Μs Shaping Time Research Articles

N3G project: front-end electronics and mechanical advances

The higher counting-rate and radiation hardness required by modern gamma spectroscopy experiments highlight the need for a new generation of High-Purity Germanium detectors based on electrons-collecting electrodes. To achieve this goal, new doping technologies are required. The one studied by the N3G (Next Generation Germanium Gamma detectors) project is the Pulsed Laser Melting. Besides the development of innovative segmented High-Purity Germanium crystals, the project is also aimed at developing a detector case complete of contact structures and front-end electronics. A specific integrated circuit pre-amplifier is being designed: a first version was tested at room temperature, using a pulser as pre-amplifier input. A resolution of 1.08 keV with 15 pF input capacitance, reproducing the one of a detector single segment, was obtained with 6 µs shaping time.

Scintillation properties of (Ph4P)2ZnX4 (X = Cl, Br)

We fabricated (Ph4P)2ZnCl4 and (Ph4P)2ZnBr4 crystals (Ph4P: tetraphenylphosphonium) with zero-dimensional structures via solvent evaporation and evaluated their optical and scintillation properties. Fluorescence and phosphorescence peaks derived from Ph4P+ cations appeared at 345 and 510 nm, respectively, for both crystals, while an emission originating from self-trapped excitons was also detected for (Ph4P)2ZnBr4. In the scintillation spectra, both samples exhibited a phosphorescence peak, while a weak fluorescence peak was also observed for (Ph4P)2ZnCl4. In addition, the scintillation light yield (LY) was determined by pulse-height spectra with 1 μs shaping time. A pulse-height peak was observed from (Ph4P)2ZnCl4, and the scintillation LY was about 670 photons/5.5 MeV-α, which was higher than that of a ZnO single crystal.

Ce 3+:Lu 3Al 5O 12–Al 2O 3 optical nanoceramic scintillators elaborated via a low-temperature glass crystallization route

Transparent Ce:lutetium aluminum garnet (Ce:Lu₃Al₅O₁₂, Ce:LuAG) ceramics have been regarded as potential scintillator materials due to their relatively high density and atomic number (<i>Z</i>_eff). However, the current Ce:LuAG ceramics exhibit a light yield much lower than the expected theoretical value due to the inevitable presence of Lu_Al antisite defects at high sintering temperatures. This work demonstrates a low-temperature (1100 ℃) synthetic strategy for elaborating transparent LuAG–Al₂O₃ nanoceramics through the crystallization of 72 mol% Al₂O₃–28 mol% Lu₂O₃ (ALu28) bulk glass. The biphasic nanostructure composed of LuAG and Al₂O₃ nanocrystals makes up the whole ceramic materials. Most of Al₂O₃ is distributed among LuAG grains, and the rest is present inside the LuAG grains. Fully dense biphasic LuAG–Al₂O₃ nanoceramics are highly transparent from the visible region to mid-infrared (MIR) region, and particularly the transmittance reaches 82% at 780 nm. Moreover, Lu_Al antisite defect-related centers are completely undetectable in X-ray excited luminescence (XEL) spectra of Ce:LuAG–Al₂O₃ nanoceramics with 0.3–1.0 at% Ce. The light yield of 0.3 at% Ce:LuAG–Al₂O₃ nanoceramics is estimated to be 20,000 ph/MeV with short 1 μs shaping time, which is far superior to that of commercial Bi₄Ge₃O₁₂ (BGO) single crystals. These results show that a low-temperature glass crystallization route provides an alternative approach for eliminating the antisite defects in LuAG-based ceramics, and is promising to produce garnet-based ceramic materials with excellent properties, thereby meeting the demands of advanced scintillation applications.

The TRISTAN 166-pixel detector: Preliminary results with a planar setup

We present the first experimental results achieved with a monolithic array of 166 Silicon Drift Detectors (SDD). This detector was developed for the TRISTAN experiment, targeting the search for a sterile neutrino in the keV mass range by means of accurate Beta spectroscopy of the Tritium decay. We briefly report on the design and characterization with X-rays of the full signal chain: from the SDD array, operated in a planar configuration with all the components of the final system, to the acquisition platform simultaneously acquiring all 166 channels. The average energy resolution is better than 250eV FWHM at 5.9keV at a temperature of 0 °C, a 6 μs shaping time, and an average count rate of 1kcps per channel, 100 times smaller than the final experiment one.

