An experiment was performed with the Gammasphere Ge-detector array, and the Microball charged particle detector, to search for transitions involved in the decay from the yrast superdeformed band in ${}^{143}\mathrm{Eu}.$ Sum spectra in coincidence with single, double, and triple gates on SD transitions were produced to search for previously reported two-step links between the superdeformed and the near-yrast ND levels. The sum spectra contained no evidence of peaks corresponding to sums of two-step linking transitions. Several discrete γ rays were observed in coincidence with the yrast SD band. One previously reported single-step transition at 3361 keV was confirmed to decay out of the SD band.

The $K$-electron capture half-life of ${}^{123}\mathrm{Te}$ has been recently measured to be $t_{\exp }^K=2.4\mathrm{}\times {10}^{19}\mathrm{yr}$ and constitutes the longest half-life ever measured in a single β-transition of any nuclear species. We have calculated this second unique forbidden transition within the framework of the proton-neutron quasiparticle random phase approximation, making use of Skyrme-type effective interactions. A strong cancellation effect between particle-hole and particle-particle correlations is found. The model, without any renormalization of the force, provides a lower limit for the $K$-electron capture half-life of $\sim {10}^{17}\mathrm{yr},$ which unambiguously rules out the old experimental values of ${10}^{13}–{10}^{14}\mathrm{yr}.$ A few percent increase of the particle-particle matrix elements of the Skyrme interaction allows one to reproduce the experimental findings.

A method for making realistic estimates of the density of levels in even-even nuclei is presented making use of the Monte Carlo shell model (MCSM). The procedure follows three basic steps: (1) computation of the thermal energy with the MCSM, (2) evaluation of the partition function by integrating the thermal energy, and (3) evaluating the level density by performing the inverse Laplace transform of the partition function using maximum entropy reconstruction techniques. It is found that results obtained with schematic interactions, which do not have a sign problem in the MCSM, compare well with realistic shell-model interactions provided an important isospin dependence is accounted for.

The role of statistical fluctuations for the interpretation of Arrhenius-type plots in nuclear multifragmentation, representing scaling with transverse kinetic energy, is explored. It is shown that the observed striking “Arrhenius”-like correlations and binomial-like multiplicity distributions do not provide evidence for an underlying thermal scaling (with excitation energy or temperature) of intermediate-mass fragment (IMF) pro-duction. In fact, these striking features appear inconsistent with a dominantly thermal IMF production scenario.

Low energy scattering and bound state properties of the $\pi N$, $\pi \pi$, and $K\pi$ systems are studied as coupled channel problems using inversion potentials of phase shift data. In a first step we apply the potential model to explain recent measurements of pionic hydrogen shift and width. Second, predictions of the model for the pionium lifetime and shift confirm a well-known and widely used effective range expression. Third, as an extension of this confirmation, we predict an unexpected medium effect of the pionium lifetime which shortens by several orders of magnitude. The $\sigma$ meson shows a narrow resonance structure as a function of the medium-modified mass with the implication of being essentially energy independent. Similarly, we see this medium resonance effect realized for the $K\pi$ system. To support our findings we present also results for the $\rho$ meson and the $\Delta$(1232) resonance.

The $\mathrm{pd}\leftrightarrow {\pi }^{+}t$ process has been calculated in the energy region around the $\Delta$ resonance with elementary production/absorption mechanisms involving one and two nucleons. The isobar degrees of freedom have been explicitly included in the two-nucleon mechanism via $\pi$- and $\rho$-exchange diagrams. No free parameters have been employed in the analysis since all the parameters have been fixed in previous studies on the simpler $\mathrm{pp}\leftrightarrow {\pi }^{+}d$ process. The treatment of the few-nucleon dynamics entailed a Faddeev-based calculation of the reaction, with continuum calculations for the initial $p$-$d$ state and accurate solutions of the three-nucleon bound-state equation. The integral cross section was found to be quite sensitive to the $\mathrm{NN}$ interaction employed while the angular dependence showed less sensitivity. Approximately a 4% effect was found for the one-body mechanism, for the three-nucleon dynamics in the $p$-$d$ channel, and for the inclusion of a large, possibly converged, number of three-body partial states, indicating that these different aspects are of comparable importance in the calculation of the spin-averaged observables.

