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Thanks to a quirk of quantum theory, subatomic particles can emit light as they travel through a seemingly empty vacuum.

The speed of light varies in water, ice and other media. In some cases, an electron or other charged subatomic particle passing through a medium travels more quickly than light moving through the same medium. Such a speedy particle creates a cone of compressed waves as it zips through its surroundings. These waves emit light, called Cherenkov radiation, that has a bluish tinge.

Alexander Macleod, Adam Noble and Dino Jaroszynski at the University of Strathclyde in Glasgow, UK, find that this phenomenon can also occur in a vacuum. According to quantum theory, a vacuum is actually filled with pairs of ephemeral particles that spontaneously come into being before cancelling each other out again. The team’s calculations show that these particles can momentarily reduce the speed of light around them. As a result, a particle travelling at near the speed of light might emit Cherenkov radiation.

Under certain conditions, Cherenkov radiation in a vacuum should be detectable. If so, observations of the radiation could verify some interactions between light and matter predicted by quantum theory.

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LaTeX or Word? For physicists and mathematicians, the choice is obvious. But for scientists in other fields the merits of LaTeX have largely gone unnoticed.

The open-source software system — used to create and precisely format scientific manuscripts — is more akin to coding than writing. Since its development in 1985, LaTeX has become popular in disciplines such as mathematics, physics and computer science.

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‘Time to crop’ for 137Cs in the surface soil and its long-term effects to population based on model assessment

Van Thang Nguyen, Ngoc Ba Vu, Nguyen Phong Thu Huynh, Cong Hao Le



Long-term behavior of artificial radionuclides in surface soils is very important to assess the radiological effects to population. Among artificial radionuclides, 137Cs is most important because of its long half-life and its biggest abundance in the environment. In this study, the fate of 137Cs in the surface soil layers was assessed by the Canadian Centre for Environmental Modelling and Chemistry (CEMC) soil model which is well known as a simple assessment of the relative potential for degrading reaction, evaporation, and leaching of a pesticide applied to a surface soil. The total decrease rate of 137Cs activity concentration in the surface soil (Te1/2) was 10.4 years found in the top 0–5 cm of the soil layer. The activity decrease of 137Cs and the corresponding Te1/2 values under the different depths of surface soil layer were investigated. The influences of soil organic material, soil water content and soil porosity to the losing rate of 137Cs were considerable. Long-term effects of 137Cs to population were assessed through activity concentrations of 137Cs in any parts of the food chain. Soil-to-plant transfer factor (TF), transfer coefficients Fm (transfer to animal milk) and Ff (transfer to animal meat) collected from many literatures were used for activity calculation. The effective doses to population due to ingestion of edible parts of plants, milk and meat was evaluated. The incorporation of four terms: radiological doses, soil-to-plant transfer factors (TF), plant-to-animal coefficients (Fm and Ff) and the total decrease rate of 137Cs is the new approach. The new concept ‘Time to crop’ (TC) based on the effective doses to population was explored and first used for agricultural proposals in the topsoils of the 137Cs exclusion zone. TC was calculated for many scenarios of radioactive exposures, many type of plants, animals and plant groups. TC values were found various in order fruits < leafy vegetables < tubers < cereals < grasses. The highest TC was found for grasses group as a result of the long-term accumulation of radionuclides in animals.


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 Validation of gamma scanning method for optimizing NaI(Tl) detector model in Monte Carlo simulation

Huynh Dinh Chuong, Nguyen Quoc Hung, Nguyen Thi My Le,  Vo Hoang Nguyen, Tran Thien Thanh


The aim of this study is the validation of gamma scanning method for optimizing NaI(Tl) detector model in Monte Carlo simulation. The experimental procedure involved: scanning on front and lateral surfaces of the detector with collimated low-energy photon beam; calibrating the efficiency with energies between 31-1408 keV for point sources at distances of 0 cm and 30 cm from source to the detector. The Monte Carlo code used for the simulations was MCNP6. The diameter and the length of crystal were determined according to the measured results of gamma scanning with a collimated 241Am radioactive source. The distance from window to crystal was estimated using transmission measurement recorded on a second detector. The density of reflector was adjusted to obtain the match between measured and simulated values of efficiency ratio of 81 and 31 keV from a 133Ba radioactive source. The optimized model was applied in Monte Carlo simulations to determine the efficiency and energy spectrum response function of NaI(Tl) detector for point source measurements in two configurations. Good agreement was obtained between measured and simulated results.


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 Natural radioactivity and radon emanation coefficient in the soil of Ninh Son region, Vietnam

Huynh Nguyen Phong Thu,  Nguyen VanThang, Truong Thi Hong Loan, Nguyen Van Dong,  Le Cong Hao


The natural radioactivity (238U, 226Ra, 232Th and 40K) and radon emanation coefficient for 57 soil samples belonging to alluvial, red, forest surface, slip-debris, metamorphic and sandy soil of the Ninh Son region in Ninh Thuan province have been determined. The soil gas radon was measured by in-situ with RAD7 radon monitor coupled with a soil gas probe while activity concentrations of 238U, 226Ra, 232Th, and 40K were measured by an HPGe gamma-ray spectrometry system. The 226Ra/238U disequilibrium occurred in the soil samples and a great majority of the 226Ra/238U values lie above 1. Average activity concentrations of 226Ra, 232Th, and 40K are significantly higher than the worldwide average concentrations in soils published by UNSCEAR, 2008. The gamma dose rate ranged from 55 ± 2 to 248 ± 7 nGy h−1 with an average of 130 ± 4 nGy h−1 which is greater than the world value. Strong positive correlations were recorded between 238U and 226Ra, 232Th and 226Ra, 232Th and 238U, and 226Ra and 222Rn. The results of weathering and alteration processes were proposed to be dominated reasons for the 226Ra/238U disequilibrium occurred in the soil samples. Most of the radon in soil gas samples are considered “normal risk” or low radon index. The mean values of the emanation coefficient for alluvial, red, forest surface, slip-debris, metamorphic and sandy soil were found to be 0.51 ± 0.03, 0.40 ± 0.02, 0.36 ± 0.02, 0.30 ± 0.02, 0.26 ± 0.02 and 0.15 ± 0.01, respectively. Radon emanation was found to be an inverse function of grain size for grain sizes larger than 0.1 mm in diameter and independent on the radium content of the soil sample.


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Development of apparatus for mean-lifetime measurement of cosmic-ray muons using plastic scintillation detectors and FLASH-ADC/FPGA-based readout electronics

Vo Hong Hai, Nguyen Tri Toan Phuc

Science & Technology Development Journal, 26(1):1-7

Introduction: This paper presents the development and results of an apparatus for measuring the mean lifetime of cosmic-ray muons.

Methods: The apparatus uses three plastic scintillation detectors and a readout electronics system based on Flash Analog Digital Converter (Flash-ADC) and Embedded Field Programmable Gate Array (FPGA). The readout system has 8-bit resolution and a 125 Msample/sec sampling rate. The system's trigger and data collection are controlled through a computer interface based on LabVIEWTM. The readout electronics are calibrated with an accuracy of 8 nsec/TDC channel.

Results: Over 6000 events were recorded during the measurements performed at ground level using aluminum as the muon stopping material, and the muon decay time spectrum was obtained and fit with a combination of two exponential components and a constant background. The mean lifetimes of negative and positive muons were determined.

Conclusion: Our results indicate that the mean lifetimes of negative and positive muons in aluminum are 0.70 ± 0.24 µsec and 2.05 ± 0.16 µsec, respectively.

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