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In the present work measurements to determine the differential cross section values for the elastic scattering of 3He on 16O and 27Al were carried out at the Ruđer Bošković Institute (RBI) Tandem Accelerator Facility in Zagreb, Croatia, covering the E3He,lab=3500-5600 keV energy range, using four Silicon Surface Barrier (SSB) detectors positioned at the backscattering angles of 130°, 145°, 157.7° and 165ο. The target was constructed at the facility and was comprised of a thin, self-supporting aluminum foil, upon which a thin layer of natB (isotopic ratio: 11B 80.1%, 10B 19.9%), along with 12C, 14N, 16O, was deposited using the sputtering technique. In addition, an ultra-thin layer of 197Au was evaporated on top for wear protection and normalization purposes.

In the present work, alkyd and acrylic self-made paints containing synthetic organic pigments (SOPs) of different chemical classes (phthalocyanine, quinacridone, and diketopyrrolo-pyrrole) were analysed by Secondary Ion Mass Spectrometry with MeV primary ions (MeV-SIMS) to study the chemical changes that occur due to accelerated UV ageing. MeV-SIMS is an emerging accelerator-based, surface-sensitive mass spectrometry technique that can provide information about the chemical composition in the uppermost layers of materials. Two-component mock-up samples were prepared and aged for two and four months, to mimic environmental ageing over periods of one and two years. The obtained results show that the studied SOPs are stable under the accelerated ageing conditions used in this study and that they can be easily identified in aged paints, while the binder components undergo structural changes due to the photodegradation processes. The kinetics of binder degradation were found to be dependant on the pigment present in the paint, with phthalocyanines having the highest photostabilizing effect amongst the pigments studied. In addition, the acrylic binder exhibited slightly higher stability to UV ageing than the alkyd medium. This study allowed the identification of SOPs and binders in the selected contemporary artworks, which date from different periods and belong to both outdoor and indoor collections.

The implementation of boron in several fields, such as in the creation of p-type semiconductors in electronics, has created the need for the accurate quantitative determination of its depth profile concentrations in near surface layers of various matrices. In the framework of IBA techniques, a combination of Elastic Backscattering Spectroscopy (EBS), along with Nuclear Reaction Analysis (NRA), has been proposed in order to address the current needs for boron depth profiling, based on the use of a proton beam. Deuterons offer superior mass resolution with respect to protons, having similar stopping power values, but, unfortunately, the lack of experimental datasets concerning the deuteron elastic scattering on boron impedes their use. Thus, in the present work, the first set of measurements for the 11B(d,d0) differential cross sections covering the Ed,lab=1300-1860 keV energy range for the backscattering angles of 150°, 160° and 170° was carried out. The study was conducted at the 5.5 MV Tandem Accelerator of the Institute of Nuclear and Particle Physics, in the National Center of Scientific Research “Demokritos”, Athens, Greece. The target was a thin, self-supporting aluminum foil, upon which a thin natB (isotopic ratio: 11B 80.1%, 10B 19.9%) layer was deposited using the sputtering technique at RBI, Zagreb, Croatia, followed by the evaporation of an ultra-thin layer of 197Au on top for wear protection and normalization purposes. The outgoing particles were detected using 6 Silicon Surface Barrier (S.S.B.) detectors and the differential cross sections for the elastic scattering were determined from the resulting spectra via the relative measurement technique.

This work reports on the first systematic study using secondary ion mass spectrometry with MeV ions (MeV-SIMS) for analysis of synthetic organic pigments (SOPs) that can be usually found in modern and contemporary art paints. In order to prove the applicability of the method to different chemical classes of SOPs, 17 pigments were selected for the analyses. The focus was on blue and green phthalocyanines, yellow and red (naphthol AS) azo pigments, red quinacridone, anthraquinone, and diketopyrrolo-pyrrole pigments. Since there are no reference spectra available for this technique, pure pigment powders were measured first to create a database. Simple two-component paint systems were also prepared for testing purposes by mixing synthetic organic pigments with alkyd and acrylic binders. Commercial paints that contain the SOPs with identical C.I. numbers as in the prepared two-component samples were analyzed. All pigments were successfully identified in commercial products in the MeV-SIMS mass spectra through molecular and larger specific fragment ion peaks in the positive-ion mode. The main advantages of MeV-SIMS over other techniques used in SOPs identification, like pyrolysis gas chromatography mass spectrometry (Py-GC/MS), direct-temperature resolved mass spectrometry (DTMS), and laser desorption ionization mass spectrometry (LDIMS), can be summarized as follows: (i) pigments and binders can be detected simultaneously in the same mass spectrum acquired over a short measurement time (up to 500 s), (ii) only small sample flakes are required for the measurements, which are analyzed without any chemical treatment prior to the analyses, (iii) samples are not consumed during the analyses and can be reused for other measurements, e.g., multielemental analysis by other ion beam analysis (IBA) techniques, such as particle-induced X-ray emission (PIXE). Compared to, e.g., Raman spectroscopy, the significant benefit of MeV-SIMS is the exact identification of the SOPs in the paints even if pigments of similar structures are measured.

