Multinucleon Transfer Reactions Research Articles

Study of fission using multi-nucleon transfer reactions

Multi-nucleon transfer channels of the reactions of 18O+232Th, 18O+238U, 18O+248Cm were used to measure fission-fragment mass distribution for various nuclides and their excitation energy dependence. Predominantly asymmetric fission is observed at low excitation energies for all the studied cases, with an increase of the symmetric fission towards high excitation energies. Experimental data are compared with predictions of the fluctuation-dissipation model, where effects of multi-chance fission (neutron evaporation prior to fission) was introduced. It was shown that a reliable understanding of the observed fission fragment mass distributions can be obtained only invoking multi-chance fissions.

Multinucleon transfer dynamics in heavy-ion collisions near Coulomb-barrier energies

The multinucleon transfer reactions near barrier energies has been investigated with a multistep model based on the dinuclear system (DNS) concept, in which the capture of two colliding nuclei, the transfer dynamics and the de-excitation process of primary fragments are described by the analytical formula, the diffusion theory and the statistical model, respectively. The nucleon transfer takes place after forming the DNS and is coupled to the dissipation of relative motion energy and angular momentum by solving a set of microscopically derived master equations within the potential energy surface. Specific reactions of $^{40,48}$Ca+$^{124}$Sn, $^{40}$Ca ($^{40}$Ar, $^{58}$Ni)+$^{232}$Th, $^{40}$Ca ($^{58}$Ni)+$^{238}$U and $^{40,48}$Ca ($^{58}$Ni) +$^{248}$Cm near barrier energies are investigated. It is found that the fragments are produced by the multinucleon transfer reactions with the maximal yields along the $\beta$-stability line. The isospin relaxation is particularly significant in the process of fragment formation. The incident energy dependence of heavy target-like fragments in the reaction of $^{58}$Ni+$^{248}$Cm is analyzed thoroughly.

Inverse quasifission in the reactions Gd156,160+W186

Background: Low-energy multinucleon transfer reactions may be used for production of new neutron-enriched heavy nuclei.Purpose: Our aim is to investigate the influence of proton ($Z=82$) and neutron ($N=82$, 126) shells as well as orientation effects on the formation of reaction products in the inverse quasifission process in the reactions $^{156,160}\mathrm{Gd}+^{186}\mathrm{W}$.Methods: Mass, energy, and angular distributions of primary binary fragments formed in the reactions $^{156}\mathrm{Gd}+^{186}\mathrm{W}$ at an energy of 878 MeV, and $^{160}\mathrm{Gd}+^{186}\mathrm{W}$ at 860 and 935 MeV, have been measured using the double-arm time-of-flight spectrometer CORSET at the U400 cyclotron of the Flerov Laboratory of Nuclear Reactions (FLNR) at the Joint Institute for Nuclear Research (JINR), Dubna.Results: Enhancement in the yield of products with masses 200--215 u has been found for both reactions. The cross sections of the formation of trans-target fragments with masses around 208 u are found to be about 10 \ensuremath{\mu}b at the Coulomb barrier energy and reach the level of 0.5 mb at the energy above the barrier for side-to-side collision.Conclusions: The enhanced yield of products with masses heavier than the target mass confirms the important role of the closed shells at $Z=82$ and $N=82$, 126 in the inverse quasifission process in low-energy damped collisions. The orientation effect caused by the strong deformation of colliding nuclei can result in a gain in the yield of heavy target-like fragments.

Theoretical study on production cross sections of exotic actinide nuclei in multinucleon transfer reactions**Supported by National Natural Science Foundation of China (11605296) and Natural Science Foundation of Guangdong Province, China (2016A030310208)

Within the dinuclear system (DNS) model, the multinucleon transfer reactions 129,136Xe + 248Cm, 112Sn + 238U, and 144Xe + 248Cm are investigated. The production cross sections of primary fragments are calculated with the DNS model. By using a statistical model, we investigate the influence of charged particle evaporation channels on production cross sections of exotic nuclei. It is found that for excited neutron-deficient nuclei the charged particle evaporation competes with neutron emission and plays an important role in the cooling process. The production cross sections of several exotic actinide nuclei are predicted in the reactions 112Sn + 238U and 136,144Xe + 248Cm. Considering the beam intensities, the collisions of 136,144Xe projectiles with a 248Cm target for producing neutron-rich nuclei with Z=92−96 are investigated.

