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Recent advances in the development of cryogenic particle detectors such as magnetic microcalorimeters allow the fabrication of sensor arrays with an increasing number of pixels. Since these detectors must be operated at the lowest temperatures, the readout of large detector arrays is still quite challenging. This is especially true for the ECHo experiment, which presently aims to simultaneously run 6,000 two pixel detectors to investigate the electron neutrino mass. For this reason, we developed a readout system based on a microwave SQUID multiplexer (μ MUX) that is operated by a custom software-defined radio (SDR) at room-temperature. The SDR readout electronics consist of three distinct hardware units: a data processing board with a Xilinx ZynqUS+ MPSoC; a converter board that features DACs, ADCs, and a coherent clock distribution network; and a radio frequency front-end board to translate the signals between the baseband and the microwave domains. Here, we describe the characteristics of the full-scale SDR system. First, the generated frequency comb for driving the μ MUX was evaluated. Subsequently, by operating the SDR in direct loopback, the crosstalk of the individual channels after frequency demultiplexing was investigated. Finally, the system was used with a 16-channel μ MUX to evaluate the linearity of the SDR, and the noise contributed to the overall readout setup. [ABSTRACT FROM AUTHOR]

In the last years, the COSINUS (Cryogenic Observatory for SIgnals seen in Next generation Underground Searches) experiment has made significant progress both in the construction of its facility and in pursuing its physics goals: At Laboratori Nazionali del Gran Sasso (LNGS) in Italy, an underground facility was constructed, which will house experimental detectors for dark matter direct detection in a dry dilution cryostat. Construction of the main structures at the COSINUS site is finished, including the control building, the cryostat access level, and the water tank which will serve as a Cherenkov muon veto around the cryostat. With a nuclear recoil threshold of 4 keV, the latest COSINUS detector prototype approaches the design goal of 1 keV, and particle discrimination on event-by-event basis has been demonstrated. This contribution gives a brief overview on the status of COSINUS. [ABSTRACT FROM AUTHOR]

Liquid argon time-projection chambers (LArTPCs) have become a prominent tool for experiments in particle physics. Recent years have yielded significant advances in the techniques used to capture the signals generated by these cryogenic detectors. This article summarizes these novel developments for detection of ionization electrons and scintillation photons in LArTPCs. New methods to capture ionization signals address the challenges of scaling traditional techniques to the large scales necessary for future experiments. Pixelated readouts improve signal fidelity and expand the applicability of LArTPCs to higher-rate environments. Methods that leverage amplification in argon enable measurements in the keV regime and below. Techniques to enhance collection of argon scintillation photons improve calorimetry and expand the physics program for very large detectors. Future efforts aim to demonstrate systems for the combined detection of both electrons and photons. [ABSTRACT FROM AUTHOR]

CUPID is a next-generation bolometric experiment aiming at searching for neutrinoless double-beta decay with ∼250 kg of isotopic mass of 100Mo. It will operate at ∼10 mK in a cryostat currently hosting a similar-scale bolometric array for the CUORE experiment at the Gran Sasso National Laboratory (Italy). CUPID will be based on large-volume scintillating bolometers consisting of 100Mo-enriched Li2MoO4 crystals, facing thin Ge-wafer-based bolometric light detectors. In the CUPID design, the detector structure is novel and needs to be validated. In particular, the CUORE cryostat presents a high level of mechanical vibrations due to the use of pulse tubes and the effect of vibrations on the detector performance must be investigated. In this paper we report the first test of the CUPID-design bolometric light detectors with NTD-Ge sensors in a dilution refrigerator equipped with a pulse tube in an above-ground lab. Light detectors are characterized in terms of sensitivity, energy resolution, pulse time constants, and noise power spectrum. Despite the challenging noisy environment due to pulse-tube-induced vibrations, we demonstrate that all the four tested light detectors comply with the CUPID goal in terms of intrinsic energy resolution of 100 eV RMS baseline noise. Indeed, we have measured 70-90 eV RMS for the four devices, which show an excellent reproducibility. We have also obtained high energy resolutions at the 356 keV line from a 133Ba source, as good as Ge semiconductor γ detectors in this energy range.

