Gamma-ray transitions have been identified for the first time in the extremely neutron-deficient ($N=Z+2$) nucleus ${}^{110}\mathrm{Xe}$, and the energies of the three lowest excited states in the ground-state band have been deduced. The results establish a breaking of the normal trend of increasing first excited $2^{+}$ and $4^{+}$ level energies as a function of the decreasing neutron number as the $N=50$ major shell gap is approached for the neutron-deficient Xe isotopes. This unusual feature is suggested to be an effect of enhanced collectivity, possibly arising from isoscalar $n\mathrm{\text{−}}p$ interactions becoming increasingly important close to the $N=Z$ line.

The breakout reaction ${}^{15}\mathrm{O}(\alpha ,\gamma ){}^{19}\mathrm{Ne}$, which regulates the flow between the hot CNO cycle and the $rp$ process, is critical for the explanation of the burst amplitude and periodicity of x-ray bursters. We report on the first successful measurement of the critical $\alpha$-decay branching ratios of relevant states in ${}^{19}\mathrm{Ne}$ populated via ${}^{19}\mathrm{F}({}^3\mathrm{He},t){}^{19}\mathrm{Ne}$. Based on the experimental results and our previous lifetime measurements of these states, we derive the first experimental rate of ${}^{15}\mathrm{O}(\alpha ,\gamma ){}^{19}\mathrm{Ne}$. The impact of our experimental results on the burst pattern and periodicity for a range of accretion rates is analyzed.

An $\alpha$-decay branch of $(1.4\pm 0.4)\times {10}^{-4}$ has been discovered in the decay of ${}^{109}\mathrm{I}$, which predominantly decays via proton emission. The measured $Q_{\alpha }$ value of $3918\pm 21\mathrm{keV}$ allows the indirect determination of the $Q$ value for proton emission from ${}^{105}\mathrm{Sb}$ of $356\pm 22\mathrm{keV}$, which is approximately of 130 keV more bound than previously reported. This result is relevant for the astrophysical rapid proton-capture process, which would terminate in the ${}^{105}\mathrm{Sn}(p,\gamma ){}^{106}\mathrm{Sb}(p,\gamma ){}^{107}\mathrm{Te}(\alpha \mathrm{\text{decay}}){}^{103}\mathrm{Sn}$ cycle at the densities expected in explosive hydrogen burning scenarios, unless unusually strong pairing effects result in a ${}^{103}\mathrm{Sn}(p,\gamma ){}^{104}\mathrm{Sb}(p,\gamma ){}^{105}\mathrm{Te}(\alpha \mathrm{\text{decay}}){}^{101}\mathrm{Sn})$ cycle.

The energy splitting of the ${}^{229}\mathrm{Th}$ ground-state doublet is measured to be $7.6\pm 0.5\mathrm{eV}$, significantly greater than earlier measurements. Gamma rays produced following the alpha decay of ${}^{233}\mathrm{U}$ ($105\mu \mathrm{Ci}$) were counted in the NASA/electron beam ion trap x-ray microcalorimeter spectrometer with an experimental energy resolution of 26 eV (FWHM). A difference technique was applied to the gamma-ray decay of the 71.82 keV level that populates both members of the doublet. A positive correction amounting to 0.6 eV was made for the unobserved interband decay of the 29.19 keV state ($29.19\to 0\mathrm{keV}$).

The Gamow-Teller strength distributions below the particle threshold in ${}^{138}\mathrm{La}$ and ${}^{180}\mathrm{Ta}$, deduced from high-resolution measurements of the (${}^3\mathrm{He},t$) reaction at 0°, allow us to evaluate the role of charged-current reactions for the production of these extremely rare nuclides in neutrino-nucleosynthesis models. The analysis suggests that essentially all ${}^{138}\mathrm{La}$ in the Universe can be made that way. Neutrino nucleosynthesis also contributes significantly to the abundance of ${}^{180}\mathrm{Ta}$ but the magnitude depends on the unknown branching ratio for population of the long-lived isomer.

