Stellar Proton Events and Exoplanetary Habitability

2020 ◽  
Author(s):  
Dimitra Atri
Keyword(s):  
Radiation Dose ◽  
Monte Carlo Model ◽  
Surface Radiation ◽  
Occurrence Rate ◽  
Atmospheric Depth ◽  
Rotating Stars ◽  
Episodic Events ◽  
Order Of Magnitude ◽  
Particle Spectra ◽  
Exoplanetary Atmospheres

<p>Superflares of energies up to 10<sup>38</sup> ergs have been studied from Kepler and Gaia observations, and estimates of their energy and frequency on different types of stars is improving rapidly. Flares with energies up to 10<sup>35</sup> ergs occur about once every 2000-3000 years on slow rotating stars like the Sun, but the occurrence rate is ∼ 100 times higher for younger, faster rotating stars of the same class. More than a dozen potentially habitable planets, like Proxima Centauri b and TRAPPIST-1 e, are in close-in configurations and their proximity to the host star makes them highly sensitive to stellar activity. Episodic events such as flares have the potential to cause severe damage to close-in planets, adversely impacting their habitability. Stellar Energetic Particles (SEPs) emanating from Stellar Proton Events (SPEs) cause atmospheric damage (erosion and photochemical changes), and produce secondary particles, which in turn results in enhanced radiation dosage on planetary surfaces. Taking particle spectra from 70 major solar events (observed between 1956 and 2012) as proxy, we use the GEANT4 Monte Carlo model to simulate SPE interactions with exoplanetary atmospheres. We have demonstrated that radiation dose varies significantly with charged particle spectra and an event of a given fluence can have a drastically different effect depending on the spectrum. Our results show that radiation dose can vary by about five orders of magnitude for a given fluence. In terms of shielding, we found that atmospheric depth is a major factor in determining radiation dose on the planetary surface. Radiation dose is reduced by three orders of magnitude corresponding to an increase in the atmospheric depth by an order of magnitude. We found that the planetary magnetic field is an important but a less significant factor compared to atmospheric depth. The dose is reduced by a factor of about thirty corresponding to an increase in the magnetospheric strength by an order of magnitude.</p>

scholarly journals Stellar Proton Event-induced surface radiation dose as a constraint on the habitability of terrestrial exoplanets

2019 ◽  
Author(s):  
Dimitra Atri
Keyword(s):  
Radiation Dose ◽  
Monte Carlo Model ◽  
Surface Radiation ◽  
Proton Event ◽  
Stellar Activity ◽  
Episodic Events ◽  
Nearby Stars ◽  
Particle Spectra ◽  
Exoplanetary Atmospheres ◽  
M Stars

Abstract The discovery of terrestrial exoplanets orbiting in habitable zones around nearby stars has been one of the significant developments in modern astronomy. More than a dozen such planets, like Proxima Centauri b and TRAPPIST-1 e, are in close-in configurations and their proximity to the host star makes them highly sensitive to stellar activity. Episodic events such as flares have the potential to cause severe damage to close-in planets, adversely impacting their habitability. Flares on fast rotating young M stars occur up to 100 times more frequently than on G-type stars which makes their planets even more susceptible to stellar activity. Stellar Energetic Particles (SEPs) emanating from Stellar Proton Events (SPEs) cause atmospheric damage (erosion and photochemical changes), and produce secondary particles, which in turn results in enhanced radiation dosage on planetary surfaces. We explore the role of SPEs and planetary factors in determining planetary surface radiation doses. These factors include SPE fluence and spectra, and planetary column density and magnetic field strength. Taking particle spectra from 70 major solar events (observed between 1956 and 2012) as proxy, we use the GEANT4 Monte Carlo model to simulate SPE interactions with exoplanetary atmospheres, and we compute surface radiation dose. We demonstrate that in addition to fluence, SPE spectrum is also a crucial factor in determining the surface radiation dose. We discuss the implications of these findings in constraining the habitability of terrestrial exoplanets.

