Новые нанокомпозиции из органических люминофоров и неорганических сцинтилляторов для улучшения радиационных детекторов

Trends in scintillators that are used in many applications, such as medical imaging, security, oil-logging, high energy physics and non-destructive inspections are reviewed. First, we address traditional inorganic and organic scintillators with respect of limitation in the scintillation light yields and lifetimes. The combination of high–light yield and fast response can be found in Ce 3 + , Pr 3 + and Nd 3 + lanthanide-doped scintillators while the maximum light yield conversion of 100,000 photons/MeV can be found in Eu 3 + doped SrI 2 . However, the fabrication of those lanthanide-doped scintillators is inefficient and expensive as it requires high-temperature furnaces. A self-grown single crystal using solution processes is already introduced in perovskite photovoltaic technology and it can be the key for low-cost scintillators. A novel class of materials in scintillation includes lead halide perovskites. These materials were explored decades ago due to the large X-ray absorption cross section. However, lately lead halide perovskites have become a focus of interest due to recently reported very high photoluminescence quantum yield and light yield conversion at low temperatures. In principle, 150,000–300,000 photons/MeV light yields can be proportional to the small energy bandgap of these materials, which is below 2 eV. Finally, we discuss the extraction efficiency improvements through the fabrication of the nanostructure in scintillators, which can be implemented in perovskite materials. The recent technology involving quantum dots and nanocrystals may also improve light conversion in perovskite scintillators.

In recent years, a number of new gamma-ray scintillators are commercially available. These scintillators are either derived from known scintillators, e.g. Lu1-xYxAlO3: Ce (LuYAP) from LuAlO3:Ce and Lu(2(1-x))Y2xSiO5:Ce (LYSO) from Lu2SiO5:Ce or are the result of new discoveries, e.g. LaCl3:Ce and LaBr3:Ce. The first two materials are primarily of interest because of the relatively high detection efficiency and fast response; LYSO has found application in time-of-flight (TOF) positron-emission tomography (TOF PET) and the LuYAP-LYSO combination is used in small-animal PET. The halide scintillators have an excellent energy resolution of approximately 3% at 662 keV and they have a relatively high light yield. LaBr3:Ce is being studied for application in TOF PET. At the same time, the search for and research on new scintillator materials are going on. For example, LuI3:Ce is a new material with a very high light yield (approximately 90,000 photons MeV(-1)). Other examples of new materials are (C6H13NH3)2PbI4 and (C3H7NH3)2PbBr4, organic-inorganic hybrid compounds, of which the former has a very fast sub-nanosecond response. The new scintillators show great promise for new developments in medical applications, in particular, for PET systems.

A scintillation detector is composed of a scintillator, which converts absorbed ionizing radiation into multiple low energy (~eV) photons, and a photomultiplier tube (PMT), avalanche photodiode, or Si-PMT, which can convert the photons into an electrical signal. The performance of the scintillation detector depends greatly on the characteristics of the scintillator. Inorganic scintillators are widely used for detecting high-energy photons such as X-rays and gamma-rays. Eu-doped CsCaCl3 has been reported to display excellent properties because of the 4f65d1–4f7 transitions of Eu2+ [1]. CsCaCl3:Eu exhibits a 4f65d1–4f7 luminescence peak at 450 nm , with a high light yield (18,000 photons/MeV). Further, undoped CsCaCl3 is known to have a small scintillation decay time constant because of their Auger-free luminescence [2]. In this study, CsCaCl3 is used as the host material and luminescence and scintillation properties of CsCaCl3 crystals doped with impurity ions such as Yb and Tl are investigated. Photoluminescence spectra, X-ray-excited radioluminescence spectra, scintillation temporal profiles, and pulse-height spectra (with 662 keV gamma-ray excitation from 137Cs) of the crystals are analyzed. Single crystals of Yb- and Tl-doped CsCaCl3 were prepared with the vertical Bridgman–Stockbarger method using a sealed quartz tube. Before crystal growth, stoichiometric mixtures of CsCl and CaCl2 were dried by heating overnight ~500 K in a vacuum. After growth, the crystals were cut and polished. The Figure shows the X-ray-excited radioluminescence spectra, measured at 300 K, for Yb- and Tl-doped CsCaCl3 crystals. In the spectrum of CsCaCl3:Yb, an intense emission band was observed at 437 nm with a shoulder at 409 nm. The emission band in the radioluminescence spectrum is consistent with that at 439 nm, with a shoulder at 409 nm, in the photoluminescence spectrum. As these emission bands have similarities with emission bands of a SrI2:Yb2+ crystal, the emission bands of the CsCaCl3:Yb crystal are attributed to spin-allowed and spin-forbidden Yb2+ 4f135d–4f14 transitions. In the spectrum of CsCaCl3:Tl, an emission band observed at 327 nm is similar to that at 336 nm in the photoluminescence spectrum. In a previous study of CsCl:Tl, an emission band at 340 nm is attributed to the triplet relaxed excited state of a Tl+ ion [3]. Thus, the emission band at 327 nm can be attributed to the same state. The pulse- height spectra of these crystals were measured with 662 keV gamma-ray excitation from 137Cs. Assuming a light yield of 40,000 photons/MeV for NaI:Tl [4], the light yield is estimated to be 3,800 and 4,300 photons/MeV for CsCaCl3:Yb and CsCaCl3:Tl, respectively. The lower light yields for these crystals can be attributed to the lower concentration of impurity ions. Thus, the light yields of these crystals can be improved by increasing the concentration of impurity ions.[1] M. Zhuravleva, B. Blalock, K. Yang, M. Koschan, and C. L. Melcher, J. Cryst. Growth 352, 115 (2012).[2] M. Koshimizu, N. Yahaba, R. Haruki, F. Nishikido, S. Kishimoto, and K. Asai, Opt. Mater. 36, 1930 (2014).[3] V. Nagirnyi S. Zazubovich, and N. Jaanson, Phys. Stat. sol. 175, (1993) 155. Figure 1

