Linear Energy Response Research Articles

2D Perovskite Neutron Scintillators with Nanosecond Time Resolution and Linearity Energy Response

AbstractFast and high‐linearity detection of fast neutron is vital for special nuclear material seeking, nuclear accident emergency response, nondestructive neutron imaging, and neutron cancer therapy. Neutron scintillators with fast time resolution and linear energy response are indispensable for precisely acquiring the energy and temporal evolution of fast neutron, but none of the conventional neutron scintillators, whether organic, two‐component or inorganic, have performed well in this regard. To address these challenges, it is urgent to develop novel neutron scintillators. Here, 2D hybrid perovskite single crystals (C4H12N)2PbBr4 (BA2PbBr4) successfully combined with fast response time of 2.66 ns and linear energy response to fast neutrons, γ ray, and α particle, is reported. The rapid response time and linear energy response of 2D hybrid perovskite scintillator originate from intensive states density of lead halide frameworks, which are the key fluorescence emitters under neutron irradiation. This effectively suppresses the ionization quenching effect during the fluorescence process. This work represents a milestone in fast neutron detection, demonstrating a new type of neutron scintillator based on 2D hybrid perovskite single crystals with fast and high‐linearity detection characteristics, having great potential in high precision neutron spectrum measurement and nuclear reaction kinetics monitoring.

Energy response and spatial alignment of the perturbed electron gas.

We study the linear energy response of the uniform electron gas to an external harmonic perturbation with a focus on resolving different contributions to the total energy. This has been achieved by carrying out highly accurate abinitio path integral Monte Carlo (PIMC) calculations for a variety of densities and temperatures. We report a number of physical insights into effects such as screening and the relative importance of kinetic and potential energies for different wave numbers. A particularly interesting finding is obtained from the observed non-monotonic behavior of the induced change in the interaction energy, which becomes negative for intermediate wave numbers. This effect is strongly dependent on the coupling strength and constitutes further direct evidence for the spatial alignment of electrons introduced in earlier works [T. Dornheim et al., Commun. Phys. 5, 304 (2022)]. The observed quadratic dependence on the perturbation amplitude in the limit of weak perturbations and the quartic dependence of perturbation amplitude corrections are consistent with linear and nonlinear versions of the density stiffness theorem. All PIMC simulation results are freely available online and can be used to benchmark new methods or as input for other calculations.

Silicon drift detectors system for high-precision light kaonic atoms spectroscopy

A large area silicon drift detectors (SDDs) system and its readout electronics have been developed by the SIDDHARTA-2 Collaboration, aiming to perform high-precision light kaonic atoms x-ray spectroscopy for the investigation of the strong interaction in the low-energy QCD regime. To perform these measurements, a linear energy response and a good energy resolution are mandatory requirements for the system, to be preserved along the whole DAQ (analog and digital) chain; such task is made even harder in the experimental environment of particles colliders, where the high background due to ionizing particles and radiation is present. The energy response of the SDDs system has been characterized with the beam-originating background generated during the commissioning phase of the DAΦNE electron–positron collider (INFN-LNF) in early 2020. The data analysis has been optimized to describe the system’s response and the background. The calibration procedure demonstrates that, despite the high and variable background of the collider, the energy response of the system is linear at the level of few eV (), with an energy resolution of eV for the Fe K line.

Dosimetry and Calorimetry Performance of a Scientific CMOS Camera for Environmental Monitoring.

This paper explores the prospect of CMOS devices to assay lead in drinking water, using calorimetry. Lead occurs together with traces of radioisotopes, e.g., , producing -emissions with energies ranging from 10 to several 100 when they decay; this range is detectable in silicon sensors. In this paper we test a CMOS camera (Oxford Instruments Neo 5.5) for its general performance as a detector of X-rays and low energy -rays and assess its sensitivity relative to the World Health Organization upper limit on lead in drinking water. Energies from 6 to 60 are examined. The CMOS camera has a linear energy response over this range and its energy resolution is for the most part slightly better than 2%. The Neo sCMOS is not sensitive to X-rays with energies below . The smallest detectable rate is , corresponding to an incident activity on the chip of . The estimation of the incident activity sensitivity from the detected activity relies on geometric acceptance and the measured efficiency vs. energy. We report the efficiency measurement, which is 0.08(2)% (0.0011(2)%) at ( ). Taking calorimetric information into account we measure a minimal detectable rate of ( ) for ( ) -rays, which corresponds to an incident activity of ( ). Toy Monte Carlo and Geant4 simulations agree with these results. These results show this CMOS sensor is well-suited as a - and X-ray detector with sensitivity at the few to 100 ppb level for in a sample.

