Journal articles: 'Neutron emission calculations'

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Šíla, Ondřej, Daniel Klír, Karel Řezáč, Balzhima Cikhardtova, and Jakub Cikhardt. "MCNP calculations of neutron emission anisotropy caused by the GIT-12 hardware." Nukleonika 60, no. 2 (June 1, 2015): 323–26. http://dx.doi.org/10.1515/nuka-2015-0064.

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Abstract The MCNP6 and MCNPX calculations for the GIT-12 device in Tomsk were performed to determine the influence of the gas-puff hardware on the neutron emission anisotropy and the neutron scattering rate. A monoenergetic 2.45 MeV neutron source and F1 and F6 tallies were declared in the simulation input. A comparison between MCNP results and the measured data was made. Differences between MCNPX and MCNP6 output data were investigated. In the experiment, two nTOF scintillation detectors with the Bicron BC-408 scintillator were used to measure the neutron waveform. Four bubble BD-PND detectors were used to estimate the amount of neutrons in different places around the neutron source.

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Okumura, Shin, Toshihiko Kawano, and Satoshi Chiba. "Prompt and Delayed Neutron Emissions and Fission Product Yield Calculations with Hauser-Feshbach Statistical Decay Theory and Summation Calculation Method." EPJ Web of Conferences 211 (2019): 04005. http://dx.doi.org/10.1051/epjconf/201921104005.

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We demonstrate the neutron emission and fission product yield calculations using the Hauser–Feshbach Fission Fragment Decay (HF3D) model and β decay. The HF3D model calculates the statistical decay of more than 500 primary fission fragment pairs formed by the neutron induced fission of 235U. In order to calculate the prompt neutron and photon emissions, the primary fission fragment distributions, i.e. mass, charge, excitation energy, spin and parity are deterministically generated and numerically integrated for all fission fragments. The calculated prompt neutron multiplicities, independent fission product yield are fully consistent each other. We combine the β-decay and the summation calculations with the HF3D model calculation to obtain the cumulative fission product yield, decay heat and delayed neutron yield. The calculated fission observables are compared with available experimental data.

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Rosswog, S., and M. Liebendörfer. "High-resolution calculations of merging neutron stars - II. Neutrino emission." Monthly Notices of the Royal Astronomical Society 342, no. 3 (July 2003): 673–89. http://dx.doi.org/10.1046/j.1365-8711.2003.06579.x.

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Vorobyev, Alexander, Oleg Shcherbakov, Alexei Gagarski, Gennadi’ski Val, and Tatiana’mina Kuz. "Experimental estimation of the “scission” neutron yield in the thermal neutron induced fission of 233U and 235U." EPJ Web of Conferences 239 (2020): 05008. http://dx.doi.org/10.1051/epjconf/202023905008.

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The analysis of angular and energy distributions of prompt neutrons from the thermal neutron induced fission of 233U and 235U measured recently in the WWR-M research reactor (Gatchina, Russia) have been performed. The yield of “scission” neutrons has been estimated by comparing the measured distributions with calculations within the model of emission of neutrons from completely accelerated fragments. Besides taking into account “scission” neutrons, for the best description of measured angular and energy distributions of fission neutrons, the calculation should be performed under the assumption that neutrons with a higher (7-9%) probability are emitted along the fission axis in the center-of-mass system of fission fragments.

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Perret, G., D. Rochman, A. Vasiliev, and H. Ferroukhi. "NEUTRON EMISSION MEASUREMENTS OF PWR SPENT FUEL SEGMENTS AND PRELIMINARY VALIDATION OF DEPLETION CALCULATIONS." EPJ Web of Conferences 247 (2021): 10004. http://dx.doi.org/10.1051/epjconf/202124710004.

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Assessing neutron emission of LWR spent fuel is necessary for the back-end of the fuel cycle, such as the dimensioning of transport and storage casks of spent fuel. Although core and depletion codes can calculate the isotopic composition of the discharged fuel and therefore infer its neutron source, accurate measured neutron emission values remain rare mainly because of the difficulty to prepare, handle and characterize spent fuel. Measured neutron emission values are, however, extremely relevant to code validation, as neutrons emitted by LWR spent fuel mainly originates from spontaneous fissions of minor actinides (e.g., 242Cm, 244Cm and 252Cf) that are produced only after a large number of neutron captures in the reactor core. This paper reports on neutron emission measurements of selected LWR-PROTEUS spent fuel samples and their comparisons with a core and depletion calculation chains based on CASMO-5, SIMULATE-3 and the SNF codes. The measured LWR-PROTEUS samples are comprised of 11 samples irradiated in a Swiss PWR. The samples are UO2 or MOX and have discharge burn-ups ranging from 20 to 120 GWd/t. We measured the 40-cm long samples in a hot-cell of the Paul Scherrer Institut using a measurement station made of polyethylene and a BF3 detector. We repeated the measurements several times and in different conditions to ensure the accuracy and reproducibility of the results. We derived ratios of neutron rates emitted by the different samples and absolute neutron emission rates by comparison with a reference 252Cf source, which we re-calibrated for this exercise. The experimental uncertainty (1σ) on the absolute neutron emission varies from 3% to 4%. We compared a subset of the measured values to the calculation predictions and showed an agreement within less than 7% for all but one sample.

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Wilson, James R. "SN 1987a: Calculations Versus Observations." International Astronomical Union Colloquium 108 (1988): 348–53. http://dx.doi.org/10.1017/s0252921100094094.

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In this report the result of old calculations (Mayle 1985; Woosley, Wilson, Mayle 1986; Mayle, Wilson, Schramm 1987) of collapse driven explosions and new calculations of the kelvin-Helmholtz proto-neutron star cooling will be compared with the neutrino observations of supernova 1987a. The calculations are performed by a modern version of the computer model of Bowers and Wilson 1982. (See Mayle 1985 for more recent improvements).First we give the results of the old calculations. In the collapse, bounce and cooling of the central iron core of a massive star, about 0.1% of the binding energy of the eventual neutron star is emitted in a short deleptonization burst as the bounce shock passes through the photosphere; 5% is emitted in the total deleptonization process; and 95% is released as thermal emission in all neutrino species. In a survey of a wide range of stellar masses, stars in the range 20 to 30 Mθ are found to have the most energetic antineutrino spectra . In calculations where black holes were formed (Woosley, Wilson, Mayle 1986 and Wilson 1971) very little neutrino emission was found associated with black hole formation. The neutrinos associated with BH formation also have low energies. The time history of the neutrino pulse is sensitive to the explosion mechanism. If the mechanism is a prompt exiting through the star of the bounce shock wave, the pulse has a high peak as the shock wave passes near the photosphere. It falls rapidly for the next first few tenths of a second and then declines slowly over several seconds to effectively zero. If no prompt explosion occurs then the shock becomes an accretion shock and matter continues to fall onto the proto-neutron star keeping up the luminosity. After the late time mechanism ejects the envelope the luminosity drops several fold to the luminosity associated with the bare proto-neutron star. During the accretion phase the energy rises to about 15 mev.