Invariant mass spectra of $e^{+}{e}^{-}$ pairs have been measured in 12 GeV $p+A$ reactions to detect possible in-medium modification of vector mesons. Copper and carbon targets are used to study the nuclear-size dependence of $e^{+}{e}^{-}$ invariant mass distributions. A significant excess on the low-mass side of the $\varphi$ meson peak is observed in the low $\beta \gamma (=\beta /\sqrt{1-{\beta }^2})$ region of $\varphi$ mesons ($\beta \gamma <1.25$) with copper targets. However, in the high $\beta \gamma$ region ($\beta \gamma >1.25$), spectral shapes of $\varphi$ mesons are well described by the Breit-Wigner shape when experimental effects are considered. Thus, in addition to our earlier publications on $\rho /\omega$ modification, this study has experimentally verified vector meson mass modification at normal nuclear density.

A new frontier of discrete-line $\gamma$-ray spectroscopy at ultrahigh spin has been opened in the rare-earth nuclei ${}^{157,158}\mathrm{Er}$. Four rotational structures, displaying high moments of inertia, have been identified, which extend up to spin $\sim 65\hslash$ and bypass the band-terminating states in these nuclei which occur at $\sim 45\hslash$. Cranked Nilsson-Strutinsky calculations suggest that these structures arise from well-deformed triaxial configurations that lie in a valley of favored shell energy which also includes the triaxial strongly deformed bands in ${}^{161–167}\mathrm{Lu}$.

Theoretical calculations predict ${}^{270}\mathrm{Hs}$ ($Z=108$, $N=162$) to be a doubly magic deformed nucleus, decaying mainly by $\alpha$-particle emission. In this work, based on a rapid chemical isolation of Hs isotopes produced in the ${}^{26}\mathrm{Mg}+{}^{248}\mathrm{Cm}$ reaction, we observed 15 genetically linked nuclear decay chains. Four chains were attributed to the new nuclide ${}^{270}\mathrm{Hs}$, which decays by $\alpha$-particle emission with $Q_{\alpha }=9.02\pm 0.03\mathrm{MeV}$ to ${}^{266}\mathrm{Sg}$ which undergoes spontaneous fission with a half-life of ${444}_{-148}^{+444}\mathrm{ms}$. A production cross section of about 3 pb was measured for ${}^{270}\mathrm{Hs}$. Thus, ${}^{270}\mathrm{Hs}$ is the first nucleus for which experimental nuclear decay properties have become available for comparison with theoretical predictions of the $N=162$ shell stability.

An exclusive measurement has been made of the Coulomb dissociation of the two-neutron halo nucleus ${}^{11}\mathrm{Li}$ at $70\mathrm{MeV}/\mathrm{nucleon}$ at RIKEN. Strong low-energy (soft) $E1$ excitation is observed, peaked at about $E_{\mathrm{x}}=0.6\mathrm{MeV}$ with $B(E1)=1.42(18){\mathrm{e}}^2{\mathrm{fm}}^2$ for $E_{\mathrm{rel}}\le 3\mathrm{MeV}$, which was largely missed in previous measurements. This excitation represents the strongest $E1$ transition ever observed at such low excitation energies. The spectrum is reproduced well by a three-body model with a strong two-neutron correlation, which is further supported by the $E1$ non-energy-weighted cluster sum rule.

We present a new nucleosynthesis process that we denote as the $\nu p$ process, which occurs in supernovae (and possibly gamma-ray bursts) when strong neutrino fluxes create proton-rich ejecta. In this process, antineutrino absorptions in the proton-rich environment produce neutrons that are immediately captured by neutron-deficient nuclei. This allows for the nucleosynthesis of nuclei with mass numbers $A>64$, making this process a possible candidate to explain the origin of the solar abundances of ${}^{92,94}\mathrm{Mo}$ and ${}^{96,98}\mathrm{Ru}$. This process also offers a natural explanation for the large abundance of Sr seen in a hyper-metal-poor star.

