Atomic nuclei are finite quantum systems composed of two distinct types of fermion--protons and neutrons. In a manner similar to that of electrons orbiting in an atom, protons and neutrons in a nucleus form shell structures. In the case of stable, naturally occurring nuclei, large energy gaps exist between shells that fill completely when the proton or neutron number is equal to 2, 8, 20, 28, 50, 82 or 126 (ref. 1). Away from stability, however, these so-called 'magic numbers' are known to evolve in systems with a large imbalance of protons and neutrons. Although some of the standard shell closures can disappear, new ones are known to appear. Studies aiming to identify and understand such behaviour are of major importance in the field of experimental and theoretical nuclear physics. Here we report a spectroscopic study of the neutron-rich nucleus (54)Ca (a bound system composed of 20 protons and 34 neutrons) using proton knockout reactions involving fast radioactive projectiles. The results highlight the doubly magic nature of (54)Ca and provide direct experimental evidence for the onset of a sizable subshell closure at neutron number 34 in isotopes far from stability.

Reaction cross sections (sigma(R)) for 19C, 20C and the drip-line nucleus 22C on a liquid hydrogen target have been measured at around 40A MeV by a transmission method. A large enhancement of sigma(R) for 22C compared to those for neighboring C isotopes was observed. Using a finite-range Glauber calculation under an optical-limit approximation the rms matter radius of 22C was deduced to be 5.4+/-0.9 fm. It does not follow the systematic behavior of radii in carbon isotopes with N < or = 14, suggesting a neutron halo. It was found by an analysis based on a few-body Glauber calculation that the two-valence neutrons in 22C preferentially occupy the 1s(1/2) orbital.

Rho-associated coiled-coil protein kinase (ROCK) is an effector for the small GTPase Rho and plays a pivotal role in diverse cellular activities, including cell adhesion, cytokinesis, and gene expression, primarily through an alteration of actin cytoskeleton dynamics. Here, we show that ROCK2 is localized in the nucleus and associates with p300 acetyltransferase both in vitro and in cells. Nuclear ROCK2 is present in a large protein complex and partially cofractionates with p300 by gel filtration analysis. By immunofluorescence, ROCK2 partially colocalizes with p300 in distinct insoluble nuclear structures. ROCK2 phosphorylates p300 in vitro, and nuclear-restricted expression of constitutively active ROCK2 induces p300 phosphorylation in cells. p300 acetyltransferase activity is dependent on its phosphorylation status in cells, and p300 phosphorylation by ROCK2 results in an increase in its acetyltransferase activity in vitro. These observations suggest that nucleus-localized ROCK2 targets p300 for phosphorylation to regulate its acetyltransferase activity.The Rho family of small GTPases, which includes Rho, Rac, and Cdc42, is ubiquitously expressed and plays a pivotal role in the regulation of a wide variety of cellular processes, including cell adhesion and migration, cytokinesis, cell cycle progression, and gene expression (1-4). Like all GTPases, Rho acts as a molecular switch by cycling between two different conformational states, GTP-bound (active) and GDP-bound (inactive) forms. The GTP-bound form of Rho binds its effectors to elicit cellular responses. A number of Rho effector molecules have been identified (5-8). Among them, a family of Ser/Thr protein kinase, ROCK 2 (also called Rho kinase/ROK), has been the subject of extensive studies and appears to mediate the majority of Rho GTPase functions (9, 10). A broad range of cellular activities of Rho and ROCK is thought to be mediated primarily through the regulation of actin cytoskeleton dynamics (9, 10). ROCK phosphorylates and activates LIM kinase, which in turn phosphorylates cofilin and inhibits its actin-depolymerizing activity, leading to increased actin polymerization (10). ROCK also phosphorylates the myosin-binding subunit (MBS) of myosin phosphatase and inactivates the phosphatase activity, which results in increased myosin phosphorylation and contractility (10).Two members of the ROCK family, ROCK1 and ROCK2, have been identified. There is 65% identity in their overall amino acid sequences, and they share several common domains (11). Although ROCK1 and ROCK2 appear to have different activities on a cellular level (12), there has been little difference identified in phenotypes of ROCK1-and ROCK2-null mice, suggesting possible functional redundancy between the two ROCK isoforms (10, 13). ROCK has three main domains critical for its functions: the N-terminal catalytic domain (CAT), a coiled-coil domain in the middle portion that mediates homodimerization, and the C-terminal Rho-binding (RB) and pleckstrin homology (PH) domains (RB/PH domain) (11,...

In an experiment with the BigRIPS separator at the RIKEN Nishina Center, we observed two-proton (2p) emission from 67 Kr. At the same time, no evidence for 2p emission of 59 Ge and 63 Se, two other potential candidates for this exotic radioactivity, could be observed. This observation is in line with Q value predictions which pointed to 67 Kr as being the best new candidate among the three for two-proton radioactivity. 67 Kr is only the fourth 2p ground-state emitter to be observed with a half-life of the order of a few milliseconds. The decay energy was determined to be 1690(17) keV, the 2p emission branching ratio is 37(14)%, and the half-life of 67 Kr is 7.4(30) ms. DOI: 10.1103/PhysRevLett.117.162501 Close to the valley of β stability, nuclear β decay, which is often associated with γ-ray emission, is the only decay mode possible. When moving closer to the limits of stability in both directions, the available decay energy, the Q value, increases at the same time as the binding energy of the excess particle decreases. Therefore, emission of β-delayed particles (protons, neutrons, or α particles) becomes more and more likely. Close to the proton drip line, β-delayed one-, two-, and (in particular recently) three-proton emission has been observed [1][2][3][4][5][6].In all these cases, the excess protons are still sufficiently bound that direct particle emission is not possible.However, when moving further away from the line of stability, the protons are no longer bound by the strong nuclear force and the proton drip line is crossed. For slightly negative proton separation energies S p or S 2p , β þ decay can still compete with direct one-or two-proton emission; however, with separation energies typically below −1 MeV, one-and two-proton emission dominates for odd-and even-Z elements, respectively. We underline here that for 2p radioactivity, the one-proton separation energy has to be positive.For odd-proton-number (odd-Z) elements, one-proton radioactivity is a well-established decay mode and is PRL 117,

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