An array of twelve 0.28 kg lithium molybdate (LMO) low-temperature bolometers equipped with 16 bolometric Ge light detectors, aiming at optimization of detector structure for CROSS and CUPID double-beta decay experiments, was constructed and tested in a low-background pulse-tube-based cryostat at the Canfranc underground laboratory in Spain. Performance of the scintillating bolometers was studied depending on the size of phonon NTD-Ge sensors glued to both LMO and Ge absorbers, shape of the Ge light detectors (circular vs. square, from two suppliers), in different light collection conditions (with and without reflector, with aluminum coated LMO crystal surface). The scintillating bolometer array was operated over 8 months in the low-background conditions that allowed to probe a very low, μBq/kg, level of the LMO crystals radioactive contamination by 228Th and 226Ra.

Silicon Photomultipliers (SiPMs) have emerged as leading photon detectors in experimental physics since their introduction in the late 1990s. With performance characteristics superior to those of traditional photodetectors, SiPMs exhibit up to 60% photon detection efficiency, rapid signal rise times, and resistance to magnetic fields. Their solid-state construction enables mass production, compactness, and high spatial resolution, facilitating their integration into a wide range of experimental setups. Although susceptible to radiation damage, mitigation strategies are being studied to allow their reliable operation even in environments with elevated radiation levels. SiPMs excel in detecting low levels of light, making them well suited for applications involving scintillation and Cherenkov light. Their ability to operate effectively at cryogenic temperatures allows the construction of a new class of multi-tons rare event search experiments such as Darkside-20k. Insensitivity to the magnetic field and mitigation of the radiation damages are making SiPMs well-suited to be used in accelerator driven physics such as Cherenkov light detectors for Particle IDentification (PID) in the future Electron Ion Collider (EIC). [ABSTRACT FROM AUTHOR]

The Cryogenic Underground Observatory for Rare Events (CUORE) is the most sensitive experiment searching for neutrinoless double-beta decay (0νββ) in 130Te. CUORE uses a cryogenic array of 988 TeO2 calorimeters operated at ∼10 mK with a total mass of 741 kg. To further increase the sensitivity, the detector response must be well understood. Here, we present a non-linear thermal model for the CUORE experiment on a detector-by-detector basis. We have examined both equilibrium and dynamic electro-thermal models of detectors by numerically fitting non-linear differential equations to the detector data of a subset of CUORE channels which are well characterized and representative of all channels. We demonstrate that the hot-electron effect and electric-field dependence of resistance in NTD-Ge thermistors alone are inadequate to describe our detectors' energy-dependent pulse shapes. We introduce an empirical second-order correction factor in the exponential temperature dependence of the thermistor, which produces excellent agreement with energy-dependent pulse shape data up to 6 MeV. We also present a noise analysis using the fitted thermal parameters and show that the intrinsic thermal noise is negligible compared to the observed noise for our detectors.

Cryogenic detectors can detect the smallest energy depositions via the scattering of the incoming particle with the detector material. The deposited energy leads to minimal temperature rises of a few μK , read out via transition edge sensors and SQUIDs. Using scintillating crystals as detector material offers the possibility of discriminating between nuclear recoils from dark matter scattering and electromagnetic background events. The CRESST experiment pioneered this technology and is still among the most sensitive experiments searching for sub-GeV dark matter particles. The technology is now also used by other experiments for dark matter searches (COSINUS) and for measuring coherent elastic neutrino-nucleus scattering (NUCLEUS). We discuss cryogenic detectors' detection principle and their application. We present the latest dark matter results from CRESST, a new type of background, and the status of the COSINUS and NUCLEUS experiments. This article is part of the theme issue 'The particle-gravity frontier'. [ABSTRACT FROM AUTHOR]

