Superdeformation in the Doubly Magic NucleusC2040a20

A rotational band with seven gamma -ray transitions between states with spin 2 (h) over bar and 16 (h) over bar has been observed in the doubly magic, self-conjugate nucleus Ca-40(20)20. The measured transition quadrupole moment of 1.80(-0.29)(+0.39)eb indicates a superdeformed shape with a deformation beta (2) = 0.59(-0.07)(+0.11). The features of this band are explained by cranked relativistic mean field calculations to arise from an 8-particle 8-hole excitation.

Reevaluation of theP30(p,γ)S31astrophysical reaction rate from a study of theT=1/2mirror nuclei,S31andP31

The $^{30}\mathrm{P}$($p,\ensuremath{\gamma}$)$^{31}\mathrm{S}$ reaction rate is expected to be the principal determinant for the endpoint of nucleosynthesis in classical novae. To date, the reaction rate has only been estimated through Hauser-Feschbach calculations and is unmeasured experimentally. This paper aims to remedy this situation. Excited states in $^{31}\mathrm{S}$ and $^{31}\mathrm{P}$ were populated in the $^{12}\mathrm{C}$($^{20}\mathrm{Ne}$,$n$) and $^{12}\mathrm{C}$($^{20}\mathrm{Ne}$,$p$) reactions, respectively, at a beam energy of 32 MeV, and their resulting $\ensuremath{\gamma}$decay was detected with the Gammasphere array. Around half the relevant proton unbound states …

In-beam spectroscopy of $^{253,254}$No

In-beam conversion electron spectroscopy experiments have been performed on the transfermium nuclei 253,254No using the conversion electron spectrometer SACRED in nearly collinear geometry in conjunction with the gas-filled separator RITU at the University of Jyvaskyla. The experimental setup is discussed and the spectra are compared to Monte Carlo simulations. The implications for the ground-state configuration of 253No are discussed.

Entry distribution of 220Th: A method to determine the fission barrier of an unstable nucleus

Search for a 2-quasiparticle high-Kisomer inRf256

The energies of 2-quasiparticle (2-qp) states in heavy shell-stabilized nuclei provide information on the single-particle states that are responsible for the stability of superheavy nuclei. We have calculated the energies of 2-qp states in {sup 256}Rf, which suggest that a long-lived, low-energy 8{sup -} isomer should exist. A search was conducted for this isomer through a calorimetric conversion electron signal, sandwiched in time between implantation of a {sup 256}Rf nucleus and its fission decay, all within the same pixel of a double-sided Si strip detector. A 17(5)-{mu}s isomer was identified. However, its low population, {approx}5(2)% that of the ground state instead of the expected {a…

Fission Barrier of Superheavy Nuclei and Persistence of Shell Effects at High Spin: Cases ofNo254andTh220

We report on the first measurement of the fission barrier height in a heavy shell-stabilized nucleus. The fission barrier height of No-254 is measured to be B-f = 6.0 +/- 0.5 MeV at spin 15 (h) over bar and, by extrapolation, B-f = 6.6 +/- 0.9 MeV at spin 0 (h) over bar. This information is deduced from the measured distribution of entry points in the excitation energy versus spin plane. The same measurement is performed for Th-220 and only a lower limit of the fission barrier height can be determined: B-f (I) > 8 MeV. Comparisons with theoretical fission barriers test theories that predict properties of superheavy elements.

Structure of rotational bands in 253No

In-beam gamma-ray and conversion electron spectroscopic studies have been performed on the 253 No nucleus. A strongly coupled rotational band has been identified and the improved statistics allows an assignment of the band structure as built on the $\ensuremath 9/2^-[734]_{\nu}$ ground state. The results agree with previously known transition energies but disagree with the tentative structural assignments made in earlier work.

Exploring the stability of super heavy elements: First Measurement of the Fission Barrier of $^{254} $No

The gamma-ray multiplicity and total energy emitted by the heavy nucleus 254No have been measured at 2 different beam energies. From these measurements, the initial distributions of spin I and excitation energy E * of 254No were constructed. The distributions display a saturation in excitation energy, which allows a direct determination of the fission barrier. 254No is the heaviest shell-stabilized nucleus with a measured fission barrier. © Owned by the authors, published by EDP Sciences, 2014.

Mirror symmetry at high spin in51Feand51Mn

Gamma decays from excited states in the ${T}_{z}=\ensuremath{-}\frac{1}{2}$ nucleus ${}^{51}$Fe have been observed for the first time. The differences in excitation energies as compared with those of the mirror partner, ${}^{51}$Mn, have been interpreted in terms of Coulomb effects and the resulting Coulomb energy differences (CED) can be understood intuitively in terms of particle-alignment effects. A new CED effect has been observed, in which different CED trends have been measured for each signature of the rotational structures that characterize these mid-${f}_{7/2}$ shell nuclei. Large-scale $\mathrm{fp}$-shell model calculations have been used to compute the trends of the CED as a func…

Kπ=8−isomers andKπ=2−octupole vibrations inN=150shell-stabilized isotones

Isomers have been populated in {sup 246}Cm and {sup 252}No with quantum numbers K{sup {pi}}=8{sup -}, which decay through K{sup {pi}}=2{sup -} rotational bands built on octupole vibrational states. For N=150 isotones with (even) atomic number Z=94-102, the K{sup {pi}}=8{sup -} and 2{sup -} states have remarkably stable energies, indicating neutron excitations. An exception is a singular minimum in the 2{sup -} energy at Z=98, due to the additional role of proton configurations. The nearly constant energies, in isotones spanning an 18% increase in Coulomb energy near the Coulomb limit, provide a test for theory. The two-quasiparticle K{sup {pi}}=8{sup -} energies are described with single-pa…