The extraction of scintillation light from an inorganic scintillator is one of the major bottlenecks in time-of-flight positron emission tomography (ToF-PET) because it directly affects the energy and time resolution of the gamma detector. To increase the light extraction efficiency, we use photonic crystal slabs (PCS), defined as thin dielectric layers structured with a 2-D, or 3-D, periodic pattern. A higher light output, combined with a reduction of the average path length traversed by the photons in the crystal before extraction, leads to a more precise evaluation of the particle time detection. This also implies a better coincidence time resolution (CTR). These improvements translate to ToF-PET reconstructed images with a higher signal-to-noise ratio and lead to more accurate diagnoses, faster exams, and possibly a reduced patient radiation dose. In this paper, we present the results obtained using lutetium-yttrium oxyorthosilicate, Lu2(1-x)Y2xSiO5 samples patterned with nanoimprinted PCS. Comparative light yield (LY) measurements show an improvement of a factor 1.68 for a naked configuration, whereas CTR goes from 535 to 315 ps

Structural, photoluminescence and scintillation properties of Ce-doped Al(PO3)3–Sr(PO3)2–CsPO3 inorganic glass scintillators for gamma- and X-ray detection

The composite scintillators from inorganic scintillators and organic phosphors provide unique combination of high light yield and nanosecond temporal resolution. Preparation of microfibers of these composites by means of centrifugation resulted in forming of axial nanosplitting and transverse micromodulation of their structure and optical properties, These modulations result in essential improvement of scintillation parameters of the composite providing the development of relatively simple and cheap X-Ray microscope. Ball rolling of inorganic solids provides superfast introduction of organic and inorganic components into subsurface layers for the special modifications of their properties. The superfast introduction is explained by propagation of nanocracks involving necessary dopants into the solid.

Cs2HfCl6 doped with Zr: Influence of tetravalent substitution on scintillation properties

Cerium doped lutetium pyrosilicate Lu2Si2O7:Ce3+ (LPS), anew inorganic scintillator, displays particularly promising performance. This material canbe readily pulled from the melt. A high light output (average value: 26 300 ph MeV−1),a relatively good energy resolution (9%) and a fast decay time (38 ns)without afterglow make this new scintillator very attractive, in particular formedical imaging. Optical characterizations and scintillation properties ofLPS:Ce large single crystals are presented, including timing properties andstudy of the scintillation yields as a function of incident energy.

Growth and luminescent properties of Ce and Eu doped Cesium Hafnium Iodide single crystalline scintillators

Thin scintillating tiles with high light yield for the OPAL endcaps

LaCl3:Ce scintillator for γ-ray detection

Gamma and beta intra-operative imaging probes

Ce doped (YGd)3(GaAl)5O12:Ce (YGAG) is a ceramic scintillator with high light output, and its decay times are different between alpha particles and gamma photons or beta particles. This characteristic may be applied to the direct measurement of alpha particles in water where the gamma photons or beta particles become background counts. Thus we proposed a radiation detector using a YGAG plate dipped in water that contained alpha radionuclides to detect alpha particles in water. The scintillation photons from the YGAG plate were detected by a position sensitive photomultiplier tube (PSPMT) set in water that contained alpha radionuclides. A YGAG plate (20 × 20 × 0.5 mm) was set on the bottom of a glass cup filled with water containing alpha radionuclides that emit alpha particles. The alpha particles near the YGAG plate were detected by the scintillator, and the scintillation light was detected by the PSPMT . For radon-containing water sampled from a hot spring, pulse shape spectra showed two peaks: one for the alpha particles and another for the beta particles and the gamma photons. By pulse shape discrimination for the peak of the alpha particles, their count rate decreased with a decay of Rn-222 (3.8 days). For tap water, the pulse shape distribution showed only one peak and the count rate was almost constant, indicating these counts were mainly from the background beta particles or gamma photons. We could show a detection principle for alpha radionuclides in water and this detection principle for alpha radionuclides in water might be a new method for estimating the alpha radionuclide concentration in water.

The measurement of diffuse refl ectance spectra below 230 nm for ceramic luminescent materials is usually not performed although it is of tremendous interest, e.g., to determine their quantum effi ciency upon VUV excitation. In contrast, the recording of VUV excitation spectra is well established, e.g., to evaluate VUV phosphors. The lack of access to diffuse powder refl ection spectra in this range is caused by the absorption edge (optical band gap) of the most common refl ectance standards; for instance, BaSO4 or CaCO3–VUV photons with energies higher than the absorption edge are not refl ected but absorbed and thus not amenable to detection in a synchronous scan. The measurement technique presented in this paper allows monitoring refl ection properties of powder samples in the range from 120 to 300 nm (10.3 to 4.1 eV). To this end, all VUV photons refl ected by the sample are converted into visible photons, which are collected in an Ulbricht sphere and fi nally counted by a photomultiplier tube (PMT). This requires a custom-built integrating sphere, viz. one that is coated with a (V)UV to Vis converter, e.g., a phosphor such as BaMgAl10O17:Eu2+ (BAM:Eu) showing a spectrally independent and high light output in the respective wavelength range. This paper sketches the technique and procedure for recording VUV refl ection spectra and shows the results for several standard phosphors. It also reveals the limits of this new technique.

Components from wheat roots modify the bioactivity of ZnO and CuO nanoparticles in a soil bacterium