We describe a technique to optimize the dynamic performance of microwave SQUID multiplexer (µMUX)-based systems. These systems proved to be adequate for reading out multiple cryogenic detectors simultaneously. However, the requirement for denser detector arrays to increase the sensitivity of scientific experiments makes its design a challenge. When modifying the readout power, there is a trade-off between decreasing the signal-to-noise ratio (SNR) and boosting the nonlinearities of the active devices. The latter is characterized by the spurious free dynamic range (SFDR) parameter and manifests as an increment in the intermodulation products and harmonics power. We estimate the optimal spectral location of the SQUID signal containing the detector information for different channels. Through the technique, what we refer to as Spectral Engineering, it is possible to minimize the SNR degradation while maximizing the SFDR of the detector signal, thus, overcoming the trade-off. [ABSTRACT FROM AUTHOR]

The AnaBHEL experiment aims to detect the analog Hawking radiation emitted by an accelerated relativistic plasma mirror for which the effective event horizon is analogous to that of a black hole, thanks to the equivalence principle. This radiation is composed of a few Hawking photons emitted simultaneously in the infrared band and the 'partner photons' in the ultraviolet band. The former is emitted in the opposite direction of the mirror propagation and is redshifted in the laboratory frame. In the AnaBHEL scheme, high-intensity petawatt laser pulses, will be used to produce the relativistic accelerated plasma mirrors from a helium gas jet. Infrared and ultraviolet photons generated by the mirrors will be detected by dedicated superconducting nanowire single-photon detectors (SNSPDs) at very low temperature and by multichannel plates at room temperature, respectively. Details of the setup design are discussed. [ABSTRACT FROM AUTHOR]

The Cryogenic Underground Observatory for Rare Events (CUORE) is the first bolometric experiment searching for neutrino-less double-beta (0νββ) decay that has been able to reach the one-ton scale. The detector, located at the Laboratori Nazionali del Gran Sasso in Italy, consists of an array of 988 TeO2 crystals arranged in a compact cylindrical structure of 19 towers. Following the completion of the detector construction in August 2016, CUORE began its first physics data run in 2017 at a base temperature of about 10 mK. Following multiple optimization campaigns in 2018, CUORE is currently in stable operating mode. In 2019, CUORE released its second result of the search for 0νββ corresponding to a TeO2 exposure of 372.5 kgyr and a median exclusion sensitivity to a 130Te 0νββ decay half-life of 1.7 1025 yr. We find no evidence for 0νββ decay and set a 90% C.I. Bayesian lower limit of 3.2 1025 yr on the 130Te 0νββ decay half-life. We present the current status of CUORE's search for 0νββ. We give an update of the CUORE background model and the measurement of the 130Te two neutrino double-beta (2νββ) decay half-life. Eventually, we show the preliminary results on half-life limits from the analysis of 130Te 0νββ and 2νββ decay to the first 0+ excited state of 130Xe.

A novel system formed by a Microwave Superconducting Quantum Interference Device (SQUID) Multiplexer (μ MUX) and a room temperature electronics employs frequency division multiplexing (FDM) technique to read out multiple cryogenic detectors. Since the detector signal is embedded in the phase of the SQUID signal, a Digital Quadrature Demodulator (DQD) is widely implemented to recover it. However, the DQD also generates a signal that aliases into the first Nyquist zone affecting the demodulated detector signal. In this work, we demonstrate how this spurious signal is generated and a mathematical model of it is derived and validated. In addition, we discuss different proposals to improve the attenuation of this undesired signal. Lastly, we implement one of the proposals in our readout system. Our measurements show an enhancement in the spurious signal attenuation of more than 35 dB. As a result, this work contributes to attenuate the spurious below the system noise. [ABSTRACT FROM AUTHOR]