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Soheyli, Saeed, and Marzieh Varasteh Khanlari. "Effect of the energy spectrum and angular momentum of pre-scission neutrons on the prediction of fission fragment angular anisotropy by the models." International Journal of Modern Physics E 25, no. 04 (April 2016): 1650031. http://dx.doi.org/10.1142/s0218301316500312.

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Effects of the various neutron emission energy spectra, as well as the influence of the angular momentum of pre-scission neutrons on theoretical predictions of fission fragment angular anisotropies for several heavy-ion induced fission systems are considered. Although theoretical calculations of angular anisotropy are very sensitive to neutron emission correction, the effects of the different values of kinetic energy of emitted neutrons derived from the various neutron emission energy spectra before reaching to the saddle point on the prediction of fission fragment angular distribution by the model are not significant and can be neglected, since these effects on angular anisotropies of fission fragments for a wide range of fissility parameters and excitation energies of compound nuclei are not more than 10%. Furthermore, the theoretical prediction of fission fragment angular anisotropy is not sensitive to the angular momentum of emitted neutrons.

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TEL, E., İ. DEMİRKOL, A. ARASOĞLU, and B. ŞARER. "PRE-EQUILIBRIUM EMISSION IN DIFFERENTIAL CROSS-SECTION CALCULATIONS AND ANALYSIS OF EXPERIMENTAL DATA FOR 232Th." Modern Physics Letters A 19, no. 21 (July 10, 2004): 1597–614. http://dx.doi.org/10.1142/s0217732304014136.

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In this study, neutron-emission spectra produced by (n,xn) reactions on nuclei 232 Th have been calculated. Angle-integrated cross-sections in neutron induced reactions on targets 232 Th have been calculated at the bombarding energies from 2 MeV to 18 MeV. We have investigated multiple pre-equilibrium matrix element constant from internal transition for 232 Th (n,xn) neutron emission spectra. In the calculations, the geometry dependent hybrid model and the cascade exciton model including the effects of pre-equilibrium have been used. Pre-equilibrium direct effects have been examined by using full exciton model. In addition, we have described how multiple pre-equilibrium emissions can be included in the Feshbach–Kerman–Koonin (FKK) fully quantum-mechanical theory. By analyzing (n,xn) reaction on 232 Th , with the incident energy from 2 MeV to 18 MeV, the importance of multiple pre-equilibrium emission can be seen clearly. All calculated results have been compared with experimental data. The obtained results have been discussed and compared with the available experimental data and found agreement with each other.

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Arasoğlu, Ali, and Ömer Faruk Özdemir. "Neutron Cross Section and Emission Spectra Calculations of Na Nucleus." Journal of Fusion Energy 33, no. 6 (July 20, 2014): 731–35. http://dx.doi.org/10.1007/s10894-014-9742-1.

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Soheyli, Saeed, Morteza Khalil Khalili, and Ghazaaleh Ashrafi. "Pre-saddle and pre-scission neutron emission rates in heavy-ion induced fission of 16O +208Pb and 16O +209Bi systems." International Journal of Modern Physics E 28, no. 03 (March 2019): 1950013. http://dx.doi.org/10.1142/s0218301319500137.

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Whereas there is a slight information on the pre-saddle neutron emission rate and neutron multiplicity, as well as it is impossible to separate the pre-saddle and saddle to scission neutron contributions experimentally, the theoretical studies of pre-saddle neutron emission rate and neutron multiplicity are of great importance. In the present work, the calculations of pre-saddle neutron multiplicity are performed using the analysis of fission fragment angular anisotropy data for [Formula: see text] and [Formula: see text] reaction systems. The obtained results show that the pre-saddle neutron multiplicity decreases by increasing the initial excitation energy and it has found to be characterized by a nonlinear behavior. Through the analysis of pre-saddle neutron multiplicity and pre-saddle transition time by means of the neutron clock method, the pre-saddle neutron emission rate is calculated for the first time. The findings of this study show that the pre-scission neutron emission rate is lower than the pre-saddle neutron emission rate.

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GRIDNEV, K. A., V. N. TARASOV, D. V. TARASOV, D. K. GRIDNEV, V. V. PILIPENKO, and W. GREINER. "THEORETICAL PREDICTION OF EXTREMELY NEUTRON RICH Zr AND Pb." International Journal of Modern Physics E 19, no. 03 (March 2010): 449–57. http://dx.doi.org/10.1142/s0218301310014868.

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The properties of even–even Zr and Pb isotopes in the ground state are studied up to the neutron drip-lines on the basis of the Hartree–Fock method with Skyrme forces allowing for deformation (DHF). The DHF calculations with Ska forces predict the existence of stability peninsula (or island) around 152 Zr . On the example of Zr isotopes it is shown that adding neutrons to an already unstable nucleus with neutron excess can restore the stability. It is demonstrated that extremely neutron-rich Pb isotopes for 222≤A≤230 have abnormally large deformation parameters of proton and neutron density distributions. The existence of 266–288 Pb stable against one-neutron emission is also predicted.

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Čufar, Aljaž, Paola Batistoni, Sean Conroy, Zamir Ghani, Igor Lengar, Alberto Milocco, Lee Packer, Mario Pillon, Sergey Popovichev, and Luka Snoj. "Calculations to support JET neutron yield calibration: Modelling of neutron emission from a compact DT neutron generator." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 847 (March 2017): 199–204. http://dx.doi.org/10.1016/j.nima.2016.12.009.

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GRIDNEV, K. A., D. K. GRIDNEV, V. G. KARTAVENKO, V. E. MITROSHIN, V. N. TARASOV, D. V. TARASOV, and W. GREINER. "ON STABILITY OF THE NEUTRON-RICH OXYGEN ISOTOPES." International Journal of Modern Physics E 15, no. 03 (April 2006): 673–83. http://dx.doi.org/10.1142/s0218301306004053.

