Analysis of the Dosimetry Cross Sections Measurements up to 35 MeV with a ^7Li(p,xn) Quasi-Monoenergetic Neutron Source

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.

Numerical Modeling of in-Band Pumped Ho-Doped Silica Fiber Lasers

Wang, Jiachen,Yeom, Dong-il,Simakov, Nikita,Hemming, Alexander,Carter, Adrian,Lee, Sang Bae,Lee, Kwanil IEEE 2018 Journal of Lightwave Technology Vol.36 No.24

<P>A theoretical model to describe in-band pumped holmium doped silica fiber lasers is presented. The model is established based upon theory and parameters obtained from published research works. Both core-pumped system and cladding-pumped system are simulated with the model. The simulation results agree well with most experimental results, and for the cases in which the simulation results show discrepancy with the experimental results the disagreement can be reasonably explained. Through numerical analysis it is found that besides common negative factors such as non-radiative decay, fiber loss, and non-optimized resonator configuration, energy transfer upconversion plays a deleterious role in the performance of in-band pumped holmium doped silica fiber lasers. In particular, inhomogeneous upconversion associated with ion clustering is found to cause significant degradation of slope efficiencies of lasers, a fact that is useful to understand the unsolved problem regarding the lower-than-expected slope efficiencies observed in previous studies of in-band pumped holmium doped fiber lasers.</P>

Atomic displacement cross-sections for neutron irradiation of materials from Be to Bi calculated using the arc-dpa model

A. Yu. Konobeyev,U. Fischer,S.P. Simakov 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.1

Displacement cross-sections for an advanced assessment of radiation damage rates were obtained for anumber of materials using the arc-dpa model at neutron incident energies from 10-5 eV to 10 GeV. Evaluated data files, CEM03 and ECIS codes, and an approximate approach were applied for the calculationof recoil energy distributions in neutron induced reactions. Three sets of displacement cross-sections based on the use of low-energy data from JEFF-3.3, ENDF/BVIII. 0, and JENDL-4.0u were prepared. Files contain also cross-sections calculated using the standard NRTmodel. Special efforts were made to estimate the uncertainty of obtained displacement cross-sections

On Low and Medium Energy Deuteron-Induced Reactions on ^(63,65)Cu

E. Simeckov,P. Bem,M. Honusek,L. Zavorka,U. Fischer,S. P. Simakov,R. A. Forrest,M. Avrigeanu,V. Avrigeanu,F. L. Roman 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23

The activation cross sections of (d,p), (d,2n), (d,3n), and (d,2p) reactions on ^(63,65)Cu were measured in the energy range from 4 to 20 MeV using the stacked-foils technique. Errors of present experimental cross section data are composed of the scale factor (∼5%, due to energy and beam current uncertainty) and datum uncertainty of the foil thickness (∼2%) and a mean statistical error in the determination of specific activities (∼3%). Following a previous extended analysis of elastic-scattering, breakup and direct-reaction of deuterons on light nuclei, for energies from 3 to 60 MeV, the pre-equilibrium and statistical emissions are considered in the same energy range. Finally, all available deuteron-induced reaction cross sections for ^63,65Cu have been involved within a simultaneous analysis of the deuteron elastic-scattering and reaction data.

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.