A cryogenic low-background low-noise CMOS preamplifier for HPGe detectors

A cryogenic low-noise CMOS preamplifier has been successfully developed for HPGe detectors in low-background experiments. Commonly used auxiliary off-chip devices, such as decoupling capacitors and resistors, were removed to control the radioactive emission. The prototype chip was implemented in XFAB 350 nm CMOS process and was fully evaluated. A minimum ENC of 8.9 electrons was obtained at a 12 μs shaping time at 77 K, and the rise time was measured to be 60 ns through a 1-meter-long cable. The performances with and without decoupling capacitors for the power supply and bias voltages were compared, and there was no evident difference between these cases. The performance upon connection to a 0.5 kg point-contact HPGe detector was also measured. A minimum ENC of 15.5 electrons was achieved. The energy spectrum of the 57Co radiation source was obtained, and the FWHM of the 122 keV energy peak was measured to be 0.6 keV.

Preliminary Design of Readout Electronics for CDEX-10 in CJPL

CDEX (China Dark Matter Experiment) is now upgraded to about 10 kg HPGe (High Purity Germanium) detectors and new dedicated readout electronics is in operation. The readout system is interfaced to the front preamplifiers, which have two “slow” outputs with typical 20 μs shaping time and two “fast” output with typical 200 ns shaping time. 8 channels 14-Bit 100 MSPS FADC and 2 channels 12Bit 2000 MSPS FADC are embedded in the readout 6U prototype board. The RAIN1000Z2 readout module based on ZYNQ SoC is used for readout with Gigabit Ethernet.

Electronic band modification for faster and brighter Ce,Mg:Lu3-xYxAl5O12 ceramic scintillators

Ce,Mg:LuYAG transparent ceramics were successfully fabricated by the solid state reaction method. The results of x-ray diffraction, photoluminescence, light yield, scintillation decay and thermoluminescence are analyzed to provide better understanding of the influence of the Y3+ admixture in LuAG on the lattice structure, electronic band structure, energy-level structure of Ce3+ centers and scintillation properties. The lattice parameter of Ce,Mg:LuYAG ceramics shows a linear growth with the increasing Y content, which is in agreement with Vegard's law. Reducing the Lu-to-Y ratio in the LuYAG matrix, the Ce3+ 5d1 energy level shifts to a lower energy, the forbidden gap becomes narrower and the electron traps become shallower. Furthermore, the increase of light yield and accelerated slow scintillation component are found with increasing Y admixture. After optimization, the light yield of Ce,Mg:Lu0.5Y2.5Al5O12 ceramics is achieved to 24,500 ph/MeV with 1 μs shaping time, which is 40% higher than the value in the Y-free Ce,Mg:LuAG ceramic sample.

Suppression of the slow scintillation component of Pr:Lu3Al5O12 transparent ceramics by increasing Pr concentration

Pr:Lu3Al5O12 transparent ceramics with different doping concentrations (0% − 1 at%) were fabricated using the solid-state reaction and vacuum sintering method. The influence of doping concentration on the luminescent properties was investigated in detail. The 5d-4f emission slightly redshifts with the increase of doping concentration under UV light and X-ray excitation. The slow emission below 290 nm related to antisite defects can be suppressed by the increase of doping concentration at room temperature. The suppression of exciton related emission around 250 nm at 77 K is remarkable. The 0.3 at% Pr doped ceramics show the highest light yield that is 6900 ph/MeV with 1 μs shaping time under the excitation of γ-rays (137Cs). There exists slow components of scintillation process in all the Pr-doped transparent ceramics. Higher doping concentration was found to be beneficial for the suppression of the slow components in the scintillation response and therefore acceleration of the scintillation decay and light yield increase up to certain level. These effects are mainly due to competition of Pr3+ ions with the antisite defects for charge carrier capture in the scintillation process which is also supported by the trends observed in the TSL measurements.

