inside the detector absorber. We present the analysis of first data taken with this detector and compare the result of activity measurement with liquid scintillation counting. We also propose some ways for reducing the uncertainty on the activity determination with this new technique.

We present a comprehensive review of keV-scale sterile neutrino Dark Matter, collecting views and insights from all disciplines involved - cosmology, astrophysics, nuclear, and particle physics - in each case viewed from both theoretical and experimental/observational perspectives. After reviewing the role of active neutrinos in particle physics, astrophysics, and cosmology, we focus on sterile neutrinos in the context of the Dark Matter puzzle. Here, we first review the physics motivation for sterile neutrino Dark Matter, based on challenges and tensions in purely cold Dark Matter scenarios. We then round out the discussion by critically summarizing all known constraints on sterile neutrino Dark Matter arising from astrophysical observations, laboratory experiments, and theoretical considerations. In this context, we provide a balanced discourse on the possibly positive signal from X-ray observations. Another focus of the paper concerns the construction of particle physics models, aiming to explain how sterile neutrinos of keV-scale masses could arise in concrete settings beyond the Standard Model of elementary particle physics. The paper ends with an extensive review of current and future astrophysical and laboratory searches, highlighting new ideas and their experimental challenges, as well as future perspectives for the discovery of sterile neutrinos., v2: 257 pages, 57 figures, content matches published version [JCAP01(2017)025]; over 100 authors from several different communities