A new model, based on the BCS approach, is especially designed to describe nuclear phenomena (A, Z) → (A, Z ± 2) of double-charge exchange (DCE). Although it was proposed and applied in the particle-hole limit, by one of the authors [Krmpotić, Fizika B 14, 139 (2005)], it has not yet been applied within the BCS mean-field framework, nor has its ability to describe DCE processes been thoroughly explored. It is a natural extension of the pn-QRPA model, developed by Halbleib and Sorensen [Nucl. Phys. A 98, 542 (1967)] to describe the single β decays (A, Z) → (A, Z ± 1), to the DCE processes. As such, it exhibits several advantages over the pn-QRPA model when used in the evaluation of the double beta decay (DBD) rates. For instance, (i) the extreme sensitivity of the nuclear matrix elements (NMEs) on the model parametrization does not occur; (ii) it allows us to study the NMEs, not only for the ground state in daughter nuclei, as the pn-QRPA model does, but also for all final 0⁺ and 2⁺ states, accounting at the same time for their excitation energies and the corresponding DBD Q values; (iii) together with the DBD-NMEs it also provides the energy spectra of Fermi and Gamow-Teller DCE transition strengths, as well as the locations of the corresponding resonances and their sum rules; (iv) the latter are relevant for both the DBD and the DCE reactions, since the underlying nuclear structure is the same; this correlation does not exist within the pn-QRPA model. As an example, detailed numerical calculations are presented for the (A, Z) → (A, Z + 2) process in ⁴⁸Ca → ⁴⁸Ti and the (A, Z) → (A, Z − 2) process in ⁹⁶Ru → ⁹⁶Mo, involving all final 0⁺ states and 2⁺ states., Facultad de Ciencias Exactas, Instituto de Física La Plata

We present a study of the nonmesonic weak decay (NMWD) of charmed hypernuclei using a relativistic formalism. We work within the framework of the independent particle shell model and employ a ($\pi$,$K$) one-meson-exchange model for the decay dynamics. We implement a fully relativistic treatment of nuclear recoil. Numerical results are obtained for the one-neutron-induced transition NMWD rates of the $_{\Lambda^{+}_{c}}^{12}$N. The effect of nuclear recoil is sizable and goes in the direction to decrease the nuclear decay rate. We found that the NMWD decay rate of $_{\Lambda^{+}_{c}}^{12}$N is of the same order of magnitude as the partial decay rate for the corresponding mesonic decay $\Lambda^+_c \rightarrow \Lambda + \pi^+$, suggesting the feasibility of experimental detection of such heavy-flavor nuclear processes., Comment: 24 pages, 3 figures

Radiocarbon (14C) method is a very powerful method for fast and accurate determination of bio-based fraction in any material containing carbon. Any radiocarbon measurement technique can be applied ; however, for liquid fuels the best technique is a direct measurement of liquids mixed with a scintillation cocktail in liquid scintillation counters – the direct LSC technique. At the first conference Natural Resorces, Greeen Technology & Sustainable Development in 2014 we presented a new data evaluation technique for determination of biogenic fraction in liquid fuel by the 14C direct LSC method. The idea was to use various purely biogenic compounds of different colours and quenching properties to construct the “modern calibration curve”, as well as various purely fossil liquids to construct the “background calibration curve”. The fraction of the biogenic component in an unknown sample was determined as the ratio of net count rates of the unknown sample and the biogenic sample having the same quenching properties. The proposed data evaluation technique depended neither on the fossil matrix nor on the biogenic additive type. It did not require 14C spikes or other expensive standards. One did not need to know the qualitative composition of liquid fuels, as it was the case for other evaluation techniques. Mixtures of biogenic and 14C-free liquids demonstrated the potential of the proposed technique for determining the biogenic fraction of a mixture. In this presentation we would like to report developments in the direct LSC technique, results of intercomparison studies with other laboratories that apply a conventional evaluation technique, as well as results of determination of the biogenic component fraction in mixtures of various fossil matrices and various biogenic blends. The limit when the count rates of the biogenic and the fossil samples become close to each other or indistinguishable is set to SQP ≈ 700, where SQP denotes the Standard Quench Parameter determined by LSC Quantulus 1220. Below this value the obtained results for biogenic fractions are not reliable. The method gives comparable results with other data evaluation techniques, and the results are very good for SQP > 700. Influence of aging of both original mixtures and prepared scintillation cocktails on SQP and count rate will be discussed.