Spectroscopy of transfermium nuclei: No-252(102)

An in-beam study of excited states in the transfermium nucleus 252 No has been performed using the recoil separator RITU together with the JUROSPHERE II array at the University of Jyväskylä. This is the second transfermium nucleus studied in an in-beam experiment. Levels up to spin 20 were populated and compared to levels in 254 No . An upbend is seen at a frequency of 200 keV/ħ corresponding to spin 16. We also use an improved systematics to connect the energy of the lowest 2 + state with its half-life and find that the deformation of both 2 5 2 , 2 5 4 No is slightly larger than previously assumed. peerReviewed

Mirror energy differences in theA=31mirror nuclei,S31andP31, and their significance in electromagnetic spin-orbit splitting

Excited states in $^{31}\mathrm{S}$ and $^{31}\mathrm{P}$ were populated in the $^{12}\mathrm{C}$($^{20}\mathrm{Ne}$,n) and $^{12}\mathrm{C}$($^{20}\mathrm{Ne}$,p) reactions, respectively, at a beam energy of 32 MeV. High spin states of positive and negative parity have been observed in $^{31}\mathrm{S}$ for the first time, and the yrast scheme of $^{31}\mathrm{P}$ has been extended. Large mirror energy differences between the first $9/{2}^{\ensuremath{-}}$ and $13/{2}^{\ensuremath{-}}$ states were observed, but only small differences for the first $7/{2}^{\ensuremath{-}}$ and $11/{2}^{\ensuremath{-}}$ levels. The significance of these observations is discussed in relation to the electromag…

Candidate superdeformed band in 28Si

Structure of the Odd-A, Shell-Stabilized NucleusNo102253

In-beam {gamma}-ray spectroscopic measurements have been made on {sub 102}{sup 253}No. A single rotational band was identified up to a probable spin of 39/2({Dirac_h}/2{pi}), which is assigned to the 7/2{sup +}[624] Nilsson configuration. The bandhead energy and the moment of inertia provide discriminating tests of contemporary models of the heaviest nuclei. Novel methods were required to interpret the sparse data set associated with cross sections of around 50 nb. These methods included comparisons of experimental and simulated spectra, as well as testing for evidence of a rotational band in the {gamma}{gamma} matrix.

Stability and synthesis of superheavy elements: Fighting the battle against fission – example of $^{254}$No

International audience; Superheavy nuclei exist solely due to quantum shell effects,which create a pocket in the potential-energy surface of the nucleus, thusproviding a barrier against spontaneous fission. Determining the height ofthe fission barrier and its angular-momentum dependence is important toquantify the role that microscopic shell corrections play in enhancing andextending the limits of nuclear stability. In this talk, the first measurement ofa fission barrier in the very heavy nucleus 254No will be presented.

Coulomb shifts and shape changes in the mass 70 region

The technique of recoil beta tagging has been developed which allows prompt gamma decays in nuclei from excited states to be correlated with electrons from their subsequent short-lived beta decay. This technique is ideal for studying nuclei very far from stability and improves in sensitivity for very short-lived decays and for high decay Q-values. The method has allowed excited states in 78Y to be observed for the first time, as well as an extension in the knowledge of T=1 states in 74Rb. From this new information it has been possible to compare Coulomb energy differences (CED) between T=1 states in 70Br/70Se, 74Rb/74Kr, and 78Y/78Sr. The A=70 CED exhibit an anomalous behavior which is inco…

Competing T = 0 and T = 1 structures in the N = Z nucleus $^{62}_{31}$Ga

Abstract The low-lying levels in the odd-odd N = Z nucleus 62 Ga have been identified for the first time. These data reveal a cascade of stretched-E2 transitions based on a T =0, 1 + bandhead which decays directly to the T =1, 0 + ground state. The observed levels are interpreted in the context of theshell model, using as a basis, the pf 5/2 g 9/2 orbits with a 56 Ni core.

Bridging the nuclear structure gap between stable and super heavy nuclei

International audience; Due to recent advances in detection techniques, excited states in several trans-fermium nuclei were studied in many laboratories worldwide, shedding light on the evolution of nuclear structure between stable nuclei and the predicted island of stability centered around spherical magic numbers. In particular, studies of K-isomers around the Z=100 and N=152 deformed shell closures extended information on the energies of Nilsson orbitals at the Fermi surface. Some of these orbitals originate from spherical states, which are relevant to the magic gaps in super-heavy nuclei. The single-particle energies can be used to test various theoretical predictions and aid in extrapo…

Shape isomerism and shape coexistence effects on the Coulomb energy differences in theN=Znucleus66As and neighboringT=1multiplets

Excited states of the $N=Z=33$ nucleus ${}^{66}$As have been populated in a fusion-evaporation reaction and studied using $\ensuremath{\gamma}$-ray spectroscopic techniques. Special emphasis was put into the search for candidates for the $T=1$ states. A new 3${}^{+}$ isomer has been observed with a lifetime of 1.1(3) ns. This is believed to be the predicted oblate shape isomer. The excited levels are discussed in terms of the shell model and of the complex excited Vampir approaches. Coulomb energy differences are determined from the comparison of the $T=1$ states with their analog partners. The unusual behavior of the Coulomb energy differences in the $A=70$ mass region is explained through…

Anomalous Coulomb matrix elements in thef7/2shell

γ decays from high-spin states in the N=Z-1 nucleus 2753Co26 have been identified for the first time. Level energies and Coulomb energy differences between these states and their analogs in its mirror nucleus 53Fe have been compared with large-scale pf shell-model calculations, which offer excellent agreement. New information has been obtained on two-proton Coulomb matrix elements needed in the interpretation. These have been extracted from the data via a number of methods and are shown to exhibit an anomalous behavior for the J=2 coupling.