Yazar "Nyberg, J." seçeneğine göre listele

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    LIFETIME MEASUREMENTS WITH THE DOPPLER SHIFT ATTENUATION METHOD USING A THICK HOMOGENEOUS PRODUCTION TARGET - VERIFICATION OF THE METHOD
    (Jagiellonian Univ Press, 2017) Ertoprak, A.; Cederwall, B.; Jakobsson, U.; Nyako, B. M.; Nyberg, J.; Davies, P.; Doncel, M.
    Doppler Shift Attenuation Method (DSAM) analysis of excited-state lifetimes normally employs thin production targets mounted on a thick stopper foil (backing) serving to slow down and stop the recoiling nuclei of interest in a well-defined manner. Use of a thick, homogeneous production target leads to a more complex analysis as it results in a substantial decrease in the energy of the incident projectile which traverses the target with an associated change in the production cross section of the residues as a function of penetration depth. Here, a DSAM lifetime analysis using a thick homogeneous target has been verified using the Doppler broadened lineshapes of gamma rays following the decay of highly excited states in the semi-magic (N = 50) nucleus Ru-94. Lifetimes of excited states in the Ru-94 nucleus have been obtained using a modified version of the LINESHAPE package from the Doppler broadened lineshapes resulting from the emission of the gamma rays, while the residual nuclei were slowing down in the thick (6 mg/cm(2)) metallic Ni-58 target. The results have been validated by comparison with a previous measurement using a different (RDDS) technique.
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    Monte Carlo simulation of a single detector unit for the neutron detector array NEDA
    (ELSEVIER SCIENCE BV, 2012) Jaworski, G.; Palacz, M.; Nyberg, J.; de Angelis, G.; de France, G.; Di Nitto, A.; Hueyuek, T.
    A study of the dimensions and performance of a single detector of the future neutron detector array NEDA was performed by means of Monte Carlo simulations, using GEANT4. Two different liquid scintillators were evaluated: the hydrogen based BC501A and the deuterated BC537. The efficiency and the probability that one neutron will trigger a signal in more than one detector were investigated as a function of the detector size. The simulations were validated comparing the results to experimental measurements performed with two existing neutron detectors, with different geometries, based on the liquid scintillator BC501. (C) 2012 Elsevier B.V. All rights reserved.
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    Pulse pile-up identification and reconstruction for liquid scintillator based neutron detectors
    (Elsevier Science Bv, 2018) Luo, X. L.; Modamio, V.; Nyberg, J.; Valiente-Dobon, J. J.; Nishada, Q.; de Angelis, G.; Agramunt, J.
    The issue of pulse pile-up is frequently encountered in nuclear experiments involving high counting rates, which will distort the pulse shapes and the energy spectra. A digital method of off-line processing of pile-up pulses is presented. The pile-up pulses were firstly identified by detecting the downward-going zero-crossings in the first-order derivative of the original signal, and then the constituent pulses were reconstructed based on comparing the pile-up pulse with four models that are generated by combining pairs of neutron and.. standard pulses together with a controllable time interval. The accuracy of this method in resolving the pile-up events was investigated as a function of the time interval between two pulses constituting a pile-up event. The obtained results show that the method is capable of disentangling two pulses with a time interval among them down to 20 ns, as well as classifying them as neutrons or gamma rays. Furthermore, the error of reconstructing pile-up pulses could be kept below 6% when successive peaks were separated by more than 50 ns. By applying the method in a high counting rate of pile-up events measurement of the NEutron Detector Array (NEDA), it was empirically found that this method can reconstruct the pile-up pulses and perform neutron-gamma discrimination quite accurately. It can also significantly correct the distorted pulse height spectrum due to pile-up events.
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    Test of digital neutron-gamma discrimination with four different photomultiplier tubes for the NEutron Detector Array (NEDA)
    (ELSEVIER SCIENCE BV, 2014) Luo, X. L.; Modamio, V.; Nyberg, J.; Valiente-Dobon, J. J.; Nishada, Q.; de Angelis, G.; Hueyuek, T.
    A comparative study of the neutron-gamma discrimination performance of a liquid scintillator detector BC501A coupled to four different 5 in photomultiplier tubes (ET9390kb, R11833-100, XP4512 and R4144) was carried out Both the Charge Comparison method and the Integrated Rise-Time method were implemented digitally to discriminate between neutrons and gamma rays emitted by a Cf-252 source. In both methods, the neutron-gamma discrimination capabilities of the four photomultiplier tubes were quantitatively compared by evaluating their figure-of-merit values at different energy regions between 50 keVee and 1000 keVee. Additionally, the results were further verified qualitatively using time-of-flight to distinguish gamma rays and neutrons. The results consistently show that photomultiplier tubes R11833-100 and ET9390kb generally perform best regarding neutron-gamma discrimination with only slight differences in figure-of-merit values. This superiority can be explained by their relatively higher photoelectron yield, which indicates that a scintillator detector coupled to a photomultiplier tube with higher photoelectron yield tends to result in better neutron-gamma discrimination performance. The results of this work will provide reference for the choice of photomultiplier tubes for future neutron detector arrays like NEDA. (C) 2014 Elsevier B.V. All rights reserved.