Excited States Of Nuclei Research Articles

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.

Correspondence between isoscalar monopole strengths and $\alpha$ inelastic cross sections on 24Mg

Abstract The correspondence between the isoscalar monopole (IS0) transition strengths and $\alpha$ inelastic cross sections, the $B({\rm IS0})$–$(\alpha,\alpha')$ correspondence, is investigated for $^{24}$Mg($\alpha,\alpha'$) at 130 and 386 MeV. We adopt a microscopic coupled-channel reaction framework to link structural inputs, diagonal and transition densities, for $^{24}$Mg obtained with antisymmetrized molecular dynamics to the ($\alpha,\alpha'$) cross sections. We aim at clarifying how the $B({\rm IS0})$–$(\alpha,\alpha')$ correspondence is affected by the nuclear distortion, the in-medium modification to the nucleon–nucleon effective interaction in the scattering process, and the coupled-channel effect. It is found that these effects are significant and the explanation of the $B({\rm IS0})$–$(\alpha,\alpha')$ correspondence in the plane wave limit with the long-wavelength approximation, which is often used, makes no sense. Nevertheless, the $B({\rm IS0})$–$(\alpha,\alpha')$ correspondence tends to remain because of a strong constraint on the transition densities between the ground state and the $0^+$ excited states. The correspondence is found to hold at 386 MeV with an error of about 20%–30%, while it is seriously compromised at 130 MeV, mainly by the strong nuclear distortion. It is also found that when a $0^+$ state that has a different structure from a simple $\alpha$ cluster state is considered, the $B({\rm IS0})$–$(\alpha,\alpha')$ correspondence becomes less valid. For a quantitative discussion on the $\alpha$ clustering in $0^+$ excited states of nuclei, a microscopic description of both the structure and reaction parts will be necessary.

Estimations of first 2+ energy states of even–even nuclei by using artificial neural networks

The first excited 2+ energy states of nuclei give many substantial information related to the nuclear structure. Including these levels, all excited states of nuclei are shown regularities in spin, parity and energy. In the even-even nuclei, the first excited state is generally 2+ and the energy values of them increase as the closed shells are approached. The excited levels in nuclei can be investigated by using theoretical nuclear models such nuclear shell model. In the present study for the first time, we have used artificial neural networks for the determination of the energies of first 2+ states in the even-even nuclei in nuclidic chart as a function of Z, N and A numbers. We have used adopted literature values for the estimations. According to the results, the method is convenient for this goal and one can confidently use the method for the determination of first 2+ state energy values whose experimental values do not exist in the literature.

Sensitivity studies on the excited states of nuclei in beta decays in the r-process of neutron star mergers

Sensitivity studies conducted in this paper aim to examine the influence of uncertainties in beta decay rates on simulations of rapid neutron capture (r-process) nucleosynthesis. However, previous studies multiplied the ground states of the theoretical rates or the ground states of the experimental rates by 10, and most of the theoretical rates and the experimental rates consider only the beta decay rates of the ground states but not the rates in stellar conditions because of the thermally excited states. In this study, we performed the first sensitivity test on the excited states of nuclei having A > 120 in the r-process. The ground state beta decay rates and estimated excited state rates are folded together to estimate a thermal decay rate as a function of temperature. We examined how the thermally excited states affect the stellar rates for all A > 120 nuclei. We found that there is a slight change in the second peak of final abundance in the r-process by Lu isotopes. This is the same as that in Famiano’s paper (Famiano and Boyd 2008 J. Phys. G: Nucl. Part. Phys. 35 2).

TPEN: A Triple-foil differential Plunger for lifetime measurements of excited states in Exotic Nuclei

A Triple-foil differential Plunger for Exotic Nuclei (TPEN) has been developed to measure the lifetimes of excited states in nuclei with small production cross-sections. TPEN utilises one target foil and two degrader foils to make differential lifetime measurements: directly determining the decay function and its derivative at a single plunger distance setting. The direct measurement of the decay function and its derivative removes the requirement to measure γ-ray intensities at several target-to-degrader distances, thereby reducing the beam-time required relative to a conventional plunger with a single-degrader foil. This paper describes the commissioning of TPEN in the lifetime measurement of the first excited 4+ state in 156Dy using this differential lifetime technique. The 46(2) ps measured lifetime was found to be in good agreement with the 45.6(5) ps deduced from a previous high-statistics experiment using a conventional two-foil plunger. A comparison between the differential mode with TPEN, and that using TPEN as a conventional two-foil plunger reveals that it achieves the same statistical accuracy with a ∼4-fold reduction in beam-time in the differential mode, for the reaction and experimental setup used in this work. TPEN opens up new opportunities to study exotic nuclei with lower production cross-sections that were previously not accessible.

