Scintillators, materials that produce light pulses upon interaction with ionizing radiation, are widely employed in radiation detectors. In advanced medical-imaging technologies, fast scintillators ...enabling a time resolution of tens of picoseconds are required to achieve high-resolution imaging at the millimetre length scale. Here we demonstrate that composite materials based on fluorescent metal–organic framework (MOF) nanocrystals can work as fast scintillators. We present a prototype scintillator fabricated by embedding MOF nanocrystals in a polymer. The MOF comprises zirconium oxo-hydroxy clusters, high-Z linking nodes interacting with the ionizing radiation, arranged in an orderly fashion at a nanometric distance from 9,10-diphenylanthracene ligand emitters. Their incorporation in the framework enables fast sensitization of the ligand fluorescence, thus avoiding issues typically arising from the intimate mixing of complementary elements. This proof-of-concept prototype device shows an ultrafast scintillation rise time of ~50 ps, thus supporting the development of new scintillators based on engineered fluorescent MOF nanocrystals.Composites of fluorescent metal–organic framework nanocrystals in a polymer are exploited to create fast scintillators with a rise time of about 50 ps.
•Neutron/γ–ray discrimination via optical light filtration instead of PSD methods.•Study of the CVL in CLYC: an ultra-fast mechanism emitting in the deep-near UV.•Correlation between the time and the ...wavelength domain of the scintillation light.•Correlation between the RL spectra with the TCSPC technique and a fast PMT results.•LET dependence of the quenching effect on the CVL emission in CLYC.
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7Li enriched Cs2LiYCl6:Ce3+ (CLYC) is a promising inorganic scintillator for real-time γ-ray and fast neutron spectrometry. The neutron/γ-ray discrimination is usually accomplished exploiting the different quenching effects of high Linear Energy Transfer (LET) particles on different scintillation mechanisms, usually by means of the time analysis of the pulse shape. In principle, the emission wavelength information could be used to address the same task. However, a systematic study of the correlations between the CLYC decay time, its radio-luminescence spectrum and the LET of the impinging particle has not yet been performed. We therefore investigated the CLYC scintillation process under neutron and γ-ray irradiation, correlating the time response to the scintillation wavelength spectrum using a 1–inch right cylinder>99% 7Li enriched CLYC. We found that the relative intensity of the Core to Valence Luminescence (CVL) is almost constant with photons in the energy range 20–660 keV, i.e. 0.5–5 keV/μm LET, and is only partially quenched by neutrons. Instead, the direct electron-hole capture scintillation mechanism is completely cut under neutron irradiation. The luminescence in between the deep-Ultraviolet and the Near Ultraviolet region (250–350 nm) might be attributed to both the CVL and the host luminescence, also in thick highly Ce3+-doped crystals.
A new inorganic scintillation material based on Ba-Gd silica glass doped with cerium (BGS) is fabricated and studied. With the highest light yield among heavy glasses at the level of 2500 ph/MeV and ...fast scintillation response, the new scintillator ensures a good coincidence time resolution of < 230 ps FWHM for 511 keV γ-quanta from a 22Na source and SiPM readout. In addition to good performance in γ-quanta detection, the material demonstrates capability for efficient detection of low-energetic neutrons. The scintillator is produced by exploiting the standard industrial glass technology, which allows for an unlimited scaling up the conversion of raw material into a high-quality scintillator at a high rate. The glass can be casted in application-specific molds, so minimizing the material losses. The presented glass scintillator has potential for further improvement of its light output and scintillation response time.
A novel technique for testing the timing properties of scintillators is presented. The technique is based on transient absorption (TA) induced in a scintillating material by a selective excitation of ...the activator ion. A figure of merit to assess the timing properties of scintillators is suggested. This parameter was estimated for a set of cerium doped lutetium–yttrium oxyorthosilicate (LYSO:Ce) bars, which have been fabricated for Barrel Timing Layer sensor of Compact Muon Solenoid detector (CMS BTL) and exhibited different timing properties, and compared with the results obtained by conventional coincidence time resolution (CTR) measurements. The figure of merit applied for the tested bars shows a strong correlation (Pearson's correlation coefficient R = 0.95) with the CTR. These results suggest that the TA technique could be used as an experimental method to expand in a complementary way the extensive qualification procedure of LYSO:Ce crystals that will be performed for the production of the CMS BTL detector.
•Coincidence time resolution correlates with activator population rise time.•Population rise time can be probed by transient absorption in femtosecond domain.•Transient absorption can be exploited for testing of scintillator timing properties.
After the discovery of a cross-luminescence (CL) in BaF2 in 1982, a large number of CL scintillators were investigated. However, no CL scintillator superior to BaF2 has been discovered, and the ...research of CL scintillators has subsided. Recent technological development in medical imaging and high-energy physics created a new demand for ultra-fast scintillators further supported by the development of UV-sensitive semiconductor photodetectors. As a consequence, renewed interest in CL scintillators appeared. To satisfy the requirements of fast timing applications high photo-detection efficiency, e. i. a good spectral match between the scintillator and photodetector must be achieved. Cesium-based ternary chlorides could provide a red-shift (∼1.5 eV) of CL towards the sensitive region of the photodetector (PMT or SiPM) while keeping light output and timing characteristics comparable to BaF2.
•Two families of Cs-based cross-luminescence halide scintillators investigated .•All Cs containing samples exhibit cross-luminescence in the 250–300 nm region.•The best sample achieved CTR comparable to commercial BaF2.•Cs-based cross-luminescence halide scintillator could reach CTR ∼50 ps.
