In a series of the experiments at different time-of-flight spectrometers of heavy ions we have observed manifestations of a new at least ternary decay channel of low excited heavy nuclei. Due to specific features of the effect, it was called collinear cluster tri-partition (CCT). The experimental results obtained initiated a number of theoretical articles dedicated to different aspects of the CCT. We compare theoretical predictions with our experimental data, only partially published so far. The model of one of the most populated CCT modes that gives rise to the so called Ni-bump is discussed. Detection of the 68-72Ni fission fragments with a kinetic energy E<25 MeV at the mass-separator Lohengrin is proposed for an independent experimental verification of the CCT.

Careful studies of the fission fragments mass correlation distributions let us to reveal specific linear structures in the region of a big missing mass. It became possible due to applying of effective cleaning of this region from the background linked with scattered fragments. One of the most pronounced structure looks like a rectangle bounded by the magic nuclei. The fission events aggregated in the rectangle show a very low total kinetic energy. We propose possible scenario of forming and decay of the multi-cluster prescission configuration decisive for the experimental findings. This approach is valid as well for treating of another rare decay modes discovered in the past.

Background: In a series of experiments at different time-of-flight spectrometers of heavy ions we have observed manifestations of a new at least ternary decay channel of low excited heavy nuclei. Due to specific features of the effect, it was called collinear cluster tri-partition (CCT). The obtained experimental results have initiated a number of theoretical articles dedicated to different aspects of the CCT. Special attention was paid to kinematics constraints and stability of collinearity. Purpose: To compare theoretical predictions with our experimental data, only partially published so far. To develop the model of one of the most populated CCT modes that gives rise to the so-called "Ni-bump." Method: The fission events under analysis form regular two-dimensional linear structures in the mass correlation distributions of the fission fragments. The structures were revealed both at a highly statistically reliable level but on the background substrate, and at the low statistics in almost noiseless distribution. The structures are bounded by the known magic fragments and were reproduced at different spectrometers. All this provides high reliability of our experimental findings. The model of the CCT proposed here is based on theoretical results, published recently, and the detailed analysis of all available experimental data. Results: Under our model, the CCT mode giving rise to the Ni bump occurs as a two-stage breakup of the initial three body chain like the nuclear configuration with an elongated central cluster. After the first scission at the touching point with one of the side clusters, the predominantly heavier one, the deformation energy of the central cluster allows the emission of up to four neutrons flying apart isotropically. The heavy side cluster and a dinuclear system, consisting of the light side cluster and the central one, relaxed to a less elongated shape, are accelerated in the mutual Coulomb field. The "tip" of the dinuclear system at the moment of its rupture faces the heavy fragment or the opposite direction due to a single turn of the system around its center of gravity. Conclusions: Additional experimental information regarding the energies of the CCT partners and the proposed model of the process respond to criticisms concerning the kinematic constraints and the stability of collinearity in the CCT. The octupole deformed system formed after the first scission is oriented along the fission axis, and its rupture occurs predominantly after the full acceleration. Noncollinear true ternary fission and far asymmetric binary fission, observed earlier, appear to be the special cases of the decay of the prescission configuration leading to the CCT. Detection of the Ni68-72 fission fragments with a kinetic energy E < 25MeV at the mass-separator Lohengrin is proposed for an independent experimental verification of the CCT.

We discuss the manifestations of a new original effect appeared at crossing of the metal foils by fission fragments. We have observed significant mass deficit in the total mass M of the fission fragments detected in coincidence with ions knocked out from the foil. It was shown that at the large angles of scattering of the knocked-out ions from the foil predominantly conventional elastic Rutherford scattering takes place. As the result M corresponds to the mean mass of the mother system after emission of fission neutrons (no missing mass). In contrast, in near frontal impacts fission fragment misses essential part of it mass. Residual nuclei at least for the fragments from the heavy mass peak show magic nucleon composition.

In recent publications [1–3], we have presented experimental indications of existence of a new at least ternary decay channel of low excited heavy nuclei known as collinear cluster tripartition (CCT). A fragment mass M is calculated by the energy E and the velocity V. Mainly a scattering of fragments at the entrance of an E-detector gives background events simulating ternary decay. Selection of the “true” events was provided by applying the gates on the fragments momenta, velocities, experimental neutron multiplicity, and the parameters sensitive to the fragment nuclear charge. Observation of the specific linear structures in the M1–M2 distributions (mass correlation plots) served as a criterion for a sufficient suppression of the background. The structures were reproduced at the spectrometers of two types. Earlier experiments were performed using gas filled detectors (modules of the FOBOS setup [4]). Later we switched to solid-state detectors, namely timing detectors, on the microchannel plates and the mosaics of PIN diodes (COMETA setup [2] and the similar ones [3]). Even though mass reconstruction procedures for these two types of spectrometers strongly differ, the obtained results are in good agreement. Estimation of the expected parameters of the CCT products was performed in the recent theoretical works [5–7]. The results obtained were taken into account in our model of the most populated CCT mode known as “Ni-bump”.