An ultra-low noise cryogenic CMOS charge sensitive preamplifier for large volume point-contact HPGe detectors

The paper presents the development of an ultra-low noise cryogenic CMOS charge sensitive preamplifier dedicated for the point-contact HPGe detectors for the CDEX dark matter search experiments. The noise of the preamplifier was optimized for 2 pF input capacitance, which was simulated including the detector capacitance and the parasitic capacitance of the interconnection. The prototype chip was implemented in a 0.35 μm CMOS process and the chip was electrically characterized. The rise time of the preamplifier output was increased to 31.7 ns when directly driving 11.5 meter long cable. The ENC was measured to be 10 and 13.3 electrons for 0 and 2 pF input capacitances at 12 μs shaping time at 77 K. A low mass front-end board was also developed and was mounted with a 0.5 kg point-contact HPGe detector. The energy spectrum of the 133Ba and 57Co radiation sources were measured. The energy resolutions of 530 eV FWHM and 640 eV FWHM have been achieved at 81 keV and 122 keV peaks respectively. The resolution for pulser signals was also monitored to be 186 eV, corresponding to 26 electrons (r.m.s.) ENC noise.

Fabrication, optical and scintillation properties of (Lu0.75,Y0.25)AG:Pr ceramic scintillators

Y3+ admixing Lu3Al5O12:Pr ceramics are fabricated successfully by the solid state reaction method and further optimized by an air-annealing process. Optical absorption, photoluminescence spectra and scintillation properties such as radioluminescence, and light output are measured and compared with those of the Y3+ free LuAG:Pr ceramics. Positive effect of Y3+ codopant consists mainly in the significant increase of scintillation light output, as well as the decrease of relative intensity of slow component. With 0.15% Pr3+ codoping, the obtained LuYAG:Pr ceramic displays a light output of 28500 ph/MeV at 3 μs shaping time, higher than that of the LuAG:Pr ceramic scintillators ever report. The effect of Y3+ admixture is further explained by vacuum ultraviolet and electron spin resonance experiment.

Effect of Li+ ions co-doping on luminescence, scintillation properties and defects characteristics of LuAG:Ce ceramics

Monovalent Li+ codoped Lu3Al5O12:Ce (LuAG:Ce) optical ceramics were fabricated by solid state reaction method and further optimized by an air-annealing process. Optical absorption, radioluminescence spectra and scintillation properties such as light yield, scintillation decay times and afterglow were measured and compared with those of the Li+ free LuAG:Ce ceramic and the commercial LuAG:Ce single crystal samples. Positive effect of Li+ codopant consists mainly in the significant increase of scintillation light yield, acceleration of scintillation decay as well as the decrease of afterglow intensity. With 0.3% Li codoping, the obtained LuAG:Ce,Li ceramic displays a light yield of ∼29200 ph/MeV at 10 μs shaping time, higher than that of the LuAG:Ce single crystal and optical ceramic scintillators ever reported. The partial conversion of the stable Ce3+ to Ce4+ centers and the shallow and deep traps effect suppression by the Li+ codoping are discussed.

Characterisation of Al0.52In0.48P mesa p-i-n photodiodes for X-ray photon counting spectroscopy

Results characterising the performance of thin (2 μm i-layer) Al0.52In0.48P p+-i-n+ mesa photodiodes for X-ray photon counting spectroscopy are reported at room temperature. Two 200 μm diameter and two 400 μm diameter Al0.52In0.48P p+-i-n+ mesa photodiodes were studied. Dark current results as a function of applied reverse bias are shown; dark current densities &amp;lt;3 nA/cm2 were observed at 30 V (150 kV/cm) for all the devices analysed. Capacitance measurements as a function of applied reverse bias are also reported. X-ray spectra were collected using 10 μs shaping time, with the device illuminated by an 55Fe radioisotope X-ray source. Experimental results showed that the best energy resolution (FWHM) achieved at 5.9 keV was 930 eV for the 200 μm Al0.52In0.48P diameter devices, when reverse biased at 15 V. System noise analysis was also carried out, and the different noise contributions were computed.