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Stability with respect to neutron emission is studied for highly neutron-excessive Oxygen isotopes in the framework of Hartree-Fock approach with Skyrme forces Sly4 and Ska. Our calculations show increase of stability around 40 O .

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Tudora, Anabella. "Prompt neutron and gamma-ray emission calculations for 232Th(n,f)." Nuclear Physics A 916 (October 2013): 79–101. http://dx.doi.org/10.1016/j.nuclphysa.2013.07.011.

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Meyer, Bradley S., W. Michael Howard, Grant J. Mathews, Koji Takahashi, Peter Möller, and George A. Leander. "Beta-delayed fission and neutron emission calculations for the actinide cosmochronometers." Physical Review C 39, no. 5 (May 1, 1989): 1876–82. http://dx.doi.org/10.1103/physrevc.39.1876.

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Nativi, L., M. Bulla, S. Rosswog, C. Lundman, G. Kowal, D. Gizzi, G. P. Lamb, and A. Perego. "Can jets make the radioactively powered emission from neutron star mergers bluer?" Monthly Notices of the Royal Astronomical Society 500, no. 2 (October 28, 2020): 1772–83. http://dx.doi.org/10.1093/mnras/staa3337.

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ABSTRACT Neutron star mergers eject neutron-rich matter in which heavy elements are synthesized. The decay of these freshly synthesized elements powers electromagnetic transients (‘macronovae’ or ‘kilonovae’) whose luminosity and colour strongly depend on their nuclear composition. If the ejecta are very neutron-rich (electron fraction Ye < 0.25), they contain fair amounts of lanthanides and actinides that have large opacities and therefore efficiently trap the radiation inside the ejecta so that the emission peaks in the red part of the spectrum. Even small amounts of this high-opacity material can obscure emission from lower lying material and therefore act as a ‘lanthanide curtain’. Here, we investigate how a relativistic jet that punches through the ejecta can potentially push away a significant fraction of the high opacity material before the macronova begins to shine. We use the results of detailed neutrino-driven wind studies as initial conditions and explore with 3D special relativistic hydrodynamic simulations how jets are propagating through these winds. Subsequently, we perform Monte Carlo radiative transfer calculations to explore the resulting macronova emission. We find that the hole punched by the jet makes the macronova brighter and bluer for on-axis observers during the first few days of emission, and that more powerful jets have larger impacts on the macronova.

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Krasil'nikov, V. N., A. P. Tyutyunnik, I. V. Baklanova, A. N. Enyashin, I. F. Berger, and V. G. Zubkov. "Synthesis, crystal structure and optical properties of Me(OH)(HCOO)2 (Me = Al, Ga)." CrystEngComm 20, no. 19 (2018): 2741–48. http://dx.doi.org/10.1039/c8ce00309b.

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Aluminium and gallium hydroxide diformates have been synthesized. Both compounds exhibit similar monoclinic lattice, according to the X-ray, neutron diffraction and IR spectroscopy data. Their samples possess a bright light-blue emission under UV excitation. The origin of intrinsic emission is elucidated by means of DFT calculations.

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Bisnovatyi-Kogan, G. S. "Numerical simulations in astrophysics:Supernovae explosions, magnetorotational model and neutrino emission." Discrete Dynamics in Nature and Society 3, no. 4 (1999): 267–80. http://dx.doi.org/10.1155/s1026022699000291.

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Theories of stellar evolution and stellar explosion are based on results of numerical simulations and even qualitative results are not available to get analytically. Supernovae are the last stage in the evolution of massive stars, following the onset of instability, collapse and formation of a neutron star. Formation of a neutron star is accompanied by a huge amount of energy, approximately 20% of the rest mass energy of the star, but almost all this energy is released in the form of weakly interacting and hardly registrated neutrino. About 0.1% of the released neutrino energy would be enough for producing a supernovae explosion, but even transformation of such a small part of the neutrino energy into the kinetic energy of matter meets serious problems. Two variants are investigated for obtaining explosion. The first one is based on development of convective instability, and more effective heating of the outer layers by a neutrino flux.The second model is based on transformation of a rotational energy of a rapidly rotating neutron star with its envelope into the energy of explosion due to action of a magnetic field as a transformation mechanism. Calculations in this model in 1- and 2-dimensions give a stable value of transformation of the rotational energy into the energy of explosion on the level of few percents. This occurrance to be enough for explanation of the energy release in supernova explosion. The last model gives a direct demonstration of nonlinear interaction between hydrodynamical and hydromagnetic systems. At first a field is amplified by differential rotation, then this enhanced field leads to transformation of the rotational energy into the energy of explosion.

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Sahan, M., E. Tel, H. Sahan, A. Kara, A. Aydin, A. Kaplan, I. H. Sarpun, B. Demir, S. Akca, and E. Yildiz. "Calculations of Double-Differential Neutron Emission Cross Sections for 9Be Target Nucleus at 14.2 MeV Neutron Energy." Journal of Fusion Energy 34, no. 3 (December 19, 2014): 493–99. http://dx.doi.org/10.1007/s10894-014-9823-1.

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Watanabe, Yukinobu, Hiroki Sadamatsu, Shouhei Araki, Keita Nakano, Shoichiro Kawase, Tadahiro Kin, Yosuke Iwamoto, et al. "Study of the Li(d, xn) reaction for the development of accelerator-based neutron sources." EPJ Web of Conferences 239 (2020): 20012. http://dx.doi.org/10.1051/epjconf/202023920012.

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Double-differential neutron production cross sections (DDXs) for deuteron-induced reactions on Li at 200 MeV were measured for emission angles ranging from 0◦ to 25◦ in steps of 5◦ by means of a time of flight (TOF) method with EJ301 liquid organic scintillators at the Research Center for Nuclear Physics (RCNP), Osaka University. The measured DDXs were compared to theoretical model calculations with the DEURACS and PHITS codes and TENDL-2017 nuclear data. It was found that the DEURACS calculation is in better agreement with the measured DDXs than the PHITS calculation, while TENDL-2017 fails to reproduce both the spectral shape and magnitude of the measured DDXs for all angles.