scholarly journals Rossby Waves in Astrophysics

2021 ◽  
Vol 217 (1) ◽  
Author(s):  
T. V. Zaqarashvili ◽  
M. Albekioni ◽  
J. L. Ballester ◽  
Y. Bekki ◽  
L. Biancofiore ◽  
...  
Keyword(s):  
Large Scale ◽  
Rossby Waves ◽  
Magnetic Activity ◽  
Future Research ◽  
Rotating Stars ◽  
Spatial And Temporal Scales ◽  
Physical Role ◽  
Astrophysical Objects ◽  
Exoplanetary Atmospheres ◽  
Rapidly Rotating Stars

AbstractRossby waves are a pervasive feature of the large-scale motions of the Earth’s atmosphere and oceans. These waves (also known as planetary waves and r-modes) also play an important role in the large-scale dynamics of different astrophysical objects such as the solar atmosphere and interior, astrophysical discs, rapidly rotating stars, planetary and exoplanetary atmospheres. This paper provides a review of theoretical and observational aspects of Rossby waves on different spatial and temporal scales in various astrophysical settings. The physical role played by Rossby-type waves and associated instabilities is discussed in the context of solar and stellar magnetic activity, angular momentum transport in astrophysical discs, planet formation, and other astrophysical processes. Possible directions of future research in theoretical and observational aspects of astrophysical Rossby waves are outlined.

scholarly journals ESTIMATION OF ENTRANCE SURFACE RADIATION DOSE TO THYROID REGION IN COMPUTED TOMOGRAPHY BRAIN EXAMINATION

2019 ◽  
Vol 12 (1) ◽  
pp. 121
Author(s):  
Visakh T ◽  
Suresh Sukumar ◽  
Abhimanyu Pradhan
Keyword(s):  
Computed Tomography ◽  
Radiation Dose ◽  
Maximum Dose ◽  
Surface Radiation ◽  
Ct Scans ◽  
Surface Dose ◽  
Brain Scan ◽  
Convenience Sampling ◽  
Ct Brain ◽  
Brain Examination

Objective: The objective of this study was to estimate the entrance surface radiation dose to the thyroid region in a computed tomography (CT) brain scan.Methods: Unfors Multi-O-Meter equipment was used to measure the entrance surface at the thyroid region of adult patients ranging from 18 to 70 years of age. A total of 115 patients were included in the study based on convenience sampling. The Multi-O-Meter was kept at the thyroid region during the scan, and the values for entrance surface dose (ESD) were noted from its monitor after the scan was complete.Results: The obtained data were analyzed and violate normal distribution; therefore, the median and quartiles were computed. The overall median (Q1, Q2), ESD of the patients, was 1.335 (1.213, 1.529) mGy. The minimum and maximum dose values recorded were 1.015 mGy and 1.964 mGy, respectively.Conclusions: The result showed a significant amount of entrance surface radiation dose to the thyroid region while taking a brain scan. This data can be used for optimization of radiation protection while undergoing CT scans of brain to reduce exposure to thyroid region.

scholarly journals Monte-Carlo simulations of external dose contributions from the surrounding ground areas of residential homes in a typical Northern European suburban area after a radioactive fallout scenario

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Yvonne Hinrichsen ◽  
Robert Finck ◽  
Johan Martinsson ◽  
Christopher Rääf
Keyword(s):  
Monte Carlo ◽  
Radiation Dose ◽  
Negative Impact ◽  
Theoretical Calculations ◽  
Source Region ◽  
Monte Carlo Model ◽  
Observation Point ◽  
Suburban Area ◽  
Radiation Doses ◽  
Property A

