odd-N Nuclei Research Articles

Structural Investigation of 101Pd and Systematic in Neighboring Even-Z and Odd-N nuclei

Structural Investigation of 101Pd and Systematic in Neighboring Even-Z and Odd-N nuclei

Spectroscopy along flerovium decay chains. II. Fine structure in odd- A Fl289

Fifteen correlated α-decay chains starting from the odd-A superheavy nucleus Fl289 were observed following the fusion-evaporation reaction Ca48+Pu244. The results call for at least two parallel α-decay sequences starting from at least two different states of Fl289. This implies that close-lying levels in nuclei along these chains have quite different spin-parity assignments. Further, observed α-electron and α-photon coincidences, as well as the α-decay fine structure along the decay chains, suggest a change in the ground-state spin assignment between Cn285 and Ds281. Our experimental results, on the excited level structure of the heaviest odd-N nuclei to date, provide a direct testing ground for theory. This is illustrated by comparison with new nuclear structure calculations based on the symmetry-conserving configuration mixing theory.Received 12 April 2022Revised 1 September 2022Accepted 16 December 2022DOI:https://doi.org/10.1103/PhysRevC.107.L021301Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by Bibsam.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlpha decayLow & intermediate energy heavy-ion reactionsNuclear structure & decaysPropertiesA ≥ 220TechniquesNuclear density functional theoryNuclear Physics

Reviewing relative longevity of beta-stable odd-n nuclei in actinides: Using alpha preformation probabilities from cluster formation model

Reviewing relative longevity of beta-stable odd-n nuclei in actinides: Using alpha preformation probabilities from cluster formation model

Possibilities of direct production of superheavy nuclei with Z=112–118 in different evaporation channels

The production cross sections of heaviest isotopes of superheavy nuclei with charge numbers 112–118 are predicted in the xn–, pxn–, and αxn–evaporation channels of the 48Ca-induced complete fusion reactions for future experiments. The estimates of synthesis capabilities are based on a uniform and consistent set of input nuclear data. Nuclear masses, deformations, shell corrections, fission barriers and decay energies are calculated within the macroscopic-microscopic approach for even-even, odd-Z and odd-N nuclei. For odd systems the blocking procedure is used. To find saddle points, the Imaginary Water Flow technique is used and non-axiallity is taken into account. As shown, our calculations, based on a new set of mass and barriers, agree very well with the experimentally known cross-sections, especially in the 3n–evaporation channel. The dependencies of these predictions on the mass/fission barriers tables, the ratio af/a, and fusion models are discussed. A way is shown to produce directly unknown superheavy isotopes in the 1n– or 2n–evaporation channels. The synthesis of new superheavy isotopes unattainable in reactions with emission of neutrons is proposed in the promising channels with emission of protons (σpxn≃10−200 fb) and alphas (σαxn≃50−500 fb).

Lifetime measurements of excited states in 163W and the implications for the anomalous B(E2) ratios in transitional nuclei

This letter reports lifetime measurements of excited states in the odd-N nucleus 163W using the recoil-distance Doppler shift method to probe the core polarising effect of the i13/2 neutron orbital on the underlying soft triaxial even-even core. The ratio B(E2:21/2+→17/2+)/B(E2:17/2+→13/2+) is consistent with the predictions of the collective rotational model. The deduced B(E2) values provide insights into the validity of collective model predictions for heavy transitional nuclei and a geometric origin for the anomalous B(E2) ratios observed in nearby even-even nuclei is proposed.

Using excitation-energy dependent fission yields to identify key fissioning nuclei in r-process nucleosynthesis