Using selective laser extraction technique combined with sensitive ion-counting mass spectrometry, we have analyzed the isotopic structure of fission noble gases in U-free La-Ce-Sr-Ca aluminous hydroxy phosphate associated with the 2 billion yr old Oklo natural nuclear reactor. In addition to elevated abundances of fission-produced Zr, Ce, and Sr, we discovered high (up to $0.03{\mathrm{c}\mathrm{m}}^3\mathrm{S}\mathrm{T}\mathrm{P}/\mathrm{g}$) concentrations of fission Xe and Kr, the largest ever observed in any natural material. The specific isotopic structure of xenon in this mineral defines a cycling operation for the reactor with 30-min active pulses separated by 2.5 h dormant periods. Thus, nature not only created conditions for self-sustained nuclear chain reactions, but also provided clues on how to retain nuclear wastes, including fission Xe and Kr, and prevent uncontrolled runaway chain reaction.

We first define a series of $NN$ interaction models ranging from very simple to fully realistic. We then present Green’s function Monte Carlo calculations of light nuclei to show how nuclear spectra evolve as the nuclear forces are made increasingly sophisticated. We find that the absence of stable five- and eight-body nuclei depends crucially on the spin, isospin, and tensor components of the nuclear force.

We measured the strength of the $0_{\mathrm{gs}}^{+}\to 2_1^{+}$ excitations in the radioactive mirror nuclei ${}^{32}\mathrm{Ar}$ and ${}^{32}\mathrm{Si}$ using the techniques of intermediate-energy Coulomb excitation for ${}^{32}\mathrm{Ar}$ and inelastic proton scattering in inverse kinematics for ${}^{32}\mathrm{Si}$. The ${}^{32}\mathrm{Ar}$ measurement, taken together with previously existing Coulomb excitation data for ${}^{32}\mathrm{Si}$, yields the isoscalar and isovector multipole matrix elements for the $0_1^{+}\to 2_1^{+}$ transition between $T=2\mathrm{}$ states in the $A=32\mathrm{}$ system. The proton scattering measurement for ${}^{32}\mathrm{Si}$, when combined with the Coulomb excitation data for this nucleus, yields a ratio of neutron and proton matrix elements, $M_n{/M}_p$, for ${}^{32}\mathrm{Si}$.

Transverse momentum spectra for charged hadrons and for neutral pions in the range $1\mathrm{GeV}/c<\mathrm{}{p}_T<5\mathrm{}\mathrm{GeV}/c$ have been measured by the PHENIX experiment at RHIC in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=130\mathrm{}\mathrm{GeV}$. At high $p_T$ the spectra from peripheral nuclear collisions are consistent with scaling the spectra from $p+p$ collisions by the average number of binary nucleon-nucleon collisions. The spectra from central collisions are significantly suppressed when compared to the binary-scaled $p+p$ expectation, and also when compared to similarly binary-scaled peripheral collisions, indicating a novel nuclear-medium effect in central nuclear collisions at RHIC energies.

The differences between neutron and proton density distributions at large nuclear radii in stable nuclei were determined. Two experimental methods were applied: nuclear spectroscopy analysis of the antiproton annihilation residues one mass unit lighter than the target mass and the measurements of strong-interaction effects on antiprotonic x rays. Assuming the validity of two-parameter Fermi neutron and proton distributions at these large radii, the conclusions are that the two experiments are consistent with each other and that for neutron rich nuclei it is mostly the neutron diffuseness which increases and not the half-density radius. The obtained neutron and proton rms radii differences are in agreement with previous results.

