Isotopic distributions of fragments from fission of the neutron-deficient ^{178}Hg nuclide are reported. This experimental observable is obtained for the first time in the region around lead using an ...innovative approach based on inverse kinematics and the coincidence between the large acceptance magnetic spectrometer VAMOS++ and a new detection arm close to the target. The average fragment N/Z ratio and prompt neutron M_{n} multiplicity are derived and compared with current knowledge from actinide fission. A striking consistency emerges, revealing the unexpected dominant role of the proton subsystem with atomic number between the Z=28 and 50 magic numbers. The origin of nuclear charge polarization in fission and fragment deformation at scission are discussed.
The kinetic energy of a neutron is determined experimentally by measuring its time-of-flight and flight distance from the source to the detector. However, this determination is vitiated by errors ...since the exact location of the interaction of the neutron within the detector is unknown. Moreover, more than one interaction may be necessary for the deposited energy to reach the detector threshold. We compare the different existing energy determination methods and introduce the method which gives the minimum-variance unbiased estimator of the neutron energy. The method is based of the inversion of the detector response function, for which we propose a universal algorithm. It is shown that the precision of the new method does not deteriorate with the length of the detector, which opens the possibility of conceiving detectors with a higher efficiency.
Experimental neutron distributions have been investigated in the spontaneous fission of
252
Cf at IPHC in Strasbourg. The CORA experiment associating the CODIS twin ionisation chamber and the neutron ...multi-detector DEMON aimed to solve an long-standing problem in fission: the possible emission of scission neutrons and/or the presence of a dynamical anisotropy in the neutron evaporation by the moving fission fragments. A new method allowing to establish the dynamical anisotropy in an independent way is presented. The results obtained from a comparison with simulations based on GEANT4 are shown.
.
Neutron angular distributions in spontaneous fission of
252
Cf are investigated. The CORA experiment, performed at IPHC Strasbourg, aims at elucidating neutron emission mechanisms in the fission ...process. The experimental setup is composed of the angle-sensitive twin ionisation chamber CODIS for the detection of fission fragments and the DEMON neutron detector assembly. The development of a simulation toolkit based on GEANT4 and MENATE_R is described, adapted as a strategy to investigate the influence of experimental conditions on the observed properties of neutrons emitted. Besides the kinematic neutron anisotropy in the laboratory system due to neutron evaporation from moving fragments, two additional effects are discussed which may have an influence on the angular distributions of neutrons: scission neutrons and dynamic neutron emission anisotropy in the CM system of fragments due to the spin carried by fragments. A new analysis method is presented to disentangle the dynamic anisotropy from the other effects in an independent way. For the dynamic anisotropy only an upper limit could be found. Results for the angular correlation
(
n
,
n
)
between two evaporated neutrons and the correlation
(
n
,
LF
)
between an evaporated neutron and the Light Fragment direction of flight are reported.
New gas-filled mode of the large-acceptance spectrometer VAMOS Schmitt, C.; Rejmund, M.; Navin, A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2010, Letnik:
621, Številka:
1
Journal Article
Recenzirano
Odprti dostop
A new gas-filled operation mode of the large-acceptance spectrometer VAMOS at GANIL is reported. A beam rejection factor greater than 10
10 is obtained for the
40Ca+
150Sm system at 196
MeV. The ...unprecedented transmission efficiency for the evaporation residues produced in this reaction is estimated to be around 80% for
α
x n channels and above 95% for
x n
y p channels. A detailed study of the performance of the gas-filled VAMOS and future developments are discussed. This new operation mode opens avenues to explore the potential of fusion reactions in various kinematics.
The low-lying level structure of the unbound system $^{16}$B has been investigated via single-proton removal from a 35 MeV/nucleon $^{17}$C beam. The coincident detection of the beam velocity ...$^{15}$B fragment and neutron allowed the relative energy of the in-flight decay of $^{16}$B to be reconstructed. The resulting spectrum exhibited a narrow peak some 85 keV above threshold. It is argued that this feature corresponds to a very narrow (GAMMA ≪100 keV) resonance, or an unresolved multiplet, with a dominant PI(p3/2)$^{−1=$ ⊗ V(d$^{3}$$_{5/2}$)J=3/2+ PI(p3/2)$^{−1}$ ⊗ V (d$^{2}$$_{5/2, s1/2}$)J=3/2+ configuration which decays by d-wave neutron emission.
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