Spectral broadening by quasiparticle pile-up in X-ray microcalorimeters with superconducting absorbers

Long-living quasiparticles can pile-up in a superconducting absorber of an X-ray microcalorimeter when photons are detected at high count rate. These quasiparticles can give a non-negligible contribution to the total heat capacity of the detector thus affecting the pulse height spectrum of detected photons. We investigated this effect with numerical simulations and evaluated the resulting spectral broadening as a function of the photon absorption rate, and the heat capacity of the detector for a NTD germanium microcalorimeter with pure Sn absorber.     

Fabrication of High-Resolution Gamma-Ray Metallic Magnetic Calorimeters with Ag:Er Sensor and Thick Electroplated Absorbers

We are developing metallic magnetic calorimeters for high-resolution gamma-ray spectroscopy for non-destructive assay of nuclear materials. Absorbers for these higher-energy photons can require substantial thickness to achieve adequate stopping power. We developed a new absorber fabrication process using dry-film photoresists to electroform cantilevered, thick absorbers. Gamma detectors with these absorbers have an energy resolution of 38 eV FWHM at 60 keV. In this report, we summarize modifications to STARCryo’s “Delta 1000” process for our devices and describe the new absorber fabrication process.     

Characterization of an Al-STJ-based X-ray detector with monochromatized synchrotron radiation

The characterization of an Al-STJ-based detector with Pb absorber was performed with monochromatized synchrotron radiation. Detector response was measured in the energy range from 3 to 10 keV. A small non-linearity of the signal pulse height was detected, probably due to the escape of recombination phonons from the detector. The non-linearity can be described by a second order polynomial function. Additionally, detector signals were recorded while an X-ray beam of 50 μm diameter was directed to several locations on and near the absorber. For a well-aligned beam, detector artefacts are of at least two orders of magnitude lower intensity than the absorber events.     

A Novel Type of Absorber Presenting a Constant Detection Efficiency for up to 25 keV X-Ray Photons

A novel type of absorber, dedicated to cryogenic detectors, was conceived to reach a high and constant intrinsic detection efficiency (>98%) for up to 25?keV X-ray photons. The absorber consists of two layers having a different atomic number?Z. The role of the first layer (large?Z) is to make negligible the transmission through the absorber; while the second layer (medium?Z) has to reabsorb the escape photons from the first layer. A?metallic magnetic calorimeter was realized with an Au-Ag absorber. The required thicknesses of both layers were determined using Monte Carlo simulation of the efficiency. To show the advantages of such a detector, its efficiency and its energy resolution are compared to the efficiency and energy resolution of a gold absorber using a ²⁴¹Am source.     

Detection of single X-ray quanta with a magnetic calorimeter

We give a status report on the development of a particular low temperature calorimeter with new experimental results. On absorption of an X-ray photon the increase of temperature changes the magnetization of a diluted magnetic sample, and this quantity is measured with a SQUID-magnetometer. It is a special feature of this experimental method that the magnetic sample has a very high heat capacity and an additional absorber for a compound detector does not change the sensitivity essentially. Besides a short summary on earlier measurements we present new results with metallic magnetic samples, which give shorter signal rise times (below 100 μs). On a compound detector with 0.1 g of LaB₆:Er and an absorber of 12 g sapphire, the energy resolution for 5.9 keV and 60 keV X-ray sis 1.6 keV and 2.6 keV (FWHM), respectively. With a silicon absorber an energy resolution of 1.4 keV at 5.9 keV has been found. The energy resolution is in any case limited by two effects. On the one hand the signal height is strongly reduced due to an additional heat capacity of the magnetic sample and on the other had we have an additional noise from the conduction electrons of the metallic sample. Possible improvements with respect to both effects are discussed.     

Energy Resolution of a Superconducting Nanowire Single-Photon Detector

An energy resolution of 0.6 eV was achieved with an NbN superconducting nanowire single-photon detector for near infrared photons in the energy range from 1.2 eV to 0.8 eV. The detector operates at 6 K and is read out with a room-temperature amplifier. The photon-energy dependent response of the detector is associated with the change of the detection scenario from the hot-spot formation to unbinding of paired magnetic vortices.      