Production mechanism of new neutron-rich heavy nuclei in the [formula omitted] reaction

The multinucleon transfer reaction of Xe136+198Pt at Elab=7.98 MeV/nucleon is investigated by using the improved quantum molecular dynamics model. The quasielastic, deep-inelastic, and quasifission collision mechanisms are studied via analyzing the angular distributions of fragments and the energy dissipation processes during the collisions. The measured isotope production cross sections of projectile-like fragments are reasonably well reproduced by the calculation of the ImQMD model together with the GEMINI code. The isotope production cross sections for the target-like fragments and double differential cross sections of 199Pt, 203Pt, and 208Pt are calculated. It is shown that about 50 new neutron-rich heavy nuclei can be produced via deep-inelastic collision mechanism, where the production cross sections are from 10−3 to 10−6 mb. The corresponding emission angle and the kinetic energy for these new neutron-rich nuclei locate at 40∘–60∘ and 100–200 MeV, respectively.

Neutron effective single-particle energies above Ni78 : A hint from lifetime measurements in the N=51 isotones Se85 and Kr87

Background: While the N=50 shell-gap evolution towards Ni78 is presently in the focus of nuclear structure research, experimental information on the neutron effective single-particle energy sequence above the Ni78 core remain scarce. Direct nucleon-exchange reactions are indeed difficult with presently available post-accelerated radioactive-ion beams (especially for high orbital-momentum orbitals) in this exotic region. Purpose: In this study we probe the evolution of the ν1g7/2 effective single-particle energy which is a key to understanding the possible evolution of the spin-orbit splitting due to the proton-neutron interaction in the Ni78 region. To achieve this goal, a method based on lifetime measurements is used for the first time. The obtained lifetimes of the 7/21+ states in Kr87 and Se85 are used to investigate the ν1g7/2 evolution. Method: Yrast and near-yrast states in the light N=51 isotones Se85 and Kr87 were populated via multinucleon transfer reactions, using a Se82 beam and a U238 target at the LNL tandem-ALPI facility. The prompt γ rays were detected by the AGATA Demonstrator and particle identification was performed using the PRISMA spectrometer. Lifetime measurements were performed by using the Cologne plunger device for deep inelastic reactions and the Recoil Distance Doppler Shift technique. Results: We obtain τ(7/21+)=0.4−0.4+1.6 ps for Kr87. In the case of Se85 an upper limit of 3(2) ps is obtained for the τ7/21+ value. Conclusion: For Kr87, the measured (7/21+) lifetime is consistent with a core-coupled 2+⊗ν2d5/2 configuration for this state. This result is consistent with that obtained by direct reaction, which validates our method. For Se85, the measured 7/21+ lifetime limit indicates a very small contribution of the ν1g7/2 configuration to the wave function of this state.8 MoreReceived 13 December 2016Revised 20 June 2017DOI:https://doi.org/10.1103/PhysRevC.96.044320©2017 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasEnergy levels & level densitiesLifetimes & widthsNuclear structure & decaysShell modelProperties59 ≤ A ≤ 89Nuclear Physics

Mechanism of multinucleon transfer reaction based on the GRAZING model and DNS model

Multinucleon transfer (MNT) reactions have been studied by either the GRAZING model or dinuclear system (DNS) model before. MNT reactions in the grazing regime have been described quite well by the GRAZING model. The DNS model is able to deal with MNT reactions, which happen in the closer overlapped regime after contact of two colliding nuclei. Since MNT reactions can happen in both areas and cannot be distinguished in view of experimental work, it is beneficial to compare these two models to clarify mechanism of MNT reactions. In this study, the mechanism of the MNT reaction has been studied by comparing the GRAZING model and DNS model for the first time. Reaction systems 136Xe+208Pb at MeV and 64Ni+238U at MeV are taken as examples in this paper. It is found that the gradients of transfer cross sections with respect to the impact parameter of the GRAZING model and DNS model are mainly concentrated on two different areas, which represents two kinds of transfer mechanisms. The theoretical framework of these two models are exclusive according to whether capture happens, which guarantees that the theoretical results calculated by these two models have no overlap and can be added up. Results indicate that the description of experimental MNT reaction cross sections can be significantly improved if calculations of the GRAZING model and DNS model are both considered.

