Enhancing excitons by oleic acid treatment in WS2, MoS2, and WS2/MoS2 heterostructure

The neutral and interlayer exciton originates from intralayer and interlayer coupling, respectively. Unlike neutral exciton, the interlayer excitons at room temperature are hard to observe and manipulate due to instability. In this work, we show the photoluminescence of WS$_2$ and MoS$_2$ neutral exciton can be improved by oleic acid passivation, allowing trion peaks to be observed at room temperature. More importantly, a 3-fold increase in peak intensity of interlayer excitons is achieved, and the energy peak is blue-shifted 107 meV. Our work paves the way to investigate excitons in two-dimensional transition metal dichalcogenides monolayers and heterostructures at room temperature.

Discrete Convolution-Based Energy Spectrum Configuring Method for the Analysis of the Intrinsic Radiation of 176Lu

There has been considerable interest in inorganic scintillators based on lutetium due to their favorable physical properties. Despite their advantages, lutetium-based scintillators could face issues because of the natural occurring radioisotope of 176Lu that is contained in natural lutetium. In order to mitigate its potential shortcomings, previous works have studied to understand the energy spectrum of the intrinsic radiation of 176Lu (IRL). However, few studies have focused on the various principal types of photon interactions with matter; in other words, only the full-energy peak according to the photoelectric effect or internal conversion have been considered for understanding the energy spectrum of IRL. Thus, the approach we have used in this study considers other principal types of photon interactions by convoluting each energy spectrum with combinations for generating the spectrum of the intrinsic radiation of 176Lu. From the results, we confirm that the method provides good agreement with the experiment. A significant contribution of this study is the provision of a new approach to process energy spectra induced by mutually independent radiation interactions as a single spectrum.

Development of a New Quantification Method Using Partial Volume Effect Correction for Individual Energy Peaks in 111In-pentetreotide SPECT/CT

BackgroundSomatostatin receptor scintigraphy (SRS) using 111In-pentetreotide has no established quantification method. The purpose of this study was to develop a new quantitative method to correct the partial volume effect (PVE) for individual energy peaks in 111In-pentetreotide single-photon emission computed tomography (SPECT). MethodsPhantom experiments were performed to construct a new quantitative method. In the phantom experiments, a NEMA IEC body phantom was used. Acquisition was performed using two energy peaks (171 keV and 245 keV) on the SPECT/CT system. In the SPECT images of each energy peak, the region of interest was set at each hot sphere and lung insert, and the recovery coefficient (RC) was calculated to understand the PVE. A new quantitative index, the indium uptake index (IUI), was calculated using the RC to correct the PVE. The quantitative accuracy of the IUI in the hot sphere was confirmed. Case studies were performed to clarify the quantitative accuracy. In a case study, the relationship between the IUI and the Krenning score, which is used as a visual assessment, was evaluated for each lesion. ResultsThe obtained RCs showed that the energy peak at 171 keV was faster in recovering the effect of PVE than that at 245 keV. The IUI in the 17 mm diameter hot sphere was overestimated by 3.1% at 171 keV and underestimated by 0.5% at 245 keV compared to the actual IUI. In case studies, the relationship between IUI and Krenning score was rs = 0.805 (p < 0.005) at sum, rs = 0.77 (p < 0.005) at 171 keV, and rs = 0.84 (p < 0.005) at 245 keV.Conclusion We have developed a new quantification method for 111In-pentetreotide SPECT/CT using RC-based PVE correction for an individual energy peak of 171 keV. The quantitative accuracy of this method was high even for accumulations of less than 20 mm, and it showed a good relationship with the Krenning score; therefore, the clinical usefulness of IUI was demonstrated.

Detection Efficiency of a NaI (Tl) Gamma Spectrometry System for Measurement of Low Level Radioactivity

Qualitative analysis of radionuclides requires the use of reliable gamma-ray detection system. The NaI(Tl) detector has been widely used and still one of the most used detectors today. It is therefore imperative to validate the reliability of the 5x5 cm2 NaI(Tl) gamma spectrometry system used in carrying out gamma-ray analysis of soil samples in the Radiation and Health Laboratory, Federal University of Agriculture Abeokuta, Nigeria. The gamma ray spectrometer is housed in a 5 cm thick cylindrical lead shield. Calibration was executed using standard materials produced under the auspices of the International Atomic Energy Agency (IAEA). Resolution and detection limit (LD) of the detector were determined using full width at half the maximum of the energy peak of 137Cs and background signal level of the reference materials respectively. Counting efficiencies of the detector was calculated using energies of 1460 keV, 1764keV and 2615 keV for 40K, 226Ra and 232Th respectively. Secondary samples, RGMIX1 and RGMIX2 were formulated and counted to calculate activity concentrations using the NaI(Tl) detector. Resolution of the detector was calculated to be 7.8% of 137Cs, which is good for a NaI(Tl) detector. The counting efficiency of the detector is seen to depend on the gamma ray energy. The results from this work shows that the detector system is suitable gamma spectrometry, and will give quality measurements when used for quantitative determination of radionuclides in environmental samples. The efficiency and resolution of the NaI(Tl) detector should also be determined using photon energies obtained from other radioactive sources.

