The half-life and decay scheme of ${}_{}{}^{138}{}_{}{}^{}\mathrm{La}$ have been reinvestigated using a large-volume Ge(Li) detector. The partial half-lives for electron-capture decay and ${\beta }^{-}$ decay have been determined to be (1.58±0.02) × ${10}^{11}$ yr and (3.19±0.22) × ${10}^{11}$ yr, respectively. The resulting total ${}_{}{}^{138}{}_{}{}^{}\mathrm{La}$ half-life is (1.06±0.03) × ${10}^{11}$ yr. The results of the present work are compared with those of previous investigations.

RADIOACTIVITY ${}_{}{}^{138}{}_{}{}^{}\mathrm{La}$: Measured $I_{\gamma }$, $T_{\frac{1}{2}}$, $log\mathrm{ft}$. Ge(Li) detector.

We propose simple electronic counter experiments to test the existence and properties of anomalous particle fragments previously reported in emulsion experiments. We also suggest experiments to establish whether such phenomena extend to fragments in high energy elementary particle reactions.

NUCLEAR REACTIONS Electronic counter experiments based on anomalous absorption suggested to study anomalous high energy nuclear fragments. Extension to particle physics.

The available data on the energy loss versus the fragment charge distributions for the reaction ${}_{}{}^{136}{}_{}{}^{}\mathrm{Xe}$ + ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ at the three bombarding energies of 940, 1130, and 1422 MeV are analyzed in the framework of the transport model which was modified in an earlier work to include the effects of isospin correlation in the nucleon-exchange process in a consistent manner. The data show satisfactory agreement with the model predictions, nearly independent of the assumptions made about the isospin correlations in the exchange process, bringing out in an unambiguous way the dominant role of the nucleon-exchange process in the energy loss.

NUCLEAR REACTIONS Heavy-ion reactions, energy loss, nucleon exchanges, isospin correlations.

Axial blocking of $\alpha$ particles from the ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}(p, {\alpha }_0)$ resonance at $E_p=504.9\mathrm{}$ keV has been used to measure the "long lifetime" of the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ 12.073 MeV level by projecting the effective mean displacement to a "short lifetime" value. The resulting value for $\tau ={750}_{-180\mathrm{}}^{+220\mathrm{}}$ as has allowed us to study the behavior of the method in the limiting case of mean displacement comparable with the interstring distance.

NUCLEAR REACTIONS ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}(p, {\alpha }_0){}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$, $E=0.505\mathrm{}$ MeV; measured resonance yield and blocking effect for different mean transverse displacements. ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ deduced level width. Single crystal thick Al target. LR 115 cellulose nitrate detectors.

Fusion excitation function of the ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ + ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ system has been studied at energies close to the threshold through the measurements of $\gamma$ activity following particle evaporation from the ${}_{}{}^{80}{}_{}{}^{}\mathrm{Zr}$ compound nucleus. Our results are in strong disagreement with early results of Doubre et al. and in good agreement with recent results of Tomasi et al. The excitation function of the various evaporation channels are consistent with the estimates of a crude statistical evaporation calculation. The experimental fusion excitation function is in good agreement with current model predictions.

NUCLEAR REACTIONS ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}({}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}, X)$, $E^{*}=42-57\mathrm{}$ MeV; measured $E_{\gamma }$, $I_{\gamma }$; deduced $\sigma$ (fragment $E$). Measured fusion cross sections.

The double differential cross section for the reaction $p+\mathrm{C}\to {\pi }^{+}+X$ has been measured at laboratory angles of 7°, 15°, 20°, and 30°.

NUCLEAR REACTIONS $E=800\mathrm{}$ MeV, $p+{}_{}{}^{12}{}_{}{}^{}\mathrm{C}\to {\pi }^{+}+X$; measured $\frac{d\sigma }{d{E}_{\pi }}$ for ${\theta }_{\pi }=7\mathrm{}°, 15°, 20°, 30°$.

High-spin states in ${}_{}{}^{194,196}{}_{}{}^{}\mathrm{Pb}$ are studied with ${}_{}{}^{188}{}_{}{}^{}\mathrm{Os}({}_{}{}^{12}{}_{}{}^{}\mathrm{C}, xn)$ reactions and in-beam $\gamma$-ray spectrometric techniques. $K$ x-ray multiplicities are measured and found lower than previously reported. Newly established states with $12<J<~20$ are interpreted as four-quasiparticle configurations. No evidence for population of the recently suggested low-lying collective bands is found.

NUCLEAR REACTIONS ${}_{}{}^{188}{}_{}{}^{}\mathrm{Os}({}_{}{}^{12}{}_{}{}^{}\mathrm{C}, xn)$, $x=4, 6$. Measured $E_{\gamma }$, $I_{\gamma }$, $I_{\gamma }\left(\theta \right)$, $I_{\mathrm{ce}}$, $\Sigma E_{\gamma }$, $\gamma -\gamma \mathrm{}\left(t\right)\mathrm{}$, $\gamma -\mathrm{x}\mathrm{}\left(t\right)\mathrm{}$ coincidences. Deduced levels, $J$, $\pi$, $K$ x-ray multiplicities. Enriched target. Ge, Ge(Li), miniorange spectrometer, NaI(T1) sum spectrometer.

