Kinematic Coincidence Research Articles

Ground state and excited state multinucleon transfer channels in interactions of 28Si with 90,94Zr in near barrier region

Multinucleon transfer reactions were measured in interactions of 28Si with 90,94Zr at a near barrier energy using recoil mass separator, Heavy Ion Reaction Analyzer (HIRA) at Inter University Accelerator Centre (IUAC), New Delhi. The effects of shell closure, positive Q-value transfer channels on the relative strengths of ground state and excited state transfer in multinucleon transfer processes were investigated. The kinematic coincidence technique was employed to reduce the background. The m/q ambiguity was resolved by time of flight (TOF) technique. Based on the Q-value considerations, it was observed that pickup channels were predominantly of neutron transfer, whereas, stripping channels were mainly of proton transfer. A 14-element BGO array was used to extract the relative strength of excited state transfer. In interactions of 28Si with 90Zr, it was observed that the ground state and excited states competes for populating all the transfer channels. In reactions of 28Si with 94Zr, nearly similar behavior was observed except for two-neutron pickup channel, where excited state transfer was dominant and four-neutron pickup channel where ground state transfer was dominant.

Systematic evidence for quasifission in Be9−, C12−, and O16 -induced reactions forming No258,260

Background: Cross sections for the formation of superheavy elements (SHE) by heavy ion fusion are suppressed by the competing quasifission process. This results in a fissionlike decay after capture but before formation of a compact compound nucleus. Fast quasifission is evident from very mass-asymmetric fission, focused in angle. In contrast, slow quasifission shows no significant mass-angle correlation, and a mass distribution peaked at symmetry. However, it shows angular distributions more anisotropic than those calculated for fission following fusion. Following fusion, low excitation energies should increase SHE survival through reduced competition from fission. However, in reactions with deformed actinide target nuclei, subbarrier fusion is highly suppressed by both fast and slow quasifission.Purpose: To investigate the threshold for quasifission by investigating signatures of slow quasifission in both fission angular and mass distributions, as a function of beam energy with respect to the capture barrier, for the projectiles $^{9}\mathrm{Be}$, $^{12}\mathrm{C},$ and $^{16}\mathrm{O}$ that form the neighboring compound nuclei $^{258,260}\mathrm{No}$.Methods: Fission mass and angular distributions have been measured from below to above-barrier energies using the kinematic coincidence method for the reactions $^{9}\mathrm{Be}+^{249}\mathrm{Cf}$, $^{12}\mathrm{C}+^{248}\mathrm{Cm}$, and $^{16}\mathrm{O}+^{244}\mathrm{Pu}$. Fission following transfer reactions can significantly contaminate fission events that follow capture, and must be rejected. Existing methods to reject transfer-induced fission have been refined to allow quantitative subtraction of the transfer fission component.Results: The capture-fission mass-angle distributions show no evidence for fast quasifission, as might be expected. However, measured fission fragment angular anisotropies are larger than transition state model (TSM) calculations for fusion fission. The deviations increase with larger projectile charge and for bombarding energies below the mean capture barrier energy. Even for the $^{9}\mathrm{Be}+^{249}\mathrm{Cf}$ reaction, the subbarrier angular anisotropy significantly exceeds the TSM calculation. Fission mass distributions measured at the same excitation energies also show a consistent dependence on the projectile charge.Conclusions: New refined analysis techniques have been developed to enable reliable separation of fission following capture from sequential fission following transfer reactions. For fission following capture at above-barrier energies, the $^{9}\mathrm{Be}$ angular anisotropies are close to the TSM predictions, supporting the validity of TSM calculations of fusion-fission for such heavy elements. At subbarrier energies the angular anisotropy data indicate a component of slow quasifission even for $^{9}\mathrm{Be}$, and a probability that increases rapidly with projectile charge. It is concluded that the probability of slow quasifission changes smoothly with projectile charge, having no sharp threshold.