Investigation of spatial manifestation of α clusters in 16O via α-transfer reactions

Recently, we have determined surface distributions of α clusters in the ground state of Ne20 from α-transfer cross sections, without investigating the properties of its excited states. In this paper we extend our comprehension of α-cluster structures in excited states of nuclei through reaction studies. In particular we focus on O16, for which attention has been paid to advances of structure theory and assignment regarding 4+-resonance states. We study the surface manifestation of the α-cluster states in both the ground and excited states of O16 from the analysis of the α-transfer reaction C12(Li6,d)16O. The α-transfer reaction is described by the distorted-wave Born approximation. We test two microscopic wave functions as an input of reaction calculations. Then a phenomenological potential model is introduced to clarify the correspondence between cluster-wave functions and transfer-cross sections. Surface peaks of the α-wave function of O16(0+) are sensitively probed by transfer-cross sections at forward angles, while it remains unclear how we trace the surface behavior of O16(4+) from the cross sections. From inspection of the cross sections at forward angles, we are able to specify that the α-cluster structure in the 01+ and 02+ states prominently manifests itself at the radii ∼4 and ∼4.5 fm, respectively. It is remarkable that the 41+ state has the C12+α-cluster component with the surface peak at the radius ∼4 or outer, whereas the C12+α-cluster component in the 42+ state is found not to be dominant. The 42+ state is difficult to be interpreted by a simple potential model assuming the C12+α configuration only.

Symmetrical level schemes of the even–even Sm[formula omitted] and Yb[formula omitted] nuclei up to 10+ in the yrast bands

For the first time, we show here that three isotopes of the Sm isotopic chain almost overlay with three isotopes of the Yb isotopic chain in terms of experimental observables within the NπNν scheme. A recent systematic work by Sayğı on reduced transitional probabilities in pseudo-mirror nuclei revealed that nuclei having particle–hole symmetry tend to manifest alike experimental structures. The NπNν quantity is an indicator of the symmetry and depends on valence nucleon (or holes) number from the nearest closed shell by considering the subshell closures, which simplifies the systematics of excitation energies and related B(E2; L+→(L−2)+) values of excited states in nuclei placed in the different mass regions of nuclear chart. In the light of available data, the experimental observables in the group of 136Sm–160Yb, 134Sm–162Yb and 132Sm–164Yb nuclei have been analyzed in a vertical and horizontal perspectives and the ratio of reduced transition probabilities of the first excited states compared with existing theoretical predictions. The data brought to light that the structure of each group reflects identical yrast bands up to 10+.

Conditions for Population of Energy Levels Inversion when Active Medium Based on Gadolinium Isotopes Gd155 and Gd156 Couple Neutron Pumping

The paper theoretically studies the possibility of energy transformation of fast and epithermal neutrons to energy of coherent photon radiation at the expense of a neutron pumping of the active medium formed by nucleus with longliving isomerous states. The channel of the nucleus formation in isomeric state as a daughter nucleus resulting from the nuclear reaction of neutron capture by a lighter nucleus is taken into consideration for the first time. Assessment of neutron flux spectrum parameters providing transition from the main state into one of the excited ones for the nuclei of isotopes54Xe130,10Ne22is made. It was shown that to transit the isotope nuclei into the excited state by forward neutron scattering on the nuclei it is necessary to “select” the isotopes not only with great specific energy of nucleons coupling but also with a small value of the neutron absorption cross section. Moreover, the paper performs the analysis of cross sections dependence of radiative neutron capture by the nuclei of gadolinium isotopes Gd155and Gd156. As a result, the speed of Gd156nuclei formation is stated to exceed the speed of their “burnup” in the neutron flux. It is provided by a unique combination of absorbing properties of two isotopes of gadolinium Gd155 and Gd156 in both thermal and resonance regions of neutron energy. We have formulated the conditions required for making isotope nuclei excited by forward neutron scattering on nuclei and for storing nuclei in excited states. The relation which allows estimating processes parameters of neutron capture by nuclei, formation and decay of nuclei isomeric states is obtained as a result of analytical solution of differential equations system of nuclide kinetics taking into account the decay of nuclei isomeric states. The paper makes the possibility analysis of neutron pumping of the participating medium created by the hafnium isotope nuclei. The properties of hafnium isotopes nuclei is found to do not allow providing conditions for population inversion of energy levels due to the formation of hafnium nuclei in isomeric state Hf178m2in the neutron flux. The paper shows the possibility of excess energy accumulation in the participating medium created by the nuclei of the pair of gadolinium isotopes Gd155and Gd156due to formation and storage of nuclei in isomeric state at radiative neutron capture by the nuclei of the stable isotope with a smaller mass. It is concluded that when the active medium created by gadolinium nuclei is pumped by neutrons with the flux density of the order of 1013cm-2·s-1, the condition of levels population inversion can be achieved in a few tens of seconds. The wave length of the radiation generated by the medium is 0.0006 nm. Sintered ceramics Gd2O3based on enriched in the 155-th isotope of gadolinium can be considered a possible active medium. Thus, there is a possibility of creation of the laser techniques of new generation with the parameters providing its application in pulse power engineering of the future.