Doughnut-shaped gas cell for KEK Isotope Separation System

Abstract We have developed a doughnut-shaped argon gas cell with a rotating target for the KEK Isotope Separation System (KISS). The new gas cell increased extraction yields for target-like fragments (TLFs) produced in multi-nucleon transfer (MNT) reactions. KISS is an on-line isotope separator, which makes use of a laser ion source combined with an argon gas cell as a gas catcher for TLFs. This system has been implemented for nuclear spectroscopy of neutron-rich isotopes in the region of N = 126 . A gas flow simulation was performed to optimize the design of the gas cell for efficient and fast transport of TLFs. To confirm the performance expected at the design stage, we performed off- and on-line experiments by using iridium atoms evaporated from a filament in the gas cell and TLFs produced by a 136 Xe beam and 198 Pt target system respectively. We could increase the extraction yield by more than an order of magnitude by applying a doughnut-shaped gas cell with a rotating target. Thus, we could perform nuclear spectroscopy in this heavy region with the use of KISS.

High-spin structures in Xe132 and Xe133 and evidence for isomers along the N=79 isotones

The transitional nuclei Xe132 and Xe133 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in Xe136+Pb208 MNT reactions employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (ii) in the Xe136+Pt198 MNT reaction employing the GAMMASPHERE spectrometer in combination with the gas-detector array CHICO, and (iii) as an evaporation residue after a Te130(α,xn)Xe134−xn fusion-evaporation reaction employing the HORUS γ-ray array at the University of Cologne. The high-spin level schemes are considerably extended above the Jπ=(7−) and (10+) isomers in Xe132 and above the 11/2− isomer in Xe133. The results are compared to the high-spin systematics of the Z=54 as well as the N=78 and N=79 chains. Furthermore, evidence is found for a long-lived (T1/2≫1μs) isomer in Xe133 which closes a gap along the N=79 isotones. Shell-model calculations employing the SN100PN and PQM130 effective interactions reproduce the experimental findings and provide guidance to the interpretation of the observed high-spin features.3 MoreReceived 9 June 2017DOI:https://doi.org/10.1103/PhysRevC.96.024321©2017 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectromagnetic transitionsIsomer decaysLifetimes & widthsNuclear spin & parityNuclear structure & decaysShell modelProperties90 ≤ A ≤ 149Nuclear Physics

In-gas-cell laser spectroscopy of the magnetic dipole moment of the N≈126 isotope Pt199

Magnetic dipole moment and mean-square charge radius of $^{199}$Pt ($I^{\pi}=$ 5/2$^-$) have been evaluated for the first time from the investigation of the hyperfine splitting of the $\lambda_1=$ 248.792 nm transition by in-gas-cell laser ionization spectroscopy. Neutron-rich nucleus $^{199}$Pt was produced by multi-nucleon transfer reaction at the KISS where the nuclear spectroscopy in the vicinity of $N=$ 126 is planed from the aspect of an astrophysical interest as well as the nuclear structure. Measured magnetic dipole moment $+$0.63(13)$\mu_{\rm N}$ is consistent with the systematics of those of nuclei with $I^{\pi}=$ 5/2$^-$. The deformation parameter $|<\beta_2^2>^{1/2}|$ evaluated from the isotope shift indicates the gradual shape change to spherical shape of platinum isotopes with increasing neutron number toward $N=$ 126.

Production of heavy neutron-rich nuclei with radioactive beams in multinucleon transfer reactions

The production mechanism of heavy neutron-rich nuclei is investigated by using the multinucleon transfer reactions of $$^{136,148}{\hbox {Xe}}+^{208}$$ Pb and $$^{238}{\hbox {U}}+^{208}$$ Pb in the framework of a dinuclear system model. The evaporation residual cross sections of target-like fragments are studied with the reaction system $$^{148}{\hbox {Xe}}+^{208}$$ Pb at near barrier energies. The results show that the final isotopic production cross sections in the neutron-deficient side are very sensitive to incident energy while it is not sensitive in the neutron-rich side. Comparing the isotopic production cross sections for the reactions of $$^{208}$$ Pb bombarded with stable and radioactive projectiles, we find that neutron-rich radioactive beams can significantly increase the production cross sections of heavy neutron-rich nuclei.