Study the influences of the radionuclide depth distributions on the FEPE for the measurements of the soil activity using in situ HPGe gamma spectrometry

In this work, the influences of the soil densities and the radionuclide depth distributions(RDD) on the Full Energy Peak Efficiency (FEPE) calculation of the in-situ gamma rayspectrometer using the In Situ Object Counting Systems (ISOCS) software were studied. The data of the RDDs at the sites were investigated by using laboratory HPGe gamma spectrometer. Six different RDDs of 40K, 226Ra and 232Th were found at four studied sites with radionuclide deposition moving from surface to deeper positions. The results show that FEPE values vary strongly for the different RDDs, especially for the low gamma ray energies. Use of the uniform model for calculating FEPEs can result in noticeable errors from 29% to 101% for the realistic RDD of the exponential form (surfaceradionuclide deposition), negative variations from 14% to 30% for the realistic RDD of having a radionuclide deposition at the 30 cm depth, and negligible variations of less than 5 % for the realistic RDD of quasi uniform form in the range of gamma ray energies of interest.

Investigation of the substituting effect of Se on the physical properties and performances of Cd〖Se〗_x 〖Te〗_(1-x)and Zn〖Se〗_x 〖Te〗_(1-x) materials for semiconductor radiation detectors

The structural and electronic properties of and semiconductor detectors at various concentrations x = 0, 0.25, 0.5, 0.75 and 1 of Selenium (Se) were determined by using the full potential-linearized augmented plane wave (FP-LAPW) based on the density functional theory (DFT). The compositional dependence of such properties was analysed and discussed. The concentration dependence of lattice parameter and bulk modulus show nonlinearity. All the investigated alloys have a direct bandgap (Γ-Γ) which decreasesnonlinearly with increase in Se concentration. On the other hand, Geant4 simulations have been performed for studying the absolute and full-energy peak detection efficiencies and energy resolution at 1.5”×1.5” of these alloys as semiconductor detectors in the 511-1332 keV gamma-ray energy range. Ours findings are in a good agreement with the available theoretical and experimental data. We hope that our results serve as are reference for future theoretical and experimental researches.

Development of a semi-empirical calibration method by using a LaBr3(Ce) scintillation detector for NORM samples analyses

In this study, a semi-empirical calibration method for NORM samples measurement by using a LaBr3(Ce) scintillator was developed based on a combination of experimental gamma spectrometry measurements and MCNP-X simulations. The aim of this work is to provide us with full energy peak efficiency calibration curves in a wide photon energy range which is of particular importance when selected photon energies of 234Th, 214Pb, 214Bi, 228Ac, 208Tl and 226Ra are to be measured with accuracy.

Variability of near-inertial waves in the lower stratosphere from balloon observations and the ECMWF (re)analyses

&lt;p&gt;Near-inertial waves (NIWs) with intrinsic frequency close to the local Coriolis parameter &lt;em&gt;f&lt;/em&gt; constitute a striking component of the kinetic energy spectrum in both the atmosphere and the ocean. However, contrary to the oceanic case, the strong and variable background atmospheric winds tend to shift the frequency of the waves (Doppler effect). As a consequence, atmospheric NIWs cannot generally be observed directly as a kinetic energy peak at ground-based frequency &lt;em&gt;f &lt;/em&gt;but are instead diagnosed indirectly (e.g. using the polarisation and dispersion relations). This complication does not appear when analyzing quasi-lagrangian observations from superpressure balloons (SPB), which drift together with the flow and are thus exempt from Doppler shift. Past SPB observations in the lower stratosphere have revealed the magnitude of the kinetic energy peak associated with NIWs and it was recently shown that state-of-the-art reanalyses partly represent this feature.&lt;/p&gt;&lt;p&gt;In this presentation, we will investigate the variability of NIWs using ECMWF (re)analysis products (the operational analysis and ERA5) and balloon observations from recent CNES campaigns (2005, 2010 and 2019-2020) at various latitudes ranging from the equator to the pole (and hence different inertial frequencies). As in Podglajen et al. (2020), NIWs are extracted from the (re)analyses by computing Lagrangian trajectories using the analyzed wind and temperature fields. We will illustrate the remarkable realism of model NIWs, both statistically and for specific case studies. Then, we will characterize the geographic and seasonal variability of NIW properties. In light of those results, possible factors influencing the near-inertial energy peak (horizontal wave propagation, refraction near critical levels, tide interactions) and the parallel with the oceanic situation will be discussed, as well as the ability of the model and data assimilation system to simulate them.&lt;/p&gt;&lt;p&gt;Reference&amp;#160;:&lt;/p&gt;&lt;p&gt;Podglajen, A., Hertzog, A., Plougonven, R., and Legras, B.: Lagrangian gravity wave spectra in the lower stratosphere of current (re)analyses, Atmos. Chem. Phys., 20, 9331&amp;#8211;9350, https://doi.org/10.5194/acp-20-9331-2020, 2020.&lt;/p&gt;