A chiral-perturbative consideration of the near-threshold $\mathrm{pp}\to \mathrm{pp}{\pi }^0$ reaction indicates that the pion-rescattering term has a substantial energy and momentum dependence. The existing calculations that incorporate this dependence give pion rescattering contributions significantly larger than those of the conventional treatment, and this enhanced rescattering term interferes destructively with the one-body impulse term, leading to theoretical cross sections that are much smaller than the observed values. However, since the existing calculations are based on coordinate-space representation, they involve a number of simplifying assumptions about the energy-momentum flow in the rescattering diagram, even though the delicate interplay between the one-body and two-body terms makes it desirable to avoid these kinematical assumptions. We carry out here a momentum-space calculation that retains the energy-momentum dependence of the vertices as predicted by chiral perturbation theory. Our improved treatment increases the rescattering amplitude by a factor of $\sim$3 over the value obtained in the $r$-space calculations. The $\mathrm{pp}\to \mathrm{pp}{\pi }^0$ transition amplitude, which is now dominated by the rescattering term, leads to the cross section much larger than what was reported in the approximate $r$-space calculations. Thus, the extremely small cross sections obtained in the previous chiral perturbative treatments of this reaction should be considered as an accidental consequence of the approximations employed rather than a general feature.

Low-lying electric and magnetic dipole excitations in the transitional nucleus ${}^{144}$Nd have been studied in nuclear resonance fluorescence experiments performed with a bremsstrahlung beam (end point energy 4.1 MeV). The use of high-resolution $\gamma$-ray spectrometers and a sectored single-crystal Compton polarimeter provided detailed information on excitation energies, spins, parities, decay widths, transition probabilities, and branching ratios of numerous new spin-1 states in ${}^{144}$Nd. The strong $E$1 excitation at 2185 keV in this $N$ = 84 nucleus is interpreted as the quadrupole-octupole coupled two-phonon excitation which has been observed systematically in the neighboring $N$ = 82 isotones. The decay properties of this 1${}^{-}$ state are compared with the systematics of the low-lying 1${}^{-}$ levels in the other even-even, stable Nd isotopes. The $M$1 excitations in ${}^{144}$Nd are discussed with respect to the deformation dependence of the orbital $M$1 “scissors mode,” the so-called “${\delta }^2$ law,” which has been studied previously in the other stable even-even Nd nuclei and in the Sm isotopes.

In this paper experiments are described that have led to the assignment of spins of a large number of $s$- and $p$-wave resonances in reactions of epithermal neutrons with the nuclei ${}^{238}$U and ${}^{113}$Cd. The gamma-ray spectra of the $(n,\gamma )$ reactions have been measured using the time-of-flight technique at the GELINA pulsed neutron source facility. For the present spin determinations we have exploited the fact that the population through gamma radiation of low-lying nuclear states from the compound nucleus is dependent on the resonance spin. These assignments are important for the analysis of measurements of parity nonconservation in compound nuclei.

The fragmentation of low-lying dipole strength in the odd-mass nucleus ${}^{133}$Cs has been investigated in nuclear resonance fluorescence (NRF) experiments performed at the bremsstrahlung beam of the Stuttgart Dynamitron accelerator at an end-point energy of 4.1 MeV. In the excitation energy range 2.3 – 3.7 MeV in total 22 new dipole excitations were observed. From the high-resolution $\gamma$-ray spectra measured by three high-efficiency Ge detectors the reduced excitation probabilities $B\left(E1\mathrm{}\right)\mathrm{}\uparrow$ or $B\left(M1\mathrm{}\right)\mathrm{}\uparrow$ were deduced. The fragmentation and absolute total strengths of the detected dipole excitations are compared with results for the neighboring even-even, $\gamma$-soft nucleus ${}^{134}$Ba, where both, rather strong scissors mode-like $M1\mathrm{}$ and two-phonon $E1\mathrm{}$ excitations are known from recent NRF experiments.