Bismuth germanate (BGO) is a well known high density scintillating material widely used in many applications such as high energy physics and medical imaging. Bismuth silicate (BSO) features ...properties similar to BGO in terms of stopping power and Cherenkov photon yield with a lower scintillation light output but faster decay time, thus being more attractive for applications in high-rate environments. Mixed crystals such as Bi4(GexSi1−x)3O12 (BGSO, with x varying from 0 to 1) make it possible to optimize decay time and light yield based on the detector needs.
A characterization campaign of the optical and scintillation properties of two sets of BGSO mixed crystals with Ge fraction varying from 0 to 100% was performed. A coincidence time resolution (CTR) at 511 keV of 208 ±2 ps FWHM was measured for a 2 × 2 × 3 mm3 pixel with 40% Ge, while the optimum value obtained for the effective decay time is 49.9 ±1.8 ns for a 6 × 6 × 0.7 mm3 plate-shaped sample with 30% Ge. Furthermore the smallest slow decay time component achieved is 101 ±2 ns and is obtained for the plate-shaped sample with 30% Ge, while the largest is 236 ±5 ns for a pure BGO sample with the same geometry.
In addition we demonstrated the possibility to efficiently separate the Cherenkov and scintillation light produced in a pure BSO sample. Such a technique could be exploited in a crystal-based dual-readout calorimeter to improve the energy resolution for hadronic showers and jets.
An original approach intended to facilitate the intratumoral activation of Pt(IV) diamines by illumination with visible light to form photolysis products that irreversibly bind to DNA and are ...cytotoxic to human cancer cells is reported. The novel Pt(IV) complex trans,cis-Pt(OAc)2I2(en) was prepared by the acetylation of trans,cis-Pt(OH)2I2(en) with acetic anhydride in CH2Cl2; trans,cis-Pt(OH)2I2(en) was synthesized by oxidation of PtI2(en) with 30% aqueous H2O2. trans,cis-Pt(OAc)2I2(en) crystallized from methanol as deep-red needles with a = 9.029(4) Å, b = 11.443(2) Å, c = 12.822(2) Å, β = 95.48(3)°, monoclinic space group Cc, and Z = 4. The conformation of the acetato groups around the O−Pt−O axis deviated significantly from the conformation of the acetato groups in the X-ray crystal structure reported for the cis-dichloro analog, which may explain the very different aqueous solubilities of the two compounds. trans,cis-Pt(OAc)2I2(en) and trans,cis-Pt(OH)2I2(en) displayed broad ligand-to-metal charge-transfer bands centered at λ = 389 and 384 nm, respectively (ε = 1372 and 1425 M-1 cm-1, respectively), with tailing out to ca. 550 nm. When trans,cis-Pt(OAc)2I2(en) was incubated with calf thymus DNA in the absence of light, no covalent binding of Pt to DNA was measurable after 6 h; however, irradiation with light of wavelengths > 375 nm resulted in 63 ± 13% of the platinum being covalently bound to DNA after 6 h, suggesting that a photoreduction to Pt(II) species took place. Although trans,cis-Pt(OH)2I2(en) was also labile to visible light, only 10 ± 2% DNA platination was observed after 6 h of illumination; however, covalent binding of Pt to DNA took place quantitatively when a reducing agent such as glutathione was added to the photolyzed incubations. These results provide evidence that the photolysis of the trans-dihydroxo analog resulted predominately in the substitution of the iodide ligands for water rather than a reduction of Pt(IV) to Pt(II). When protected from light, trans,cis-Pt(OAc)2I2(en) and trans,cis-Pt(OH)2I2(en), both at a concentration of 10 μM, had half-lives of 6.6 ± 0.5 and 46.8 ± 8.8 h, respectively, at 37 °C in Eagle's minimum essential medium (EMEM) containing 5% fetal calf serum. When irradiated with light λirr > 375 nm, the half-lives were decreased by 24- and 53-fold for the diacetato- and dihydroxoplatinum(IV) complexes, respectively. Compared to the “dark” control, the in vitro treatment of TCCSUP human bladder cancer cells with trans,cis-Pt(OAc)2I2(en) resulted in 35% greater growth inhibitory activity when during the first 1.5 h of drug exposure the cells were irradiated with light λirr > 375 nm. The photolysis of trans,cis-Pt(OH)2I2(en) with visible light resulted in a 22% enhancement of antiproliferative activity.
The P̄ANDA Barrel-TOF Detector Böhm, M.; Götzen, K.; Gruber, L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2018, Letnik:
912
Journal Article
Recenzirano
The P̄ANDA experiment is a fixed target experiment in which antiprotons collide with stationary hydrogen atoms. The main physics program of the experiment is to study open questions in hadron physics ...by performing charmonium spectroscopy and precisely measuring the width, mass and decay branches, and investigating possible exotic states like glueballs and hybrids. The Barrel Time-of-Flight detector (Barrel TOF), located between the DIRC detector and the electromagnetic calorimeter (EMC), which is built in the P̄ANDA target spectrometer, has been designed to measure the time at which a charged particle transits the detector with a resolution superior to the other sub-detectors of P̄ANDA. A time resolution below 100 ps (sigma) is mandatory for this sub-detector to fulfil the requirements of good event separation and particle identification below the Cherenkov threshold. The implementation of the Barrel TOF is based on very fast organic scintillator tiles with a size of 87 x 29.5 x 5 mm3 coupled to Silicon Photomultipliers. The total of 1920 tiles are read out by 8 SiPMs each and cover almost the full azimuthal range and polar angles from 22.5∘ to 140∘ and an area of about 5 m2. The current prototypes achieve ∼60 ps, well below the design goal. The detector R&D is now in a matured stage.
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