Intenzivna upotreba fosilnih goriva (ugljen, nafta) za proizvodnju energije i za pokretanje prometnih vozila tijekom 20. stoljeća uzrokovala je porast koncentracije CO2 u atmosferi. Upotreba biogenih materijala kao zamjene za fosilna goriva može usporiti porast atmosferske koncentracije CO2. Europska unija poreznom politikom stimulira korištenje biogenih goriva te se javlja potreba razvoja neovisne i pouzdane metode za određivanje udjela biogene komponente u različitim vrstama materijala koji se mogu koristiti kao izvori energije. Jedna od takvih metoda je metoda radioaktivnog ugljika (14C) koja se zasniva na različitoj koncentraciji 14C u biogenim i fosilnim materijalima: biogeni materijali odražavaju koncentraciju aktivnosti 14C u suvremenoj atmosferi i biosferi, dok fosilni materijali ne sadrže 14C. Metoda se može primijeniti na različite materijale (mješoviti komunalni otpad, iskorištene auto-gume, drvena građa, tekuća goriva, proizvodi široke potrošnje, CO2 nastao spaljivanjem otpada, i slično). Ovisno o vrsti materijala, mogu se primijeniti različite tehnike mjerenja. Posebna pozornost posvetit će se tehnici određivanja biogene komponente u tekućim gorivima mjerenjem koncentracije aktivnosti 14C u gorivima pomoću tekućinskog scintilacijskog brojača.

European Union’s promotion of the use of sustainable and renewable resources requires use of at least 10 % of synthesized biodiesel in liquid fuels by the year 2020. This legislation has stimulated various types of petrodiesel and bio-based component blends production, and development of methods for exact, effective and reliable quantification of biodiesel content. The method for determination of the biogenic fraction in liquid fuels by direct measurement of the 14C activity concentration via liquid scintillation counting (LSC) technique was developed in few laboratories worldwide. It is based on different 14C signatures of the two components: the biogenic component reflects the modern atmospheric 14C activity, while no 14C is present in fossil fuels. The quantity of 14C in the fuel is the criterion for bio-fuel presence. A great variety of biogenic matrices in fuels results in a wide range of quenching properties of different fuel mixtures. The laboratories participating in this intercomparison study developed two different calibration techniques. The Ruđer Bošković Institute data evaluation method is based on calibration curves for purely biogenic and purely fossil liquids, and does not depend on the exact chemical composition of the organic liquid. The limits of the method are defined by the SQP of app. 690 below which the count rate of biogenic and fossil liquids become indistinguishable from one another. The University of Novi Sad data evaluation method is very dependent on the composition of the examined fuels, so the obtained results in this case were relatively good. Future investigation should also test whether this calibration method is suitable for some other fuel matrices, for example for various types of domestic oil used in everyday life. Testing advantages and limitations of the two methods will continue in the future.