The possibility that nucleosynthesis in neutron star mergers may reach fissioning nuclei introduces significant uncertainties in predicting the relative abundances of r-process material from such events. We evaluate the impact of using sets of fission yields given by the 2016 GEF code for spontaneous (sf), neutron-induced ((n, f)), and β-delayed (βdf) fission processes which take into account the approximate initial excitation energy of the fissioning compound nucleus. We further explore energy-dependent fission dynamics in the r process by considering the sensitivity of our results to the treatment of the energy sharing and de-excitation of the fission fragments using the FREYA code. We show that the asymmetric-to-symmetric yield trends predicted by GEF 2016 can reproduce the high-mass edge of the second r-process peak seen in solar data and examine the sensitivity of this result to the mass model and astrophysical conditions applied. We consider the effect of fission yields and barrier heights on the nuclear heating rates used to predict kilonova light curves. We find that fission barriers influence the contribution of 254Cf spontaneous fission to the heating at ∼100 d, such that a light curve observation consistent with such late-time heating would both confirm that actinides were produced in the event and imply the fission barriers are relatively high along the 254Cf β-feeding path. We lastly determine the key nuclei responsible for setting the r-process abundance pattern by averaging over thirty trajectories from a 1.2–1.4 M⊙ neutron star merger simulation. We show it is largely the odd-N nuclei undergoing (Z, N)(n, f) and (Z, N)βdf that control the relative abundances near the second peak. We find the ‘hot spots’ for β-delayed and neutron-induced fission given all mass models considered and show most of these nuclei lie between the predicted N = 184 shell closure and the location of currently available experimental decay data.

Shape and shell structure of lighter ( N≲90 ) neutron-rich nuclei based on a phenomenological Woods-Saxon potential

By using a phenomenologically successful Woods-Saxon potential, I study the shape and shell structure of (A) neutron drip line nuclei with 10 \leq N \leq 60, (B) neutron-rich nuclei related to the r- process with 40 \leq N \leq 90, and (C) one-particle spectra in the potential provided by the nucleus 70Fe as a representative of so-called N=40 "island of inversion (IoI)" nuclei. First, the shell structure that is unique in very weakly-bound neutrons is systematically studied, and the approximate neutron number of odd-N nuclei at which spherical (or deformed) halos can be found is pinned down. Second, the difference of the shell structure in r-process nuclei from that in stable nuclei is examined. Third, the similarity and the difference between the shell structure of N=20 IoI nuclei and that of N=40 IoI nuclei are analyzed. As a result of it, it is concluded that in Fe and Cr isotopes the deformation called "N=40 IoI" continuing up to N=50 is unlikely.

Properties of the 3/2−[521] band in the odd-N rare-earth nuclei

High-spin states in 161Er have been studied experimentally via the 150Nd(16O, 5n) reaction at a beam energy of 86 MeV. Three rotational bands built on the 5/2+[642], 3/2−[521], and 11/2−[505] configurations have been extended up to high-spin states, and particularly, the α = −1/2 branch of the ground state 3/2−[521] band has been revised significantly. It is found that signature inversion occurs in the 3/2−[521] band after the band crossing in 161Er. The systematics of the signature inversion associated with the 3/2−[521] configuration in the rare-earth region is discussed. The band properties are analyzed within the framework of a triaxial particle-rotor model, and a triaxial deformation is proposed to the 3/2−[521] band.

Change of shell structure and magnetic moments of odd-N deformed nuclei towards the neutron drip line

Examples of the change of neutron shell structure in both weakly bound and resonant neutron one-particle levels in nuclei towards the neutron drip line are exhibited. It is shown that the shell-structure change due to the weak binding may lead to the deformation of those nuclei with the neutron numbers N ≈ 8, 20, 28 and 40, which are known to be magic numbers in stable nuclei. Nuclei in the ‘island of inversion’ are most easily and in a simple manner understood in terms of deformation. As an example of spectroscopic properties other than single-particle energies, magnetic moments of some weakly bound possibly deformed odd-N nuclei with neutron numbers close to those traditional magic numbers are given, which are calculated using the wavefunction of the last odd particle in deformed Woods–Saxon potentials.

One-particle properties of deformedN≈28odd-Nnuclei with weakly bound or resonant neutrons

Possible deformation of odd-N nuclei with N approximate to 28 toward the neutron drip line is investigated using the Nilsson diagram based on deformed Woods-Saxon potentials. Both weakly-bound and resonant one-particle levels are properly obtained by directly solving the Schrodinger equation in mesh of space coordinate with the correct boundary condition. If we use the same diffuseness of the potential as that of beta-stable nuclei, the energy difference between the neutron 2p(3/2) and 1f(7/2) levels becomes very small or the N = 28 energy gap almost disappears, as the binding energies of those levels approach zero. This suggests that the ground states of those neutron drip line nuclei are likely to be deformed. In particular, the spin-parity and the magnetic moment of the ground state of odd-N nuclei, S-43(16)27 and S-45(16)29, are examined. Moreover, it is suggested that in Mg-39(12)27 lying outside the drip line the lowest resonant state may have 5/2(-), if the N = 28 energy gap almost vanishes. (Less)

Correction to Relativistic Mean Field binding energy and [formula omitted] scheme

The differences between the experimental and Relativistic Mean Field binding energies have been calculated for a large number of even–even nuclei from A=50 to 220. Excluding certain mass regions, the differences, after suitable corrections for particular isotope chains, are found to be proportional to the Casten factor P, chosen as a measure of n–p interaction strength in a nucleus. Results for even-Z odd-N nuclei are also seen to follow the same relation, if the odd–even mass difference is taken into account following the semiempirical formula. This indicates that the n–p interaction is the major contributor to the difference between the calculated and the experimental binding energies.