Kinematics parameter identification and accuracy evaluation method for neurosurgical robot

The kinematic model parameter deviation is the main factor affecting the positioning accuracy of neurosurgical robots. To obtain more realistic kinematic model parameters, this paper proposes an automatic parameters identification and accuracy evaluation method. First, an identification equation contains all robot kinematics parameter was established. Second, a multiple-pivot strategy was proposed to find the relationship between end-effector and tracking marker. Then, the relative distance error and the inverse kinematic coincidence error were designed to evaluate the identification accuracy. Finally, an automatic robot parameter identification and accuracy evaluation system were developed. We tested our method on both laboratory prototypes and real neurosurgical robots. The results show that this method can realize the neurosurgical robot kinematics model parameters identification and evaluation stably and quickly. Using the identified parameters to control the robot can reduce the robot relative distance error by 33.96% and the inverse kinematics consistency error by 67.30%.

Hidden-charm pentaquark formation in antiproton-deuterium collisions

The possibility of observing formation of hidden-charm pentaquarks as $s$-channel resonances in antiproton - deuteron collisions is discussed. It is pointed out that the masses of the reported by LHCb pentaquark resonances in the $J/\psi \, p$ channel are very close to a special value of the mass at which formation of a pentaquark by antiproton incident on a deuteron at rest requires exactly the same momentum of the $\bar p$ as needed for the formation in the $s$ channel of the charmonium resonance in $\bar p p$ collisions with the proton being at rest. For this reason the former process can be rather completely described within the notion of the deuteron being a shallow bound state of two nucleons without resorting to models describing its short-distance structure. It is argued that a similar kinematical coincidence can be expected for (yet) hypothetical pentaquark resonances in the $\eta_c \, N$ channel, and that these can be sought for once antiproton - deuterium collisions become available for experimentation.

Recent studies of heavy ion transfer reactions using large solid angle spectrometers

We present selected results recently obtained in the study of heavy ion transfer reactions at energies close to the Coulomb barrier by employing the large solid angle magnetic spectrometer PRISMA. We discuss the production of neutron-rich heavy nuclei via multinucleon transfer processes and the related effects of secondary processes, in particular nucleon evaporation, studied in a high resolution kinematic coincidence experiment. We also present the recent results in the studies of neutron-neutron correlations for closed shell and superfluid systems.

A gas detection system for fragment identification in low-energy heavy-ion collisions

A gas detection system has been developed for the identification in atomic number Z and the measurement of energy E, timing and scattering angles of the fragments produced in low-energy heavy-ion induced reactions. In particular, it has been designed to be used in kinematic coincidence measurements in conjunction with the large solid angle magnetic spectrometer PRISMA. The detection system is composed of a multiwire parallel plate avalanche counter (MWPPAC) followed by an axial field ionization chamber. Both detectors have been fully characterized with analog electronics by means of heavy-ion beams delivered by the Tandem-ALPI accelerator complex of LNL. Digital electronics has also been tested for the processing of anode signal of the ionization chamber.

Investigation of the Hoyle state in12C with a new hodoscope detector

The state in12C (7.654MeV, the Hoyle state) is important for the understanding of clustering phenomena in nuclei. The pronounced cluster nature of this state allows the triple-α process in stars with a reaction rate regulated by its structure properties. To precisely estimate the direct component in the 3α decay mechanism of the Hoyle state, we developed a new experiment using the14N(d,α)12C reaction at 10.5MeV. An anti-coincidence telescope was used to identify the α ejectiles leading the residual12C in the Hoyle state, while its decays in 3α were studied by means of a new hodoscope of silicon detectors, superOSCAR, placed in kinematical coincidence to fully reconstruct the events. Details of the experiment and preliminary results are discussed in the text.