Construction and response of a highly granular scintillator-based electromagnetic calorimeter

A highly granular electromagnetic calorimeter with scintillator strip readout is being developed for future linear collider experiments. A prototype of 21.5 X0 depth and 180×180mm2 transverse dimensions was constructed, consisting of 2160 individually read out 10×45×3mm3 scintillator strips. This prototype was tested using electrons of 2–32 GeV at the Fermilab Test Beam Facility in 2009. Deviations from linear energy response were less than 1.1%, and the intrinsic energy resolution was determined to be (12.5±0.1(stat.)±0.4(syst.))%∕E[GeV]⊕(1.2±0.1(stat.)−0.7+0.6(syst.))%, where the uncertainties correspond to statistical and systematic sources, respectively.

The Fabrication and Characterization of Ni/4H-SiC Schottky Diode Radiation Detectors with a Sensitive Area of up to 4 cm².

Silicon carbide (SiC) detectors of an Ni/4H-SiC Schottky diode structure and with sensitive areas of 1–4 cm2 were fabricated using high-quality lightly doped epitaxial 4H-SiC material, and were tested in the detection of alpha particles and pulsed X-rays/UV-light. A linear energy response to alpha particles ranging from 5.157 to 5.805 MeV was obtained. The detectors were proved to have a low dark current, a good energy resolution, and a high neutron/gamma discrimination for pulsed radiation, showing the advantages in charged particle detection and neutron detection in high-temperature and high-radiation environments.

(Invited) Laser Sintering of Polycrystalline Ceramic Scintillators: The Case Study of YAG:Ce

Scintillators are sensors used for the detection and measurement of ionizing radiation that find application in numerous strategic fields. Among the many possible scintillator forms, polycrystalline ceramics have received increasing attention due to advantages over single crystals, including faster and lower cost fabrication methods, higher homogeneity of the dopant, greater shape control, and easier fabrication of materials with high melting temperatures. Polycrystalline ceramic scintillators are commonly fabricated by high temperature vacuum sintering [1] and more recently by spark plasma sintering [2,3]. However, additional high-cost processing by means of hot isostatic pressing is many times necessary especially because it has been shown that the use of sintering aids is detrimental to scintillation performance [4]. On the other hand, despite the advantages of extremely short sintering times and high heating rates, laser sintering remains mostly unexplored as a viable method to fabricate these materials. To date, the only polycrystalline ceramic scintillator fabricated by this method was Bi4Ge3O12 (BGO) [5-7]. In this work, the fabrication of Y3Al5O12:Ce (YAG:Ce) polycrystalline ceramic scintillators by laser sintering is evaluated against a Czochralski-grown single crystal in terms of the microstructure characteristics as well as luminescent and scintillating properties. YAG:Ce powders were prepared by a polymeric precursor method using Y(NO3)3×6H2O, AlCl3×6H2O, and CeH8O18N8 as metal precursors such that the concentration of Ce substituting for Y was 0.1 and 0.3 %. Metal precursors were dissolved in citric acid:distilled water solutions at 70 oC under continuous stirring followed by the addition of ethylene glycol. The final solution was heated up to 100 oC to eliminate water and promote polymerization. The resultant material was pre-calcined at 600 oC for 5 h followed by calcination at 1000 oC for 6 h, and then pressed into 4 mm dia. x 1.2 mm thick pellets. Laser sintering was executed using a Coherent GEM-100L CO2 laser generating a power density of ~3.3 W/mm2for 90 s. The microstructure was characterized by means of density, X-ray diffraction (XRD), scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR FTIR), and X-ray absorption near edge structure (XANES) measurements. Optical transparency and luminescence were evaluated in terms of UV-visible transmittance, photoluminescence emission (PL) and excitation (PLE), radioluminescence (RL), and thermoluminescence (TL) measurements, while differential pulse height distribution measurements were used to characterize the scintillation response as a function of the gamma-ray energy. Density measurements revealed the laser beam-induced densification yielded 97-99 % relative density. SEM results confirmed the presence of pores and an average grain size of 2 mm was extracted from image analysis. These results justified the optically opaque nature of the polycrystalline ceramics due to light scattering at the numerous internal interfaces. In addition to that, a higher degree of structural disorder in the polycrystalline ceramics that was revealed by inhomogeneous broadening of the optical absorption, PLE and absorption ATR FTIR bands when compared to the single crystal. XANES results of the YAG:Ce polycrystalline ceramics together with Ce(OH)CO3 and CeO2 commercial powders used as references for the 3+ and 4+ oxidation states of Ce, respectively, demonstrated the dominance of the +3 state. PL and RL confirmed luminescence to be dominated by the emission of Ce3+, and showed the presence of F+-related centers and antisite defects in both the polycrystalline ceramics and the single crystal. TL analysis revealed the presence of four first-order kinetics glow peaks, with the trap depths of the single crystal being similar or deeper than those of the polycrystalline ceramics. In terms of scintillation response, the relative light yield of the polycrystalline ceramics was significantly lower than that of the single crystal as expected from its optically opaque nature. Also, the polycrystalline ceramics presented a less linear energy response than the single crystal. Acknowledgements This material is based upon work supported by the National Science Foundation under Grant no. 1207080. This work has been supported by the Brazilian Synchrotron Light Laboratory (LNLS) beamline XAFS2 under proposals 15871 and 18854.