Abstract The emissions of $$^{137}\hbox {Cs}$$ 137 Cs into the environment from the nuclear accidents in Chernobyl in 1986 and Fukushima in 2011 led to the need to decontaminate large areas to avert radiation doses to the population in the affected areas. To be able to perform cost-effective and sustainable remediation, knowledge is needed about how radiation doses can be minimized through optimized interventions such that the greatest possible reduction in radiation dose is obtained with the smallest possible negative impact on the area. Theoretical calculations have been performed to determine how radiation doses in single family houses in a typical Swedish residential suburb arise from a hypothetical $$^{137}\hbox {Cs}$$ 137 Cs deposition on the ground. The intention was to highlight how remediation of different parts of the surroundings affects the radiation dose to the residents in a particular property. A Monte Carlo model of the houses and the environment in a suburban area was set up to allow calculations of the dose contributions from different contaminated ground areas such as their own property, neighbouring properties, streets and surrounding recreational areas. Calculations were performed for eleven observation points inside different rooms of the house and one observation point in the garden outside the house, for four houses in the neighbourhood, and for two types of building construction material. The influence of the time spent in different rooms of the house and the contamination of areas surrounding the house was studied. The results show that in general the main dose contribution originates from their own property, but that a significant part (30–80%, depending on the observation point) can come from other areas, showing the importance of considering the surroundings in remediation actions. More detailed analysis of the results showed that the dose contribution from a source region is in general highly dependent on the position of windows in a brick house, whereas for a wooden house the distance to the source region is also of relevance.

scholarly journals 241Am and 137Сs in the Khoiniki district of Belarus: updated radiological assessment of the local existing exposure situation

2021 ◽  
Vol 14 (4) ◽  
pp. 17-30
Author(s):  
E. K. Nilova ◽  
V. N. Bortnovsky ◽  
S. A. Tagai ◽  
N. V. Dudareva ◽  
A. N. Nikitin
Keyword(s):  
Radiation Dose ◽  
Selective Extraction ◽  
Food Samples ◽  
Alpha Spectroscopy ◽  
Internal Exposure ◽  
Radiochemical Analysis ◽  
Residential Areas ◽  
Internal Radiation ◽  
Annual Dose ◽  
Order Of Magnitude

The results covered in this paper relate to the “Khoiniki” research sub-unit of a larger-scale sequence of studies focused on the local assessments of the present-day 241Am and 137Cs concentrations in the soils and locally produced foods, with the estimation of the public internal radiation doses in the residential areas of the Gomel region of the Republic of Belarus most closely adjacent to the ChNPP resettlement zone. The objective was to make a conservative estimate of a committed annual dose of internal exposure from 241Am and 137Сs received by the villagers of 96 farmsteads in 30 settlements of the private sector of Khoiniki countryside through both, inhalation and consumption of local foodstuffs. The results obtained in this study include an update of the existing contamination levels of 241Am and 137Сs present in the local soils and foods grown or produced in private backyards and households. 241Am in food samples was determined by alpha-spectroscopy radiochemical analysis with the use of selective extraction-chromatographic resins. Gamma-spectrometry techniques were used to measure 241Am in soil samples and 137Сs in soil and food samples. Based on our findings, the present-day deposition density of 241Am in the soils does not exceed 4 kBq/m2 , while the values of 137Cs contamination are by one to two orders of magnitude higher than that of 241Am and vary between 30 and 500 kBq/m2 . Generally, the values of activity concentration of 241Am detected in local soils are well within 10 Bq/kg in the majority of inspected villages, with the exception of three sites where higher levels of 241Am contamination is soils were detected ranging from 14 to 16 Bq/kg. The ambient dose rates in the countryside range from 0.05 to 0.38 μSv/hour, with the average of 0.15 μSv/hour. No cases of 137Сs contamination above the established reference levels of 80, 100 and 90 Bq/ kg have been found in the local food samples of, respectively, potatoes, vegetables (incl. roots and tubers) and grains. The content of 241Am in the staple foods produced in the area varies from single digits to tenths of mBq/ kg, which is less by three orders of magnitude than 137Сs activities concentrationd found in the same staples. Of the two pathways contributing to the local committed internal exposure from 241Am, the dominant one is through inhalation (0.006–0.038 mSv/year) prevailing over the consumption pathway of this same radioisotope by at least one order of magnitude. At the time of gardening and other household field works, the existing levels of 241Am contamination in soils are estimated to produce from 85 to 98% of the internal radiation dose received by individuals from inhaling the total of 241Am and 137Сs. The maximum committed annual doses of internal exposure from 137Сs are estimated to be above 1 mSv/year in 6 out of 30 villages engaged in our study. At the same time, the estimated internal radiation dose due to 241Am does not surpass 0.04 mSv/year. The 137Сs major contribution to the internal exposure of villages in the Khoiniki countryside is through food consumption. 