The EDELWEISS collaboration aims for direct detection of light dark matter using germanium cryogenic detectors with low threshold phonon sensor technologies and efficient charge readout designs. We describe here the development of Ge bolometers equipped with high impedance thermistors based on a NbxSi1−x TES alloy. High aspect ratio spiral designs allow the TES impedance to match with JFET or HEMT front-end amplifiers. We detail the behavior of the superconducting transition properties of these sensors and the detector optimization in terms of sensitivity to a-thermal phonons. We report preliminary results of a 200 g Ge detector that was calibrated using 71Ge activation by neutrons at the LSM underground laboratory. [ABSTRACT FROM AUTHOR]

The Photon Detection Systems of the first two Liquid Argon Time Projection Chambers (LArTPCs) of the DUNE Far Detector exploit the Horizontal and Vertical Drift technologies and are composed of 6000 and 672 photon detection units respectively, named X-Arapuca. The Photon Detection Systems will complement and improve the calorimetry and vertex reconstruction for beam events and the prompt light detection will enable the trigger for non-beam events, such as Supernova Neutrino Bursts. In the Horizontal Drift, the Photon Detection System is placed behind the anode planes of the LArTPC, while in the Vertical Drift it is located on the cathode, biased at 320 kV, thus requiring targeted solutions to power and read the X-Arapuca devices. The X-Arapuca is a photon trap with two light downshifting stages, where the light is conveyed to SiPMs with a large area Wavelength Shifting light guide. Its Photon Detection Efficiency, and consequently the Photon Detection Systems sensitivity to the DUNE physics reaches, is determined by the grade and coupling of its several components. The Photon Detection Systems of both Horizontal and Vertical Drift are presented and discussed in their individual features, with a focus on the photon collector components and on the performances achieved by the X-Arapuca units measured in laboratory and in the CERN facilities at the Neutrino Platform. Possible changes in the baseline X-Arapuca designs proposed to further enhance the Photon Detection Efficiency of both Horizontal and Vertical Drift are also discussed. The Horizontal and Vertical Drift scale 1:20 prototypes at the NP04 and NP02 CERN Neutrino Platform, instrumented with the baseline versions of the X-Arapuca, will be operated with Liquid Argon throughout 2024. [ABSTRACT FROM AUTHOR]

The fractional electron capture probabilities of 59Ni were measured using metallic magnetic calorimeters (MMCs). 59Ni was one of the radionuclides chosen as a part of the European Metrology Research (EMPIR) project MetroMMC. The measurement was performed by using the decay energy spectroscopy (DES) technique, where the radionuclide is embedded in the absorber to have a 4π geometry. Two different source preparation techniques adapted for the measurement are also discussed: electroplating on gold foil and micro-drop-dispensing on gold nanofoam. The total energy spectra obtained from both sources are compared with each other, and the measured fractional electron capture probabilities are compared with those available in the literature and from the BetaShape code. [ABSTRACT FROM AUTHOR]

Athena (advanced telescope for high-energy astrophysics) is an ESA large-class mission, at present under a re-definition “design-to-cost” phase, planned for a prospective launch at L1 orbit in the second half of the 2030s. It will be an observatory alternatively focusing on two complementary instruments: the X-IFU (X-ray Integral Field Unit), a TES (TransitionEdge Sensor)-based kilo-pixel array which is able to perform simultaneous high-grade energy spectroscopy (~3 eV@7 keV) and imaging over 4′ FoV (field of view), and the WFI (Wide Field Imager), which has good energy spectral resolution (~170 eV@7 keV) and imaging on wide 40′ × 40′ FoV. Athena will be a truly transformational observatory, operating in conjunction with other large observatories across the electromagnetic spectrum available in the 2030s like ALMA, ELT, JWST, SKA, CTA, etc., and in multi-messenger synergies with facilities like LIGO A+, Advanced Virgo+, LISA, IceCube and KM3NeT. The Italian team is involved in both instruments. It has the co-PIship of the cryogenic instrument for which it has to deliver the TES-based Cryogenic AntiCoincidence detector (CryoAC) necessary to guarantee the X-IFU sensitivity, degraded by a primary particle background of both solar and galactic cosmic ray (GCR) origins, and by secondary electrons produced by primaries interacting with the materials surrounding the main detector. The outcome of Geant4 studies shows the necessity for adopting both active and passive techniques to guarantee the residual particle background at 5 × 10−3 cts cm−2 s−1 keV−1 level in 2–10 keV scientific bandwidth. The CryoAC is a four-pixel detector made of Si-suspended absorbers sensed by Ir/Au TESes placed at

