• Journal of The Korean Astronomical Society
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• v.43 no.5
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• pp.161-168
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• 2010

Magnetars are neutron stars possessing a magnetic field of about $10^{14}-10^{15}$ G at the surface. Thermodynamic properties of neutron star matter, approximated by pure neutron matter, are considered at finite temperature in strong magnetic fields up to $10^{18}$ G which could be relevant for the inner regions of magnetars. In the model with the Skyrme effective interaction, it is shown that a thermodynamically stable branch of solutions for the spin polarization parameter corresponds to the case when the majority of neutron spins are oriented opposite to the direction of the magnetic field (i.e. negative spin polarization). Moreover, starting from some threshold density, the self-consistent equations have also two other branches of solutions, corresponding to positive spin polarization. The influence of finite temperatures on spin polarization remains moderate in the Skyrme model up to temperatures relevant for protoneutron stars. In particular, the scenario with the metastable state characterized by positive spin polarization, considered at zero temperature in Phys. Rev. C 80, 065801 (2009), is preserved at finite temperatures as well. It is shown that, above certain density, the entropy for various branches of spin polarization in neutron matter with the Skyrme interaction in a strong magnetic field shows the unusual behavior, being larger than that of the nonpolarized state. By providing the corresponding low-temperature analysis, we prove that this unexpected behavior should be related to the dependence of the entropy of a spin polarized state on the effective masses of neutrons with spin up and spin down, and to a certain constraint on them which is violated in the respective density range.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.64.1-64.1
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• 2021

Accretion flows around black holes and neutron stars emit high energy radiation with varying spectral and timing properties. Observed timing variations, both short and long-term, point to the existence of a mechanism, dictated by the flow dynamics, and not by the stellar surface or magnetic fields, that is common in both. Spectral energy distributions of multiple sources indicate that the Comptonization process, the dominant mechanism for changing states in X-ray, takes place inside the flow that has similar physical properties in both the objects. In a series of observational and numerical studies, we enquire about the following: 1. Is there a steady state configuration for accreting matter around black holes that can explain spectral and timing properties? 2. Could a similar formalism explain spectral and timing properties of accretion around neutron stars? 3. Could there be a generalized flow configuration for accreting matter around such compact objects? Furthermore, we show that a unified spectral model can be constructed based on the generalized flow configuration, common to black holes and neutron stars.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.569-572
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• 2015

We first deduce a uniform formula forthe Fermi energy of degenerate and relativistic electrons in the weak-magnetic field approximation. Then we obtain an expression of the special solution for the electron Fermi energy through this formula, and express the electron Fermi energy as a function of electron fraction and matter density. Our method is universally suitable for relativistic electron- matter regions in neutron stars in the weak-magnetic field approximation.

• Journal of Environmental Impact Assessment
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• v.15 no.6
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• pp.425-433
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• 2006

Instrumental neutron activation analysis was used to measure the concentrations of 27 elements associated with respirable particulate matter (PM10) that were collected from the Third and Fourth Industrial Complex Area of Daejeon City. The distribution patterns of elements were clearly distinguished with their concentrations varying across more than four orders of magnitude. The mean for Al were recorded to be the highest value of 1,527 $ng/m^3$, while that for In showed the lowest value of 0.1 $ng/m^3$. If compared in terms of enrichment factors, it was found that certain elements (e.g., As, Br, Cl, Cr, I, In, Sb, Se, and Zn) are enriched in PM10 samples of the study site. The results of factor analysis indicated six factors with statistical significance, which may exert dominant controls on regulating the elemental concentration levels in the study area.

• Nuclear Engineering and Technology
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• v.36 no.5
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• pp.450-459
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• 2004

For the evaluation of emission sources by air sampling, airborne particulate matter for fine (<2.5 ${\mu}m2$ EAD : $PM_{2.5}$) and coarse partical (2.5-10 ${\mu}m2$ EAD : $PM_{2.5-10}$ fractions were collected using a Gent stacked filter unit low volume sampler and two types of polycarbonate filters. Air samples were collected twice monthly at two regions in and around Daejeon city in the Republic of Korea from January to December 2002. Monthly mass concentration of $PM_{2.5}$ and $PM_{2.5-10}$ were measured and the concentrations of 10 marker elements (Al, Sc, Ti ; Na, Cl ; As, V. Sb, Br, Se) were determined by an instrumental neutron activation analysis. Analytical quality control was corried out using certified reference materials. Enrichment factors were also calculated from the monitoring data to classify the anthropogenic and crustal origins.

