Radiotherapy is a well-established and important treatment for cancer tumors, and advanced technologies can deliver doses in complex three-dimensional geometries tailored to each patient’s specific anatomy. A 3D dosimeter, based on optically stimulated luminescence (OSL), could provide a high accuracy and reusable tool for verifying such dose delivery. Nanoparticles of an OSL material embedded in a transparent matrix have previously been proposed as an inexpensive dosimeter, which can be read out using laser-based methods. Here, we show that Cu-doped LiF nanocubes (nano-LiF:Cu) are excellent candidates for 3D OSL dosimetry owing to their high sensitivity, dose linearity, and stability at ambient conditions. We demonstrate a scalable synthesis technique producing a material with the attractive properties of a single dosimetric trap and a single near-ultraviolet emission line well separated from visible-light stimulation sources. The observed transparency and light yield of silicone sheets with embedded nanocubes hold promise for future 3D OSL-based dosimetry.
In this contribution, we study the optically stimulated luminescence (OSL) exhibited by commercial $$\hbox {Lu}_{(2-x)}\hbox {Y}_x\hbox {SiO}_5$$ Lu ( 2 - x ) Y x SiO 5 :Ce crystals. This photon emission mechanism, complementary to scintillation, can trap a fraction of radiation energy deposited in the material and provides sufficient signal to develop a novel post-irradiation 3D dose readout. We characterize the OSL emission through spectrally and temporally resolved measurements and monitor the dose linearity response over a broad range. The measurements show that the $$\hbox {Ce}^{3+}$$ Ce 3 + centers responsible for scintillation also function as recombination centers for the OSL mechanism. The capture to OSL-active traps competes with scintillation originating from the direct non-radiative energy transfer to the luminescent centers. An OSL response on the order of 100 ph/MeV is estimated. We demonstrate the imaging capabilities provided by such an OSL photon yield using a proof-of-concept optical readout method. A 0.1 $$\hbox {mm}^3$$ mm 3 spatial resolution for doses as low as 0.5 Gy is projected using a cubic crystal to image volumetric dose profiles. While OSL degrades the intrinsic scintillating performance by reducing the number of scintillation photons emitted following the passage of ionizing radiation, it can encode highly resolved spatial information of the interaction point of the particle. This feature combines ionizing radiation spectroscopy and 3D reusable dose imaging in a single material.
Summary Converting arable land to permanent grassland remains an efficient option for increased carbon (C) storage in agricultural land. We quantified changes in C and nitrogen (N) in topsoil from the Sandmarken experiment (initiated in 1894 in Denmark) before and after its conversion to semi‐natural grassland in 1998. Because of different fertilizer application in the arable phase, the grass was established on soils with different initial fertility. Archived soils sampled during 1942–2012 from plots subjected to different treatments in the arable phase were analysed for C, N, 13C and 15N. With crop yields, topsoil C contents and the C‐TOOL model, we estimated mean C inputs in the arable phase of 0.4, 1.4 and 1.7 Mg C ha−1 year−1 for unmanured, mineral‐fertilized and animal‐manured plots, respectively, and C inputs in the grassland phase of 3.2–3.8 Mg C ha−1 year−1. In the arable phase, topsoil showed mean losses of 0.10 Mg C and 0.012 Mg N ha−1 year−1, whereas δ13C increased by 0.002‰ and δ15N by 0.013‰. Grassland establishment reverted losses of C and N to gains of 0.29 Mg C and 0.017 Mg N ha−1 year−1; δ13C now decreased by 0.065‰ and δ15N by 0.074‰. Fertilizer history did not affect these changes markedly. Converting this low‐yielding sandy soil from arable to grassland use provided an overall annual gain of 0.39 Mg C and 0.029 Mg N ha−1 in the topsoil. Changes in δ13C and δ15N indicated a reduced rate of C turnover and a less leaky N cycle under grassland. Highlights Assessed change in C and N storage with change in land use from arable to semi‐natural grassland Overall soil C sequestration was 0.39 Mg C ha−1 year−1 because C loss was avoided from continued arable use Soil δ13C and δ15N decreased when arable land was converted into grassland In the grassland phase, the modelled C input was not affected by fertilizer history
Context. Models of stellar structure and evolution can be constrained using accurate measurements of the parameters of eclipsing binary members of open clusters. Multiple binary stars provide the means to tighten the constraints and, in turn, to improve the precision and accuracy of the age estimate of the host cluster. In the previous two papers of this series, we have demonstrated the use of measurements of multiple eclipsing binaries in the old open cluster NGC 6791 to set tighter constraints on the properties of stellar models than was previously possible, thereby improving both the accuracy and precision of the cluster age. Aims. We identify and measure the properties of a non-eclipsing cluster member, V56, in NGC 6791 and demonstrate how this provides additional model constraints that support and strengthen our previous findings. Methods. We analyse multi-epoch spectra of V56 from FLAMES in conjunction with the existing photometry and measurements of eclipsing binaries in NGC6971. Results. The parameters of the V56 components are found to be Mp = 1.103 ± 0.008 M⊙ and Ms = 0.974 ± 0.007 M⊙, Rp = 1.764 ± 0.099 R⊙ and Rs = 1.045 ± 0.057 R⊙, Teff,p = 5447 ± 125 K and Teff,s = 5552 ± 125 K, and surface [Fe/H] = +0.29 ± 0.06 assuming that they have the same abundance. Conclusions. The derived properties strengthen our previous best estimate of the cluster age of 8.3 ± 0.3 Gyr and the mass of stars on the lower red giant branch (RGB), which is MRGB = 1.15 ± 0.02 M⊙ for NGC 6791. These numbers therefore continue to serve as verification points for other methods of age and mass measures, such as asteroseismology.
With the introduction of highly conformal treatment modalities, dose verification in 3D is becoming more important than ever for patient-specific quality assurance of radiotherapy. Reusability of 3D dosimeters may be the path to cope with the cost-benefit issues caused by batch-to-batch fluctuations and intense calibration protocols in existing 3D systems. We present the idea of an envisioned (optically stimulated luminescence) OSL-based 3D readout system, which exploits the inherently reusable dosimetry properties of OSL. We provide the emission spectra of the OSL active material LiF:Mg, Cu, P (MCP) for three stimulation wavelengths (460 nm, 532 nm, and 664 nm), and summarize recently published optical characterization results to highlight the requirements of a readout system for an MCP-based dosimeter.
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