scholarly journals Sculpting the Sub-Saturn Occurrence Rate via Atmospheric Mass Loss

2022 ◽  
Vol 924 (1) ◽  
pp. 9
Author(s):  
Tim Hallatt ◽  
Eve J. Lee
Keyword(s):  
Mass Loss ◽  
Mass Function ◽  
Occurrence Rate ◽  
Rotating Stars ◽  
Core Mass ◽  
Orbital Periods ◽  
M Stars ◽  
Gas Accretion ◽  
Rapidly Rotating Stars ◽  
Atmospheric Mass

Abstract The sub-Saturn (∼4–8 R ⊕) occurrence rate rises with orbital period out to at least ∼300 days. In this work we adopt and test the hypothesis that the decrease in their occurrence toward the star is a result of atmospheric mass loss, which can transform sub-Saturns into sub-Neptunes (≲4 R ⊕) more efficiently at shorter periods. We show that under the mass-loss hypothesis, the sub-Saturn occurrence rate can be leveraged to infer their underlying core mass function, and, by extension, that of gas giants. We determine that lognormal core mass functions peaked near ∼10–20 M ⊕ are compatible with the sub-Saturn period distribution, the distribution of observationally inferred sub-Saturn cores, and gas-accretion theories. Our theory predicts that close-in sub-Saturns should be ∼50% less common and ∼30% more massive around rapidly rotating stars; this should be directly testable for stars younger than ≲500 Myr. We also predict that the sub-Jovian desert becomes less pronounced and opens up at smaller orbital periods around M stars compared to solar-type stars (∼0.7 days versus ∼3 days). We demonstrate that exceptionally low-density sub-Saturns, “super-puffs,” can survive intense hydrodynamic escape to the present day if they are born with even larger atmospheres than they currently harbor; in this picture, Kepler 223 d began with an envelope ∼1.5× the mass of its core and is currently losing its envelope at a rate of ∼2 × 10−3 M ⊕ Myr−1. If the predictions from our theory are confirmed by observations, the core mass function we predict can also serve to constrain core formation theories of gas-rich planets.

scholarly journals Evaluation of Ionizing Radiation in Five Private Radiology Centers in Khuzestan

2020 ◽  
Author(s):  
Behzad Fouladi Dehaghi ◽  
Jamileh Deris ◽  
Maryam Mosavi Qahfarokhi ◽  
Ameneh Golbaghi ◽  
Leila Nematpour
Keyword(s):  
Radiation Dose ◽  
Ionizing Radiation ◽  
Gamma Spectroscopy ◽  
Surface Radiation ◽  
Annual Dose ◽  
Waiting Room ◽  
X Ray ◽  
Medicine Research ◽  
Ionization Radiation ◽  
Diagnostic Radiography