Relative longevity of odd-N nuclei in the heavy actinide region

It is shown that, contrary to the normal feature witnessed all across the periodic table that even–even nuclei are more abundant/longer-lived than their odd-A neighbours, many odd-mass heavy nuclei are seen to be much longer-lived than their even–even neighbours. In the trans-plutonium domain of even-Z actinides, all the predominantly alpha-decaying odd-N nuclei are longer-lived than their even-mass neighbours. Similar behaviour is observed for heavy odd-Z actinides as well. A semi-empirical criterion is stated to determine the relative longevity of the odd-N and even-N nuclei. This feature is sought to be explained by examining the respective alpha decay rates. A detailed discussion of α-decays of the β-stable curium (Z = 96) isotopic chain is presented to illustrate this phenomenon. Correspondence with a similar occurrence in spontaneously fissioning nuclei is briefly pointed out.

Enhancement of then−pinteraction in odd-odd nuclei

A comprehensive study of the mass-data-based interaction energy of the last i proton(s) and the last j neutron(s) indicates that the last proton-neutron interaction energy ${\ensuremath{\epsilon}}_{1p\ensuremath{-}1n}$ in odd-odd nuclei is greater than half of the average value of the last proton-dineutron interaction energy ${\ensuremath{\epsilon}}_{1p\ensuremath{-}2n}$ in odd-Z nuclei and the last diproton-neutron interaction energy ${\ensuremath{\epsilon}}_{2p\ensuremath{-}1n}$ in odd-N nuclei, and the phenomenon of the enhancement of the $n\ensuremath{-}p$ interaction energy in odd-odd nuclei is universal. In proton rich nuclei, the enhancement is generally more remarkable than that in neutron rich ones. To one's surprise, the ${\ensuremath{\epsilon}}_{1p\ensuremath{-}1n}$ in some odd-odd nuclei near proton drip line is even greater than the average value of ${\ensuremath{\epsilon}}_{1p\ensuremath{-}2n}$ and ${\ensuremath{\epsilon}}_{2p\ensuremath{-}1n}.$ Additionally, it is found that ${\ensuremath{\epsilon}}_{1p\ensuremath{-}2n}$ in odd-Z nuclei is approximate to ${\ensuremath{\epsilon}}_{2p\ensuremath{-}1n}$ in odd-N nuclei with the same mass number A, which is equivalent to the Garvey-Kelson relation proposed long ago.

Superdeformed rotational bands with density dependent pairing interactions

Abstract The cranked Hartree-Fock-Bogoliubov method, applied in a previous study to SD bands of even Hg and Pb isotopes, is extended by including pairing correlations described by a zero-range density-dependent interaction. This more realistic description of the pairing channel modifies the balance between the neutron and proton pairing energies and introduces an orbital variation of the pairing gaps. This results in a retarded alignment, significantly improving the agreement with data in both the A = 150 and 190 mass regions. The behavior expected for SD bands in odd-N or odd-Z nuclei is discussed on the basis of the quasiparticle routhians calculated for the even-even isotopes.

Search for identical bands at normal deformation in the A=130 mass region.

A search for sequences of identical transition energies at normal deformations in odd-A nuclei relative to the average even-even neighbors in the mass A=130 region has been carried out. Four such sequences in odd-N nuclei and one in odd-Z nuclei have been found. It is suggested that the identity in the moments of inertia in these bands may be the result of a precise cancellation between the reduction in pairing, and the reduction in quadrupole deformation, caused by the odd particle.

