The 4π-fragment-spectrometer FOBOS

Ortlepp, H.-G.; Wagner, W.; Herbach, Claus-Michael; Александров, А. А.; Александрова, И. А.; Andrassy, M.; Budzanowski, A.; Czech, B.; Danziger, M.; Dietterle, L.; Doronin, V. N.; Dshemuchadse, S.; Fomichev, A. S.; Fromm, W.D.; Gebhardt, Markus; Gippner, P.; Heidel, K.; Heinitz, Sh.; Homeyer, H.; Ivanovsky, Sergey A.; Kamanin, D. V.; Kolesov, I. V.; Matthies, A.; May, D. P.; Merzlyakov, S.I.; Oertzen, W. von; Oganessian, Yu. Ts.; Pausch, G.; Penionzhkevich, Yu. É.; Pyatkov, Yu. V.; Radnev, S; Renz, G.; Rubinskaya, L.A.; Sandrev, I.D.; Schilling, K. D.; Seidel, W.; Shishkin, D.I.; Sirotin, A. P.; Sodan, H.; Strekalovsky, O. V.; Tishchenko, V. G.; Trofimov, V.; Tsurin, I.; Umlauf, C.; Vakatov, D. V.; Vasko, V.M.; Vitenko, V.A.; Will, E.; Wilpert, M.; Yáñez, R.; Zhuchko, V. E.; Ziem, P.; Zrodlowski, L.

doi:10.1016/s0168-9002(97)00777-8

Cited by 31 publications

(6 citation statements)

References 24 publications

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“…Therefore, it came as a great surprise when the FO-BOS collaboration reported new experiments indicating true ternary fission events with a yield of 5 · 10 −3 per fission [20][21][22]. These experiments were performed with arXiv:1612.06583v2 [nucl-th] 6 Jan 2017 the fission fragment spectrometers FOBOS and mini-FOBOS [23], in which detector modules are placed at opposite sides (180 • angle) of a thin fission target. The fission target backing creates an intrinsic asymmetry of the setup since fragments detected in one of the arms have to traverse the backing.…”

Section: Introductionmentioning

confidence: 99%

Collinear cluster tri-partition: Kinematics constraints and stability of collinearity

et al. 2017

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Background: A new mode of nuclear fission has been proposed by the FOBOS collaboration, called Collinear Cluster Tri-partition (CCT), suggesting that three heavy fission fragments can be emitted perfectly collinearly in low-energy fission. This claim is based on indirect observations via missing-energy events using the 2v2E method. This proposed CCT seems to be an extraordinary new aspect of nuclear fission. It is surprising that CCT escaped observation for so long given the relatively high reported yield, of roughly 0.5% relative to binary fission. These claims call for an independent verification with a different experimental technique.Purpose: Verification experiments based on direct observation of CCT fragments with fission fragment spectrometers require guidance with respect to the allowed kinetic energy range, which we present in this paper. Furthermore, we discuss corresponding model calculations which, if CCT is found in such verification experiments, could indicate how the breakups proceed. Since CCT refers to collinear emission, we also study the intrinsic stability of collinearity.Methods: Three different decay models are used that together span the timescales of three-body fission. These models are used to calculate the possible kinetic energy ranges of CCT fragments by varying fragment mass splits, excitation energies, neutron multiplicities and scission-point configurations. Calculations are presented for the systems 235 U(n th , f) and 252 Cf(sf), and the fission fragments previously reported for CCT, namely isotopes of the elements Ni, Si, Ca and Sn. In addition, we use semi-classical trajectory calculations with a Monte-Carlo method to study the intrinsic stability of collinearity.Results: CCT has a high net Q-value, but in a sequential decay, the intermediate steps are energetically and geometrically unfavorable or even forbidden. Moreover, perfect collinearity is extremely unstable, and broken by the slightest perturbation.Conclusions: According to our results, the central fragment would be very difficult to detect due to its low kinetic energy, raising the question of why other 2v2E experiments could not detect a missingmass signature corresponding to CCT. Considering the high kinetic energies of the outer fragments reported in our study, direct-observation experiments should be able to observe CCT. Furthermore, we find that a realization of CCT would require an unphysical fine-tuning of the initial conditions. Finally, our stability calculations indicate that, due to the pronounced instability of the collinear configuration, a prolate scission configuration does not necessarily lead to collinear emission, nor does equatorial emission necessarily imply an oblate scission configuration. In conclusion, our results enable independent experimental verification and encourage further critical theoretical studies of CCT.