SiC Detector for Sub-MeV Alpha Spectrometry

4H-SiC silicon carbide (SiC) Schottky diodes, with a 25 μm thick n-type epitaxial active layer and a very thin front electrode contact are studied and proposed for the detection of low energetic ions. For a first evaluation of the detection properties of the SiC detectors, a standard alpha emitting radiation source was used obtaining an energy resolution of 0.85% at 5.15 MeV energy. Then the devices were employed to monitor low energetic alpha particles. From these tests it was found that the 4H-SiC diodes are able to monitor the alpha particles backscattered by different single and multilayers metallic targets (Au, Ag, Cu on Si substrates) in the energy range between 300 keV and 600 keV. In this energy range a linear energy response and a good energy resolution, close to those of a traditional commercial silicon detector, were obtained. The possibility to use these detectors for material analysis and for plasma monitoring is also discussed.

Energy dispersive CdTe and CdZnTe detectors for spectral clinical CT and NDT applications

We are developing room temperature compound semiconductor detectors for applications in energy-resolved high-flux single x-ray photon-counting spectral computed tomography (CT), including functional imaging with nanoparticle contrast agents for medical applications and non-destructive testing (NDT) for security applications. Energy-resolved photon-counting can provide reduced patient dose through optimal energy weighting for a particular imaging task in CT, functional contrast enhancement through spectroscopic imaging of metal nanoparticles in CT, and compositional analysis through multiple basis function material decomposition in CT and NDT. These applications produce high input count rates from an x-ray generator delivered to the detector. Therefore, in order to achieve energy-resolved single photon counting in these applications, a high output count rate (OCR) for an energy-dispersive detector must be achieved at the required spatial resolution and across the required dynamic range for the application. The required performance in terms of the OCR, spatial resolution, and dynamic range must be obtained with sufficient field of view (FOV) for the application thus requiring the tiling of pixel arrays and scanning techniques. Room temperature cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) compound semiconductors, operating as direct conversion x-ray sensors, can provide the required speed when connected to application specific integrated circuits (ASICs) operating at fast peaking times with multiple fixed thresholds per pixel provided the sensors are designed for rapid signal formation across the x-ray energy ranges of the application at the required energy and spatial resolutions, and at a sufficiently high detective quantum efficiency (DQE). We have developed high-flux energy-resolved photon-counting x-ray imaging array sensors using pixellated CdTe and CdZnTe semiconductors optimized for clinical CT and security NDT. We have also fabricated high-flux ASICs with a two dimensional (2D) array of inputs for readout from the sensors. The sensors are guard ring free and have a 2D array of pixels and can be tiled in 2D while preserving pixel pitch. The 2D ASICs have four energy bins with a linear energy response across sufficient dynamic range for clinical CT and some NDT applications. The ASICs can also be tiled in 2D and are designed to fit within the active area of the sensors. We have measured several important performance parameters including: the output count rate (OCR) in excess of 20 million counts per second per square mm with a minimum loss of counts due to pulse pile-up, an energy resolution of 7keV full width at half-maximum (FWHM) across the entire dynamic range, and a noise floor about 20keV. This is achieved by directly interconnecting the ASIC inputs to the pixels of the CdZnTe sensors incurring very little input capacitance to the ASICs. We present measurements of the performance of the CdTe and CdZnTe sensors including the OCR, FWHM energy resolution, noise floor, as well as the temporal stability and uniformity under the rapidly varying high flux expected in CT and NDT applications.