Study of the population of neutron-rich heavy nuclei in the A~200 mass region via multinucleon transfer reactions

Multineutron and multiproton transfer channels, populated in the inverse kinematics reaction 197 Au+130 Te at Elab =1.07 GeV, were measured at Laboratori Nazionali di Legnaro using the presently heaviest ion beam delivered by the PIAVE-ALPI accelerator complex and detecting both projectile-like and targetlike ions. To this end the large solid angle magnetic spectrometer PRISMA was coupled to a second arm for the detection of the heavy fragments in kinematic coincidence with the light ones selected and identified with the spectrometer. The data analysis is still in progress and will allow to compare the yields of both light and heavy partner with theoretical predictions performed with the GRAZING code to get quantitative information on transfer channels and the effect of evaporation and fission on the production rate of primary fragments. The mass integrated Z distribution, extracted from the experimental data, evidenced the population of proton pickup channels that, in conjunction with the neutron stripping ones from the 130 Te, open the path for the production of neutron-rich heavy nuclei. In the following, we will present some preliminary results as well as details on the experimental configuration and perspectives for future investigations in the neutron-rich heavy region.

Status and perspectives of fragmentation beams at LNS with CHIMERA detector

Relatively large yields of various exotic beams produced through in-flight fragmentation are available at LNS. Using the CHIMERA detector, we performed various experiments to study elastic and inelastic scattering, transfer, break-up, and reaction dynamics with targets from proton and deuteron to carbon and heavier. For reactions with relatively light systems we used the kinematical coincidence method to extract high resolution angular distributions of binary reactions from the measured light particle energy spectra. We also used the CsI detectors of CHIMERA to detect gamma rays emitted in the reactions. Some of most recent results are presented together with future perspectives with the coupling of CHIMERA with FARCOS array.

Sub-barrier transfer reactions studied with the magnetic spectrometer PRISMA

Transfer reactions in the sub-barrier region have been studied at Laboratori Nazionali di Legnaro (LNL) by using the large solid angle magnetic spectrometer PRISMA. In particular, excitation functions of multinucleon transfer channels have been measured for the systems 96Zr+40Ca (closed shell nuclei), 116Sn+60Ni (super-fluid nuclei) from the Coulomb barrier to 25% below. Results of these measurements are presented in this contribution.An ancillary detection system has been designed and built in order to perform kinematic coincidence measurements in conjunction with PRISMA. It will allow to study the effects of secondary processes, such as evaporation and fission, which strongly affect the final yield of the reaction products. The status of this development is also reported.

Detector system for the study of low energy heavy ion reactions using kinematic coincidence technique

The characteristics and performance of a new detector system developed for the study of low energy heavy ion binary reactions using the kinematic coincidence technique are presented. The detector system has been developed to carry out experiments such as multi-nucleon transfer reactions using the General Purpose Scattering Chamber (GPSC) facility at IUAC [1,2]. The detector system consists of a pair of two-dimensional position sensitive multi wire proportional counter (MWPC) and a ΔE−E gas ionization chamber. Both MWPC have an active area of 5×5cm2, and provide position signals in horizontal (X) and vertical (Y) plane, and timing signal for time of flight measurements. The main design feature of MWPC is the reduced wire pitch of 0.025in. (0.635mm) in all electrodes, giving uniform field and faster charge collection, and usage of 10μm diameter in anode frame which gives higher gains. The position resolution of the detectors was determined to be 0.45mm FWHM and time resolution was estimated to be 400ps FWHM. The detector could handle heavy ion count rates exceeding 100kHz without any break down. The timing and position signals of the detectors are used for kinematic coincidence measurements and subsequent extraction of their mass and angular distributions. The ionization chamber has a conventional transverse field geometry with segmented anode providing multiple ΔE signals for nuclear charge (Z) identification. This article describes systematic study of these detectors in terms of efficiency, count rate handling capability, time, position and energy resolution.

Transfer reactions on light exotic nuclei studied with CHIMERA detector at LNS

The kinematical coincidence method is used to extract angular distribution of elastic scattering and transfer reactions. The detected light particle energy spectra are used to extract the angular distribution with around 1° resolution in the Center of Mass (CM) system. Examples with 10 Be beam are presented. In the case of proton scattering, γ -ray coincidences are used to discriminate excited levels population from elastic scattering.

The differential cross-section on dp-elastic scattering at 400–880 MeV obtained at Nuclotron

The results on the cross-section of dp-elastic scattering obtained at 400-880 MeV at internal target at Nuclotron are presented. The measurements have been performed using CH2 and C targets and kinematic coincidence of signals from scintillation counters.