Comparison of methods for reducing the effects of scattering in spectrophotometry

Light scattering provides a problem in optical spectroscopy as the relationship between attenuation and absorption in the presence of scattering is nonlinear. Three simple methods of reducing the effects of scattering and hence returning to an approximately linear relationship are considered in this paper, namely, extracting light that has maintained its original polarization state through subtraction of orthogonal polarization states, use of an added absorber, and spatial filtering. These can all be applied relatively easily to conventional spectrophotometers. However, there is an inevitable trade-off between the accuracy of the measurement and the signal-to-noise ratio as scattered light is rejected from the detector. It is demonstrated that polarization subtraction is the most efficient technique at selecting weakly scattered photons from a scattered light background as it enables the relationship between attenuation and absorption coefficient to become more linear while maintaining a higher number of detected photons. In practical use, the drawback of polarization subtraction over added absorber and spatial filtering methods is that a large dc background light level is maintained, which contributes to a higher shot noise. This means that when the scattering coefficient is high (micros > or = 7 mm(-1)) the added absorber method offers better performance for shot noise limited detection.     

Interactions of 200 GeV muons in an electromagnetic streamer tube calorimeter

We have investigated the response of an electromagnetic streamer tube calorimeter to 200 GeV muons. Muons undergo electromagnetic interactions in the absorber plates and produce electrons, photons or electron pairs the energy of which is measured by the calorimeter. Occasionally also catastrophic energy losses occur, so that in these very rare cases muons could even be misinterpreted as electrons.     

Detecting photons: Properties and challenges

This paper reports on work being carried out on detector characterisation at the National Physical Laboratory in the UK. It focuses on the development of a new technique based on correlated photons produced via parametric downconversion which can be used to directly measure the quantum efficiency of photon counting detectors. The main drivers for these measurements are the wide uptake of few photon optical technologies and the rapidly progressing field of quantum information processing which operates in the photon counting regime. Photodetection in the fields of biology, nuclear physics and astrophysics will also benefit from this work. The potential of this technique for realising primary radiometric scales will also be briefly discussed.     

A modular NaI(Tl) detector for intermediate energy photons

We describe the properties of a detector array made up of 64 NaI(Tl) 406 × 63 × 63 mm³ modules, used as an intermediate energy photon spectrometer. We obtain an energy resolution of 6% FWHM at 129 MeV, a time resolution of 1 ns FWHM and a resolution of 48 mm FWHM for the location of the impact point on the front face of the detector. The modularity allows to some extent a discrimination between photons and neutrons. We also present the response of the detector to 69 MeV neutrons.     

A Metallic Magnetic Calorimeter for Hard X-Ray and Gamma Ray Spectrometry

The CEA/LNHB is responsible for the determination and publication of atomic and nuclear data such as X-ray and gamma ray emission probabilities. In order to reduce uncertainties on the determination of these data, a high energy resolution associated with a good intrinsic detection efficiency is required. Hence taking into account these two aspects, we are developing cryogenic detectors, especially metallic magnetic calorimeters (MMCs) for photon spectrometry from few keV up to 200 keV. A MMC using a meander pick-up coil made of niobium thin films has been optimized. The gold absorber (diameter: 1.1 mm, thickness: 335 μm) has an intrinsic detection efficiency larger than 70% for photons from few keV up to 100 keV. From an energy spectrum obtained with a ¹³³Ba multi-gamma source, we have characterized this first detector. The energy resolution is 320 eV and 560 eV respectively at 30 keV and 357 keV. Possible improvements of the performance of the detector are discussed.     

Sensitivity of a superconducting nanowire detector for single ions at low energy

We report on the characterization of a superconducting nanowire detector for ions at low kinetic energies. We measure the absolute single-particle detection efficiency η and trace its increase with energy up to η = 100%. We discuss the influence of noble gas adsorbates on the cryogenic surface and analyze their relevance for the detection of slow massive particles. We apply a recent model for the hot-spot formation to the incidence of atomic ions at energies between 0.2 and 1 keV. We suggest how the differences observed for photons and atoms or molecules can be related to the surface condition of the detector and we propose that the restoration of proper surface conditions may open a new avenue for SSPD-based optical spectroscopy on molecules and nanoparticles.     