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Egidy, T. von, F. J. Hartmann, S. Schmid, W. Schmid, K. Gulda, J. Jastrzebski, W. Kurcewicz, et al. "Nuclear Physics with Antiprotons." Zeitschrift für Naturforschung A 50, no. 11 (November 1, 1995): 1077–82. http://dx.doi.org/10.1515/zna-1995-1115.

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Abstract Information on the neutron distribution in the nuclear periphery was obtained by the annihilation of stopped antiprotons and the yield of residual nuclei. The last atomic transitions of the antiproton before annihilation gives complementary results. Properties of very hot nuclei (up to 1 GeV) after annihilation of stopped antiprotons were studied by neutron emission and fission. Absolute prob abilities of fission induced by stopped and fast antiprotons were determined. The experimental data are compared with elaborate calculations taking into account the annihilation process, the fast cascade and pre-equilibrium emission, thermalisation, particle evaporation and fission.

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Sahan, H., M. Sahan, and E. Tel. "Calculations of Double-Differential Neutron and Proton Emission Cross Sections on 19F at 14.2-MeV Incident Neutron Energy." Physics of Atomic Nuclei 81, no. 6 (November 2018): 703–13. http://dx.doi.org/10.1134/s1063778819010149.

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Melatos, A. "Neutrinos from Pulsar Environments." Highlights of Astronomy 13 (2005): 18–23. http://dx.doi.org/10.1017/s1539299600014970.

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AbstractRecent calculations of the neutrino fluxes and spectra from pulsar magnetospheres and wind nebulae are reviewed. The neutrinos, produced in pp and pγ collisions via pion decays, are a signature of TeV ions accelerated electrostatically in the magnetosphere, in the wind termination shock (Fermi), or in the wind neutral sheet (wave surfing and/or reconnection). The fluxes and spectra are related to the energy and density of the accelerated ion beam and the densities of the target species, thereby constraining ion-loaded pulsar wind models originally developed to explain the variable wisps in pulsar-driven supernova remnants. The neutrino signal may be detectable by km2 telescopes (e.g. IceCube) and is correlated with TeV γ-ray emission. Related sources are also reviewed, such as early-phase post-supernova pulsar winds, pulsar-driven γ-ray-burst afterglows, and accreting neutron stars. The possibility of long baseline oscillation experiments, to search for fine splitting of neutrino mass eigenstates and non-radiative neutrino decays, is noted.

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Shibata, S. "Modes of Energy Loss from Isolated Magnetized Neutron Star." Symposium - International Astronomical Union 125 (1987): 450. http://dx.doi.org/10.1017/s0074180900161121.

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Pulsar may be regarded as a discharge tube by electron-positron pair creation. On this viewpoint we carry out two numerical calculations. The obtained magnetic field is consistent with the flow. We find that pulsars emit their rotational energy through three modes simultaneously. The three modes are (1)relativistic acceleration and following gamma-ray emission in the closed current circuit in the magnetosphere, (2)wind of the electron-positron pair plasma, and (3)dipole radiation.

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Singh, N. L., and S. Mukherjee. "Effects of level density in the cross sections of (α, xn), (α, pxn), (α, 2pxn) and (α, αxn) reactions in 197Au, 181Ta, natIn and 93Nb and pre-equilibrium analysis." Canadian Journal of Physics 87, no. 9 (September 2009): 1037–46. http://dx.doi.org/10.1139/p09-067.

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Excitation functions are measured for α-particle-induced reactions on 197Au, 181Ta, natIn, and 93Nb in the energy region 18 to 60 MeV using the activation method and γ-ray spectrometry. The experimental results are compared with semiclassical model codes, STAPRE, ALICE-91, and COMPLET. These models take into account compound nuclei as well as pre-equilibrium emissions. The angular momentum removal effects have also been included in the COMPLET code. The Monte Carlo simulation code PACE4 is also employed for the calculations of equilibrium cross sections. In the case of neutron emission channels, both the model codes give fairly good agreement. The COMPLET code on the other hand, explains the α-particle emission channels in a more convincing manner.

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Konobeyev, A. Yu, U. Fischer, P. E. Pereslavtsev, and S. P. Simakov. "New evaluation of general purpose neutron data for stable W-isotopes up to 200 MeV." EPJ Web of Conferences 239 (2020): 11002. http://dx.doi.org/10.1051/epjconf/202023911002.

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In the frame of the Power Plant Physics and Technology of EUROfusion, new evaluations of general purpose neutron cross-section data were performed for the 180,182,183,184,186W isotopes covering the neutron energy up to 200 MeV. A special version of the TALYS nuclear model code implementing the geometry dependent hybrid model supplied with models for the non-equilibrium cluster emission was applied for calculations of the nuclide production and the energy distribution of the emitted particles. The parameters of the GDH model were properly estimated using measured data for individual tungsten isotopes. The neutron cross-sections were evaluated making use of available experimental data, systematics including estimated A-dependence of components of gas production cross-sections, and covariance information produced as part of the evaluation process. The BEKED code package, developed at KIT, was applied for calculations of co-variances using a dedicated Monte Carlo method. The evaluated data were processed into standard ENDF data format using the TEFAL code and the FOX module of the BEKED system. The evaluated data files were checked for errors and inconsistencies, processed with the NJOY code into ACE data format, and benchmarked against available integral experiments with MCNP neutron transport calculations.

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Chiba, Go, and Tadashi Narabayashi. "Uncertainty quantification of total delayed neutron yields and time-dependent delayed neutron emission rates in frame of summation calculations." Annals of Nuclear Energy 85 (November 2015): 846–55. http://dx.doi.org/10.1016/j.anucene.2015.07.001.

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Tanaka, Masaomi, Daiji Kato, Gediminas Gaigalas, and Kyohei Kawaguchi. "Systematic opacity calculations for kilonovae." Monthly Notices of the Royal Astronomical Society 496, no. 2 (June 5, 2020): 1369–92. http://dx.doi.org/10.1093/mnras/staa1576.

