Multinucleon Transfer Reactions Research Articles

Shell effects on the drift and fluctuation in multinucleon transfer reactions

Shell effects on the drift and fluctuation in multinucleon transfer reactions

First investigation on the isomeric ratio in multinucleon transfer reactions: Entrance channel effects on the spin distribution

The multinucleon transfer (MNT) reaction approach was successfully employed for the first time to measure the isomeric ratios (IRs) of 211Po isomer (25/2+) and its ground state (9/2+) at the IGISOL facility using a 945 MeV 136Xe beam impinged on 209Bi and natPb targets. The dominant production of isomers compared to the corresponding ground states was consistently revealed in the α-decay spectra. Deduced IR of 211Po populated through the 136Xe+natPb reaction was found to have an enhancement of ≈1.8-times than that observed for the 136Xe+209Bi. State-of-the-art Langevin-type model calculations have been utilized to estimate the spin distribution of an MNT residue. The computations qualitatively corroborate with the considerable increase in the IRs of 211Po produced from 136Xe+natPb compared to 136Xe+209Bi. Theoretical investigations indicate a weak dependence of target spin on the IRs. The enhancement of the 211Po isomer in the 136Xe+natPb over 136Xe+209Bi can be attributed to the different proton (p)-transfer production routes. Estimations demonstrate an increment in the angular momentum transfer, favorable for isomer production, with increasing projectile energy. Comparative analysis reveals the two entrance channel parameters, projectile mass and p-transfer channels, strongly influencing the population of the high-spin isomer of 211Po (25/2+). This letter reports the first experimental and theoretical study on the IRs of nuclei formed from two different p-transfer channels via two independent MNT reactions.

New model based on coupling the Master and Langevin equations in the study of multinucleon transfer reactions

The multinucleon transfer process plays a crucial role for accessing unexplored isotopes far from the β-stable line. Developing reliable models is always one of biggest challenges for understanding the mechanism of the multinucleon transfer (MNT) process and providing accurate predictions. In this work, a new model, combining the Master and Langevin equations (CML), is developed for investigating the mechanism of the MNT reactions. The reaction 136Xe+208Pb is studied. The CML calculations are in rather good agreement with the experimental data. The effects of the incident energy and the entrance angular momentum on the production cross sections are investigated. One intriguing phenomenon is found that the dependence of the incident energy on the production yields in symmetry region is more intense than that for producing trans-target fragments.

Fabrication and characterization of thin [formula omitted]Sn films for heavy-ion nuclear reaction measurements

The fabrication of thin isotopically enriched 120,124Sn targets have been presented. The thin film targets prepared have been used in nuclear physics experiments to apprehend the heavy-ion fusion and multi-nucleon transfer reaction dynamics around the Coulomb barrier. Vacuum evaporation viz. resistive heating technique has been used for the fabrication of the targets with varying areal densities in the range of 50–250 μg/cm2 backed with a carbon layer of ≈20μg/cm2 using a nominal amount of 30 mg isotopically enriched material. The fabricated targets have been characterized using multiple advanced techniques viz. Energy Dispersive X-ray Spectroscopy (EDS), Scanning Electron Microscopy (SEM), and X-ray Diffractometry (XRD). The thickness of the targets has been measured using Rutherford Back-scattering Spectrometry (RBS). The isotopic contamination levels have been ascertained with an in-beam experiment using Heavy Ion Reaction Analyzer at IUAC, New Delhi.

Increasing the rate capability for the cryogenic stopping cell of the FRS Ion Catcher

At the FRS Ion Catcher (FRS-IC), projectile and fission fragments are produced at relativistic energies, separated in-flight, energy-bunched, slowed down, and thermalized in the ultra-pure helium gas-filled cryogenic stopping cell (CSC). Thermalized nuclei are extracted from the CSC using a combination of DC and RF electric fields and gas flow. This CSC also serves as the prototype for the CSC of the Super-FRS, where exotic nuclei will be produced at unprecedented rates making it possible to go towards the extremes of the nuclear chart. Therefore, it is essential to efficiently extract thermalized exotic nuclei from the CSC under high beam rate conditions, in order to use the rare exotic nuclei, which come as cocktail beams. The dependence of the extraction efficiency on the intensity of the impinging beam into the CSC was studied with a primary beam of 238U and its fragments. Tests were done with two different versions of the DC electrode structure inside the cryogenic chamber, the standard 1 m long and a short 0.5 m long DC electrode systems. In contrast to the rate capability of 104 ions/s with the long DC electrode system, results show no extraction efficiency loss up to the rate of 2 × 105 ions/s with the new short DC electrode. This order of magnitude increase of the rate capability paves the way for new experiments at the FRS-IC, including studies of exotic nuclei with in-cell multi-nucleon transfer reactions. The results further validate the design concept of the CSC of the Super-FRS, which was developed to effectively manage beams of even higher intensities.

