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실린더 금속판에 의해 뒤쪽산란된 감마선이 핵에너지 준위에 미치는 효과
정문택,최남길,천명기,Jeong, M.T.,Chol, N.G.,Cheoun, M.K. 한국자기학회 2007 韓國磁氣學會誌 Vol.17 No.2
본 연구에서는 고체 안에 둘러쌓인 감마선 원천핵 $^{133}Cs$를 금판(gold plate)으로 된 실린더 안에 놓았을 때 첫 여기상태인 81 keV 에너지 준위폭이 더 좁아짐을 볼 수 있었다. 이러한 결과는 에너지 준위의 수명이 연장된 것을 의미한다. 두께 0.5 mm, 길이 5 cm, 반경 1 mm의 실린더를 사용했을 때 4.2 K에서 에너지 준위폭은 6.1 %정도 좁아지는 결과를 얻었다. When the gamma-ray source, $^{133}Cs$, embedded in a solid is placed at the center of a gold cylinder, the width of 81 keV level is shown to become narrower. This result implies a prolongation of the lifetime of that energy level. With a 0.5-mm-thick, 5-cm-long, 2-mm-diameter platinum cylinder, we obtain a width narrower by 6.1 % at 4.2 K.
Asymmetry in the neutrino and anti-neutrino reactions in a nuclear medium
Cheoun, M.K.,Choi, K.S.,Kim, K.S.,Saito, K.,Kajino, T.,Tsushima, K.,Maruyama, T. North-Holland Pub. Co 2013 Physics letters: B Vol.723 No.4
We study the effect of the density-dependent axial and vector form factors on the electron-neutrino (ν<SUB>e</SUB>) and anti-neutrino (ν@?<SUB>e</SUB>) reactions for a nucleon in nuclear matter or in <SUP>12</SUP>C. The nucleon form factors in free space are presumed to be modified for a bound nucleon in a nuclear medium. We adopt the density-dependent form factors calculated by the quark-meson coupling (QMC) model, and apply them to the ν<SUB>e</SUB> and ν@?<SUB>e</SUB> induced reactions with the initial energy E=8-80 MeV. We find that the total ν<SUB>e</SUB> cross sections on <SUP>12</SUP>C as well as on a nucleon in nuclear matter are reduced by about 5% at the nuclear saturation density, ρ<SUB>0</SUB>. This reduction is caused by the modification of the nucleon structure in matter. Although the density effect for both cases is relatively small, it is comparable with the effect of Coulomb distortion on the outgoing lepton in the ν-reaction. In contrast, the density effect on the ν@?<SUB>e</SUB> reaction reduces the cross section significantly in both nuclear matter and <SUP>12</SUP>C cases, and the amount maximally becomes of about 35% around ρ<SUB>0</SUB>. Such large asymmetry in the ν<SUB>e</SUB> and ν@?<SUB>e</SUB> cross sections, which seems to be nearly independent of the target, is originated from the differences in the helicities of ν@?<SUB>e</SUB> and ν<SUB>e</SUB>. It is expected that the asymmetry influences the r-process and also the neutrino-process nucleosynthesis in core-collapse supernovae.
Astrophysically Important 26Si States Studied with the 28Si(4He,6He)26Si Reaction
Y. K. Kwon,이춘식,J. Y. Moon,J. H. Lee,J. Y. Kim,M. K. Cheoun,S. Kubono,H. Yamaguchi,J. J. He,A. Saito,Y. Wakabayashi,H. Fujikawa,G. Amadio,N. Iwasa,K. Inafuku,L. H. Khiem,M. Tanaka,Y. Fuchi,A. A. Chen,S 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2
The emission of a 1.809-MeV γ-ray from the first excited state of 26Mg, followed by β-decay of 26Al in its ground state (denoted as 26Alg.s.), has been identied by several gamma-ray telescopes. To resolve the controversy over the possible sources of the observational 1.809-MeV γ-rays, one needs accurate knowledge of the production rate of 26Alg.s.. The 25Al(p,γ)26Si reaction is one of the most important astrophysical reactions to be investigated, but its rate is uncertain due to the lack of level information on 26Si above the proton threshold (Qpγ = 5.518 MeV). Illiadis et al. suggested that the 25Al(p,γ)26Si reaction should be dominated by a 3+ unnatural parity state at Ex = 5970 keV. Recent studies proposed several states as candidates for the 3+ states. However, the spin-parity assignments for these states are still uncertain. In the present work, we measured the 28Si(4He,6He)26Si reaction at 120 MeV to confirm the unnatural parity states just above the proton threshold. The measurement was performed with the high-resolution particle analyzer at the Center for Nuclear Study, University of Tokyo. We observed a total of 22 excited states in 26Si. The 7018-keV level, which was only observed by Bardayan et al. with the 28Si(p; t)26Si reaction, was confirmed in our measurement. Among the candidates of unnatural parity states at Ex = 5678, 5916, and 5945 keV, the 5918-keV state was only observed within the error of the excitation energy. A new state at Ex = 6101 keV was also identified.