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ABSTRACT Coalescence of neutron stars (NSs) gives rise to kilonova, thermal emission powered by radioactive decays of freshly synthesized r-process nuclei. Although observational properties are largely affected by bound–bound opacities of r-process elements, available atomic data have been limited. In this paper, we study element-to-element variation of the opacities in the ejecta of NS mergers by performing systematic atomic structure calculations of r-process elements for the first time. We show that the distributions of energy levels tend to be higher as electron occupation increases for each electron shell due to the larger energy spacing caused by larger effects of spin–orbit and electron–electron interactions. As a result, elements with a fewer number of electrons in the outermost shells tend to give larger contributions to the bound–bound opacities. This implies that Fe is not representative for the opacities of light r-process elements. The average opacities for the mixture of r-process elements are found to be κ ∼ 20–30 cm2 g−1 for the electron fraction of Ye ≤ 0.20, κ ∼ 3–5 cm2 g−1 for Ye = 0.25–0.35, and κ ∼ 1 cm2 g−1 for Ye = 0.40 at $T = 5000\!-\!10\, 000$ K, and they steeply decrease at lower temperature. We show that, even with the same abundance or Ye, the opacity in the ejecta changes with time by one order of magnitude from 1 to 10 d after the merger. Our radiative transfer simulations with the new opacity data confirm that ejecta with a high electron fraction (Ye ≳ 0.25, with no lanthanide) are needed to explain the early, blue emission in GW170817/AT2017gfo while lanthanide-rich ejecta (with a mass fraction of lanthanides ∼5 × 10−3) reproduce the long-lasting near-infrared emission.

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Zhang, Jianming, Rahma Tabti, Charles Gale, and Kevin Haglin. "Another Look at "Soft" Lepton Pair Production in Nucleon-Nucleon Bremsstrahlung." International Journal of Modern Physics E 06, no. 03 (September 1997): 475–96. http://dx.doi.org/10.1142/s0218301397000263.

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We compare different formalisms for the calculation of lepton pair emission in hadron-hadron collisions and discuss the consequences of the approximations inherent to each of them. Using a Lorentz-covariant and gauge-invariant formalism proposed by Lichard, we calculate lepton pair emission via bremsstrahlung in proton-proton and neutron-proton reactions at energies between 1 and 5 GeV to leading order in the virtual photon four-momentum. These new results suggest that some previous bremsstrahlung calculations based on varieties of the soft-photon approximation might have somewhat overestimated the DLS low-mass dilepton cross sections. We find that the respective intensities of dilepton production through pp and np bremsstrahlung are energy-dependent and become comparable at E kin ≳ 2 GeV. We also calculate the polar angle anisotropy of the lepton spectrum.

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TARASOV, V. N., D. V. TARASOV, K. A. GRIDNEV, D. K. GRIDNEV, V. G. KARTAVENKO, and W. GREINER. "PROPERTIES OF Fe, Ni AND Zn ISOTOPES NEAR THE DRIP-LINES." International Journal of Modern Physics E 17, no. 07 (August 2008): 1273–91. http://dx.doi.org/10.1142/s021830130801043x.

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The position of the neutron and proton drip-lines as well as properties of the isotopes Fe , Ni and Zn with neutron excess and neutron deficit are studied within the Hartree–Fock approach with the Skyrme interaction (Ska, SkM*, Sly4). The pairing is taken into account on the basis of the BCS approach with the pairing constant G = (19.5/A)[1 ± 0.51(N-Z)/A]. Our calculations predict that for Ni isotopes around N = 62 there appears a sudden increase of the deformation parameter up to β = 0.4. The zone with such big deformation, where Ni isotopes are stable against one neutron emission stretches up to N = 78. The magic numbers effects for the isotopes 48 Ni , 56 Ni , 78 Ni , 110 Ni are discussed. The universality of the reasons standing behind the enhancement of stability of the isotopes 40 O and 110 Ni which are beyond the drip-line is demonstrated. Calculated values of the two-neutron separation energy, and proton and neutron root mean square radii for the chain of Ni isotopes show a good agreement with existing Hartree–Fock–Bogoliubov calculations of these values.

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Foligno, Daniela, Pierre Leconte, Olivier Serot, Olivier Litaize, and Abdelhazize Chebboubi. "Summation calculation of delayed neutron yields for 235U, 238U and 239Pu, based on various fission yield and neutron emission probability databases." EPJ Web of Conferences 193 (2018): 03004. http://dx.doi.org/10.1051/epjconf/201819303004.

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Summation calculations have been performed in order to compare the quality of several nuclear data libraries. The objective was to obtain the average delayed neutron yield, as well as the average delayed-neutron half-life for different fissioning systems (235U, 238U and 239Pu) at different energies (thermal and fast) by using microscopic data. Each quantity is presented with a first evaluation of the uncertainty, computed under the assumption that the variables are all independent of each other.

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Villafañe, Roberto Mendez, Marco Aurélio de Sousa Lacerda, Xandra Campo Blanco, Francisco González Sánchez, and Héctor René Vega-Carrillo. "ESTIMATION OF THE ANISOTROPY EMISSION OF LPN/CIEMAT NEUTRON SOURCES: EFFECT OF HEAVY CAPSULE HOLDERS." Radiation Protection Dosimetry 186, no. 4 (April 23, 2019): 452–61. http://dx.doi.org/10.1093/rpd/ncz050.

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Abstract In order to estimate the anisotropy emission of 241Am-Be and 252Cf neutron sources from the Spanish Neutron Standards Laboratory (LPN/CIEMAT) detailed models of sources capsules and capsule holders were designed with the MCNPX code. Simulations of the sources inside the capsules without the capsule holders were done to validate the MC model by comparison with experimental results provided by other authors. After that, the capsule holders were incorporated to the simulation. In general, a good agreement has been found between measurements and our calculations. Results show the additional encapsulations have significant influence on anisotropy factors, energy spectra and dose rates.

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Sperduti, A., I. Klimek, S. Conroy, M. Cecconello, M. Gorelenkova, and A. Snicker. "Validation of neutron emission and neutron energy spectrum calculations on a Mega Ampere Spherical Tokamak with directional relativistic spectrum simulator." Plasma Physics and Controlled Fusion 63, no. 1 (December 5, 2020): 015015. http://dx.doi.org/10.1088/1361-6587/abca7d.

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34

Dimitriou, Paraskevi, Iris Dillmann, Balraj Singh, Vladimir Piksaikin, Jose-Luis Tain, Krzysztof Rykaczewski, Alejandro Algora, et al. "A new reference database for beta-delayed neutrons." EPJ Web of Conferences 239 (2020): 04001. http://dx.doi.org/10.1051/epjconf/202023904001.