Helium gas cell with RF wire carpets for KEK Isotope Separation System

We have developed radio-frequency (RF) wire carpets and installed them in a cryogenic helium gas cell to increase the extraction yields of target-like fragments (TLFs) produced in multi-nucleon transfer (MNT) reactions at the KEK Isotope Separation System (KISS). KISS is an on-line isotope separator based on a gas cell system, and has been implemented for nuclear spectroscopy of isotopes approaching the N=126 neutron shell closure below lead and neutron-rich actinides. We optimized the design of the RF wire carpet for efficient ion transport of TLFs from the simulations. We then performed experiments both off-line using rubidium ions from an alkali thermal ion-source in the gas cell, and on-line using TLFs produced by a 136Xe beam impinging upon a 198Pt target system, to confirm the performance expected of the design. We confirmed an increase in the extraction yields of more than an order of magnitude when using the cryogenic He gas cell with RF wire carpets as compared to our typical argon gas cell system with laser resonant ionization. The techniques and knowledge acquired in the development of these RF wire carpets will be applied to new RF wire carpets for use in a large-volume helium gas cell which will be installed at an upgraded KISS facility in the near future.

Fabrication and characterization of CaF2 target for multi-nucleon transfer reaction studies

Thin CaF2 targets with carbon backing are fabricated for the first time using physical vapour deposition technique at the target laboratory of IUAC, New Delhi to perform a multi nucleon transfer reaction on 10,11B＋40Ca systems using General Purpose Scattering Chamber (GPSC) facility. Ca being an oxidizing material, we have used molecular CaF2 as the target material instead of Ca. Using turbo-molecular pump based coating unit (TMPU), carbon is deposited on cleaned glass slide and then CaF2 is deposited on diffusion pump based coating unit (DPU). We are successful in fabricating CaF2 targets of thickness ≈264.4μg/cm2 on carbon backing of thickness ≈21.5μg/cm2. The thickness and purity measured by the crystal thickness monitor equipped with the vacuum chamber is verified by different techniques like alpha energy loss, Rutherford Back Scattering (RBS), Electron Diffraction Spectroscopy (EDS) and X-ray Diffraction (XRD). Small impurity level were smeared during the observation and the target is successfully used for nuclear reaction experiment. The fabrication of molecular Ca target is found to be more conducive to experimentation since they exhibit less oxidation and herewith we discuss about fabrication technique, experimentation and characterization.

Production of neutron-rich actinide isotopes in isobaric collisions via multinucleon transfer reactions

Production of neutron-rich actinide isotopes in isobaric collisions via multinucleon transfer reactions

In-flight separation of rare heavy transfer products with a velocity filter

Multinucleon transfer reactions are considered as a possible pathway to synthesize new heavy and superheavy nuclei. Regarding the expected small yields of exotic transfer products, efficient separation and detection techniques, which allow the identification of single nuclei, are mandatory. Our approach is to use a velocity filter for separation of (super)heavy transfer products. Respective experiments which we performed at GSI Helmholtz Center revealed promising results. The method allowed us for the first time a discovery of new transuranium isotopes produced in transfer reactions, the observation of the so far heaviest and most neutron-rich transfer product 260No, related with the so far smallest measured transfer cross-section of 0.5 nb.

Paricle identification at VAMOS++ with machine learning techniques

Multi-nucleon transfer reaction between 136Xe beam and 198Pt target was performed using the VAMOS++ spectrometer at GANIL to study the structure of n-rich nuclei around N=126. Unambiguous charge state identification was obtained by combining two supervised machine learning methods, deep neural network (DNN) and positional correction using a gradient-boosting decision tree (GBDT). The new method reduced the complexity of the kinetic energy calibration and outperformed the conventional method improving the charge state resolution by 8%.

Nuclear structure advancements with multi-nucleon transfer reactions

Multi-Nucleon Transfer (MNT) reactions have been used for decades as a reaction mechanism, in order to populate excited states in nuclei far from stability and to perform nuclear structure studies. Nevertheless, the development of set-ups involving high acceptance tracking magnetic spectrometers (mainly existing in Europe), coupled with the Advanced GAmma Tracking Array (AGATA) opens new possibilities, especially if they are used in conjunction with high-intensity stable beams or ISOL RIBs. In this article, we will discuss the capabilities of such set-ups aiming at different goals, including complete information in high-resolution spectroscopy as well as lifetime measurements.