We report on the first measurement of a hypernuclear $\gamma$-transition probability. $\gamma$ rays emitted in the $E2\mathrm{}(5/2^{+}\to 1/2^{+})$ transition of ${}_{\Lambda }^7\mathrm{Li}$ were detected by a large-acceptance germanium detector array (Hyperball), and the lifetime of the parent state ( $5/2^{+}$) was determined by the Doppler shift attenuation method. The obtained result, ${5.8}_{-0.7\mathrm{}}^{+0.9\mathrm{}}\pm 0.7\mathrm{ps}$, was then converted into the reduced transition probability [ $B\left(E2\mathrm{}\right)$] to be $B({E2;5/2\mathrm{}}^{+}\to {1/2}^{+})=3.6\mathrm{}\pm {0.5}_{-0.4\mathrm{}}^{+0.5\mathrm{}}{e}^2{\mathrm{fm}}^4$. Compared with the $B\left(E2\mathrm{}\right)$ of the corresponding $E2\mathrm{}(3^{+}\to 1^{+})$ transition in the ${}^6\mathrm{Li}$ nucleus, our result gives evidence that the size of the ${}^6\mathrm{Li}$ core in ${}_{\Lambda }^7\mathrm{Li}$ is smaller than the ${}^6\mathrm{Li}$ nucleus in the free space.

New sideband partners of the yrast bands built on the $\pi h_{11/2}\nu h_{11/2}$ configuration were identified in ${}_{55}\mathrm{Cs}$, ${}_{57}\mathrm{La}$, and ${}_{61}\mathrm{Pm}$ $N=75\mathrm{}$ isotones of ${}^{134}\mathrm{Pr}$. These bands form with ${}^{134}\mathrm{Pr}$ unique doublet-band systematics suggesting a common basis. Aplanar solutions of 3D tilted axis cranking calculations for triaxial shapes define left- and right-handed chiral systems out of the three angular momenta provided by the valence particles and the core rotation, which leads to spontaneous chiral symmetry breaking and the doublet bands. Small energy differences between the doublet bands suggest collective chiral vibrations.

We have succeeded in observing nuclear excitation by electron transition (NEET) in ${}^{197}\mathrm{Au}$ by a new method. Monochromatic x-rays of synchrotron radiation were used to ionize the $K$ shell of gold atoms in a target foil. The internal-conversion electrons emitted from excited nuclei were detected with a silicon avalanche photodiode. At a photon energy of 80.989 keV, the NEET probability in ${}^{197}\mathrm{Au}$ was determined to be $(5.0\pm 0.6)\times {10}^{-8\mathrm{}}$ from a comparison of the event number per photon between NEET and the nuclear resonance at 77.351 keV.

The transmission of ultracold neutrons through natural Gd and isotopic enriched ${}^{157}\mathrm{Gd}$ samples has been measured. Absorption cross sections in the order of 100 Mb have been identified. Here one touches a region where fluctuations of the physical parameters influence the result and can cause a basic deviation from the exponential attenuation law and where a purely imaginary interaction potential exists within the sample.

Following a prediction by Smolańczuk [Phys. Rev. C 59, 2634 (1999)], we searched for superheavy element formation in the bombardment of ${}^{208}\mathrm{Pb}$ with 449-MeV ${}^{86}\mathrm{Kr}$ ions. We have observed three decay chains, each consisting of an implanted heavy atom and six subsequent $\alpha$ decays, correlated in time and position. In these decay chains, a rapid (ms) sequence of high energy $\alpha$ particles ( $E_{\alpha }\ge 10\mathrm{MeV}$) indicates the decay of a new high- $Z$ element. The observed chains are consistent with the formation of ${}_{}{}^{293}{}_{}{}^{}118$ and its decay by sequential $\alpha$-particle emission to ${}_{}{}^{289}{}_{}{}^{}116$, ${}_{}{}^{285}{}_{}{}^{}114$, ${}_{}{}^{281}{}_{}{}^{}112$, ${}_{}{}^{277}{}_{}{}^{}110$, ${}^{273}\mathrm{Hs}$ ( $Z=108\mathrm{}$) and ${}^{269}\mathrm{Sg}$ ( $Z=106\mathrm{}$). The production cross section is ${2.2}_{-0.8\mathrm{}}^{+2.6\mathrm{}}\mathrm{pb}$.