The influence of nucleon excitations to $N^{*}\text{'}\mathrm{s}$ on the giant dipole (or other electric resonances) is estimated. The correction is found to be very small.

NUCLEAR STRUCTURE Influence of nucleon internal degrees of freedom on giant resonances.

An event by event analysis is carried out for all charged particles observed in central collisions of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ + KCl and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ + Pb at 1.808 and 0.772 GeV/nucleon, respectively. Total transverse energy is used for impact parameter selection within the central trigger condition. The central Ar + KCl reaction exhibits a forward-backward oriented momentum flux. The flux distribution of the most central Ar + Pb events is approximately isotropic in the fireball center of mass.

NUCLEAR REACTIONS ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ + KCl, $\frac{E}{A}=1.808\mathrm{}$ GeV, and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ + Pb, $\frac{E}{A}=0.772\mathrm{}$ GeV. Central collision trigger, all charged particles measured event by event, streamer chamber. Momentum flux distribution parameters deduced.

The beta decay of ${}_{}{}^{16}{}_{}{}^{}\mathrm{C}$ to ${}_{}{}^{16}{}_{}{}^{}\mathrm{N}$($0^{-}$, 120 keV) has been observed. The branching ratio is (${0.68}_{-0.11\mathrm{}}^{+0.09\mathrm{}}$)% and the $log f_{0}t={6.70}_{-0.05\mathrm{}}^{+0.07\mathrm{}}$. The rate of this $0^{+}$→$0^{-}$ transition is dominated by the time component of the axial-vector current, which is expected to receive a large enhancement from pion-exchange currents. An upper limit of <0.1% has also been set for the beta-decay branching ratio of ${}_{}{}^{16}{}_{}{}^{}\mathrm{N}$($1^{-}$, 398 keV).

RADIOACTIVITY ${}_{}{}^{16}{}_{}{}^{}\mathrm{C}$ from ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}(t, p)$: measured $\beta \mathrm{}\left(t\right)\mathrm{}$, $\gamma \mathrm{}\left(t\right)\mathrm{}$, $n\left(t\right)\mathrm{}$; deduced branching ratios; first-forbidden transitions.

We present two group structures [SU(4) and SU(3,1)] which are generalizations of the SU(3) model, by allowing for excitations outside major shells. We discuss an application on ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$.

NUCLEAR STRUCTURE SU(3) model, ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$.

It is assumed that the rescattering of the quasifree particles on the spectator part of the target nucleus constitutes the major source of the pre-equilibrium events situated beyond the fourbody kinematic limit in the reaction phase space. A preliminary analysis suggests that the preequilibrium spectrum can be calculated in terms of the inelastic scattering of the quasifree particles on the spectator nucleus. Comparison with the ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}(p, 2p){}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$ data at $E_0=198\mathrm{}$ MeV supports the model prediction.

NUCLEAR REACTIONS ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}(p, 2p){}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$, $E=198\mathrm{}$ MeV; measured $\frac{d^4\sigma }{d{\Omega }_{1}d{E}_{1}d{\Omega }_{2}d{E}_2}$; discussion of continuum spectrum mechanism; DWIA calculations; connection with inelastic scattering analyzed.

An experimental value of the electric polarizability of the deuteron is extracted from deuteron photoabsoption data, a dispersion relation, and the low-energy theorem for Compton scattering. The experimental number requires the calculation of several small corrections, which are primarily magnetic in origin. Our value is somewhat smaller than, but consistent with, a recently reported experimental determination.

NUCLEAR STRUCTURE Deuteron; electric polarizability; photodisintegration; sum rules.

Candidates for shape-isomeric rotational bands, relevant to the controversy over anomalous events in relativistic heavy ion collisions, are specified in the spectra of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$, and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. No such band is found in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, and ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$.

NUCLEAR STRUCTURE Predicted shape-isomeric rotational bands in $p$, $\mathrm{sd}$ shell.

We argue that the strong interaction model dependence of the electromagnetically corrected ${}_{}{}^1{}_{}{}^{}\mathrm{S}_0^{}{}_{}{}^{}\mathrm{pp}$ scattering length is less than about 2 fm.

NUCLEAR REACTIONS Electromagnetic effects in proton-proton scattering.

We investigate breakup effects in a three-body model of deuteron elastic scattering and stripping reactions for a variety of potential parameters, bombarding energies, and momentum matching conditions. The investigation is based on the adiabatic approximation with relative angular momentum $l=0\mathrm{}$. We test this approximation by comparisons with several available coupled-channel calculations. The adiabatic wave function is divided into elastic and breakup parts, whose contributions to stripping are discussed separately. Breakup is seen to be primarily an effect of the nuclear interior. Elastic scattering is discussed by fitting a local equivalent potential to the elastic part of the wave function. This potential shows several characteristic features which are fairly stable with respect to the potential parameters and bombarding energies. The validity and limitations of the adiabatic approximation are examined. The approximation is seen to be fairly good for elastic scattering, but of only marginal value for stripping reactions. Possible improvements of the adiabatic approximation are discussed.