Excited nuclei, resonances and reactions in neutron star crusts

The short review of research results concerning the study of reactions and processes that occur in the neutron star crusts is given. The peculiarities of electron capture reactions by a nucleus in overdense crystalline structures have been demonstrated for various nuclei, in particular some even-even nuclei at electron capture reactions give daughter nuclei in excited states. Excited nuclei due to nonlinear interactions lead to a high-order harmonic generation. High energy gammas interact with charged particles, give a neutrino radiation and also knock out nucleons from neighbour nuclei.It is also shown that interactions of neutrons with two and more nuclei in an overdence lattice give a large number of new resonance states. These resonances result in a formation of specific local oscillations in the corresponding layers of the lattice. The periodic enhancement of these processes in the dependence on the elemental composition of the primary neutron star matter is considered.

Sensitivity tests on the rates of the excited states of positron decays during the rapid proton capture process of the one-zone X-ray burst model

In this paper, we investigate the sensitivities of positron decays on a one-zone model of type-I X-ray bursts. Most existing studies have multiplied or divided entire beta decay rates (electron captures and beta decay rates) by 10. Instead of using the standard Fuller & Fowler (FFNU) rates, we used the most recently developed weak library rates [1], which include rates from Langanke et al.'s table (the LMP table) (2000) [2], Langanke et al.'s table (the LMSH table) (2003) [3], and Oda et al.'s table (1994) [4] (all shell model rates). We then compared these table rates with the old FFNU rates [5] to study differences within the final abundances. Both positron decays and electron capture rates were included in the tables. We also used pn-QRPA rates [6,7] to study the differences within the final abundances. Many of the positron rates from the nuclei's ground states and initial excited energy states along the rapid proton capture (rp) process have been measured in existing studies. However, because temperature affects the rates of excited states, these studies should have also acknowledged the half-lives of the nuclei's excited states. Thus, instead of multiplying or dividing entire rates by 10, we studied how the half-lives of sensitive nuclei in excited states affected the abundances by dividing the half-lives of the ground states by 10, which allowed us to set the half-lives of the excited states. Interestingly, we found that the peak of the final abundance shifted when we modified the rates from the excited states of the 105Sn positron decay rates. Furthermore, the abundance of 80Zr also changed due to usage of pn-QRPA rates instead of weak library rates (the shell model rates).

Use of (3He, t) charge-exchange reactions in determining radii of excited states of nuclei

A method for determining the radii of excited states of nuclei by means of (3He, t) charge-exchange reactions was proposed. Two versions of a comparison of differential cross sections for (3He, t) reactions were considered. The first relies on a comparison with cross sections for inelastic-scattering processes leading to the formation of isobaric analog states, while the second involves (3He, t) reactions leading to the production of the ground state. The two versions in question yield similar results and make it possible to determine the radius of the first excited state of the 13N nucleus. This state has the excitation energy of E* = 2.37 MeV, lying above the proton-emission threshold. The resulting radius proved to be enhanced in relation to the ground state and is close to the radius of the 3.09-MeV isobaric analog state of the 13С nucleus, which has a neutron halo. This permitted drawing the conclusion that the 13N nucleus in the 2.37-MeV state has a proton halo. The possibility of revealing a proton halo in other states of light nuclei is considered.