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Section: Introductionmentioning

confidence: 99%

Collinear cluster tri-partition: Kinematics constraints and stability of collinearity

et al. 2017

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“…The results of the first two experiments with the FOBOS-detectors built in the FLNR in Dubna [16], have been reported in Refs. [15,17].…”

Section: The Experiments Missing Mass Methodsmentioning

confidence: 99%

True Ternary Fission, Collinear Cluster Tri (CCT) Partition of <sup><span class="cmr-7">252</span></sup>Cf

Oertzen¹,

Pyatkov²,

Kamanin³

2013

Acta Phys. Pol. B

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Ternary fission" has been studied previously as a process, where a lighter fragment with A < 30 amu is emitted perpendicular to the fission axis. We use the term "true ternary fission" for a fission process with three masses of comparable size, A > 35. Theoretical considerations repeatedly predicted that true ternary fission must occur in a collinear (prolate) geometry. Over the last decade (see Pyatkov et al. in Eur. Phys. J. A45 29 (2010) and refs. therein), the true ternary fission decay in neutron induced fission 235 U (n,fff) and in spontaneous fission of 252 Cf (sf) has been studied. The name used for this process is (CCT), with three cluster-fragments of similar size in a collinear decay. The measurements are based on binary coincidences containing TOF and energy determinations, in two detector telescopes placed at 180 • . The masses and energies of the registered two fragments give complete kinematic solutions. The missing mass events in binary coincidences can be determined, these events are obtained by blocking one of the lighter fragments (after multiple scattering in the backing) on a structure in front of the detectors. The relatively high total yield of CCT (more than 10 −3 per binary fission) is explained. It is due to the favorable Q-values (more positive than for binary) and the large phase space of the CCT-decay, dominated by three (magic) clusters: e.g. isotopes of Sn, Ca and Ni. The kinetic energies of the fragments have been calculated. The fragments placed in between the other two have very low kinetic energies (below 20 MeV) and have thus escaped their detection in previous work on "ternary fission", where in addition an oblate shape and a triangle for the momentum vectors had been assumed.

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“…This property has been exploited to provide mass identification for light ions using pulse-shape discrimination [1,[3][4][5][6][7][8][9][10][11]. The pulse-shape discrimination capability of CsI(Tl) is not needed if one uses the CsI crystals as the stopping detectors in ∆E-E telescopes where Si detectors are used as ∆E detectors.…”

Section: Energy Calibrationmentioning

confidence: 99%

“…CsI(Tl) scintillation detectors are a cost effective technology for detecting charged particles with energies of E/A=30-200 MeV [1][2][3][4][5][6][7][8][9][10][11]. Less expensive than solid state detectors, less hygroscopic than NaI(Tl) crystals, and easily machined into different shapes, CsI(Tl) crystals have been incorporated in many large solid angle detection arrays [1][2][3][4][5][6][7][8][9][10][11]. In such applications, greater stability is achieved by avoiding problems related to the temperature dependence [12] of the CsI(Tl) light output by holding the temperature constant, and by reading out the detectors via photodiodes instead of photomultipliers, whose gains may vary with time.…”

Section: Introductionmentioning

confidence: 99%

Energy resolution and energy–light response of CsI(Tl) scintillators for charged particle detection

Wagner

Tan

Chalut

et al. 2001

Nuclear Instruments and Methods in Physics Research Section A:

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This article describes the crystal selection and quality control utilized to develop and calibrate a high resolution array of CsI(Tl) scintillator crystals for the detection of energetic charged particles. Alpha sources are used to test the light output variation due to thallium doping gradients. Selection of crystals with better than 1% non-uniformity in light output is accomplished using this method.Tests with a 240 MeV alpha beam reveal that local light output variations within each of the tested CsI(Tl) crystals limit the resolution to about 0.5%. Charge and mass dependences in the energy -light output relationship are determined by calibrating with energetic projectile fragmentation beams.

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The 4π-fragment-spectrometer FOBOS

Cited by 31 publications

References 24 publications

Collinear cluster tri-partition: Kinematics constraints and stability of collinearity

Collinear cluster tri-partition: Kinematics constraints and stability of collinearity

True Ternary Fission, Collinear Cluster Tri (CCT) Partition of <sup><span class="cmr-7">252</span></sup>Cf

Energy resolution and energy–light response of CsI(Tl) scintillators for charged particle detection

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