Estimating total fusion cross sections by using a coupled-channel method
Choi, K. S.,Cheoun, M. K.,Kim, K. S.,Kim, T. H.,So, W. Y. 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. No.
<P>We calculate the total fusion cross sections for the He-6 + Bi-209, Li-6 + Bi-209,Be-9 + Pb-208, Be-10 + Bi-209, and Li-11 + Pb-208 systems by using a coupled-channel (CC) method and compare the results with the experimental data. In the CC approach for the total fusion cross sections, we exploit a globally determined Wood-Saxon potential with Akyuz-Winther parameters and couplings of the ground state to the low-lying excited states in the projectile and the target nuclei. The total fusion cross sections obtained with the CC are compared with those obtained without the CC couplings. The latter approach is tantamount to a one-dimensional barrier penetration model. Finally, our approach is applied to understand new data for the Li-11+Pb-208 system. Possible ambiguities inherent in those approaches are discussed in detail for further applications to the fusion system of halo and/or neutron-rich nuclei.</P>
Lee, J. Y.,Alenkov, V.,Ali, L.,Beyer, J.,Bibi, R.,Boiko, R. S.,Boonin, K.,Buzanov, O.,Chanthima, N.,Cheoun, M. K.,Chernyak, D. M.,Choi, J.,Choi, S.,Danevich, F. A.,Djamal, M.,Drung, D.,Enss, C.,Fleisc IEEE 2016 IEEE transactions on nuclear science Vol.63 No.2
<P>A calcium molybdate (CaMoO4) crystal scintillator, with molybdenum enriched in Mo-100 and calcium depleted in Ca-48 ((CaMoO4)-Ca-40-Mo-100), was developed by the Advanced Molybdenum based Rare process Experiment (AMoRE) collaboration to search for a neutrinoless double beta (0 nu beta beta) decay of Mo-100. We are planning to use about 10 kg of (CaMoO4)-Ca-40-Mo-100 crystals as cryogenic bolometers for the first phase of the experiment (AMoRE-I) at the Yang Yang underground laboratory (Y2L) in Korea. This experiment calls for an extremely low level of radioactive contamination in detectors, particularly by thorium, uranium, and radium decay chains. We measured scintillation properties and radioactive contamination of CaMoO4 and (CaMoO4)-Ca-40-Mo-100 crystals at the Y2L. We also estimated the acceptable level of internal radioactive background using Monte Carlo simulation for the AMoRE-I.</P>
Maruyama, T.,Cheoun, M.K.,Kajino, T.,Mathews, G.J. North-Holland Pub. Co 2016 Physics letters: B Vol.757 No.-
<P>We study pion production by proton synchrotron radiation in the presence of a strong magnetic field when the Landau numbers of the initial and final protons are n(i, f) similar to 10(4)-10(5). We find in our relativistic field theory calculations that the pion decay width depends only on the field strength parameter which previously was only conjectured based upon semi-classical arguments. Moreover, we also find new results that the decay width satisfies a robust scaling relation, and that the polar angular distribution of emitted pion momenta is very narrow and can be easily obtained. This scaling implies that one can infer the decay width in more realistic magnetic fields of 10(15) G, where n(i, f) similar to 10(12)-10(13), from the results for n(i, f) similar to 10(4)-10(5). The resultant pion intensity and angular distributions for realistic magnetic field strengths are presented and their physical implications discussed. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).</P>