Computation of Gamma Buildup Factors and Heavy Ions Penetrating Depths in Clay Composite Materials Using Phy-X/PSD, EXABCal and SRIM Codes

Most investigations of the gamma-shielding abilities of materials are often based on the Beer-Lambert law including recent studies on clay-polyethylene composites. The findings are usually silent on the secondary radiation effects that commonly occur due to photon buildup, known as Energy Absorption Buildup Factor (EABF) and Exposure Buildup Factor (EBF). In this work, the computation of EABF and EBF in the region of energy 0.015–15 MeV at different penetration depths or mean free paths up to 40 mfp—and simulation of 100 keV of Cs and Sr ion-penetration profiles of clay–polyethylene composites (A–G) containing 0–30 wt% low density polyethylene (LPDE)—was carried out. The buildup factors computation was performed using Phy-X/PSD and EXABCal codes, and the ion-penetrating profile was studied using a Monte Carlo simulation code called Stopping and Range of Ions in Matter (SRIM). The EABF and EBF values are functions of the photon energy and the penetration depth. In the region of intermediate energy, the EABF and EBF values are higher for each of the samples. For a given mfp, the peak value of either EBF or EABF of each sample increases with LDPE wt% in the clay matrix. The projected range of both Cs and Sr ions in the samples decreased with increasing sample bulk densities, with Cs having a higher projected range than Sr in all the samples. The Cs and Sr ions have the lowest respective projected ranges in sample A (of bulk density 2.03 g·cm−3; 0 wt% of LDPE), while the highest projected ranges were recorded in sample G (of bulk density 1.34 g·cm−3; with 30 wt% of LDPE), respectively. This study reaffirmed the suitability of clay composite for gamma-ray shielding applications; however, it may not yet be ready to be used as a backfill material to mitigate the migration of fission products present in radioactive nuclear wastes

Modeling and X-ray Analysis of Defect Nanoclusters Formation in B4C under Ion Irradiation

In the presented work, B4C was irradiated with xenon swift heavy ions at the energy of 167 MeV. The irradiation of the substrate was done at room temperature to a fluence of 3.83 × 1014 ion/cm2. The samples were then analyzed with the X-ray diffraction technique to study the structural modification, as it can probe the region of penetration of xenon atoms due to the low atomic number of the two elements involved in the material under study. The nano-cluster formation under ion irradiation was observed. Positron lifetime (PLT) calculations of the secondary point defects forming nanoclusters and introduced into the B4C substrate by hydrogen and helium implantation were also carried out with the Multigrid instead of the K-spAce (MIKA) simulation package. The X-ray diffraction results confirmed that the sample was B4C and it had a rhombohedral crystal structure. The X-ray diffraction indicated an increase in the lattice parameter due to the Swift heavy ion (SHI) irradiation. In B12-CCC, the difference between τ with the saturation of H or He in the defect is nearly 20 ps. Under the same conditions with B11C-CBC, there is approximately twice the value for the same deviation

COVID-19 vaccine acceptance and hesitancy in low- and middle-income countries

AbstractWidespread acceptance of COVID-19 vaccines is crucial for achieving sufficient immunization coverage to end the global pandemic, yet few studies have investigated COVID-19 vaccination attitudes in lower-income countries, where large-scale vaccination is just beginning. We analyze COVID-19 vaccine acceptance across 15 survey samples covering 10 low- and middle-income countries (LMICs) in Asia, Africa and South America, Russia (an upper-middle-income country) and the United States, including a total of 44,260 individuals. We find considerably higher willingness to take a COVID-19 vaccine in our LMIC samples (mean 80.3%; median 78%; range 30.1 percentage points) compared with the United States (mean 64.6%) and Russia (mean 30.4%). Vaccine acceptance in LMICs is primarily explained by an interest in personal protection against COVID-19, while concern about side effects is the most common reason for hesitancy. Health workers are the most trusted sources of guidance about COVID-19 vaccines. Evidence from this sample of LMICs suggests that prioritizing vaccine distribution to the Global South should yield high returns in advancing global immunization coverage. Vaccination campaigns should focus on translating the high levels of stated acceptance into actual uptake. Messages highlighting vaccine efficacy and safety, delivered by healthcare workers, could be effective for addressing any remaining hesitancy in the analyzed LMICs.</jats:p