An experimental investigation of the odd-odd ${}^{162}\mathrm{Lu}$ nucleus, following the ${}^{148}\mathrm{Sm}{(}^{19}\mathrm{F},5n)$ reaction at beam energy $E_{\mathrm{lab}}=112\mathrm{}\mathrm{}\mathrm{MeV},$ has been performed through in-beam gamma-ray spectroscopy. It revealed three signature-split bands. The yrast band based on $\pi h_{11/2}\otimes \nu i_{13/2}$ configuration exhibits anomalous signature splitting (the unfavored signature Routhian lying lower than the favored one) whose magnitude $\Delta e^{\prime }\approx 25\mathrm{keV},$ is considerably reduced in contrast to sizable normal signature splitting $\Delta e^{\prime }\approx 125$ and 60 keV observed in the yrast $\pi h_{11/2}$ bands of the neighboring odd-$A$ ${}^{161,163}\mathrm{Lu}$ nuclei, respectively. The signature inversion in this band occurs at spin $\sim 20ħ$ $(\mathrm{f}\mathrm{r}\mathrm{e}\mathrm{q}\mathrm{u}\mathrm{e}\mathrm{n}\mathrm{c}\mathrm{y}=0.37\mathrm{}\mathrm{}\mathrm{MeV}).\mathrm{}$ The second signature-split band, observed above the band crossing associated with the alignment of a pair of $i_{13/2}$ quasineutrons, is a band based on the four-quasiparticle $[\pi h_{11/2}{\mathrm{}\left[523\right]7/2}^{-}\otimes \nu h_{9/2}{\mathrm{}\left[521\right]3/2}^{-}\otimes (\nu i_{13/2}{)}^2],$ i.e., ${\mathrm{EABA}}_p{(B}_p),$ configuration. The third signature-split band is also likely to be a four-quasiparticle band with configuration similar to the second band but involving $F$ quasineutron, i.e., ${\mathrm{FABA}}_p{(B}_p).\mathrm{}$ The experimental results are discussed in comparison with the existing data in the neighboring nuclei and in the framework of the cranking shell model.

Neutron-rich nuclei ${}^{147,149,151}$Ce have been studied via the prompt $\gamma$-ray spectroscopy of ${}^{248}$Cm fission fragments. A partial level scheme for ${}^{151}$Ce is presented for the first time, along with the high-spin structure in ${}^{147,149}$Ce. A rapidly changing yrast structure with neutron number is observed and it is suggested that bands in ${}^{147}$Ce and ${}^{151}$Ce are built on the $\nu i_{13/2}$ Nilsson state. The level scheme of ${}^{149}$Ce displays two bands with quite similar transition energies. There is no experimental evidence for octupole deformation in any of the three nuclei.

The differential cross sections for the reactions ${}^9\mathrm{Be}{(}^{10}\mathrm{B}{,}^{10}\mathrm{B}{)}^9\mathrm{Be}$ and ${}^9\mathrm{Be}{(}^{10}\mathrm{B}{,}^9\mathrm{Be}{)}^{10}\mathrm{B}$ have been measured at an incident energy of 100 MeV. The elastic scattering data have been used to determine the optical model parameters for the ${}^9\mathrm{Be}{+}^{10}\mathrm{B}$ system at this energy. These parameters are then used in distorted-wave Born approximation (DWBA) calculations to predict the cross sections of the ${}^9\mathrm{Be}{(}^{10}\mathrm{B}{,}^9\mathrm{Be}{)}^{10}\mathrm{B}$ proton exchange reaction, populating the ground and low-lying states in ${}^{10}\mathrm{B}$. By normalizing the theoretical DWBA proton exchange cross sections to the experimental ones, the asymptotic normalization coefficients (ANC's), defining the normalization of the tail of the ${}^{10}\mathrm{B}$ bound state wave functions in the two-particle channel ${}^9\mathrm{Be}+p$, have been found. The ANC for the virtual decay ${}^{10}\mathrm{B}(\mathrm{g}.\mathrm{s}.\mathrm{}){\to }^9\mathrm{Be}+p$ will be used in an analysis of the ${}^{10}\mathrm{B}{(}^7\mathrm{Be}{,}^8\mathrm{B}{)}^9\mathrm{Be}$ reaction to extract the ANC's for ${}^8\mathrm{B}{\to }^7\mathrm{Be}+p$. These ANC's determine the normalization of the ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ radiative capture cross section at very low energies, which is crucially important for nuclear astrophysics.

High-spin states in ${}^{50}$Cr have been investigated with the reaction ${}^{24}\mathrm{Mg}{(}^{32}\mathrm{S},\alpha 2p)$ at 130 MeV bombarding energy, using the 4$\pi$ GASP $\gamma$-ray array plus the 4$\pi$ charged-particle detector ISIS. The level scheme has been extended up to the 18${}^{+}$ state at 17.954 MeV excitation energy. Several high-spin states which deexcite by emitting high energy $\gamma$-rays have been identified. A second backbending is observed at $I=18\mathrm{}ħ$, well above the 14${}^{+}$ state which exhausts the total spin available in a pure ${(f}_{7/2}{)}^{10}$ configuration.