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A new database containing all available experimental and evaluated β-delayed neutron data is presented in this paper. The database is the product of an international effort coordinated by the International Atomic Energy Agency. It comprises a microscopic section including all available experimental data on beta-decay half-lives, β-delayed neutron emission probabilities and spectra, as well as new systematics and global theoretical calculations for comparison. The beta-delayed neutron data for individual precursors have been benchmarked against available data on macroscopic properties such as total delayed-neutron yields and spectra, delayed-neutron decay curves and time-dependent group parameters using the summation method. All available measured macroscopic data have also been compiled in the macroscopic section of the database. The dedicated database is available online on the IAEA server (URL:http://www-nds.iaea.org/beta-delayed-neutron/database.html).

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Sahan, Muhittin, Halide Sahan, Eyyup Tel, and Ahmet Bulbul. "Calculations of neutron-induced alpha emission double-differential cross section of Flourine at 14.2 MeV." EPJ Web of Conferences 154 (2017): 01004. http://dx.doi.org/10.1051/epjconf/201715401004.

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Singh, B. P., H. D. Bhardwaj, and R. Prasad. "A study of pre-equilibrium emission in α-induced reactions on 121,123Sb." Canadian Journal of Physics 69, no. 11 (November 1, 1991): 1376–82. http://dx.doi.org/10.1139/p91-205.

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Excitation functions for the 121Sb (α, n)+ 123Sb(α, 3n),,21Sb(α, 2n)+ 123Sb(α, 4n), 121Sb(α, 4n), 121Sb(α, 3np), and 123Sb(α, n) reactions are measured in the energy range 30–60 MeV using the stacked foil technique. In the cases of the 121Sb(α, n)+ 123Sb(α, 3n) and 121Sb(α, 2n)+ 123Sb(α, 4n) reaction pairs, the excitation functions for individual reactions were deduced using theoretical calculations. Excitation functions are also calculated theoretically using the compound-nucleus model with and without the inclusion of a pre-equilibrium emission. As expected, inclusion of a pre-equilibrium contribution based on the exciton model along with compound-nucleus calculations using the Hauser–Feshbach formalism reproduces well the measured excitation functions. Analysis of the data indicates a preference for a first chance neutron emission over charged-particle emission, and interesting trends in the energy and mass-number dependence of the pre-equilibrium fraction are observed.

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Galanopoulos, S., R. Vlastou, P. Demetriou, M. Kokkoris, C. T. Papadopoulos, G. Perdikakis, and M. Serris. "Statistical model calculations of 72,73Ge(n,p) and 72,74Ge(n,α) reactions on natural Ge." HNPS Proceedings 15 (January 1, 2020): 104. http://dx.doi.org/10.12681/hnps.2626.

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Systematic experimental and theoretical investigations of the 72,73Ge(n,p)72,73 Ga and 72,74Ge(n,α)69,71Znm reaction cross sections are presented in the energy range from thresh- old to about 17 MeV neutron energy. The above reaction cross sections were measured from 8.8 to 11.4 MeV by using the activation method, relative to the 27Al(n,α)24Na refer- ence reaction. The quasi-monoenergetic neutron beams were produced via the 2H(d,n)3He reaction at the 5 MV VdG Tandem T11/25 accelerator of NCSR “Demokritos”. Statisti- cal model calculations using the code EMPIRE-II (version 2.19) taking into consideration pre-equilibrium emission were performed on the data measured in this work as well as on data reported in literature.

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Ghirlanda, G., O. S. Salafia, Z. Paragi, M. Giroletti, J. Yang, B. Marcote, J. Blanchard, et al. "Compact radio emission indicates a structured jet was produced by a binary neutron star merger." Science 363, no. 6430 (February 21, 2019): 968–71. http://dx.doi.org/10.1126/science.aau8815.

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The binary neutron star merger event GW170817 was detected through both electromagnetic radiation and gravitational waves. Its afterglow emission may have been produced by either a narrow relativistic jet or an isotropic outflow. High-spatial-resolution measurements of the source size and displacement can discriminate between these scenarios. We present very-long-baseline interferometry observations, performed 207.4 days after the merger by using a global network of 32 radio telescopes. The apparent source size is constrained to be smaller than 2.5 milli–arc seconds at the 90% confidence level. This excludes the isotropic outflow scenario, which would have produced a larger apparent size, indicating that GW170817 produced a structured relativistic jet. Our rate calculations show that at least 10% of neutron star mergers produce such a jet.

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Tudora, A., F. J. Hambsch, and S. Oberstedt. "Prompt fission neutron emission calculations and description of sub-barrier fission cross section resonances for 234U()." Nuclear Physics A 917 (November 2013): 43–70. http://dx.doi.org/10.1016/j.nuclphysa.2013.09.002.

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40

Nättilä, J., and P. Pihajoki. "Radiation from rapidly rotating oblate neutron stars." Astronomy & Astrophysics 615 (July 2018): A50. http://dx.doi.org/10.1051/0004-6361/201630261.

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A theoretical framework for emission originating from rapidly rotating oblate compact objects is described in detail. Using a Hamilton-Jacobi formalism, we show that special relativistic rotational effects such as aberration of angles, Doppler boosting, and time dilatation naturally emerge from the general relativistic treatment of rotating compact objects. We use the Butterworth–Ipser metric expanded up to the second order in rotation and hence include effects of light bending, frame-dragging, and quadrupole deviations on our geodesic calculations. We also give detailed descriptions of the numerical algorithms used and provide an open-source implementation of the numerical framework called BENDER. As an application, we study spectral line profiles (i.e., smearing kernels) from rapidly rotating oblate neutron stars. We find that in this metric description, the second-order quadrupole effects are not strong enough to produce narrow observable features in the spectral energy distribution for almost any physically realistic parameter combination, and hence, actually detecting them is unlikely. The full width at tenth-maximum and full width at half-maximum of the rotation smearing kernels are also reported for all viewing angles. These can then be used to quantitatively estimate the effects of rotational smearing on the observed spectra. We also calculate accurate pulse profiles and observer skymaps of emission from hot spots on rapidly rotating accreting millisecond pulsars. These allow us to quantify the strength of the pulse fractions one expects to observe from typical fast-spinning millisecond pulsars.

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Arras, Phil, and Nevin N. Weinberg. "Urca reactions during neutron star inspiral." Monthly Notices of the Royal Astronomical Society 486, no. 1 (March 28, 2019): 1424–36. http://dx.doi.org/10.1093/mnras/stz880.

