Heavy-to-light electron transition enabling real-time spectra detection of charged particles by a biocompatible semiconductor

The current challenge of wearable/implantable personal dosimeters for medical diagnosis and radiotherapy applications is lack of suitable detector materials possessing both excellent detection performance and biocompatibility. Here, we report a solution-grown biocompatible organic single crystalline semiconductor (OSCS), 4-Hydroxyphenylacetic acid (4HPA), achieving real-time spectral detection of charged particles with single-particle sensitivity. Along in-plane direction, two-dimensional anisotropic 4HPA exhibits a large electron drift velocity of 5 × 105 cm s-1 at "radiation-mode" while maintaining a high resistivity of (1.28 ± 0.003) × 1012 Ω·cm at "dark-mode" due to influence of dense π-π overlaps and high-energy L1 level. Therefore, 4HPA detectors exhibit the record spectra detection of charged particles among their organic counterparts, with energy resolution of 36%, (μt)e of (4.91 ± 0.07) × 10-5 cm2 V-1, and detection time down to 3 ms. These detectors also show high X-ray detection sensitivity of 16,612 μC Gyabs-1 cm-3, detection of limit of 20 nGyair s-1, and long-term stability after 690 Gyair irradiation.

Surfactant-Dependent Bulk Scale Mechanochemical Synthesis of CsPbBr3 Nanocrystals for Plastic Scintillator-Based X-ray Imaging

We report a facile, solvent-free surfactant-dependent mechanochemical synthesis of highly luminescent CsPbBr3 nanocrystals (NCs) and study their scintillation properties. A small amount of surfactant oleylamine (OAM) plays an important role in the two-step ball milling method to control the size and emission properties of the NCs. The solid-state synthesized perovskite NCs exhibit a high photoluminescence quantum yield (PLQY) of up to 88% with excellent stability. CsPbBr3 NCs capped with different amounts of surfactant were dispersed in toluene and mixed with polymethyl methacrylate (PMMA) polymer and cast into scintillator discs. With increasing concentration of OAM during synthesis, the PL yield of CsPbBr3/PMMA nanocomposite was increased, which is attributed to reduced NC aggregation and PL quenching. We also varied the perovskite loading concentration in the nanocomposite and studied the resulting emission properties. The most intense PL emission was observed from the 2% perovskite-loaded disc, while the 10% loaded disc exhibited the highest radioluminescence (RL) emission from 50 kV X-rays. The strong RL yield may be attributed to the deep penetration of X-rays into the composite, combined with the large interaction cross-section of the X-rays with the high-Z atoms within the NCs. The nanocomposite disc shows an intense RL emission peak centered at 536 nm and a fast RL decay time of 29.4 ns. Further, we have demonstrated the X-ray imaging performance of a 10% CsPbBr3 NC-loaded nanocomposite disc.

Solution-Grown Formamidinium Hybrid Perovskite (FAPbBr3) Single Crystals for α-Particle and γ-Ray Detection at Room Temperature

Compared with the widely reported MAPbBr₃ single crystals, formamidinium-based (FA-based) hybrid perovskites FAPbBr₃ (FPB) with superior chemical and structure stability are expected to be more efficient and perform as more reliable radiation detectors at room temperature. Here, we employ an improved inverse temperature crystallization method to grow FPB bulk single crystals, where issues associated with the retrograde solubility behavior are resolved. A crystal growth phase diagram has been proposed, and accordingly, growth parameters are optimized to avoid the formation of NH₄Pb₂Br₅ secondary phase. The resulting FPB crystals exhibit a high resistivity of 2.8 × 10⁹ Ω·cm and high electron and hole mobility-lifetime products (μτ) of 8.0 × 10^-4 and 1.1 × 10^-3 cm²·V^-1, respectively. Simultaneously, the electron and hole mobilities (μ) are evaluated to be 22.2 and 66.1 cm²·V^-1·s^-1, respectively, based on the time-of-flight technique. Furthermore, a Au/FPB SC/Au detector is constructed that demonstrates a resolvable gamma peak from 59.5 keV ²⁴¹Am γ-rays at room temperature for the first time. An energy resolution of 40.1% is obtained at 30 V by collecting the hole signals. These results demonstrate the great potential of FAPbBr₃ as a hybrid material for γ-ray spectroscopy and imaging.

Melt-grown large-sized Cs2TeI6 crystals for X-ray detection

Large-sized lead-free perovskite Cs₂TeI₆ shows an X-ray sensitivity of 27.8 μC Gy⁻¹ cm⁻² with a detection limit as low as 72.5 nGy s⁻¹.

Gas Migration in MX80 Buffer Bentonite

Controlled flow-rate gas injection experiments have been performed on pre-compacted samples of KBS-3 specification M×801 buffer bentonite using helium as a safe replacement for hydrogen. By simultaneously applying a confining pressure and backpressure, specimens were isotropically-consolidated and fully water-saturated under pre-determined effective stress conditions, before injecting gas using a syringe pump. Ingoing and outgoing gas fluxes were monitored. All tests exhibited a conspicuous threshold pressure for breakthrough, somewhat larger than the sum of the swelling pressure and the backpressure. All tests showed a post-peak negative transient leading to steady-state gas flow. Using a stepped history of flow rate, the flow law was shown to be nonlinear. With the injection pump stationary (i.e. zero applied flow rate), gas pressure declined with time to a finite value. When gas flow was reestablished, the threshold value for gas breakthrough was found to be significantly lower than in virgin clay. There is strong evidence to suggest that the capillary pressure for the penetration of interparticle pore space of buffer bentonite is of such a magnitude that normal two-phase flow is impossible. Gas entry and breakthrough is therefore accompanied by the development of microcracks which propagate through the clay from gas source to sink. The experiments suggest that these pathways open under high gas pressure conditions and partially close if gas pressure falls, providing a possible explanation of the nonlinearity of the flow law.

Effect of size fractionation on the distribution of an albumin colloid in the reticuloendothelial system of the mouse

To study if by varying the particle size of a 99mTc albumin colloid preparation its relative bone marrow accumulation could be increased, it was separated by gel filtration and different fractions were injected into mice. Particles around and smaller than the peak size of the colloid, 31 nm, exhibited a higher bone marrow/liver-spleen uptake ratio than larger particles but the uptake ratio was similar to that of the unseparated colloid. An antimony sulphide colloid showed a similar particle size distribution, but the corresponding uptake ratio was half of the albumin colloid. This indicates that characteristics other than size determine the distribution of a colloid in the reticuloendothelial system.