http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Spectral Flux of the p-^7Li(C) Q-M Neutron Source Measured by Proton Recoil Telescope
J. Novak,P. Bem,M. Gotz,M. Honusek,E. Simeckova,M. Stefanik,U. Fischer,S. P. Simakov 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
The cyclotron-based fast neutron source at NPI produces mono-energetic neutron fields up to 35 MeV neutron energy using the p+^7Li(carbon backing) reactions. To be applied for activation cross-section measurements, not only the intensity of neutron peak, but also the contribution of low-energy continuum in the spectra must be well determined. Simulations of the spectral flux from present source at a position of irradiated samples were performed using CYRIC TOF-data validated in the present work against LA150h by calculations with the transport Monte Carlo code MCNPX. Simulated spectra were tested by absolute measurements using a proton-recoil telescope technique. The recoil-proton spectrometer consisted of a shielded scattering chamber with polyethylene and carbon radiators and the ΔE_1-ΔE_2-E telescope of silicon-surface detectors located to the neutron beam axis at 45˚ in the laboratory system. Si-detectors were handled by usual data acquisition system. Dead-time - and pulse-overlap losses of events were determined from the count rate of pulse generator registered during duty cycle of accelerator operation. The proton beam charge and data were taken in the list mode for later replay and analysis. The calculations for ^7Li(p,n) and ^(12)C(p,n) reactions reasonably reproduce CYRIC TOF neutron source spectra. The influence of neutron source set-up (proton beam dimensions, ^7Li-foil, carbon stopper, cooling medium, target support/chamber and the geometry-arrangement of irradiated sample) on the spectral flux is discussed in details.
The Measurement of Neutron Activation Cross Section of ^(59)Co Below 36 MeV
E. Simeckov,P. Bem,V. Burjan,M. Gotz,M. Honusek,V. Kroha,J. Novak,U. Fischer,S. P. Simakov,R. A. Forrest 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
An accurate knowledge of the cross section for neutron-induced reactions on ^(59)Co is of importance due to use of cobalt as a structural material in fission and fusion reactors, its applicability in neutron dosimetry and for testing theoretical models as well. The thin Co foils (0.25 mm thickness, 99.9% purity, Goodfellow product) were irradiated in the quasi-momoenergetic p-Li neutron field. For the production of the neutron fields, the proton beam from the NPI energy-variable cyclotron U120M at proton energies 19.8, 25.1, 27.6, 30.1, 32.7, 35.0, and 37.4 MeV and thin ^7Li target with carbon stopper were used. The reaction ^7Li(p,n) produces the high-energy quasi-monoenergetic neutrons with tail to lower energies. The flux density and neutron spectra were evaluated by MCNPX code using ^7Li(p,n) cross section measurement of other authors and including correction to the NPI target layout. The time profile of the neutron source strength during the irradiation was monitored by the proton beam current on the neutron-source target, recorded by a calibrated current-to-frequency converter on a PC. Au foils were used as additional monitors. The foil activity determination was performed by the nuclear spectrometry method employing two calibrated HPGe detectors of 23 and 50% efficiency and of FWHM (Full Width Half Maximum) 1.8 keV at 1.3 MeV for gamma-ray measurement. The reaction rates for ^(59)Co(n,p)^(59)Fe, ^(59)Co(n,α)^(56)Mn, ^(59)Co(n,2nα)^(54)Mn, ^(59)Co(n,3n)^(57)Co, ^(59)Co(n,2n)^(58m)Co, and ^(59)Co(n,2n)^(58g)Co were obtained. Integral activation cross sections were estimated. The preliminary results are discussed.
B. Jansky,Z. Turzik,E. Novak,M. Svadlenkova,M. Barta,L. A. Trykov,A. I. Blokhin 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
The leakage neutron and gamma spectra measurements have been done on benchmark spherical assembly-nickel sphere with diameter of 50 cm. The Cf-252 neutron sources with different emissions were placed into the centre of nickel sphere. The proton recoil method was used for neutron spectra measurement using stilbene crystals and hydrogen proportional counters. The neutron energy range of spectrometer was from 0.02 to 17 MeV. The gamma pulse shape discrimination method has been applied in stilbene measurements. The gamma energy range of spectrometer was from 0.1 to 10 MeV. The fine structure of gamma spectrum was measured by HPGe spectrometer. The experimental data were compared to results of transport calculations based on different evaluated nuclear data libraries (ENDF/B-VII.0, JENDL-3.3, JEFF-3.1.1, TENDL-2009). The continuous energy Monte Carlo transport calculation code MCNP-4C was employed for the calculations. Main observed differences between experiments and transport calculations are discussed.