Exotic Nuclei, pp. 284-287 (2017) No AccessNEW RESULTS IN STUDY OF SHAPE ISOMER STATES IN FISSION FRAGMENTSYu. V. Pyatkov, D. V. Kamanin, A. A. Alexandrov, I. A. Alexandrova, Z. I. Goryainova, E. A. Kuznetsova, A. O. Strekalovsky, O. V. Strekalovsky, V. E. Zhuchko, N. Mkaza and V. MalazaYu. V. PyatkovNational Nuclear Research University MEPhI (Moscow Engineering Physics Institute), 115 409 Moscow, RussiaJoint Institute for Nuclear Research, 141980 Dubna, Russia, D. V. KamaninJoint Institute for Nuclear Research, 141980 Dubna, Russia, A. A. AlexandrovJoint Institute for Nuclear Research, 141980 Dubna, Russia, I. A. AlexandrovaJoint Institute for Nuclear Research, 141980 Dubna, Russia, Z. I. GoryainovaJoint Institute for Nuclear Research, 141980 Dubna, Russia, E. A. KuznetsovaJoint Institute for Nuclear Research, 141980 Dubna, Russia, A. O. StrekalovskyJoint Institute for Nuclear Research, 141980 Dubna, Russia, O. V. StrekalovskyJoint Institute for Nuclear Research, 141980 Dubna, Russia, V. E. ZhuchkoJoint Institute for Nuclear Research, 141980 Dubna, Russia, N. MkazaUniversity of Stellenbosch, Faculty of Military Science, Military Academy, Saldanha 7395, South Africa and V. MalazaUniversity of Stellenbosch, Faculty of Military Science, Military Academy, Saldanha 7395, South Africahttps://doi.org/10.1142/9789813226548_0043Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: A brake-up of the fission fragments crossing metal foil was observed. In the light of the results obtained a fission fragment from conventional binary fission is supposed to be born in the shape isomer state which looks like di-nuclear system consisting of the magic core and lighter cluster. Keywords: Ternary fissionShape-isomer states FiguresReferencesRelatedDetails Exotic NucleiMetrics History KeywordsTernary fissionShape-isomer statesPDF download

Careful studies of the fission fragments mass correlation distributions let us to reveal specific linear structures in the region of a big missing mass. It became possible due to applying of effective cleaning of this region from the background linked with scattered fragments. One of the most pronounced structure looks like a rectangle bounded by the magic nuclei. The fission events aggregated in the rectangle show a very low total kinetic energy. We propose possible scenario of forming and decay of the multi-cluster prescission configuration decisive for the experimental findings. This approach is valid as well for treating of another rare decay modes discovered in the past.

We discuss the quality of heavy ions (HI) mass reconstruction in the wide range of HI energies and masses using Si PIN diodes for measuring both energy and time-of-flight. The results are based on the experimental data obtained at the IC-100 accelerator in the Flerov Laboratory of the JINR (Dubna, Russia).

Reconstruction of the heavy ion masses in the time-of-flight spectrometry is known to be a complicated task due to distortions both in timing and measuring of the ions energy using PIN diodes. Original procedure which takes into account simultaneously pulse height defect (PHD) and plasma delay for unbiased mass reconstruction was tested in series of experiments at the LIS setup using degrader foils.

In one of our experiments aimed at studying of the new multi-body decay called collinear cluster tri-partition (CCT) [1–3] additional absorber (Ti foil) was introduced just after the source at the distance of approximately 1 mm. It was motivated by the peculiarity of the CCT manifestation in the experiments namely specific structures in the region of an essential missing mass in the fission fragments (FFs) mass correlation distribution were observed in the spectrometer arm faced to the Cf source backing only. The effect was traced back to some angular divergence between two CCT partners flying in the same direction after passing the scattering medium on the flight pass due to the multiple scattering. As a result one of them can be lost in the PIN diode frame what is observed as” missing mass” or both fragments will be detected independently in the neighboring diodes. We have observed significant mass deficit in the total mass of the fission fragments detected in coincidence with Ti ions knocked out from the foil (fig. 1) [4]. For the sake of convenience, the FFs from such events are labeled as M1, M2 and M3 in an order of decreasing masses in the ternary event. The total mass of the two heavier fragments Ms = M1 + M2 is plotted vs. the mass of the lighter fragment M3. Such effect could be expected if the scattered fragment looks like a di-nuclear system destroying due to inelastic scattering on the Ti nucleus. A mean flight time between the Cf source and the foil does not exceed 0.1 ns. It can be regarded as a low limit for the life time of the di-nuclear system (shape isomer).

Basic experimental results confirming the existence a new cluster-decay type called collinear cluster tripartition (CCT) are presented. Decays of this type manifest themselves, in particular, as a two-dimensional region of a locally enhanced yield of fragments (bump) that corresponds to specific missing-mass values in the mass-mass distribution of fission fragments. One of the decay modes that contribute to the bump can be treated as a cluster-decay type that is new in relation to the well-known heavy-ion or lead radioactivity. The conclusions drawn from an analysis of correlation mass distributions are confirmed by the results obtained from neutron-gated data, measurements of the nuclear charge for CCT events, and the direct detection of new-decay products.