A method of direct measurement of 14C activity concentration via liquid scintillation counting (LSC) is recognized as good and fast method for determination of biogenic component in liquid fuels. Two laboratories that used this14C technique participated in this survey: Laboratory from University of Novi Sad (UNS), Serbia and Laboratory from Ruđer Bošković Institute (RBI), Croatia. Each laboratory used its own calibration methods on the same set of samples (produced diesel-based bio-fuels and commercially available domestic oils). From the obtained results it can be concluded that each method which uses 14C technique for determination of biogenic component in liquid fuels has its advantages and disadvantages. RBI data evaluation method is based on two calibration curves, for purely biogenic and purely fossil liquids, and the calibration does not depend on the exact chemical composition of the organic liquid. The limits of the method are defined by the SQP(E) of approximately 690. Below this value the count rates of biogenic and fossil liquids become close to each other or even indistinguishable from one another and the obtained results for biogenic fractions are not reliable. In this intercomparison UNS used two different methods, one for produced bio-diesels and the other one for domestic oils. UNS data evaluation method is very dependent on the composition of the examined fuels, so the obtained results with the "two-step" method were relatively good in the case of diesel mixtures with biogenic component. In the case of biogenic oil samples (bought on market), UNS "two-step" method did not give realistic results, and with the "one-step" method the limitation is large quenching in the samples, so for the samples with SQP(E) less than 700 this method could not give expected results. Samples prepared with liquid fuels are usually colored and the main challenge for determination of biogenic component in both laboratories is handling of highly quenched liquids. Prema preporukama Evropske Unije sa ciljem da se koriste obnovljivi i održivi izvori, do 2020. godine zahteva se da se u svim tečnim gorivima koja se koriste nalazi bar 10% sintetisanog biodizela. Da bi se koncentracija biodizela mogla proveriti, nekoliko laboratorija u svetu je razvilo metode za tačnu, efikasnu i pouzdanu kvantifikaciju sadržaja biogene komponente. Direktno merenje koncentracije aktivnosti 14C tečnim scintilacionim detektorom (LSC), koje podrazumeva određivanje količine 14C u uzorku kao meru prisutnosti biogene komponente u testiranom gorivu, pokazalo se kao dobra i brza metoda. U ovoj interkomparaciji učestvovale su dve laboratorije: Laboratorija sa Univerziteta u Novom Sadu (UNS), Srbija i Laboratorija sa Instituta Ruđer Bošković (RBI), Hrvatska. Svaka laboratorija je koristila sopstveni kalibracioni metod i isti set uzoraka za interkomparaciju (proizvedena bio-goriva bazirana na dizelu i komercijalno dostupna domaća ulja). Iz dobijenih rezultata može se zaključiti da svaki od prikazanih metoda ima svoje prednosti i mane, što zavisi od samog sastava uzorka. RBI metod se zasniva na upotrebi dve kalibracione krive, za čisto biogena i čisto fosilna goriva, i kalibracija nije zavisna od hemijskog sastava analiziranog uzorka. Ograničenje ove metode je SQP(E) vrednost niža od 690. Ispod ove vrednosti odbroji biogene i fosilne komponente postaju veoma bliski jedan drugom i samim tim rezultati koji se dobijaju nisu pouzdani. U ovoj interkomparaciji, UNS je koristila dve različite metode kalibracije, jednu za proizvedene bio-dizele, a drugu za domaća ulja. UNS metod evaluacije izmerenih podataka u mnogome zavisi od sastava ispitivanog goriva, pa su rezultati dobijeni sa "two-step" metodom relativno dobri za smeše dizela sa biogenom komponentom. U slučaju biogenih ulja, UNS "two-step" metod nije dao realistične rezultate, zbog toga je korišćen "one-step" metoda za koji je utvrđeno ograničenje za SQP(E) parametar na 700. Uzorci koji se pripremaju sa tečnim gorivima su najčešće obojeni i najveći problem koji se javlja je korekcija na prigušenje u samom uzorku, koja mora biti detaljno sprovedena kako bi se dobio pouzdan rezultat, pa najveći izazov daljnjeg razvoja ovih metoda postaje postupak merenja biogene komponente u jako prigušenim uzorcima. Зборник радова : XXIX симпозијум ДЗЗСЦГ : Сребрно језеро, 27-29. септембар 2017. године