POLARIMETRY OF DG TAU AT 350 μm
Krejny, M.,Matthews, T. G.,Novak, G.,Cho, J.,Li, H.,Shinnaga, H.,Vaillancourt, J. E. IOP Publishing 2009 The Astrophysical journal Vol.705 No.1
<P>We present the first 350 mu m polarization measurement for the disk of the T Tauri star (TTS) DG Tau. The data were obtained using the SHARP polarimeter at the Caltech Submillimeter Observatory. We measured normalized Stokes parameters q = -0.0086 +/- 0.0060 and u = -0.0012 +/- 0.0061, which gives a 2 sigma upper limit for the percent polarization of 1.7%. We obtain information about the polarization spectrum by comparing our 350 mu m measurement with an 850 mu m polarization detection previously published for this source. Comparing the two measurements in Stokes space ( not in percent polarization) shows that the two data points are not consistent, i.e., either the degree of polarization or the angle of polarization (or both) must change significantly as one moves from 850 mu m to 350 mu m. This conclusion concerning the polarization spectrum disagrees with the predictions of a recent model for TTS disk polarization. We show that this discrepancy can be explained by optical depth effects. Specifically, we demonstrate that if one were to add more mass to the model disk, one would expect to obtain a model polarization spectrum in which the polarization degree falls sharply with increasing frequency, consistent with the observations at the two wavelengths. We suggest that multiwavelength polarimetry of TTS disk emission may provide a promising method for probing the opacity of TTS disks.</P>
Study of a melt processable polymer precursor for carbon fiber
Samsuddin F. Mahmood,Benjamin L. Batchelor,Minhye Jung,Kyusoon Park,Walter E. Voit,Bruce M. Novak,Duck Yang 한국탄소학회 2019 Carbon Letters Vol.29 No.6
Carbon fibers (CF) are predominantly being manufactured from polyacrylonitrile (PAN) based precursors which require solution spinning utilizing health hazardous organic solvent. This also adds to the cost of production due to the investment for the solvent recovery. Study of melt processable precursors has long been sought as a solution for health and environmental problems associated with the use of hazardous solvent. No use of solvent for spinning will also reduce the cost of manufacturing. Our coworker Deng et al. reported the possibility of using acrylonitrile-co-1-vinylimidazole (AN/VIM) copolymer as melt processable CF precursor. Here we report a successful preparation of carbon fiber from the co-polymer. We successfully demonstrated the preparation of thinner precursor fibers and carbon fibers through our optimization study of melt spinning, annealing, stabilization and carbonization.
Study of a melt processable polymer precursor for carbon fiber
Mahmood Samsuddin F.,Batchelor Benjamin L.,정민혜,박규순,Voit Walter E.,Novak Bruce M.,Yang Duck 한국탄소학회 2019 Carbon Letters Vol.29 No.6
Carbon fibers (CF) are predominantly being manufactured from polyacrylonitrile (PAN) based precursors which require solution spinning utilizing health hazardous organic solvent. This also adds to the cost of production due to the investment for the solvent recovery. Study of melt processable precursors has long been sought as a solution for health and environmental problems associated with the use of hazardous solvent. No use of solvent for spinning will also reduce the cost of manufacturing. Our coworker Deng et al. reported the possibility of using acrylonitrile-co-1-vinylimidazole (AN/VIM) copolymer as melt processable CF precursor. Here we report a successful preparation of carbon fiber from the co-polymer. We successfully demonstrated the preparation of thinner precursor fibers and carbon fibers through our optimization study of melt spinning, annealing, stabilization and carbonization.
S. P. Simakov,U. Fischer,Pavel Bem,V. Burjan,M. Gotz,M. Honusek,V. Kroha,J. Novak,E. Simeckova,R. A. Forrest 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
To improve the status of the dosimetry reaction data above 20 MeV, the activation cross sections on Bi, Au, Co and Nb have been measured at the NPI/Rez cyclotron facility with a quasi-monoenergetic p-^7Li neutron source. The present work comprises the computational analysis of this experiment. It includes the Monte-Carlo simulation of the experimental set-up with the MCNPX code and relevant cross section data for proton and neutron induced reactions to predict the energy differential neutron flux in the irradiated foils. This approach has been validated against p-Li neutron spectra measured by different techniques. By making use of the modified unfolding code SAND-II, the dosimetry cross sections have been derived from the detected γ-ray activities. This has brought the new experimental results in the neutron energy domain between 18 and 35 MeV with estimated uncertainty at the level of 10%. They were used for validation of the activation (EAF, IEAF, IRDF) and the general purpose (ENDF) cross section files.