A long-standing crucial question with atomic nuclei is whether or not α clustering occurs there. An α particle (helium-4 nucleus) comprises two protons and two neutrons, and may be the building block ...of some nuclei. This is a very beautiful and fascinating idea, and is indeed plausible because the α particle is particularly stable with a large binding energy. However, direct experimental evidence has never been provided. Here, we show whether and how α(-like) objects emerge in atomic nuclei, by means of state-of-the-art quantum many-body simulations formulated from first principles, utilizing supercomputers including K/Fugaku. The obtained physical quantities exhibit agreement with experimental data. The appearance and variation of the α clustering are shown by utilizing density profiles for the nuclei beryllium-8, -10 and carbon-12. With additional insight by statistical learning, an unexpected crossover picture is presented for the Hoyle state, a critical gateway to the birth of life.
We study the nuclear Schiff moments of 129Xe and 199Hg induced by the nucleon electric dipole moment using large-scale shell model calculations. For 129Xe, we find a linear relation between the ...leading-order contribution and magnetic moment, which would be useful in reducing the theoretical uncertainty. The conventional model space does not contain the 0g9/2 and 0h9/2 orbitals, which are connected to the spin-orbit partners by large matrix elements. Thus, to evaluate the influence of the relevant single-particle orbitals outside the conventional model space, we apply the quasiparticle vacua shell model method. Moreover, the next-to-leading-order contribution arises from parity and time-reversal violation in the nucleus. We demonstrate that these secondary effects do not induce any significant disturbance to the correlation. Additionally, we report the shell model results for the nuclear Schiff moment coefficients of 199Hg. Compared to previous studies, the results obtained in this study are rather large, indicating a higher sensitivity to the neutron electric dipole moment.
Shapes and shape evolution in the mass-130 region, including the Te, Xe, and Ba isotopes, have long been a focus of discussion in nuclear physics. This mass region consists of complex many-body ...systems that can behave in astonishingly simple and regular ways, as classified in the Casten symmetry triangle. By applying the shell model Hamiltonian proposed recently, we carry out calculations using the Hartree-Fock-Bogolyubov plus generator coordinate method, in the large model space containing the (1g_{9/2},1g_{7/2},2d_{5/2},2d_{3/2},3s_{1/2},1h_{11/2},2f_{7/2}) orbits. Based on good reproduction of the experimentally known energy levels, spectroscopic quadrupole moments, and E2 transition probabilities, we identify the quasi-SU(3) couplings across the N=50 and 82 shell gaps, which play a role in driving shape evolution and phase transition discussed in the extended Casten triangle. Specifically, we demonstrate that the quasi-SU(3) coupling mechanism in the proton partner orbits (1g_{9/2}, 2d_{5/2}) tends to drive the system to be more γ soft, and that in the neutron partner orbits (1h_{11/2}, 2f_{7/2}) are responsible for the oblate-to-prolate shape phase transition. With an emphasis on discussing spectroscopic quadrupole moments, our Letter uncovers hidden symmetries from the vast shell-model configurations and adds microscopical insights into the empirical symmetry triangle.
In addition to micronuclei that are formed from chromosomal material (the chromosome-type micronuclei), there are also micronuclei formed from extrachromosomal elements the double minute (DM)-type ...micronuclei. These two types of micronuclei are distinct entities, which exist and arise independently in a cell. A DM is a large extrachromosomal element that consists of amplified genes that are commonly seen in cancer cells; the aggregates of DMs can eventually be expressed as DM-type micronuclei. The question of how the DM-type micronuclei arise was answered by uncovering the quite unique intracellular behaviour of DMs during the cell cycle progression. This behaviour of DMs appeared to be common among the broad spectrum of extrachromosomal elements of endogenous, exogenous or artificial origin. Therefore, studying the biology of DM-type micronuclei will enable us to understand how these extrachromosomal structures may be retained within a cell or expelled from the nucleus and eliminated from the cell. This knowledge could also be used for the treatment of cancers and the development of a new mammalian host-vector system.
Gene amplification in human cancer cells generates two cytogenetically identifiable structures: extrachromosomal double minutes (DMs) and the chromosomal homogeneously staining region (HSR). DMs are ...composed of autonomously replicating circular DNA of genomic origin, and they tell us about how the extrachromosomal elements may behave in the cells, how they were entrapped by the micronuclei and how they were eliminated from the cells. On the other hand, the episome model predicts that extrachromosomal elements excised from the chromosome arm might generate DMs, and the breakage-fusion-bridge (BFB) cycle model explains the generation of the HSR. In accordance with this, a plasmid bearing a mammalian replication initiation region (IR) and a matrix attachment region (MAR) mimics gene amplification and generates DMs and HSRs de novo. The IR/MAR gene amplification system extends our understanding on the mechanism of gene amplification and the behavior of amplified genes. Furthermore, the system may suggest the way how extrachromosomal elements in general may alter the chromosome architecture and function.
The underlying structure of low-lying collective bands of atomic nuclei is discussed from a novel perspective on the interplay between single-particle and collective degrees of freedom, by utilizing ...state-of-the-art configuration interaction calculations on heavy nuclei. Besides the multipole components of the nucleon-nucleon interaction that drive collective modes forming those bands, the monopole component is shown to control the resistance against such modes. The calculated structure of ^{154}Sm corresponds to the coexistence between prolate and triaxial shapes, while that of ^{166}Er exhibits a deformed shape with a strong triaxial instability. Both findings differ from traditional views based on β/γ vibrations. The formation of collective bands is shown to be facilitated from a self-organization mechanism.
It is notable that along the N=Z line in the nuclear chart, extremely large collectivity emerges suddenly in the mass-80 region. By applying the Monte Carlo shell model (MCSM) and the ...Hartree-Fock-Bogolyubov plus generator coordinate method (HFB+gcm), we study this problem to find the origin. On the basis that both calculations reproduce the experimental data of the N≈Z nuclei with A=64∼88, we identify the backbone from full shell-model calculations that can explain the strong prolate deformation. We find that inclusion of the 2d5/2 orbit in the model space to cooperate with 1g9/2 is the key ingredient to describe the rapid increase of collectivity from 70Se to 76Sr and to produce the observed large B(E2) values in 76Sr, 78Sr and 80Zr. The quadrupole-quadrupole (QQ) interaction acting between the quasi-SU(3) partner orbits, 1g9/2−2d5/2, is the driving force that changes the nuclear shape from oblate- to prolate-deformed. We further suggest that the quasi-SU(3) effect is particularly amplified in the N≈Z nuclei because these are the unique examples where quasi-SU(3) partner orbits can be formed, like the nuclear pairing, simultaneously in three different types: neutron-neutron (n-n), proton-proton (p-p), and neutron-proton (n-p), which respectively interact through the n-n, p-p, and n-p components of the QQ force to enhance the quadrupole collectivity coherently.
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