A novel comparison between the data and the theory is proposed for the nonmesonic (NM) weak decay of hypernuclei. Instead of confronting the primary decay rates, as is usually done, we focus our attention on the effective decay rates that are straightforwardly related with the number of emitted particles. Proton kinetic energy spectra of ΛHeΛLiΛBeΛBΛCΛCΛNΛO measured by FINUDA, are evaluated theoretically. The independent particle shell model (IPSM) is used as the nuclear structure framework, while the dynamics is described by the one-meson-exchange (OME) potential. Only for the 5Λrm HeΛLiand ΛC hypernuclei it is possible to make a comparison with the data, since for the rest there is no published experimental information on number of produced hypernuclei. Considering solely the one-nucleon-induced (1N-NM) decay channel, the theory reproduces correctly the shapes of all three spectra at medium and high energies (Ep ≥ 40 MeV). Yet, it greatly overestimates their magnitudes, as well as the corresponding transition rates when the full OME (π + K + η + δ + ω + K∗) model is used. The agreement is much improved when only the π + K mesons with soft dipole cutoff parameters participate in the decay process. We find that the IPSM is a fair first-order approximation to disentangle the dynamics of the 1N-NM decay, the knowledge of which is indispensable to inquire about the baryon-baryon strangeness-flipping interaction. It is shown that the IPSM provides very useful insights regarding the determination the 2N-NM decay rate. In a new analysis of the FINUDA data, we derive two results for this quantity with one of them close to that obtained previously. Fil: Krmpotic, Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad Estatal Paulista; Brasil Fil: De Conti, Cláudio. Universidad Estatal Paulista; Brasil

In this work we performed a systematic study of the inclusive muon capture rates for several nuclei with A < 60 using the Projected Random Quasi-particle Phase Approximation (PQRPA) as nuclear model, because it is the only RPA model that treats the Pauli Principle correctly. We reckon that the comparison between theory and data for the inclusive muon capture is not a fully satisfactory test on the nuclear model that is used. The exclusive muon transitions are more robust for such a purpose.

In this work we compute the one-nucleon-induced nonmesonic hypernuclear decay rates of Λ5He, Λ12C and Λ13C using a formalism based on the independent particle shell model in terms of laboratory coordinates. To ascertain the correctness and precision of the method, these results are compared with those obtained using a formalism in terms of center-of-mass coordinates, which has been previously reported in the literature. The formalism in terms of laboratory coordinates will be useful in the shell-model approach to two-nucleon-induced transitions.

We compute one- and two-nucleon kinetic-energy spectra and opening-angle distributions for the nonmesonic weak decay of several hypernuclei, and compare our results with some recent data. The decay dynamics is described by transition potentials of the one-meson-exchange type, and the nuclear structure aspects by two versions of the independent-particle shell model (IPSM). In version IPSM-a, the hole states are treated as stationary, while in version IPSM-b the deep-hole ones are considered to be quasi-stationary and are described by Breit-Wigner distributions., Facultad de Ciencias Exactas, Instituto de Física La Plata

The dynamical effects of ground state correlations for excitation energies and transition strengths near the superfluid phase transition are studied in the soluble two level pairing model, in the context of the particle-particle self consistent Random Phase Approximation (SCRPA). Exact results are well reproduced across the transition region, beyond the collapse of the standard particle-particle Random Phase Approximation. The effects of two-body correlation in the SCRPA are displayed explicitly.

The effect of the inclusion of ground state correlations into the QRPA equation of motion for the two-neutrino double beta ($\beta\beta_{2\nu}$) decay is carefully analyzed. The resulting model, called renormalized QRPA (RQRPA), does not collapse near the physical value of the nuclear force strength in the particle-particle channel, as happens with the ordinary QRPA. Still, the $\beta\beta_{2\nu}$ transition amplitude is only slightly less sensitive on this parameter in the RQRPA than that in the plain QRPA. It is argued that this fact reveals once more that the characteristic behaviour of the $\beta\beta_{2\nu}$ transition amplitude within the QRPA is not an artifact of the model, but a consequence of the partial restoration of the spin-isospin $SU(4)$ symmetry. It is shown that the price paid for bypassing the collapse in the RQRPA is the violation of the Ikeda sum rule.

Simple and coincidence spectra of the NM weak decay of light hypernuclei have been evaluated in a systematic way for the first time. We have only considered 1N induced processes, neglecting entirely the events induced by 2N emission, as well as the effects of the FSIt's. As the theoretical frameworkwe have used the IPSM with three different parametrizations for the transition potential. The comparison with data strongly suggests that the soft π + K exchange model could be a good starting point to describe the dynamics in the NM weak decays of s- and p-shell hypernuclei.

In the present work we evaluate the 56Fe(μ−,νμ)56Mn process using the BCS, PBCS, QRPA and PQRPA models as nuclear models. We show the behavior of the muon capture rates as a function of the t‐parameter, strength of the pp‐channel in the residual δ‐interaction. The obtained results for the muon capture rates show that the projection procedure is important for medium mass nuclei as 56Fe.