Background: Nowadays ionizing radiation is widely used in medicine, research and industry. In medicine, ionizing radiation is used to diagnose diseases and in high doses to treat diseases such as cancer. Undoubtedly, most exposure to artificial sources is in the field of medical and diagnostic radiology. Therefore, practitioners in the field of diagnostic radiography and patients are exposed to ionizing radiation and its risks. On the other hand, despite the advantages and efficacy of diagnostic radiation in the medical field, overall less attention is paid to optimizing and controlling protection in medical radiation. Therefore, the aim of this study was to evaluate the background ionizing radiation in Ahwaz diagnostic radiography centers. Methods: Ionization radiation levels were measured in and out of each center using gamma spectroscopy (Radiation Alert Inspector-EXP 15109) at a, b, c, d and e radiographic centers within one meter above the Earth's surface. Radiation levels within each center were measured at four locations (outside of center, secretary desk, and patient waiting room and behind the radiology room) both in X-ray machine operating and non-operating condition. The obtained data were analyzed by SPSS software.  Results: The inside ionization radiation dose in a, b, c, d and e radiographic centers were 0.121, 0.119, 0.126, 0132 and 0.128 μSv/h respectively. The outside ionization radiation dose in a, b, c, d and e radiographic centers were 0.094, 0.092, 0.093, 0.112 and 0.101 μSv/h respectively. Equivalent annual dose within and outside selected radiology centers were lower than the threshold (1 mSv / year). Conclusion: The results show that the ionizing radiation dose of the X-ray equipment examined in the radiology centers of Ahwaz is lower than the global standard.

scholarly journals The Rotation of Low-Mass Pre-Main-Sequence Stars

2004 ◽  
Vol 215 ◽  
pp. 113-122 ◽  
Author(s):  
Robert D. Mathieu
Keyword(s):  
Angular Momentum ◽  
Main Sequence ◽  
Rotation Period ◽  
Rotating Stars ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Star Forming ◽  
Rotation Periods ◽  
Order Of Magnitude ◽  
Critical Velocities

Major photometric monitoring campaigns of star-forming regions in the past decade have provided rich rotation period distributions of pre-main-sequence stars. The rotation periods span more than an order of magnitude in period, with most falling between 1 and 10 days. Thus the broad rotation period distributions found in 100 Myr clusters are already established by an age of 1 Myr. The most rapidly rotating stars are within a factor of 2-3 of their critical velocities; if angular momentum is conserved as they evolve to the ZAMS, these stars may come to exceed their critical velocities. Extensive efforts have been made to find connections between stellar rotation and the presence of protostellar disks; at best only a weak correlation has been found in the largest samples. Magnetic disk-locking is a theoretically attractive mechanism for angular momentum evolution of young stars, but the links between theoretical predictions and observational evidence remain ambiguous. Detailed observational and theoretical studies of the magnetospheric environments will provide better insight into the processes of pre-main-sequence stellar angular momentum evolution.

scholarly journals Some novel features of post-500°C heating blue stimulated OSL emission of fired natural quartz

2017 ◽  
Vol 44 (1) ◽  
pp. 287-298
Author(s):  
Dileep K Koul ◽  
Anuj Soni ◽  
Debabrata Datta
Keyword(s):  
Radiation Dose ◽  
Dose Range ◽  
Optically Stimulated Luminescence ◽  
Dose Assessment ◽  
High Radiation ◽  
Dose Limit ◽  
Natural Quartz ◽  
Reliable Assessment ◽  
Order Of Magnitude ◽  
High Dynamic

Abstract In this study, some novel features of the post 500°C blue stimulated optically stimulated luminescence (OSL) of fired geological quartz are reported. Different observations (i) pulse annealing and (ii) impact of bleaching on high temperature TL glow peak suggested 510°C (heating rate of 2°C/s) TL peak trap to be responsible for the observed emission. The dosimetric properties of this emission were seen to make its applicability for dose assessment till kGy range. The signal was seen to be easily bleachable, reaching background value within 100 s with blue light at 125°C. The signal qualified all the tests (i) reproducibility, (ii) negligible recuperation and (iii) accuracy of dose recovery needed for reliable assessment of the radiation dose with modified Single aliquot regenerative (SAR) protocol. Considering the bleachability and high dynamic dose range of this signal, it has the potential to stretch the upper dose limit of dating by one order of magnitude than possible with conventional OSL, corresponding to 325°C TL trap. So, combining all the results, the signal reported here could be very useful for dosimetric applications involving measurement of high radiation dose, like dating.

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