Anode-coupled readout for light collection in Liquid Argon TPCs

This paper will discuss a new method of signal read-out from photon detectors in ultra-large, underground liquid argon time projection chambers. In this design, the signal from the light collection system is coupled via capacitive plates to the TPC wire-planes. This signal is then read out using the same cabling and electronics as the charge information. This greatly benefits light collection: it eliminates the need for an independent readout, substantially reducing cost; it reduces the number of cables in the vapor region of the TPC that can produce impurities; and it cuts down on the number of feed-throughs in the cryostat wall that can cause heat-leaks and potential points of failure. We present experimental results that demonstrate the sensitivity of a LArTPC wire plane to photon detector signals. We also simulate the effect of a 1 μs shaping time and a 2 MHz sampling rate on these signals in the presence of noise, and find that a single photoelectron timing resolution of ∼30 ns can be achieved.

Towards Bright and Fast Lu3Al5O12:Ce,Mg Optical Ceramics Scintillators

The recent advent of Lu3Al5O12:Ce optical ceramics marks a turning point in scintillator material technology. Because of their lower preparation temperature, brightness, and robustness such materials can now compete with single crystals. Their further scintillation efficiency optimization includes the thorough control of the defects responsible for optical and scintillation losses. The choice of sintering agent appears critical to achieve both high optical transparency and scintillation performance. In this work, the optical investigations coupled with X‐ray absorption near‐edge spectroscopy evidence the beneficial role of MgO sintering agent. Mg2+ co‐dopants in ceramics drive the partial conversion of Ce3+ to Ce4+. The Ce4+ center, however, does not impair the scintillation performance due to its capability to positively influence the scintillation process. The importance of simultaneous application of such co‐doping and annealing treatment is also demonstrated. With 0.3 at% Mg, our ceramics display a light yield of ≈25000 photons/MeV with short 1 μs shaping time, a relative fast component intensity as high as 60%, and very low afterglow. Such performances are better than those of the isostructural single crystals ever reported. We discuss the role of co‐doping and annealing in the scintillation mechanism that make such combined treatments a positive strategy for material engineering.

A low-power CMOS ASIC for X-ray Silicon Drift Detectors low-noise pulse processing

We present an Application Specific Integrated Circuit (ASIC), named VEGA-1, designed and manufactured for low-power analog pulse processing of signals from Silicon Drift Detectors (SDDs). The VEGA-1 ASIC consists of an analog and a digital/mixed-signal section to achieve all the functionalities and specifications required for high-resolution X-ray spectroscopy in the energy range from 500 eV to 60 keV with low power consumption. The VEGA-1 ASIC has been designed and manufactured in 0.35-μm CMOS mixed-signal technology in single and 32-channel version with dimensions of 200 μm × 500 μm per channel. A minimum intrinsic ENC of 12 electrons r.m.s. at 3.6 μs shaping time and room temperature is measured for the ASIC without detector. The VEGA-1 has been tested with Q10-SDD designed in Trieste and fabricated at FBK, with an active area of 10 mm2 and a thickness of 450 μm. The aforementioned detector has an anode current of about 180 pA at +22°C. A minimum Equivalent Noise Charge (ENC) of 16 electrons r.m.s. at 3.0 μs shaping time and −30°C has been demonstrated with a total measured power consumption of 482 μW.

A Multichannel Integrated Readout Circuit for High Throughput X-Ray Spectroscopy With Silicon Drift Detectors

In this paper, we describe a front-end ASIC for the readout of multi-elements Silicon Drift Detectors (SDDs) specifically designed for high count-rate X-ray spectroscopy applications. In particular, the focus of this design is on the maximization of the event throughput and, at the same time, keeping a high energy resolution. The readout of a detector array by means of 8 separate channels allows increasing the maximum count-rate of the system. The use of one or more of these front-end ASICs allows the management of several readout channels required by a multi-SDD detector within a very compact detection system, as well as maintaining excellent noise performance. The use of a very-fast high-order processing filter and of an efficient pile-up rejection strategy allows minimizing the pile-up probability and maximizing the event throughput of the single channels for a given processing time. The use of a 3-phase peak-stretcher, together with a fast output multiplexer, permits to minimize the dead-time during the valid-data acquisition, practically to a value limited by the pure overlap of the shaped pulses. The ASIC is designed with the possibility of operating with the input JFET integrated on the detector itself as well as to operate in combination with an external preamplifier. The measured noise-contribution added by the front-end ASIC is only 2.9 electrons at 1.8 μs shaping time and just 4.1 electrons at the shortest 600 ns peaking time, exploiting at best the speed capability. In X-ray spectroscopy measurements, the ASIC connected to an SDD coupled to a CMOS preamplifier has allowed to achieve an energy resolution of 126 eV at 1.5 μs peaking time and 115 kcps/channel input rate, and 144 eV at 600 ns peaking time and 800 kcps/channel input rate.