CATLIFE (Complementary Arm for Target LIke FragmEnts): Spectrometer for Target like fragments at VAMOS++

The multi-nucleon transfer reaction between 136Xe beam and 198Pt target at the beam energy 7 MeV/u was studied using the large acceptance spectrometer VAMOS++ coupled with the newly installed second arm time-of-flight and delayed γ-ray spectrometer CATLIFE (Complementary Arm for Target LIke FragmEnts). The CATLIFE detector is composed of a large area multi-wire proportional chamber and the EXOGAM HPGe clover detectors with an ion flight length of 1230 mm. Direct measurement of the target-like fragments (TLF) and the delayed γ-rays from the isomeric state helps to improve TLF identification. The use of the velocity of TLFs and the delayed γ-ray demonstrate the proof of principle and effectiveness of the new setup.

Discovery of New Isotope ^{241}U and Systematic High-Precision Atomic Mass Measurements of Neutron-Rich Pa-Pu Nuclei Produced via Multinucleon Transfer Reactions.

The new isotope ^{241}U was synthesized and systematic atomic mass measurements of nineteen neutron-rich Pa-Pu isotopes were performed in the multinucleon transfer reactions of the ^{238}U+^{198}Pt system at the KISS facility. The present experimental results demonstrate the crucial role of the multinucleon transfer reactions for accessing unexplored neutron-rich actinide isotopes toward the N=152 shell gap in this region of nuclides.

Effect of deformation dependence and mirror nucleus corrections energy on multinucleon transfer reaction cross sections

Multinucleon transfer reactions are currently a powerful way to synthesize neutron-rich nuclei. To explore the effect of nucleus deformation and mirror nucleus shell correction energy in the nucleus mass model on the calculation of multinucleon transfer reaction cross sections in the dinuclear system (DNS) model, three macroscopic microscopic mass models are selected and the transfer reaction cross sections are calculated for 136Xe+208Pb and 64Ni+238U by improved DNS model+GEMINI++, respectively. The mirror nucleus shell correction energy does not improve the accuracy of the cross section of the transfer reaction. The introduction of a different dependence of the Coulomb and surface energy on the deformation can improve the calculation of the transfer reaction cross section when the projectile and target nuclei are deformed nuclei.

Production cross sections of new neutron-rich isotopes with Z=92–106 in the multinucleon transfer reaction Au197+Th232

The multinucleon transfer reactions $^{197}\mathrm{Au}+^{232}\mathrm{Th}, ^{186}\mathrm{W}+^{232}\mathrm{Th}$, and $^{238}\mathrm{U}+^{232}\mathrm{Th}$ are investigated within the framework of dinuclear system (DNS) model with a decay model gemini$++$. The calculated isotopic production cross sections in the $^{136}\mathrm{Xe}+^{249}\mathrm{Cf}$ reaction at ${E}_{\mathrm{c}.\mathrm{m}.}=567\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ can reproduce the experimental data well. Due to the subshell closures, the behavior of ``inverse'' quasifission process is found in the collisions of $^{186}\mathrm{W}+^{232}\mathrm{Th}$ and $^{197}\mathrm{Au}+^{232}\mathrm{Th}$. The reaction $^{197}\mathrm{Au}+^{232}\mathrm{Th}$ is more advantageous to produce neutron-rich isotopes with $Z=92--106$ than $^{186}\mathrm{W}+^{232}\mathrm{Th}$ and $^{238}\mathrm{U}+^{232}\mathrm{Th}$, because it has the lowest value of the potential energy that needed to overcome in the nucleon transfer process. Furthermore, the incident energy dependence of isotopic production cross sections in the reaction $^{197}\mathrm{Au}+^{232}\mathrm{Th}$ is studied. It is found that ${E}_{\mathrm{c}.\mathrm{m}.}=756.47$ MeV is more suitable for producing new isotopes with $Z=92--98$, while ${E}_{\mathrm{c}.\mathrm{m}.}=690.69$ MeV is the optimal incident energy for $Z=99--106$. The effect of incident energy on the interaction time is also investigated. The production cross sections of 88 unknown neutron-rich transuranium nuclei are predicted with the cross sections at the order of ${10}^{\ensuremath{-}6}$ to $10\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{b}$.