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Abstract We study the impact of Urca reactions driven by tidally induced fluid motion during binary neutron star inspiral. Fluid compression is computed for low radial order oscillation modes through an adiabatic, time-dependent solution for the mode amplitudes. Optically thin neutrino emission and heating rates are then computed from this adiabatic fluid motion. Calculations use direct and modified Urca reactions operating in a $M=1.4\, \mathrm{ M}_\odot$ neutron star, which is constructed using the Skyrme Rs equation of state. We find that the energy pumped into low-order oscillation modes is not efficiently thermalized even by direct Urca reactions, with core temperatures reaching only T ≃ 108 K during the inspiral. Although this is an order of magnitude larger than the heating due to shear viscosity considered by previous studies, it reinforces the result that the stars are quite cold at merger. Upon excitation of the lowest order g mode, the chemical potential imbalance reaches $\beta \gtrsim 1\, \rm MeV$ at orbital frequencies $\nu _{\rm orb} \gtrsim 200\, \rm Hz$, implying significant charged-current optical depths and Fermi-blocking. To assess the importance of neutrino degeneracy effects, the neutrino transfer equation is solved in the static approximation for the three-dimensional density distribution, and the reaction rates are then computed including Fermi-blocking. We find that the heating rate is suppressed by a factor of a ∼2 for $\nu _{\rm orb} \gtrsim 200\, \rm Hz$. The spectrum of emitted νe and $\bar{\nu }_e$, including radiation transfer effects, is presented for a range of orbital separations.

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Poutanen, Juri. "Accurate analytic formula for light bending in Schwarzschild metric." Astronomy & Astrophysics 640 (August 2020): A24. http://dx.doi.org/10.1051/0004-6361/202037471.

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We propose new analytic formulae describing light bending in the Schwarzschild metric. For an emission radii above the photon orbit at the 1.5 Schwarzschild radius, the formulae have an accuracy of better than 0.2% for the bending angle and 3% for the lensing factor for any trajectories that turn around a compact object by less than about 160°. In principle, they can be applied to any emission point above the horizon of the black hole. The proposed approximation can be useful for problems involving emission from neutron stars and accretion discs around compact objects when fast accurate calculations of light bending are required. It can also be used to test the codes that compute light bending using exact expressions via elliptical integrals.

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Schulc, Martin, Michal Kostal, Roberto Capote, Evzen Novak, Nicola Burianova, and Jan Simon. "Ratio of spectral averaged cross sections measured in standard 252Cf(sf) and 235U(nth,f) neutron fields." EPJ Web of Conferences 239 (2020): 19004. http://dx.doi.org/10.1051/epjconf/202023919004.

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The results of systematic evaluations of spectrum averaged cross section (SACS) measurements in the fission neutron fields of 252Cf and 235U are presented. The data form a complete database of high-threshold experimental SACS measured in the same installation under the same conditions and using the same high purity germanium gamma spectrometer. This is crucial to reduce the uncertainty of the ratio and the data scattering and therefore, to minimize discrepancies compared to cross section measured under different conditions in different laboratories. This new dataset complements and extends earlier experimental evaluations. The total emission of the 252Cf neutron source during the experiments varied from 9.5E8 to 4.5E8 neutrons per second. The emission was derived in accordance to the data in the Certificate of Calibration involving absolute flux measurements in a manganese sulphate bath. Concerning 235U fission neutron field, the irradiations were carried out in a specifically designed core assembled in the zero power light water LR-0 reactor. This special core has a well described neutron field. After the irradiation, the low volume irradiated samples to be measured by gamma spectrometry were placed directly on the upper cap of a coaxial high purity germanium (HPGe) detector in a vertical configuration (ORTEC GEM35P4). High volume samples were homogenized and strewn into the Marinelli beaker. The HPGe detector is surrounded by the lead shielding box with a thin inner copper cladding and covered with rubber for suppression of background signal and bremsstrahlung. The experimental reaction rates were derived for irradiated samples from the Net Peak Areas (NPA) measured using the semiconductor HPGe detector. The measured reaction rates are used to derive the spectrum-averaged cross sections. Furthermore, measured reaction rates are also compared with MCNP6 calculations using various nuclear data libraries, in particular IRDFF evaluations.

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Azechi, H., T. Jitsuno, T. Kanabe, M. Katayama, K. Mima, N. Miyanaga, M. Nakai, et al. "High-density compression experiments at ILE, Osaka." Laser and Particle Beams 9, no. 2 (June 1991): 193–207. http://dx.doi.org/10.1017/s0263034600003281.

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Direct-drive implosion experiments on the GEKKO XII laser (9 kJ, 0.5 μm, 2 ns) with deuterium and tritium (DT) exchanged plastic hollow shell targets demonstrated fuel areal densities (ρR) of ˜0.1 g/cm2 and fuel densities of ˜600 times liquid density at fuel temperatures of ˜0.3 keV. (The density and ρR values refer only to DT and do not include carbons in the plastic targets.) These values are to be compared with thermonuclear ignition conditions, i.e., fuel densities of 500–1000 times liquid density, fuel areal densities greater than 0.3 g/cm2, and fuel temperatures greater than 5 keV. The irradiation nonuniformity in these experiments was significantly reduced to a level of <5% in root mean square by introducing random-phase plates. The target irregularity was controlled to a 1% level. The fuel ρR was directly measured with the neutron activation of Si, which was originally compounded in the plastic targets. The fuel densities were estimated from the ρR values using the mass conservation relation, where the ablated mass was separately measured using the time-dependent X-ray emission from multilayer targets. Although the observed densities were in agreement with one-dimensional calculation results with convergence ratios of 25–30, the observed neutron yields were significantly lower than those of the calculations. This suggests the implosion uniformity is not sufficient to create a hot spark in which most neutrons should be generated.

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Gatera, Angélique, Alf Göök, Franz-Josef Hambsch, André Moens, Andreas Oberstedt, Stephan Oberstedt, Goedele Sibbens, David Vanleeuw, and Marzio Vidali. "Prompt fissionγ-ray characteristics from neutron-induced fission on 239Pu and the time-dependence of prompt-γray emission." EPJ Web of Conferences 169 (2018): 00003. http://dx.doi.org/10.1051/epjconf/201816900003.