The time-walk of analog constant fraction discriminators using very fast scintillator detectors with linear and non-linear energy response

The electronic γ–γ fast timing technique allows for direct nuclear lifetime determination down to the few picoseconds region by measuring the time difference between two coincident γ-ray transitions. Using high resolution ultra-fast LaBr3(Ce) scintillator detectors in combination with the recently developed mirror symmetric centroid difference method, nuclear lifetimes are measured with a time resolving power of around 5ps. The essence of the method is to calibrate the energy dependent position (centroid) of the prompt response function of the setup which is obtained for simultaneously occurring events. This time-walk of the prompt response function induced by the analog constant fraction discriminator has been determined by systematic measurements using different photomultiplier tubes and timing adjustments of the constant fraction discriminator. We propose a universal calibration function which describes the time-walk or the combined γ–γ time-walk characteristics, respectively, for either a linear or a non-linear amplitude versus energy dependency of the scintillator detector output pulses.

An Abridged Transition State Model To Derive Structure, Dynamics, and Energy Components of DNA Polymerase β Fidelity

We show how a restricted reaction surface can be used to facilitate the calculation of biologically important contributions of active site geometries and dynamics to DNA polymerase fidelity. Our analysis, using human DNA polymerase beta (pol β), is performed within the framework of an electrostatic linear free energy response (EFER) model. The structure, dynamics, and energetics of pol β-DNA-dNTP interactions are computed between two points on the multidimensional reaction free energy surface. "Point 1" represents a ground state activation intermediate (GSA), which is obtained by deprotonating the terminal 3'OH group of the primer DNA strand. "Point 2" is the transition state (PTS) for the attack of the 3'O(-) (O(nuc)) on the P(α) atom of dNTP substrate, having the electron density of a dianionic phosphorane intermediate. Classical molecular dynamics simulations are used to compute the geometric and dynamic contributions to the formation of right and wrong O(nuc)-P chemical bonds. Matched dCTP·G and mismatched dATP·G base pairs are used to illustrate the analysis. Compared to the dCTP·G base pair, the dATP·G mismatch has fewer GSA configurations with short distances between O(nuc) and P(α) atoms and between the oxygen in the scissile P-O bond (O(lg)) and the nearest structural water. The thumb subdomain conformation of the GSA complex is more open for the mismatch, and the H-bonds in the mispair become more extended during the nucleophilic attack than in the correct pair. The electrostatic contributions of pol β and DNA residues to catalysis of the right and wrong P-O(nuc) bond formation are 5.3 and 3.1 kcal/mol, respectively, resulting in an 80-fold contribution to fidelity. The EFER calculations illustrate the considerable importance of Arg183 and an O(lg)-proximal water molecule to pol β fidelity.

Development of scintillation detectors based on avalanche microchannel photodiodes

Avalanche Microchannel PhotoDiodes (AMPDs) are solid state photodetectors with high internal gain and a density of independent channels up to 10 4/mm 2. They are potential substitutes for photomultiplier tubes in a wide variety of applications in nuclear physics and nuclear medicine, especially when fine segmentation of the detectors and their operation in high magnetic fields is required. In this work, we study the performance of a detector based on a LYSO (2×2×10 mm 3) scintillation crystal and AMPD at detection of 511 keV γ-quanta. The detector shows linear energy response, an energy resolution of ∼12%, and sub-nanosecond time resolution. These characteristics are encouraging for using AMPDs in detector systems of positron emission tomographs (PET) of the next generation.