Fractional electron capture probability ratios of 125I were measured using metallic magnetic calorimeters (MMCs). Due to the 4π geometry of the source embedded in the absorber, detection efficiency of nearly 99% was observed for K, L, M, and N capture events. The fractional capture probabilities were calculated from peak area ratios. [ABSTRACT FROM AUTHOR]

The Ricochet reactor neutrino observatory is planned to be installed at the Laue Langevin Institute starting mid-2022. Its scientific goal is to perform a low-energy and high precision measurement of the coherent elastic neutrino-nucleus scattering spectrum in order to explore exotic physics scenarios. Ricochet will host two cryogenic detector arrays: the CryoCube (Ge target) and the Q-array (Zn target), operated at 10 mK. The 1 kg Ge CryoCube will consist of 27 Ge crystals instrumented with NTD-Ge thermal sensors and charge collection electrodes for a simultaneous heat and ionization readout to reject the electromagnetic backgrounds (gamma, beta, x-rays). We present the status of its front-end electronics. The first stage of amplification is made of High Electron Mobility Transistors developed by CNRS/C2N laboratory, optimized to achieve ultra-low noise performance at 1 K with a dissipation as low as 15 μ W per channel. Our noise model predicts that 10 eV heat and 20 eV ee RMS baseline resolutions are feasible with a high dynamic range for the deposited energy (up to 10 MeV) thanks to loop amplification schemes. Such resolutions are mandatory to have a high discrimination power between nuclear and electron recoils at the lowest energies. [ABSTRACT FROM AUTHOR]

Particle induced X-ray emission with the use of focused ion beam (µ-PIXE) utilizing a superconducting tunnel junction (STJ) X-ray spectrometer has been developed to realize light element mapping in the soft X-ray region. A five hundred pixels array of STJ detector has been installed in the µ-PIXE beamline at the accelerator facility in the University of Tsukuba. Performance of a single-pixel STJ detector is tested. The K-lines of light elements C to Al have been separately detected in the pulse height spectra with a broad background, which is attributed substrate-hit events caused by scattered protons and high-energy characteristic X-ray lines. The background is rejected by using the anticoincidence technique or rise-time discrimination. [ABSTRACT FROM AUTHOR]

This paper describes history and technical evolution of portable devices which use energy-dispersive X-ray fluorescence (EDXRF)-analysis to study works of art. The history starts in 1971, when the first transportable equipment was employed to examine the pigments of Raphael’s painting “La Deposizione” during restoration at the “Istituto Centrale del Restauro” in Rome. Then, paintings of all types were analyzed and metals (bronzes, brasses, gold and silver). The evolution of the exciting source is described (from radioisotopes or big size X-ray tubes, to miniaturized, dedicated X-ray tubes) and of X-ray detectors (from proportional gas counters, to N2-cooled Si or Ge-detectors, to Peltier cooled HgI2 and Si-PIN, to Peltier cooled Si-drift). Also, the pulse height analyzers had an important evolution, from a heavy box to a computer card, to very small electronic circuits included in the detector box. The most “modern” portable EDXRF device is currently composed of a small-size X-ray tube, a Si-drift detector, both properly collimated, a portable computer, and dedicated software for the processing of the data. The total weight of such a device is about 2 kg. The last evolution: from analysis of a limited number of points to a complete scanning of the artifact. A mechanics is also required, with a sophisticated software interfacing mechanics to measuring heads. Maps giving the distribution of all analyzed elements in all areas of the painting “La Fornarina” by Raphael could be obtained. Finally, an accurate analysis of the K or L-X rays of the elements present in the paintings allowed to determine the disposition of the pigment in the correct layer. [ABSTRACT FROM AUTHOR]