Nuclear structure studies based on the lifetime measurements of excited states in nuclei at the in-beam γ terminal of HI-13 tandem accelerator

Nuclear structure studies based on the lifetime measurements of excited states in nuclei at the in-beam γ terminal of HI-13 tandem accelerator

Spin-isospin collective excited states of nuclei and relevant physics quantities

This paper are dedicated to introduce and study the spin-isospin collective excited states of nuclei, together with the relevant HF+RPA or HFB+QRPA models which are widely used for the studies of these collective excited states. Studying of these collective excited states may attain some insights and information for the spin-dependent nucleon-nucleon interactions. Previously the self-consistent Skyrme-HF+RPA model has been applied to study the GT and SD transitions in closed-shell nuclei, where the tensor force produces strong effects on the main peak energy, which provides strong constraint for the strengths of Skyrme tensor terms. For the pf shell nuclei with N ~ Z , the Isoscalar (IS) pairing force plays a determinant role for the low energy strong GT states, which may well constrain the strength of IS pairing through the excitation energies of these strong GT states in certain nuclei.

Photodisintegration ofLi7with progeny nuclei in excited states

We study the reaction channels $^{7}\text{Li}+\ensuremath{\gamma}\ensuremath{\rightarrow}n+^{6}\text{Li}(2.19), ^{7}\text{Li}+\ensuremath{\gamma}\ensuremath{\rightarrow}n+^{6}\text{Li}(3.56)$, and $^{7}\text{Li}+\ensuremath{\gamma}\ensuremath{\rightarrow}d+^{5}\text{He}(1.27)\ensuremath{\rightarrow}n+d+^{4}\text{He}$ by detecting neutrons produced by photodisintegration events. We find absolute cross sections and angular dependence for $^{7}\text{Li}+\ensuremath{\gamma}\ensuremath{\rightarrow}n+^{6}\text{Li}(2.19)$ at photon energies 13 and 15 MeV and for $^{7}\text{Li}+\ensuremath{\gamma}\ensuremath{\rightarrow}n+^{6}\text{Li}(3.56)$ at the photon energy 15 MeV. The incident photons are linearly polarized and we report dependence of the cross sections on polarization. For the reaction channel $^{7}\text{Li}+\ensuremath{\gamma}\ensuremath{\rightarrow}d+^{5}\text{He}(1.27)\ensuremath{\rightarrow}n+d+^{4}\text{He}$ we obtain an upper bound on its cross section at photon energies 12, 13, and 15 MeV.

Progress in the structural studies of proton emitters

Studies of nuclei far from the β stability line have been at the forefront of nuclear structure research. Proton radioactivity is an important decay mode for nuclei near the proton drip-line. Studies of this decay mode can reveal valuable information on exotic nuclear structure and provide deep insights on the organization of nuclei in extreme conditions. For example, recent advances in modern experimental techniques have allowed the measurement of the detailed rotational structure of proton emitters. Yu et al. of the Oak Ridge National Laboratory identified states in the ground-state proton emitter 151Lu, which were populated by using the recoil-decay tagging technique. The systematic data suggested a possible isomeric level at high spin in 151Lu. In addition, by using the same technique, Seweryniak et al. of the Argonne National Laboratory observed rotational bands feeding the ground state and the isomeric state in the proton emitter 141Ho. These authors showed that, by using a state-of-the-art detection system, it is possible to study excited states in nuclei produced with sub 100 nb cross-sections. These new experimental data have given us valuable information for understanding the interactions in exotic systems, which motivate further theoretical development. For example, in the experimental work of Seweryniak et al., the authors challenged existing theoretical models to include non-axial degrees of freedom in the nuclear potential in calculations of proton decay rates. In this article, we provide a brief review on the recent progress in the studies of proton emitters, with an emphasis on introducing exciting theoretical models. A good model should not only yield the decay rates, but should also contain microscopic degrees of freedom that provide information on the detailed structure. This requires developing theoretical models that extend beyond the semi-classical methods, for example those based on the particle-rotor model. We mention several such attempts that are documented in the literature, including the relativistic Hartree-Bogoliubov model of Vretenar, Lalazissis, and Ring, and the most recent application of the projected shell model by the current authors.