High-resolution alpha-particle spectrometry using 4H silicon carbide semiconductor detectors

SiC detectors with active volume dimensions sufficient to stop alpha particles have been manufactured and tested. A linear energy response and excellent energy resolution have been obtained for various alpha emitters in the 3.18-MeV to 8.38-MeV energy range. Evaluation of the contributing factors to the SiC detector energy resolution indicates that the measured values for the full width at half maximum (FWHM) are limited by energy straggling of the alpha particles as they pass through the metallic contact layers that comprise the entrance window to the detector. Even with this component included in the measured FWHM, the measured values are comparable to those achievable with silicon alpha spectrometers. The possibility that the energy resolution that can be achieved with SiC may surpass that of silicon can not be excluded. SiC alpha spectrometers are expected to be useful in many nuclear applications where the ability to operate in high-temperature and high-radiation environments is required. Such applications include monitoring of alpha particles, neutrons, and low-energy gamma rays and X-rays in actinide waste-tank environments as well as neutron and gamma-ray monitoring of spent nuclear fuel assemblies.

Invited commentary

To compete with percutaneous endocardial ablation techniques for the treatment of atrial fibrillation (AF), several surgical epicardial approaches have been introduced into clinical practice, and additional techniques are currently under development. These surgical epicardial procedures make use of alternate energy sources and minimally invasive access to produce atrial lesions to ablate AF. There is a plethora of new ablation devices designed specifically to facilitate these minimally invasive procedures. Gaynor and colleagues [1] note that these devices must “be able to produce transmural lesions on the arrested and beating heart safely without producing collateral damage to vital structures. This requires the development of dose response curves on living tissue.” To their credit, they have developed a rigorous model that enables generation of such dose response curves. In their porcine beating heart model, endocardial microwave energy reliably produced transmural atrial lesions on the arrested heart; however, on the beating heart, epicardial atrial lesions were transmural in only 20%. Ventricular muscle, which was 4 times thicker than atrial tissue, had a linear energy response curve, that suggested that circulating blood is an effective heat sink and limits the success of epicardial microwave ablation on the beating heart. There is of great interest in the ability to create transmural lesions with alternate energy sources. Transplant surgeons and those of us who performed the traditional cut and sew maze procedure recognize that atrial tissue has variable thickness and composition. Some tissue is so thin that it seems to be made up of only endocardium, whereas other atrial tissue is very thick and may be covered by epicardial fat or endocardial calcium. This variability of atrial tissue may influence the performance of alternate energy sources. Currently available energy sources include microwave, radiofrequency, laser, ultrasound, and cryothermy. These have been applied to perform ablations under widely varying conditions (ie, on pump vs off pump, epicardial vs endocardial, minimally invasive vs sternotomy). The aim of these procedures is to create lines of conduction block or modify conduction, or both, such that AF will be ablated. Currently we have no practical means for intraoperative assessment of the effectiveness of these procedures; we tell the patient that we will not be able to judge procedural success for several months. Gaynor and colleagues’ [1Gaynor S.L. Byrd B.D. Diodato M.D. et al.Microwave ablation for atrial fibrillation dose response curves in the cardioplegia-arrested and beating heart.Ann Thorac Surg. 2006; 81: 72-77Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar] data suggest that we need to standardize assessment of ablation modalities in 3 separate but complementary fashions by: (1) generating standard, bench-top dose response curves for each device; (2) assessing safety and quantify collateral damage, and (3) assessing lines of conduction block created at the operation. Currently such dose-response curves are generated by the industry using a variety of different models. In most cases, this data is held as proprietary information. Standardization of bench top testing would facilitate comparison of different technologies, likely aiding clinicians in their decision-making. We must also develop standard techniques to evaluate epicardial lesions placed on the beating heart, as transmural lesions may be difficult to create under such circumstances. Such techniques require basic electrophysiologic investigations, generally including assessment of entrance or exit block, or both, at the pulmonary veins. Failure to achieve acute conduction block at the time of a minimally invasive ablation should spur the operator to continue working until there is demonstration of acute procedural success. New technology and innovative, minimally invasive approaches will enable surgeons to offer therapy to patients with isolated AF; however, critical appraisal of these technologies and electrophysiologic confirmation of procedural results are necessary before we attempt wide dissemination of these new operations.