NUCLEAR REACTIONS Adiabatic approximation, coupled-channel calculations, folding model, three-body wave function, local equivalent potential, deuteron stripping reactions.

The ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}(p, p)$ and ($p, p^{\prime }$) differential cross sections were measured in the range $E_p=1.29-3.31\mathrm{}$ MeV with an overall resolution of 350—400 eV, full width at half maximum. Resonance parameters were extracted for 66 resonances with a multilevel, multichannel $R$-matrix analysis code; these parameters include resonance energy, total angular momentum, partial elastic and inelastic widths, and channel spin and orbital angular momentum mixing ratios. Analog states were identified, and Coulomb displacement energies and spectroscopic factors are given for seven of these analog states.

NUCLEAR REACTIONS ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}(p, p)$, ($p, p^{\prime }$), $E=1.29-3.31\mathrm{}$ MeV, measured $\sigma (E, \theta )$. ${}_{}{}^{30}{}_{}{}^{}\mathrm{P}$ levels deduced $J^{\pi }$, ${\Gamma }_p$, ${\Gamma }_{p^{\prime }}$ channel spin mixing $l$ mixing; ${}_{}{}^{30}{}_{}{}^{}\mathrm{P}$ IAS deduced Coulomb energies, spectroscopic factors. Enriched target, resolution 350—400 eV.

We compare the performance of separable pole expansions for the three-body amplitude in reproducing three-body data at both negative and positive energies. In addition to the generalized unitary pole expansion and the energy dependent pole expansion, we present results for two new expansions. As benchmarks for our calculations, we use the three-boson results of Aaron, Amado, and Yam. At negative energies, we give off-shell scattering amplitudes and investigate how well the expansions are capable of generating the second bound state of the three-boson problem, if the first is put explicitly into the expansions. At positive energies, we calculate phase shifts and inelasticities. We find that the convergence properties of the expansions investigated change rather markedly above the three-particle breakup threshold and only one of the four expansions is capable of reproducing the data in this energy region. In general, the results get better the more energy dependence is explicitly contained in the expansion functions. The relevance of these findings for four-body calculations, which employ separable three-body input, is discussed briefly.

NUCLEAR REACTIONS Calculations of three-boson bound state and scattering data with separable expansions. Comparison of generalized unitary pole expansion, energy dependent pole expansion, and two new expansions.

Angular distributions have been studied in the ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}(\alpha , {\gamma }_0){}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ reaction in fine energy steps for excitation energies $14\lesssim E_x\lesssim 22$ MeV. Absolute cross sections were determined with errors smaller than 10% and were found to be substantially lower than previously determined. A total $E2\mathrm{}$ strength of (3.7±0.4)% of the energy weighted sum rule was observed, in good agreement with results obtained from ($\alpha , {\alpha }^{\prime }{\alpha }_0$) coincidence experiments. Strong interference effects as well as other deviations from statistical model expectations are interpreted as due to nonstatistical preequilibrium effects in both $E1\mathrm{}$ and $E2\mathrm{}$ channels.

NUCLEAR REACTIONS ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}(\alpha , {\gamma }_0){}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, $E=4.3-14.0\mathrm{}$ MeV; measured $\sigma (E, E_{\gamma }, {\theta }_{\gamma })$. ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ deduced $E1\mathrm{}$, $E2\mathrm{}$ strengths. Enriched target. Compared decay strengths with Hauser-Feshbach estimates, including effects of isospin.

The photoneutron cross sections for ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$, and ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$ have been measured up to 33 MeV with monoenergetic photons from the annihilation in flight of fast positrons, using neutron multiplicity counting. Average neutron energies were obtained simultaneously with the cross-section data by the ring-ratio technique. The giant dipole resonances for ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ and ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$ exhibit appreciable fragmentation; that for ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ does not. The ($\gamma , 2n$) cross section for ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$ is large; that for ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ is consistent with zero. The ($\gamma ,1n$) cross section for ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$ decreases sharply with energy to values near zero as the ($\gamma , 2n$) cross section grows, then increases to appreciable values as the ($\gamma , 2n$) cross section diminishes; this extreme behavior, although never seen before, is attributable to the competition between the ($\gamma , n$), ($\gamma , 2n$), and ($\gamma , \mathrm{pn}$) decay channels. Some properties of the isospin components of the giant resonance are inferred. Other features of the data, including the integrated cross sections, are found to be similar in many respects to corresponding results for the oxygen and magnesium isotopes. The ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ nucleus is found to be a better "core" for ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ and ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$ than might have been expected from previous descriptions of its open-shell character.

NUCLEAR REACTIONS ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}(\gamma , n)$, ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}(\gamma , n)$, ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}(\gamma , n)$, ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}(\gamma , 2n)$, $E_{\gamma }=13.4-33.1\mathrm{}$ MeV; measured $4\pi$ neutron yields for monoenergetic photons, average photoneutron energies, integrated cross sections; isospin splitting of giant dipole resonance; comparisons of results with oxygen and magnesium isotopes; ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ as a "core" nucleus.