The cross-section in dp-elastic scattering at the energies of 500, 700 and 880 MeV obtained at the internal target station of Nuclotron

The results on the cross-section of dp-elastic scattering reaction obtained at 500, 700 and 880 MeV at the internal target of Nuclotron are presented. The measurements have been performed using CH2 and C targets and kinematic coincidence of signals from scintillation counters. The cross-section data are compared with theoretical predictions and results of previous experiments.

Kinematical coincidence method in transfer reactions

A new method to extract high resolution angular distributions from kinematical coincidence measurements in binary reactions is presented. Kinematics is used to extract the center of mass angular distribution from the measured energy spectrum of light particles. Results obtained in the case of 10Be+p→9Be+d reaction measured with the CHIMERA detector are shown. An angular resolution of few degrees in the center of mass is obtained. The range of applicability of the method is discussed.

Elastic scattering studies of 16C at 50 MeV/A on proton and deuteron targets with the CHIMERA multidetector at INFN-LNS

At the Laboratori Nazionali del Sud (LNS) in Catania (Italy), light radioactive ion beams have been produced through the In Flight Fragmentation method, using 18O and 13C at 55 MeV/A as primary beams impinging on a 9Be production target. Elastic scattering angular distributions of 16C+p and 16C+d at 50 MeV/A, 10Be+p at 56 MeV/A and 13B+d at 52 MeV/A systems were measured by using the CHIMERA (Charge Heavy Ion Mass and Energy Resolving Array) multidetector and kinematical coincidence technique. The experimental data are fitted by using the optical model.

Multinucleon transfer reactions: an overview of recent results

Large acceptance magnetic spectrometers, such as PRISMA installed at Laboratori Nazionali di Legnaro, gave a further boost to the renewed interest for multinucleon transfer reactions in the last decade. The large solid angles of these devices and the high resolving powers of their detection systems allowed to investigate the transfer process around and well below the Coulomb barrier and to perform nuclear structure studies in several mass regions of the nuclide chart when coupled with large γ-ray arrays such as CLARA. Selected results obtained with the PRISMA-CLARA set-up in odd argon isotopes populated by using the multinucleon transfer process and in sub-barrier transfer measurements are presented in this contribution. The status of an ancillary detector which is being developed for PRISMA in order to perform kinematical coincidence measurements is also reported.

New data on the differential cross-section ondp-elastic scattering at 880 MeV obtained at Nuclotron

The results on the cross-section of dp-elastic scattering reaction obtained at 880 MeV at internal target of Nuclotron are presented. The measurements have been performed using CH2 and C targets and kinematic coincidence of signals from scintillation counters. The cross-section data are compared with theoretical predictions and results of previous experiments.

Measurement of the cross-section in dp-elastic scattering at the energies of 500 and 880 MeV at Nuclotron

The preliminary results on the cross-section of dp-elastic scattering reaction obtained at 880 and 500 MeV at internal target of Nuclotron are presented. The measurements have been performed using CH2 and C targets and kinematic coincidence of signals from scintillation counters. The cross-section data at 880 MeV are compared with the different theoretical predictions.

Collinear ternary cluster decay of hyperdeformed 60Zn at high angular momentum

Binary and ternary cluster decay of 60Zn compound nuclei at high angular momentum, formed in the 36Ar + 24Mg reaction at E lab(36Ar) = 195 MeV, has been measured in a unique kinematic coincidence setup consisting of two large area position sensitive (x, y) gas detector telescopes with Bragg-ionization chambers (BRS). The BRS provides the opportunity to measure the reaction angles in-and out-of-plane, and through Bragg-curve spectroscopy to achieve a complete identification of the nuclear charge for different final channels. We observed very narrow out-of-plane angular correlations for two heavy fragments emitted either in purely binary events or in events with a missing mass consisting of 2 and 3α particles. These narrow correlations are interpreted as ternary fission decay from compound nuclei at high angular momenta through an elongated (hyperdeformed) shape with a very large moment of inertia. In these stretched configurations, the lighter mass in the neck region remains at rest or with very low momentum in the center of mass.