Evaluations of pure and ytterbium doped transparent ceramic complex perovskite scintillators

Optical and scintillation properties of complex perovskite transparent ceramic scintillators of pure and Yb 3+ doped Ba(ZrMgTa)O 3 and (LaSr)(AlTa)O 3 ceramics are reported. The materials were produced by Murata Manufacturing. Their optical properties including transmittance and photoluminescence spectra were evaluated. The ceramics demonstrated high transparency (50–70%) in visible wavelength region. Additionally, strong emission peaks were observed at 470 nm in Ba(ZrMgTa)O 3 under 284 nm excitation and at 500 nm in (LaSr)(AlTa)O 3 under 324 nm excitation. The photoluminescence decay times of Ba(ZrMgTa)O 3 and (LaSr)(AlTa)O 3 samples were 14 and 16 μs, respectively. Judging from these optical properties, Yb 3+ emission was not observed in these materials. In radio luminescence spectra, all specimens exhibited the same emission peaks with relatively higher emission intensity. 241Am 5.5 MeV α-ray induced pulse height spectra of the samples were also measured, and (LaSr)(AlTa)O 3 demonstrated ∼500 ph/5.5 MeV α with 10 μs shaping time constant.

Growth, Optical Properties, and Scintillation Light Yield of CaF2:Ce Crystals with Different Ce Concentration

Present work describes the first detailed γ-ray light yield of Ce3+ perturbed emission in CaF2 host. (1-, 3-, 5-, 10-, and 20-mol %-) Ce3+-doped single crystalline CaF2 scintillator crystals were grown by the micro-pulling-down method. Their transmittances were measured to be approximately 80% at UV to visible wavelengths. All the crystals exhibited emission peaks at approximately 330 nm, which were identified as the Ce3+ perturbed emission, when they were irradiated by 1 GBq 137Cs. The photoluminescence decay kinetics was measured to be about 40 ns for all the crystals. Scintillation light yield in unit of photons/MeV (ph/MeV) was measured, and the 5% sample showed the highest light yield of around 900 ph/MeV with 2 µs shaping time.

Energy resolution of CsI(Na) scintillators

Abstract The presented paper on CsI(Na) scintillators is a continuation of systematical studies of alkali halide crystals exhibiting more than one exponential decay time. The CsI(Na) crystals are known to have short (∼550 ns) and long (few microseconds) components in the scintillation pulse. Previous studies showed that integration of slow components of the light pulse improved the light output, non-proportionality and energy resolution of CsI(Tl), NaI(Tl) in lower temperatures and undoped NaI crystal at liquid nitrogen temperature. In this work, an influence of the shaping time in the spectroscopy amplifier on the light output, non-proportional response to γ-rays, and energy resolution of two different size CsI(Na) scintillators is examined. Each crystal was coupled to the Photonis XP5212 PMT with a photocathode blue sensitivity of 12.2 μA/l mF. The data analysis showed improved proportionality of the crystal response, higher number of photoelectrons/MeV-γ, and consequently, a better overall energy resolution obtained for 12 μs shaping time constant. Finally, the CsI(Na) characteristics are compared to that obtained previously for NaI(Tl).

The α‐particle excited scintillation response of YAG:Ce thin films grown by liquid phase epitaxy

AbstractY3Al5O12:Ce (YAG:Ce) thin films were grown from PbO‐, BaO‐, and MoO3‐based fluxes using the liquid phase epitaxy (LPE) method. Photoelectron yield, its time dependence within 0.5–10 μs shaping time, and energy resolution of these samples were measured under α‐particle excitation. For comparison a sample of the Czochralski grown bulk YAG:Ce single crystal was measured as well. Photoelectron yield values of samples grown from the BaO‐based flux were found superior to other LPE films and comparable with that of the bulk single crystal. The same is valid also for the time dependence of photoelectron yield. Obtained results are discussed taking into account the influence of the flux and technology used. Additionally, α particle energy deposition in very thin films is modelled and discussed. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)