Theoretical predictions on production of neutron-deficient nuclei with Z ≥ 93 in multinucleon transfer reactions

Within the framework of dinuclear system model, the transfer reactions 58Ni + 233U, 58Ni + 238U, and 64Ni + 238U are investigated. The influences of projectile and target neutron numbers on cross sections of producing neutron-deficient actinide nuclei in transfer reactions are studied. It is found that the system 58Ni + 233U with smaller neutron excess is favorable to produce neutron-deficient nuclei. We predict the production cross sections of neutron-deficient nuclei with Z=93–98 in transfer reactions 58Ni + 233U and 40Ca + 245Cm with different incident energies. We find the transfer reactions 58Ni + 233U and 40Ca + 245Cm are feasible for producing neutron-deficient actinide nuclei in future experiments.

Modeling multi-nucleon transfer in symmetric collisions of massive nuclei

Symmetric collisions of massive nuclei, such as 238U + 248Cm, have been proposed as ways to make new n-rich heavy nuclei via multi-nucleon transfer (MNT) reactions. We have measured the yields of several projectile-like and target-like fragments from the reaction of 1360 MeV 204Hg + 198Pt. We find that current models for this symmetric collision (GRAZING, DNS, ImQMD) significantly underestimate the yields of these transfer products, even for small transfers.

Toward lifetime and g factor measurements of short-lived states in the vicinity of 208Pb

The multi-nucleon transfer reaction mechanism was used to produce and study nuclei in the vicinity of 208Pb. This mass region is a test case for the nuclear shell model. The mass identification of the fragments was performed with the large acceptance magnetic spectrometer VAMOS++ coupled to the AGATA γ-tracking array. This experiment aimed to determine both lifetimes and gyromagnetic ratios of excited states with the Cologne plunger device. The analysis indicates promising results with the possibility to determine several new lifetimes in this region.

Production of neutron-rich isotopes around N=126 in multinucleon transfer reactions

The multinucleon transfer reactions has been investigated within the dinuclear system model. The nucleon transfer is coupled to the dissipation of relative motion energy and angular momentum by solving a set of microscopically derived master equations. A barrier distribution approach is implemented in the model in order to including the contributions of different orientations and dynamical effects. The available data of fragment production via multinucleon transfer reactions could be understood with the model for the reactions of $^{136}$Xe + $^{198}$Pt/$^{208}$Pb near Coulomb barrier energies. It is found that the production of heavy neutron-rich nuclei weakly depends on the incident energy. However, the yields of proton-rich nuclei increase with the incident energy.

Radiochemical study of the kinematics of multi-nucleon transfer reactions in 48Ca + 248Cm collisions 10% above the Coulomb barrier

The kinematics of multi-nucleon transfer reactions in 48Ca + 248Cm collisions at 262 MeV (center of target) was investigated by using a stacked-foil technique and radiochemical separations of trans-curium elements. Trans-curium isotopes were identified by α-particle spectroscopy. For Fm isotopes, by comparing the centroids of the measured post-neutron emission isotope distributions with the most probable primary mass number predicted by Volkov's generalized Qgg systematics, the missing mass (number of evaporated neutrons) is estimated. The latter is compared with that deduced from the measured centroid of the laboratory angular distribution peaked closely to the grazing angle and the centroid of the range distribution, being used to determine the average total kinetic energy loss (TKEL) and the average excitation energy. The latter agrees within the uncertainties with the missing mass so that a consistent picture of the reaction mechanism emerges. For products closer to the target Z, e.g., Cf and Bk, the distributions of kinetic energies are much broader than for Fm, reflecting the fact that in the former, values of TKEL reach from quasi-elastic scattering all the way to deep inelastic scattering. The measured laboratory angular distribution and the average laboratory kinetic energy of the Fm isotopes, being the prototypes for multi-nucleon transfer products, are benchmark values for the design of electromagnetic separators to be constructed for the separation and detection of unknown neutron-rich transactinides produced in this nuclear reaction type.