Measurement of the intrinsic quadrupole moments in the upsilon i13/2 bands of 135,137Sm

The quadrupole moments of the upsilon i13/2 intruder bands in 135,135Sm have been deduced from nuclear lifetimes measured using the Doppler shift attenuation method. A centroid shift analysis of the data yielded values of Q0=7.0 eb and 5.0 eb for 135Sm and 137Sm respectively. The value for the band in 135Sm is the largest yet measured for an odd-N nucleus in this mass region and is consistent with the deformations of superdeformed (SD) bands in this mass region. This implies that the odd-N SD and single upsilon i13/2 intruder bands wound mass 135 are all based on the same single particle configuration, upsilon 61. In addition, a lineshape analysis has been performed on the 135Sm data in order to assess the nature of the sidefeeding into the band. The results indicate a value for the static quadrupole moment which is consistent with that obtained using the centroid shift method. There is little evidence of any significantly slow sidefeeding component in the lineshapes.

Neutron i13/2 orbital in the A=120-140 mass region.

The decoupled \ensuremath{\nu}${\mathit{i}}_{13/2}$ bandhead energies and deformations of odd-N nuclei with Z=56--64 and N=69--77 have been calculated systematically with the newly modified Nilsson parameters. The results show that the occupation of the low-K \ensuremath{\nu}${\mathit{i}}_{13/2}$ orbitals does favor large deformation. Possible candidates for the experimental observation of such structures are discussed. The strong \ensuremath{\beta}-driving effect of those orbitals at higher frequency is examined as well.

Spectroscopy of the light rare-Earth nuclei 133Pm and 133Sm: Configuration-dependent pairing and evidence for strong residual proton-neutron interactions in neighbouring odd-N and odd-Z nuclei

The low-lying, rotational band structures of the highly neutron-deficient light rare-earth nuclei, 133Sm and 133Pm have been investigated using the 40Ca + 96Ru reaction at a beam energy of approximately 180 MeV. Five new bands have been observed in both nuclei. 133Sm possesss two strongly coupled bands which are thought to be built upon the vh112[523]72−and vd52[402]52+ Nilsson configurations. In addition to the previously reported vi132 intruder band, there is also evidence for a second decoupled, negative-parity structure in 133Sm based on the vh92[541]12− orbital. In 133Pm evidence is presented for both signature partners of the πh112 band. The expected h112 neutron alignment in these bands has not been observed. It is suggested that this provides evidence for a strong pn interaction. A strongly coupled band built on the πg72[413]52+ configuration has also been established. Both signature partners of this band show clear evidence for the alignment of a pair of h112 protons followed by a pair of h112 neutrons. A strongly coupled three quasi-particle configuration has also been identified which feeds into the unfavoured signature of the πh112 band. The results are discussed in terms of cranked shell model, total routhian surface calculations and the systematics of the A ∼ 135 region.

Quasiparticle-Vibration Couplings in Rotating Triaxial Odd-A Nuclei

_ A new microscopic model which takes into account both the static and dynamic triaxial deformations in the high·spin states of odd-A nuclei is developed. The model is based on the rotating shell model and treats the quasiparticle-vibration couplings in the uniformly rotating frame of reference. Effects of the static and dynamic triaxial deformations on the signature splitting of the quasiparticle energies and on the signature dependence of B(M1), B(E2; I -+ I -1) and B(E2; 1-+ I - 2) for the transitions within the unique·parity bands in odd-A nuclei are discussed. Numerical exam­ ples are presented for odd-Z nuclei 157Ho, l59Tm and 161, 165Lu, and for odd-N nuclei 161Dy,167Er and 16l,l63, l67 Yb to which experimental data for B(M1) and B(E2) are available.

Collective systematics in the mass 80 region.

The deformation of nuclei around A\ensuremath{\sim}80 is found to vary systematically as a function of the product of the number of protons and neutrons (or holes) (${N}_{\mathrm{p}{N}_{\mathrm{n})}}$ in the shell extending from 28 to 50 particles. A similar result was reported previously for heavier even A nuclei, but this is the first investigation of a region in which neutrons and protons fill the same major shell and the first application of the technique to odd A nuclei. The systematic behavior is seen in both energy level spacings and electromagnetic quadrupole transition strengths and in both even-even and odd A nuclei. These systematics hold for the measures of deformation not involving the positions of the ${0}^{+}$ states, which are strongly affected by the coexistence of weakly and strongly deformed shapes in some A\ensuremath{\sim}80 nuclei. A rather surprising result is that the deformations of the odd-Z--even-N nuclei are substantially larger than those of the even-Z--odd-N nuclei.