Time-resolved diffraction and interference: Young's interference with photons of different energy as revealed by time resolution

We present time-resolved diffraction and two-slit interference experiments using a streak camera as a detector for femtosecond pulses of photons. These experiments show how the diffraction pattern is built by adding frames of a few photons to each frame. It is estimated that after 300 photons the diffraction pattern emerges. With time resolution we can check the speed of light and put an upper limit of 2 ps at our resolution to the time for wave function collapse in the quantum measurement process. We then produce interference experiments with photons of different energies impinging on the slits, i.e. we know which photon impinges on each slit. We show that for poor time resolution, no interference is observed, but for high time resolution, we have interference that is revealed as beats of 100 GHz frequency. The condition for interference is that the two pulses should overlap spatially at the detector, even if the pulses have different energies but are generated from the same pulse of the laser. The interference seems to be in agreement with classical theory at first sight. However, closer study and analysis of the data show deviations in the visibility of the interference fringes and of their phase. These experiments are discussed in connection with quantum mechanics and it may be concluded that the time resolution provides new data for understanding the longstanding and continuing arguments on wave-particle duality initiated by Newton, Young, Fresnel, Planck and others. A thought experiment is presented in the appendix to try to distinguish the photons at the detector by making it sensitive to colour.     

某乏燃料运输容器减震器设计及验证

目的 研发用于某运输容器的减震器,同时探究减震器尺寸和填充材料的分散性对减震器设计的影响。方法 开展减震器尺寸对运输容器减震效果的分析计算,通过木材抗压强度试验获取木材压缩强度分散性,并使用有限元方法对运输容器进行9 m过重心角跌落分析,并进行9 m过重心角跌落测试验证。结果 一般来说减震器尺寸越大,其吸收能量越多,但其尺寸超过某临界点后减震效果反而下降;低抗压强度的填充木材吸能力不如较高抗压强度的,但填充木材抗压强度较大时,减震器偏硬会导致较大的容器刚体加速度。结论 该减震器设计合理,满足规范要求。填充木材的力学性能分散性,偏大或偏小都会对设计产生影响,因此,使用木材作为缓冲填充材料,设计时需要充分考虑木材压缩强度分散性对缓冲效果的影响。     

Recent developments in detector research

Recently developed methods of cryogenic particle detection and potential applications will be introduced. The main part of this article focuses on our experimental results on two different approaches of detecting nuclear radiation with superconducting tunnel junctions. The best energy resolution is obtained when the junction itself serves as absorber. Using Sn/SnO_x/Sn tunnel junctions we obtained an energy resolution of about 90 eV for 6 keV X-rays up to now. The processes limiting the resolution of the present devices will be discussed. Larger absorber masses and position resolution are realized by an entirely new type of particle detector based on the detection of nonthermal phonons which are generated by the absorption of radiation within a single-crystalline absorber of dielectric material. We report on experimental tests of a detector composed of a silicon single crystal (size: 10 × 20 × 3 mm³) and of an array of superconducting Al/Al₂O₃/Al tunnel junctions evaporated onto the surface of the crystal, serving as phonon detectors. Pulse height analysis and the investigation of time differences between pulse onsets in different junctions are shown to yield information about the absorption point of -particles.     

A massive bolometer on the international space station to measure energy deposition by the space radiation environment

We describe a novel space-based low-temperature radiation detector, the “Particle Heating Detector” (PhD), which was recently selected to be part of the first mission of the Low-Temperature Microgravity Physics Facility, scheduled to fly on the International Space Station in 2008. This massive bolometer will measure total heating induced in an aluminum absorber by the space radiation environment. The use of paramagnetic alloy thermometers with SQUID readout, giving resolution, combined with a large-area absorber, will enable the detector to perform high-resolution, real-time measurement of the low energy deposition levels caused by galactic cosmic rays in low-Earth orbit.     

A High Energy Resolution Gamma-Ray TES Microcalorimeter with Fast Response Time

We report on the development of the fast response gamma-ray TES microcalorimeter composed of a bulk Sn absorber coupled to a Ti/Au TES. In order to realize a TES microcalorimeter with a large absorber and a fast response time, besides taking saturation and linearity into account, study of the effect of thermal diffusion in the absorber on energy resolution is essential. Therefore, we performed 3 dimensional simulations using SPICE to calculate the effect of thermal diffusion in the absorber on energy resolution. By fabricating a device with the optimized heat capacity of the absorber and the thermal conductance between the absorber and the TES based on the simulation result, we have demonstrated an energy resolution of 38.4±0.9 eV at 60 keV with a time constant of 0.5 ms.