The use of High Purity Germanium detectors operated in ionization mode at cryogenic temperatures is investigated as an external background mitigation solution for bolometers used in rare-event search experiments. A simple experimental setup, running a 52-g Li 2 WO 4 bolometer sandwiched in-between two 2-cm thick High Purity Germanium cylindrical detectors in a dry cryostat, shows promising rejection to environmental gammas and atmospheric muons backgrounds. The acquired data are used together with a Monte Carlo simulation of the setup to extract the main contributions to the external backgrounds expected in an above ground experiment, such as e.g. current and future experimental efforts targeting the detection of coherent elastic neutrino-nucleus scattering at reactor facilities. Based on all these results, a 4 π coverage similar veto system achieving a O (10 keV) energy threshold is expected to achieve a ≳ 73% and a ≳ 92% rejection power for gamma-like and muon-like events, respectively. [ABSTRACT FROM AUTHOR]

There is a global trend to increase the light yield of CsI scintillators used in neutrino and dark matter detection by operating undoped crystals at cryogenic temperatures. However, high light yield alone is not sufficient to guarantee a low-energy threshold. The response of undoped crystals to nuclear recoils at cryogenic temperatures is equally important. A liquid nitrogen-based cryostat was developed to measure the nuclear quenching factor of a small undoped CsI crystal using monoenergetic neutron beams at the Triangle Universities Nuclear Laboratory (TUNL). To minimize neutron scattering, high-Z materials were reduced around the crystal. The structure and performance of the cryostat are described in detail. Using this cryostat, a system light yield of 33. 4 ± 2. 0 photoelectrons per keV electron-equivalent (PE/keV ee) was observed at 5.9 keV ee , enabling the measurement of nuclear quenching factors at very low energies. The results of the quenching factor measurement will be reported in a subsequent paper. Non-negligible negative overshoot was observed in the tails of the observed light pulses. The origin of this issue and the correction procedure are described in detail. This information may be useful for others who encounter similar technical challenges. [ABSTRACT FROM AUTHOR]

Core-collapse Supernovae (SNe) are one of the most energetic events in the Universe, during which almost all the star's binding energy is released in the form of neutrinos. These particles are direct probes of the processes occurring in the stellar core and provide unique insights into the gravitational collapse. RES-NOVA will revolutionize how we detect neutrinos from astrophysical sources, by deploying the first ton-scale array of cryogenic detectors made from archaeological lead. Pb offers the highest neutrino interaction cross-section via coherent elastic neutrino-nucleus scattering (CE ν NS). Such process will enable RES-NOVA to be equally sensitive to all neutrino flavours. For the first time, we propose the use archaeological Pb as sensitive target material in order to achieve an ultra-low background level in the region of interest (O (1 keV)). All these features make possible the deployment of the first cm-scale neutrino telescope for the investigation of astrophysical sources. In this contribution, we will characterize the radiopurity level and the performance of a small-scale proof-of-principle detector of RES-NOVA, consisting in a PbWO 4 crystal made from archaeological-Pb operated as cryogenic detector. • RES-NOVA: first-proposed cryogenic detector made from archaeological lead for background suppression. • Coherent elastic neutrino-nucleus scattering: innovative way to detect neutrinos from astrophysical sources. • Radiopurity level measured on kg-scale prototype allows supernovae neutrino detection. [ABSTRACT FROM AUTHOR]