Isomers and high-spin structures in the N=81 isotones Xe135 and Ba137

The high-spin structures of the N = 81 isotones 135Xe and 137Ba are investigated after multinucleontransfer (MNT) and fusion-evaporation reactions. Both nuclei are populated in (i) 136Xe+238U and (ii) 136Xe+208Pb MNT reactions employing the high-resolution Advanced Gamma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (iii), in the 136Xe+198Pt MNT reaction employing the -ray array GAMMASPHERE in combination with the gas detector array Chico, and (iv) via a 11B+130Te fusion-evaporation reaction. The high-spin level schemes of 135Xe and 137Ba are considerably extended to higher energies. The 2058-keV (19=2 ) state in 135Xe is identified as an isomer, completing the systematics for the N = 81 isotones. Its half-life is measured to be 8.6(10) ns, corresponding to a transition probability of B(E2; 19=2 ! 15=2 ) = 0:539(69) W.u. Latest shell model calculations considering 132Sn as a closed core reproduce the experimental findings and provide guidance to the interpretation of the new levels. The experimentally deduced reduced quadrupole transition probabilities of the isomeric states are compared to shell-model predictions.

Current status of GALS setup in JINR

This is a brief report on the current status of the new GAs cell based Laser ionization Setup (GALS) at the Flerov Laboratory for Nuclear Reactions (FLNR) of the Joint Institute for Nuclear Research (JINR) in Dubna. GALS will exploit available beams from the U-400M cyclotron in low energy multi-nucleon transfer reactions to study exotic neutron-rich nuclei located in the “north-east” region of nuclear map. Products from 4.5 to 9 MeV/nucleon heavy-ion collisions, such as 136Xe on 208Pb, are thermalized and neutralized in a high pressure gas cell and subsequently selectively laser re-ionized. In order to choose the best scheme of ion extraction the results of computer simulations of two different systems are presented. The first off- and online experiment will be performed on osmium atoms that is regarded as a most convenient element for producing isotopes with neutron number in the vicinity of the magic N = 126.

Measurement of lifetimes in Fe62,64,Co61,63 , and Mn59

Lifetimes of the 41+ states in 62,64Fe and the 11/21− states in 61,63Co and 59Mn were measured at the Grand Accelerateur National d'Ions Lourds (GANIL) facility by using the Advanced Gamma Tracking Array (AGATA) and the large-acceptance variable mode spectrometer (VAMOS++). The states were populated through multinucleon transfer reactions with a U238 beam impinging on a Ni64 target, and lifetimes in the picosecond range were measured by using the recoil distance Doppler shift method. The data show an increase of collectivity in the iron isotopes approaching N=40. The reduction of the subshell gap between the ν2p1/2 and ν1g9/2 orbitals leads to an increased population of the quasi-SU(3) pair (ν1g9/2,ν2d5/2), which causes an increase in quadrupole collectivity. This is not observed for the cobalt isotopes with N<40 for which the neutron subshell gap is larger due to the repulsive monopole component of the tensor nucleon-nucleon interaction. The extracted experimental B(E2) values are compared with large-scale shell-model calculations and with beyond-mean-field calculations with the Gogny D1S interaction. A good agreement between calculations and experimental values is found, and the results demonstrate in particular the spectroscopic quality of the Lenzi, Nowacki, Poves, and Sieja (LNPS) shell-model interaction.

γ -ray spectroscopy of Tl209

States in $^{209}\mathrm{Tl}$ were populated using a multinucleon transfer reaction with a $^{136}\mathrm{Xe}$ beam impinging on a thick $^{208}\mathrm{Pb}$ target at $E=785$ MeV. The beam was pulsed at 825-ns intervals in order to perform isomer decay spectroscopy. The known ${J}^{\ensuremath{\pi}}=17/{2}^{+}$ isomer in $^{209}\mathrm{Tl}$ was located at 1228(4) keV and measured to have a half-life of ${T}_{1/2}=146(10)$ ns. A second isomer with ${J}^{\ensuremath{\pi}}=13/{2}^{+}$ was found to have ${T}_{1/2}=14(5)$ ns. The previously suggested low-energy X and Y transitions were found to have energies 57(2) and 47(2) keV respectively, while the measurement of conversion coefficients and a new decay path make the spin assignments below the isomers experimentally firm. Correlating the delayed $\ensuremath{\gamma}$ transitions with the prompt beam flash allowed the decay of states above the isomer to be found. The longer-lived isomer represents full alignment of the simplest two-particle, one-hole configuration and illuminates the remarkably weak coupling of the proton hole to the $^{210}\mathrm{Pb}$ core.