Transfer reactions in Pb206+Sn118 : From quasielastic to deep-inelastic processes

We measured multinucleon transfer reactions for the $^{206}\mathrm{Pb}+^{118}\mathrm{Sn}$ system at ${E}_{\mathrm{lab}}=1200$ MeV by employing the large solid angle magnetic spectrometer PRISMA. Differential and total cross sections and $Q$-value distributions have been obtained for a variety of neutron and proton pick-up and stripping channels. The $Q$-value distributions show how the quasielastic and deep inelastic processes depend on the mass and charge of the transfer products. The corresponding cross sections have been compared with calculations performed with the grazing code. An overall good agreement is found for most of the few nucleon transfer channels. The underestimation of the data for channels involving a large number of transferred nucleons indicates that more complicated processes populate the given isotopes.

Dynamics of charge equilibration and effects on producing neutron-rich isotopes around N=126 in multinucleon transfer reactions

The dynamics of the charge equilibration (CE) and the effects on the production of the neutron-rich isotopes around $N = 126$ in multinucleon transfer reactions are still not well understood. In this Letter, we investigate the mechanism of the CE from different viewpoints by using the extended version of the dinuclear system model (DNS-sysu) and the improved quantum molecular dynamics (ImQMD) model. From the macroscopic and microscopic dynamical viewpoints, we find incomplete CE for the mass asymmetry reaction systems even in the very deep collisions, and the behavior of "inverse CE" that the tendency of the fragments is away from the $N/Z$ value of the compound system in the reaction $^{140}$Xe + $^{198}$Pt. Unlike the slow process presented in the ImQMD model, the behavior of fast equilibration with the characteristic time $\sim$ 0.52 zs is obtained based on the DNS-sysu model, which is consistent with the experimental data. By performing the systematic calculation, the correlation between the CE and the mass asymmetry of the reaction systems is clarified, which not only accounts for the observed intriguing phenomena of the CE but also provides essential information for producing the neutron-rich isotopes around $N = 126$.

Progress on production cross-sections of unknown nuclei in fusion evaporation reactions and multinucleon transfer reactions

The progresses on production cross-sections of unknown nuclei in fusion evaporation (FE) reactions and multinucleon transfer (MNT) reactions are reviewed. The synthesis of the superheavy nuclei (SHN) with [Formula: see text], 119, 120, 121, and 122 in FE reactions is presented. As a promising pathway to produce neutron-rich nuclei, the MNT reactions near the Coulomb barrier are applied to investigate the generation of neutron-rich heavy nuclei and the transuranium nuclei. The predicted production cross-sections of unknown neutron-rich nuclei in MNT reactions are summarized. We make a comparison of the radioactive beam-induced FE reactions and MNT process for producing the predicted double magic nuclei [Formula: see text]Fl, which provides a possible pathway to approach the island of stability.

Multinucleon Transfer Reactions in the \(^{238}\mathrm {U}+{^{238}}\)U System Studied with the VAMOS\(+\)AGATA\(+\)ID-Fix

Multinucleon Transfer Reactions in the \(^{238}\mathrm {U}+{^{238}}\)U System Studied with the VAMOS\(+\)AGATA\(+\)ID-Fix

New K isomers in Cf248

The nuclear structure of $^{248}\mathrm{Cf}$ was investigated at the Tokai Tandem Accelerator Laboratory of the Japan Atomic Energy Agency. $^{248}\mathrm{Cf}$ was one of the nuclei produced in the $^{18}\mathrm{O}+^{249}\mathrm{Cf}$ multinucleon transfer reaction. An array of Ge and ${\mathrm{LaBr}}_{3}$ detectors was used to detect the $\ensuremath{\gamma}$ rays emitted. More than ten new $\ensuremath{\gamma}$-ray transitions from $^{248}\mathrm{Cf}$ were observed and, for the first time, lifetimes of excited states in the nanosecond range were measured. For the previously known bandhead of the ${2}^{\ensuremath{-}}$ octupole vibrational band at 592 keV, a lifetime of 6.7(2) ns was found. Another, new isomeric state, with a lifetime of 16.8(5) ns, decays via a 48-keV $E1$ transition to a much longer-lived state lying at 0.9(3) MeV, for which a lifetime larger than $\ensuremath{\approx}200$ ns is estimated. For this latter state, the unobserved decay points to $K\ensuremath{\geqslant}5$. Considering available theoretical models, possible spin-parity assignments of new states are discussed.