Several detectors for the next generation of particle physics experiments will make use of silicon photo-multipliers (SiPMs) to detect scintillation photons in liquid Argon. Cryogenic operation reduces dark counts by orders of magnitude, and makes it possible to retain single photon sensitivity even if large arrays of SiPMs are readout by a single amplifier. The total capacitance of a SiPM array with a total area of tens of cm 2 can range up to 200 nF. The series noise of the amplifier is the dominant factor that determines the signal to noise ratio of the readout chain. In this contribution, we present a cryogenic amplifier designed to operate in liquid Argon. The base version has a series white noise of 0.37 nV/ H z , while dissipating just 2.4 mW. Design variants have been also tested, which reduce noise to 0.22 nV/ H z , with a power consumption close to 4.5 mW. The amplifier base design and variants have been tested reading out SiPM arrays consisting of up to 96 6 × 6 mm 2 SiPMs, for a total photosensitive area of 35 cm 2 , demonstrating good single photon sensitivity even at low over-voltage values. [ABSTRACT FROM AUTHOR]

The spectral shape of forbidden beta-decays is a crucial benchmark for nuclear physics calculations and has important implications also for astroparticle physics. Among the interesting isotopes in this field, 115In is an excellent candidate, being a primordial nuclide featuring a good compromise among Q-value (497.489(10) keV) and half-life (4. 41 × 1 0 14 yr). In this paper, we propose to exploit a cryogenic calorimeter based on a In 2 O 3 crystal to perform a high-precision measurement of the β -decay energy spectrum, discussing also the results obtained within a preliminary test of this crystal and the next steps to improve the detector performance. [ABSTRACT FROM AUTHOR]

Energy dispersive photon spectrometry is a common analysis technique to quantify radionuclides present in a sample, the analysis is based on the knowledge of the photon emission intensities specific to each radionuclide. Among them, actinides have in general intense emission of L X-rays during the decay. However, their emission intensities are not well known and not detailed in the nuclear and atomic data tables due to the complexity of their spectra that cannot be resolved by conventional semiconductor spectrometers. Using a dedicated high energy resolution cryogenic detector, based on metallic magnetic calorimeter sensor technology, the L X-ray spectra of the decays of 238Pu(α) → 234U, 244Cm(α) → 240Pu, 237Np(α) → 233Pa and 233Pa(β − ) → 233U were measured with an energy resolution between 23 eV and 43 eV (full width at half maximum) given access to an unprecedented level of detail. Moreover, the detector was conceived to provide a quasi-constant efficiency in the energy range of the L X-rays, minimizing the uncertainty for relative L X-ray emission intensities. Prior to the measurements, the full energy peak efficiency was carefully characterized, which enabled the determination of absolute emission intensities, with an uncertainty of the order of 1%. Some corrections had to be introduced using Monte Carlo simulations, in particular to take into account the surface activity inhomogeneities of the sources. Total and group L X-ray emission intensities are compared with the available data and with the recommended values. In addition, nearly 30 individual L X-ray intensities are presented. [Display omitted] • Measurement of tens of L X-ray emission intensities emitted by actinides • A cryogenic spectrometer with an energy resolution of 23 to 43 eV • An intrinsic efficiency close to 100% between 10 keV and 25 keV • Detailed uncertainty contributions from the efficiency and the sources • Comparison of the measured intensities with available data [ABSTRACT FROM AUTHOR]

We present a new paradigm for the primary standardization of radionuclide activity per mass of solution (Bq/g). Two key enabling capabilities are 4π decay-energy spectrometry using chip-scale sub-Kelvin microcalorimeters and direct realization of mass by gravimetric inkjet dispensing using an electrostatic force balance. In contrast to traditional traceability, which typically relies on chemical separation of single-radionuclide samples, 4π integral counting, and additional spectrometry methods to verify purity, the system described here has both 4π counting efficiency and spectroscopic resolution sufficient to identify multiple radionuclides in the same sample at once. This enables primary standardization of activity concentrations of mixed-radionuclide samples. A major benefit of this capability, beyond metrology, is in assay of environmental and forensics samples, for which the quantification of multiplenuclide samples can be achieved where presently inhibited by interferences. This can be achieved without the need for chemical separations or efficiency tracers, thereby vastly reducing time, radioactive waste, and resulting measurement uncertainty.