A Slope Instability Case History Involving Swelling Clay in Southern Brazil

This paper describes a slope instability case history involving swelling clay. A 9-m high slope was cut in 3 sedimentary layers during the construction of a single-carriage road. A complex slope failure mechanism was identified during site investigation, consisting of: (a) a progressive surficial degradation, particularly of the lower swelling clay layer. (b) a deep-seated slope failure, and (c) the toppling failure of the upper stronger layers. Site investigation included SPT testing, undisturbed sampling and in situ suction measurement. Laboratory testing consisted of: (a) soil characterization by X-ray diffraction analysis, particle-size analysis and Atterberg limits tests; (b) evaluation of effective shear strength parameters using direct shear tests and ring shear tests: and (c) determination of soil-water characteristic curves. Slope stability analyses were carried out followed by comparison with observed field performance

First determination of the one-proton induced Non-Mesonic Weak Decay width of p-shell {\Lambda}-Hypernuclei

Previous studies of proton and neutron spectra from Non-Mesonic Weak Decay of eight Lambda-Hypernuclei (A = 5-16) have been revisited. New values of the ratio of the two-nucleon and the one-proton induced decay widths, Gamma_2N/Gamma_p, are obtained from single proton spectra, Gamma_2N/Gamma_p = 0.50 +/- 0.24, and from neutron and proton coincidence spectra, Gamma_2N/Gamma_p = 0.36 +/- 0.14stat +0.05sys -0.04sys , in full agreement with previously published ones. With these values, a method is developed to extract the one-proton induced decay width in units of the free Lambda decay width, Gamma_p/Gamma_Lambda, without resorting to Intra Nuclear Cascade models but by exploiting only experimental data, under the assumption of a linear dependence on A of the Final State Interaction contribution. This is the first systematic determination ever done and it agrees within the errors with recent theoretical calculations.Comment: 16 pages, 3 figures, 2 table

Production of Λ6^{6}_{\Lambda}H and Λ7^{7}_{\Lambda}H with the (Kstop−^{-}_{stop},π+\pi^+) reaction

The production of neutron rich $\Lambda$-hypernuclei via the ($K^-_stop$,$\pi^+$) reaction has been studied using data collected with the FINUDA spectrometer at the DA$\Phi$NE $\phi$-factory (LNF). The analysis of the inclusive $\pi^+$ momentum spectra is presented and an upper limit for the production of $^6_\Lambda$H and $^7_\Lambda$H from $^6$Li and $^7$Li, is assessed for the first time.Comment: 11 pages, 3 figures. Accepted for publication in PL

Hypernuclear spectroscopy with K−^- at rest on 7^7Li, 9^9Be, 13^{13}C and 16^{16}O

The FINUDA experiment collected data to study the production of hypernuclei on different nuclear targets. The hypernucleus formation occurred through the strangeness-exchange reaction K^-_{stop} + \; ^AZ \rightarrow \; ^A_{\Lambda}Z + \pi^-. From the analysis of the momentum of the emerging $\pi^-$, binding energies and formation probabilities of $^7_{\Lambda}$Li, $^9_{\Lambda}$Be, $^{13}_{\Lambda}$C and $^{16}_{\Lambda}$O have been measured and are here presented. The behavior of the formation probability as a function of the atomic mass number A is also discussed.Comment: Accepted for publication in PL

Σ−p\Sigma^- p emission rates in K−K^- absorptions at rest on 6^6Li, 7^7Li, 9^{9}Be, 13^{13}C and 16^{16}O

An experimental study of the $K^-_{stop}A\rightarrow \Sigma^- p A'$ reaction on $A=^6$Li, $^7$Li, $^9$Be, $^{13}$C and $^{16}$O $p$-shell nuclei is presented. The data were collected by the FINUDA spectrometer operating at the DA$\Phi$NE $\phi$-factory (LNF-INFN, Italy). Emission rates for the reaction in the mentioned nuclei are measured and compared with the few existing data. The spectra of several observables are discussed; indications of Quasi-Free absorptions by a $(np)$ pair embedded in the $A$ nucleus can be obtained from the study of the missing mass distributions.Comment: Version accepted by PR