• Nuclear Engineering and Technology
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• v.55 no.8
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• pp.2984-2996
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• 2023

A 100 kW thermal power pool-type light water reactor and Pu(Be) as a fast neutron source were used to determine the appropriate carrier for irradiating boron-containing samples with neutron beams. The tested materials (carriers) were subjected to neutron beams in the reactor's tangential channel. The geometrical arrangement of experimental facilities relative to the neutron beam trajectory, as well as the effect of sample thickness on the count rate, were investigated. The majority of the detectable charged particles emitted by the neutron beam's interaction with tested materials and the detector's detecting layer are protons (recoiled hydrogen) and particles generated in nuclear reactions (protons and alpha particles), respectively. Stopping and Range of Ions in Matter (SRIM) software was used to do theoretical calculations for the range of expected released particles in various materials, including human tissue. The results of measurement and calculation are in good agreement. According to experiments and theoretical calculations, the number of protons emitted by tissue-like materials may commit a dose comparable to that of boron capture reactions. Furthermore, the range of protons is significantly larger than that of alpha particles, which most probably changes dose distribution in healthy cells surrounding the tumor, which is undesirable in the BNCT approach.

• Journal of Korean Society for Atmospheric Environment
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• v.16 no.5
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• pp.453-467
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• 2000

The aim of this research is to collect and characterize fine particles (FPM:$\leq$2.5${\mu}{\textrm}{m}$) and coarse particles (CPM: 2.5~10${\mu}{\textrm}{m}$) using a low volume air sampler provided by the IAEA, at urban (Taejon) and rural area(Wonju) for a period of about two years(April 1996 to May 1998) and to promote a use of nuclear analytical techniques for air pollution studies. For the collection of airborne particulate matter (PM(sub)10), the Gent stacked filter unit sampler and polycarbonate membrane filters were employed. The concentration of trace elements in collected APM samples were determined byu instrumental Neutron Activation Analysis. For validation of the analytical data, internal quality control were implemented by using both the comparison of the analytical results of standard reference materials(NIST SRM 1648) and interlaboratory comparison for proficiency test (NAT-3). The standard uncertainty was less than 15% and Z-score of two samples were within $\pm$1. The monitoring of (PM(sub)10) mass concentration and elemental concentrations were carried out weekly. The average mass concentration of (PM(sub)10) in urban and rural areas were 59.2$\pm$36.5$\mu\textrm{g}$/㎥ and 41.4$\pm$23.7$\mu\textrm{g}$/㎥, respectively. To investigate the emission source, the enrichment factors were calculated for the fine and coarse particle fractions at two sites, respectively and these values were classified for anthropogenic and soil origin elements.

• Analytical Science and Technology
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• v.15 no.5
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• pp.433-438
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• 2002

Trace elements in two air filters (V-50, P-50) artificially loaded with urban dust provided from IAEA were determined non-destructively using instrumental neutron activation analysis. Standard reference material (Urban Particulate Matter, SRM 1648) of National Institute of Standard and Technology was used for analytical quality control. About 20 elements in both of loaded filter samples were determined. To evaluate inter-laboratory comparison and proficiency test, analytical data were statistically treated with the results which collected from 49 laboratories, 40 countries participated in this study using neutron activation analysis, particle induced X-ray emission, inductively coupled plasma mass spectroscopy, etc,. From the results of statistical treatment, Z-scores are within ${\pm}2$. Furthermore, accuracy and precision of obtained analytical values are passed according to the criteria of the proficiency test. Consequently, it was proved that analytical quality for air dust samples being performed has been controlled properly.

• Journal of The Korean Astronomical Society
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• v.25 no.1
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• pp.47-64
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• 1992

Cores of globular clusters are an ideal place for close encounters between stars. The outcome of tidal capture can be stellar mergers, close binaries between normal stars (W UMa type), cataclysmic variables composed of white dwarf and normal star pairs, or low-mass X-ray binaries consisting of a neutron star and a normal star pairs. Stellar mergers can be the origin of blue stragglers in dense globular clusters although they are hard to observe. Low mass X-ray binaries would eventually become binary pulsars with short pulse periods after the neutron stars accrete sufficient amount of matter from the companion. However, large number of recently discovered, isolated millisecond pulsars (as opposed to binary pulsars) in globular clusters may imply that they do not have to gain angular speeds during the X-ray binary phase. We propose that these isolated millisecond pulsars may have formed through the disruptive encounters, which lead to the formation of accretion disk without Roche lobe filling companion, between a neutron star and a main-sequence star. Based on recently developed multicomponent models for the dynamical evolution of globular clusters, we compute the expected numbers of various systems formed by tidal capture as a function of time.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.55.2-55.2
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• 2018

Neutron stars (NS) are rapidly spinning compact objects. Their rotation energy is released by particles, electromagnetic waves, and even gravitational waves. The source of the energy is of course the rotation, so by studying the rotational properties of neutron stars, we can gain some insights into matter under extreme conditions. In particular, it is known that the braking index n is sensitive to the moment of inertia and/or NS winds. The neutron star PSR B0540-69 exhibits interesting timing behavior; previous measurements of the braking index for this pulsar may suggest a change in time. In order to see if the change is real, We investigate the timing properties of B0540-69 using recent ~1000-days Swift satellite data.