Excited states in ${}^{208}$Pb have been studied by measuring $\gamma$ rays in time coincidence with reaction charged particles. ${}^{208}$Pb states were produced with both the ${}^{207}$Pb${\mathrm{}(d,p)\mathrm{}}^{208}$Pb and ${}^{209}$Bi$(t,\alpha )$${}^{208}$Pb reactions. The energy resolution of the particle spectra of 100 keV allowed a rough determination of level excitation, which then was determined with high resolution from the coincident $\gamma$ decay measured in Ge detectors. Many new $\gamma$ transitions have been found and previously unresolved multiplets of states resolved. The data give spectroscopic factors for neutron transfer and proton pickup. Spins and parities of levels could be deduced from their $\gamma$ decays. A least squares fit of all $\gamma$ energies gave very precise (0.1 keV) level energies. All states predicted by the shell model below 4.6 MeV are now found and their spins determined unambiguously.

The four-quasiparticle magnetic dipole band in ${}^{128}$Ba has been investigated with the ${}^{96}\mathrm{Zr}{(}^{36}\mathrm{S}{,4n)}^{128}$Ba reaction at the GASP spectrometer of the Laboratori Nazionali di Legnaro. Linking transitions to the previously known positive parity states have been observed for the first time in this mass region and new transitions on top of the band have been found. The experimental results are compared to previously made tilted axis cranking calculations.

Ten new transitions in ${}^{107}$Mo have been observed and levels in ${}^{109}$Mo are identified for the first time in a $\gamma$-$\gamma$-$\gamma$ coincidence study from the spontaneous fission of ${}^{252}$Cf with 72 Compton suppressed Ge detectors in Gammasphere. Two sets of bands, each set intertwined by $E1\mathrm{}$ transitions are observed in ${}^{107}$Mo and one such set in ${}^{109}$Mo. The observed level schemes are interpreted in terms of possible octupole deformation originating from the strong interaction of the $h_{11/2}$ and $d_{5/2}$ neutron shells.

It is shown that the part of the nuclear Hamiltonian which contains the products of $\mathrm{pp}$ and $\mathrm{hh}$ pair operators (the scattering terms) and which has been usually neglected in the calculations of the giant dipole resonance turns out to be definitely important in the study of the double giant dipole resonance (DGDR). The complete energy-weighted sum of strengths (EWSS) for the DGDR and a possible deviation from its value in the harmonic oscillators' limit are derived for the first time with the full nuclear Hamiltonian taken into account. The numerical calculations within a schematic model show an example where this deviation turns to a strong enhancement of the EWSS for the DGDR at various particle numbers.

Collective $P$- and $T$-odd moments produced by parity and time invariance violating forces in reflection asymmetric nuclei are considered. The enhanced collective Schiff, electric dipole, and octupole moments appear due to the mixing of rotational levels of opposite parity. These moments can exceed single-particle moments by more than 2 orders of magnitude. The enhancement is due to the collective nature of the intrinsic moments and the small energy separation between members of parity doublets. In turn these nuclear moments induce enhanced $T$- and $P$-odd effects in atoms and molecules. A simple estimate is given and a detailed theoretical treatment of the collective $T$-, $P$-odd electric moments in reflection asymmetric, odd-mass nuclei is presented. In the present work we improve on the simple liquid drop model by evaluating the Strutinsky shell correction and include corrections due to pairing. Calculations are performed for octupole deformed long-lived odd-mass isotopes of Rn, Fr, Ra, Ac, and Pa and the corresponding atoms. Experiments with such atoms may improve substantially the limits on time reversal violation.

We show in this paper that the superdeformed nuclear states can be described with a four parameter formula in the spirit of the perturbated SU(3) limit of the $\mathrm{sdg}$ IBM. The $E$2 transition $\gamma$-ray energies, the dynamical moments of inertia of the lowest superdeformed (SD) bands in even-even Hg, Pb, Gd, and Dy isotopes, and the energy differences $\Delta E_{\gamma }-\Delta E_{\gamma }^{\mathrm{ref}}$ of the SD band 1 of ${}^{194}$Hg are calculated. The calculated results agree with experimental data well. This indicates that the SD states are governed by a rotational interaction plus a perturbation with ${\mathrm{SO}}_{\mathrm{sdg}}\mathrm{}\left(5\right)\mathrm{}$ symmetry. The perturbation causing the $\Delta I=4\mathrm{}$ bifurcation to emerge in the $\Delta I=2\mathrm{}$ superdeformed rotational band may then possess ${\mathrm{SO}}_{\mathrm{sdg}}\mathrm{}\left(5\right)\mathrm{}$ symmetry.