Energy resolution of 12 eV at 5.9 keV from Al-superconducting tunnel junction detectors

An energy resolution of ΔE=12 eV [full width at half maximum (FWHM)] has been measured for the Mn55 Kα1 line (E=5.9 keV) using a superconducting lead absorber (90×90×1.3 μm3) readout by a single aluminum superconducting tunnel junction (100×100 μm2). The total detector area has been illuminated, while a slit mask of 150 μm width was used to partially shadow the detector leads and substrate area from impinging x rays. The total electronic noise contribution was measured as ΔEelec=4 eV (FWHM). The superconducting tunnel junction is located on a Si3N4 membrane of thickness 0.3 μm, the lead absorber is separated from the superconducting tunnel junction’s top layer by a thin layer of natural aluminum oxide. No deviations from linear energy response were observed in the energy range between E=1.74 keV and E=6.49 keV. The same resolution was obtained for a single aluminum superconducting tunnel junction, where the influence of substrate events was suppressed by a metallic buffer layer between tunnel junction and substrate. The escape of recombination phonons into the substrate causes small nonlinearities in the tunnel junction’s energy response.

Development of superconducting tunnel junction detectors for high-resolution X-ray spectroscopy

The energy resolution of aluminum superconducting tunnel junctions (Al-STJs) has been improved by the introduction of a metallic buffer layer underneath the junction. When irradiated by 5.9 keV X-rays, a resolution of 12 eV (FWHM) was achieved for a junction size of 100×100 μm 2. A mobile refrigerator system allowed to characterize these devices at the PTB-beamlines of the electron storage rings Bessy I and Bessy II. They showed linear energy response in the range between 200 eV and 6.5 keV and a strong increase in reduced energy events if irradiated at X-ray energies below the Al absorption edge at 1.56 keV.

A scintillating fiber beam-energy monitor for electron beam therapy.

A new type of beam-energy monitor is described, which has been developed to check the energies of electron beams from radiotherapy accelerators. The monitor consists of a pair of scintillating fibers and photodiode read-out circuits that measure the energy dependence of electron transmission through a wedge-shaped absorber. A linear energy response and 1% accuracy for energy constancy measurements are attained with the monitor. The monitor having advantages of simple mechanical and electronic constructions, small size, and low cost is suitable for practical use as a portable device.

Response linearity of Nb tunnel junction detectors for photon energies from 1.5 to 6.4 keV

Recent experimental results show a linear energy response in high quality Nb-Al-AlOx-Nb superconducting tunnel junction detectors for photon energies between 1.5 and 6.4 keV. The experimental data are based on both direct x-ray illumination and on the escape and re-absorption of fluorescent photons created in the junction electrodes and in the silicon substrate. The observed linearity of the energy response raises questions on the validity of some theoretical models which describe the relaxation process occurring in a superconducting thin film after x-ray photoabsorption. Such models generally predict nonlinear effects due to large quasiparticle number densities and short recombination times.

The sat calorimeter of the DELPHI experiment at LEP; results of a module test

Abstract The construction of an electromagnetic calorimeter using scintillating plastic fibres and lead plates is described. The calorimeter is part of the Small Angle Tagger (SAT) of the DELPHI experiment at the LEP collider, recording high-energy electrons, positrons and photons. Results from a test of a module of similar construction are presented. The module was found to have a linear energy response when exposed to electrons of 10–70 GeV, with an energy resolution given by σ/E[%] = (1.162 + (11.4/√E[GeV])2) 1 2 .

A neutron detector for use in strong gamma backgrounds

We describe the simulation of a new concept for a neutron detector system involving polyethylene radiators and multiwire proportional detectors which detect protons produced by neutron interactions in the radiators. The detector system is relatively insensitive to gamma radiation as long as the individual proportional counters maintain their stability. The detector system has a linear energy response and good energy resolution from threshold (determined by the radiator thickness) up to approximately 20 MeV. By detecting events in which two proton tracks are produced, the detector system can be used for imaging with a spatial resolution of ∼9°.