Cluster decay analysis and related structure effects of fissionable heavy and superheavy nuclei

Collective clusterization approach of dynamical cluster decay model (DCM) has been applied to study the attributes of hot (T ≠ 0) and rotating (l ≠ 0) nuclei lying in heavy and superheavy mass regimes. We present here an overview of the characteristic fission decay properties such as shell effect, role of entrance channel, quadrupole (β2) deformations and impact of hot (equatorial) compact orientation degree of freedom in comparison to cold (polar) elongated configuration. The presence of non-compound nucleus process, i.e., quasifission, is also investigated. Apart from studying the decay of excited state nuclei, the dynamics of heavy particle cluster emission is also addressed using the preformed cluster model (PCM).

Measurement of 232Th(n,5n γ) cross sections from 29 MeV to 42 MeV

The excitation function of the reaction 232 Th(n, 5nγ)228 Th from 29 to 42 MeV has been measured for the first time at the quasi-monoenergetic neutron beam of the UCL cyclotron CYCLONE employing the 7Li(p,n) source reaction. Taking advantage of the good energy resolution of the planar High-Purity Germanium (HPGe) detectors, prompt γ-ray spectroscopy was used to detect the γ-rays resulting from the decay of excited states of nuclei created by the (n,xn) reactions. The neutron beam was characterized by a combination of time of flight measurements carried out using a liquid scintillation detector and a 238U fission ionization chamber. Fluence measurements were performed using a proton recoil telescope. The results are compared with TALYS-1.4 code calculations.

Dynamic deformation of light nuclei in excited states

An important property—the dynamic deformation of B* light aligned nuclei—is investigated for the nuclear reactions A(x, y)B* → γ + B 0 by measuring the y-γ correlations. Dynamic deformation is determined from the orientation tensors of multipolar moments. Normalization constants of the contributions from even-rank orientation tensors are determined from the condition of coincidence between dynamic and static deformations of the B* nucleus for θ y = 0°. Experimental dynamic deformations of 12C(2+) nuclei caused by the inelastic scattering of α particles and deuterons are determined, along with the 10Be(2+) nuclei formed in reaction 9Be(d, p)10Be(2+). It is shown that the dynamic deformation of the aligned nuclei depends on how they are formed and their structure, and evolves substantially when the angle θ y is varied.

SU-E-T-111: Estimation of Characteristics for Dose Distribution in Polymer Gel by Means of Monte Carlo Simulation

Purpose: To estimate the three dimensional dose distributions for proton, proton induced gamma rays and proton induced neutron particles, in case of exposing the proton beam to a polymer gel dosimeter and a water phantom. Methods: The polymer gel dosimeter was compositeness material of gelatin, methacrylic acid, hydroquinone, tetrakis and distilled water. The density of the gel dosimeter was 1.04g/cm3 which density was similar to water. The proton beam energies of 72 and 116 MeV were used in the simulation. Proton beam was directed to the top of a cylindrical phantom which radius was 5 cm and height was 12.2 cm for covering the proton Bragg‐peak (on X‐axis). The proton beam interacted with the nuclei of the phantom and the nuclei in excited states emitted prompt gamma rays and proton induced neutron particles during the process of de‐excitation. The proton particles, gamma prays and induced neutron were detected by the gel dosimeter and water phantom, respectively. The gap of the X‐axis was 2 mm. Results: The Bragg‐peak for proton particles in the gel dosimeter was similar to water phantom. The dose distribution for proton and prompt gamma rays in the gel dosimeter and water phantom was approximately identical in case of 72 and 116 MeV for proton beam. However, in case of proton induced neutron particles for 72 and 116 MeV proton beam, particles were not detected in the gel dosimeter, while the water phantom absorbed neutron. Conclusion: For the evaluation of proton dose distribution, the gel dosimeter was valuable tools for three dimensional measurements. This work indicates the evaluation for dose distribution of proton, induced gamma, and neutron in the gel dosimeter compared with the water phantom. Considering the Result data, the gel dosimeter which was developed in the normoxic state attentively detected the dose distribution for proton beam exposure except neutron particles.

Excited nuclei in neutron star crusts

The paper considers the chains of successive electron capture reactions by nuclei of the iron group which take place in the crystal structures of neutron star envelopes. It is shown that as a result of such reactions the daughter nuclei in excited states accumulate within certain layers of neutron star crusts. The phonon model of interactions is proposed between the excited nuclei in the crystalline structure, as well as formation of highly excited nuclear states which emit neutrons and higher energy photons.