A study of the proton spectra following the capture of K−K^- in 6^6Li and 12^{12}C with FINUDA

Momenta spectra of protons emitted following the capture of $K^-$ in $^6$Li and $^{12}$C have been measured with 1% resolution. The $^{12}$C spectrum is smooth whereas for $^6$Li a well defined peak appears at about 500 MeV/$c$. The first observation of a structure in this region was identified as a strange tribaryon or, possibly, a $\bar K$-nuclear state. The peak is correlated with a $\pi^-$ coming from $\Sigma^-$ decay in flight, selected by setting momenta larger than 275 MeV/$c$. The $\Sigma^-$ could be produced, together with a 500 MeV/$c$ proton, by the capture of a $K^-$ in a deuteron-cluster substructure of the $^6$Li nucleus. The capture rate for such a reaction is (1.62\pm 0.23_{stat} ^{+0.71}_{-0.44}(sys))%/K^-_{stop}, in agreement with the existing observations on $^4$He targets and with the hypothesis that the $^6$Li nucleus can be interpreted as a $(d+\alpha)$ cluster.Comment: 21 pages, 10 figures. Accepted for publication in NP

First Results on 12Lambda-C production at DAPHNE

Lambda-hypernuclei are produced and studied, with the FINUDA spectrometer, for the first time at an e+e- collider: DAPHNE, the Frascati phi-factory. The slow negative kaons from phi(1020) decay are stopped in thin (0.2 g/cm^2) nuclear targets, and Lambda-hypernuclei formation is detected by measuring the momentum of the outgoing pi^-. A preliminary analysis on 12Lambda-C shows an energy resolution of 1.29 MeV FWHM on the hypernuclear levels, the best obtained so far with magnetic spectrometers at hadron facilities. Capture rates for the ground state and the excited ones are reported, and compared with previous experiments.Comment: 15 pages, 5 figures. v2: one reference updated. Accepted for publication in Phys. Lett.

Correlated Λd\Lambda d pairs from the Kstop−A→ΛdA′K^{-}_{stop} A \to \Lambda d A' reaction

Correlated $\Lambda d$ pairs emitted after the absorption of negative kaons at rest $K^{-}_{stop}A\to \Lambda d A'$ in light nuclei $^6Li$ and $^{12}C$ are studied. $\Lambda$-hyperons and deuterons are found to be preferentially emitted in opposite directions. The $\Lambda d$ invariant mass spectrum of $^6Li$ shows a bump whose mass is 3251$\pm$6 MeV/c$^2$. The bump mass (binding energy), width and yield are reported. The appearance of a bump is discussed in the realm of the [$\bar{K}3N$] clustering process in nuclei. The experiment was performed with the FINUDA spectrometer at DA$\Phi$NE (LNF).Comment: 13 pages, 5 figures, accepted for publication in Phys. Lett.

Proton spectra from Non-Mesonic Weak Decay of p-shell Lambda-Hypernuclei and evidence for the two-nucleon induced process

New spectra from the FINUDA experiment of the Non Mesonic Weak Decay (NMWD) proton kinetic energy for 9(Lambda)Be, 11(Lambda)B, 12(Lambda)C, 13(Lambda)C, 15 (Lambda)N and 16(Lambda)O are presented and discussed along with the published data on 5(Lambda)He and 7(Lambda)Li. Exploiting the large mass number range and the low energy threshold (15 MeV) for the proton detection of FINUDA, an evaluation of both Final State Interactions (FSI) and the two nucleon induced NMWD contributions to the decay process has been done. Based on this evaluation, a linear dependence of FSI on the hypernuclear mass number A is found and for the two nucleon stimulated decay rate the experimental value of Gamma2/Gammap=0.43+-0.25 is determined for the first time. A value for the two nucleon stimulated decay rate to the total decay rate Gamma2/GammaNMWD=0.24+-0.10 is also extracted.Comment: 11 pages and 2 figure