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Recent years have seen an increased interest in prompt fission γ-ray (PFG) measurements motivated by a high priority request of the OECD/NEA for high precision data, mainly for the nuclear fuel isotopes 235U and 239Pu. Our group has conducted a PFG measurement campaign using state-of-the-art lanthanum halide detectors for all the main actinides to a precision better than 3%. The experiments were performed in a coincidence setup between a fission trigger and γ-ray detectors. The time-of-flight technique was used to discriminate photons, traveling at the speed of light, and prompt fission neutrons. For a full rejection of all neutrons below 20 MeV, the PFG time window should not be wider than a few nanoseconds. This window includes most PFG, provided that no isomeric states were populated during the de-excitation process. When isomeric states are populated, PFGs can still be emitted up to 1 yus after the instant of fission or later. To study these γ-rays, the detector response to neutrons had to be determined and a correction had to be applied to the γ-ray spectra. The latest results for PFG characteristics from the reaction 239Pu(nth,f) will be presented, together with an analysis of PFGs emitted up to 200 ns after fission in the spontaneous fission of 252Cf as well as for thermal-neutron induced fission on 235U and 239Pu. The results are compared with calculations in the framework of the Hauser-Feshbach Monte Carlo code CGMF and FIFRELIN.

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Karpuz Demır, N., B. Çetın, İ. Akkurt, and S. S. Noori. "Calculations of Double Differential Cross Sections on 56Fe, 63Cu and 90Zr Neutron Emission in Proton Induced Reactions." Acta Physica Polonica A 132, no. 3-II (September 2017): 1181–85. http://dx.doi.org/10.12693/aphyspola.132.1181.

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Kyratzis, D., and I. Savvidis. "Study and detection of relativistic Solar Neutrons at ground level with the Spherical Proportional Counter." HNPS Proceedings 26 (April 1, 2019): 75. http://dx.doi.org/10.12681/hnps.1801.

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A novel method of high energy solar neutron detection is proposed with the Spherical Proportional Counter (SPC), taking advantage of the 209Bi(n,f) reaction. This reaction, is considered as a standard for high energy neutron detection, due to large cross section values in the 100 MeV – 1 GeV energy interval, obtained in the n_TOF facility at CERN. A thin spherical shell of Bismuth will be situated in the large volume of the SPC, serving as target for high energy neutrons bombarding the detector, thus resulting in fission fragment emission. Detailed simulation of the 209Bi(n,f) reaction with the INCL++ model, coupled with the ABLA07 de–excitation code is performed (cross section, mass & atomic number distribution, kinetic energy per fragment) in the 100 MeV – 10 GeV energy interval, together with SRIM for the fragments’ projected range in 209Bi. Experimental data from a 252Cf source are obtained, in order to validate the SPC’s efficiency in fission fragment detection. Calculations for the expected reactions in the 209Bi shell have been performed in different atmospheric depths (700 & 1000 g/cm2), and various spherical detector radii.

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Tong, Hao, and Renxin Xu. "The spectral energy distributions of isolated neutron stars in the resonant cyclotron scattering model." Proceedings of the International Astronomical Union 8, S291 (August 2012): 517. http://dx.doi.org/10.1017/s1743921312024714.

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AbstractThe X-ray dim isolated neutron stars (XDINSs) are peculiar pulsar-like objects, characterized by their very well Planck-like spectrum. In studying their spectral energy distributions, the optical/UV excess is a long standing problem. Recently, Kaplan et al. (2011) have measured the optical/UV excess for all seven sources, which is understandable in the resonant cyclotron scattering (RCS) model previously addressed. The RCS model calculations show that the RCS process can account for the observed optical/UV excess for most sources. The flat spectrum of RX J2143.0+0654 may due to contribution from bremsstrahlung emission of the electron system in addition to the RCS process.

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Bernuzzi, Sebastiano, Matteo Breschi, Boris Daszuta, Andrea Endrizzi, Domenico Logoteta, Vsevolod Nedora, Albino Perego, et al. "Accretion-induced prompt black hole formation in asymmetric neutron star mergers, dynamical ejecta, and kilonova signals." Monthly Notices of the Royal Astronomical Society 497, no. 2 (June 27, 2020): 1488–507. http://dx.doi.org/10.1093/mnras/staa1860.

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ABSTRACT We present new numerical relativity results of neutron star (NS) mergers with chirp mass 1.188 M⊙ and mass ratios q = 1.67 and q = 1.8 using finite-temperature equations of state (EOS), approximate neutrino transport, and a subgrid model for magnetohydrodynamics-induced turbulent viscosity. The EOS are compatible with nuclear and astrophysical constraints and include a new microphysical model derived from ab initio calculations based on the Brueckner–Hartree–Fock approach. We report for the first time evidence for accretion-induced prompt collapse in high-mass-ratio mergers, in which the tidal disruption of the companion and its accretion on to the primary star determine prompt black hole (BH) formation. As a result of the tidal disruption, an accretion disc of neutron-rich and cold matter forms with baryon masses ∼0.15 M⊙, and it is significantly heavier than the remnant discs in equal-masses prompt-collapse mergers. Massive dynamical ejecta of the order of ∼0.01 M⊙ also originate from the tidal disruption. They are neutron-rich and expand from the orbital plane with a crescent-like geometry. Consequently, bright, red, and temporally extended kilonova emission is predicted from these mergers. Our results show that prompt BH mergers can power bright electromagnetic counterparts for high-mass-ratio binaries, and that the binary mass ratio can be, in principle, constrained from multimessenger observations.

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Nakayama, Shinsuke, Osamu Iwamoto, and Yukinobu Watanabe. "Recent progress of a code system DEURACS toward deuteron nuclear data evaluation." EPJ Web of Conferences 239 (2020): 03014. http://dx.doi.org/10.1051/epjconf/202023903014.

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Toward deuteron nuclear data evaluation, we have been developing a code system dedicated for deuteron-induced reactions, called DEURACS. In this paper, we review the recent progress in the development of DEURACS. To meet increasing and diversifying demands for deuteron nuclear data, DEURACS has been developed aiming at accurate and comprehensive prediction of deuteron-induced reactions. We present the results of some comparisons between the DEURACS calculations and experimental data for a variety of deuteron-induced reactions at incident energies up to 200 MeV. Double-differential cross sections for emission of neutrons or light ions up to A = 4 and cross sections for production of residual nuclei are analyzed. Neutron yields from deuteron bombardment on thick targets are also analyzed by the Monte Carlo transport simulation based on the deuteron nuclear data provided with DEURACS. Through comparison with experimental and other calculated data, validation of the present modeling in DEURACS is discussed.

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Journal articles on the topic 'Neutron emission calculations'

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