We extend the formalism of weak interaction processes, obtaining new expressions for the transition rates, which greatly facilitate numerical calculations, both for neutrino-nucleus reactions and muon capture. Explicit violation of CVC hypothesis by the Coulomb field, as well as development of a sum rule approach for the inclusive cross sections have been worked out. We have done a thorough study of exclusive (ground state) properties of $^{12}$B and $^{12}$N within the projected quasiparticle random phase approximation (PQRPA). Good agreement with experimental data achieved in this way put in evidence the limitations of standard RPA and the QRPA models, which come from the inability of the RPA in opening the $p_{3/2}$ shell, and from the non-conservation of the number of particles in the QRPA. The inclusive neutrino/antineutrino ($\nu/\tilde{\nu}$) reactions $^{12}$C($\nu,e^-)^{12}$N and $^{12}$C($\tilde{\nu},e^+)^{12}$B are calculated within both the PQRPA, and the relativistic QRPA (RQRPA). It is found that the magnitudes of the resulting cross-sections: i) are close to the sum-rule limit at low energy, but significantly smaller than this limit at high energies both for $\nu$ and $\tilde{\nu}$, ii) they steadily increase when the size of the configuration space is augmented, and particulary for $\nu/\tilde{\nu}$ energies $> 200$ MeV, and iii) converge for sufficiently large configuration space and final state spin. The quasi-elastic $^{12}$C($\nu,\mu^-)^{12}$N cross section recently measured in the MiniBooNE experiment is briefly discussed. We study the decomposition of the inclusive cross-section based on the degree of forbiddenness of different multipoles. A few words are dedicated to the $\nu/\tilde{\nu}$-$^{12}$C charge-exchange reactions related with astrophysical applications., Comment: 21 pages, 13 figures, 1 table, submitted to Physical Review C

After a short introduction to the nonmesonic weak decay (NMWD) $\Lambda N\go nN$ of $\Lambda$-hypernuclei we discuss the long-standing puzzle on the ratio $\Gamma_n/\Gamma_p$, and some recent experimental evidences that signalized towards its final solution. Two versions of the Independent-Particle-Shell-Model (IPSM) are employed to account for the nuclear structure of the final residual nuclei. They are: (a) IPSM-a, where no correlation, except for the Pauli principle, is taken into account, and (b) IPSM-b, where the highly excited hole states are considered to be quasi-stationary and are described by Breit-Wigner distributions, whose widths are estimated from the experimental data. We evaluate the coincidence spectra in $^{4}_\Lambda$He, $^{5}_\Lambda$He, $^{12}_\Lambda$C, $^{16}_\Lambda$O, and $^{28}_\Lambda$Si, as a function of the sum of kinetic energies $E_{nN}=E_n+E_N$ for $N=n,p$. The recent Brookhaven National Laboratory experiment E788 on $^4_\Lambda$He, is interpreted within the IPSM . We found that the shapes of all the spectra are basically tailored by the kinematics of the corresponding phase space, depending very weakly on the dynamics, which is gauged here by the one-meson-exchange-potential. In spite of the straightforwardness of the approach a good agreement with data is achieved. This might be an indication that the final-state-interactions and the two-nucleon induced processes are not very important in the decay of this hypernucleus. We have also found that the $\pi+K$ exchange potential with soft vertex-form-factor cutoffs $(\Lambda_\pi\approx 0.7$ GeV, $\Lambda_K\approx 0.9$ GeV), is able to account simultaneously for the available experimental data related to $\Gamma_p$ and $\Gamma_n$ for $^4_\Lambda$H, $^4_\Lambda$He, and $^5_\Lambda$He., Comment: Proceedings of the 32nd Brazilian Workshop on Nuclear Physcis, \'Aguas de Lind\'oia, S\~ao Paulo, Brazil, 7-11 Sep 2009

Using a 252 Cf neutron source we have calibrated the response of Ge detectors to fast neutrons and deduced the expression for determination of the flux of fast environmental neutrons based on the intensity of the spectral structure at 691.3 keV. We also suggest an approximate expression for estimation of the flux of environmental thermal neutrons from the intensity of the 139.9 keV line.

Using as a tool the s-wave approximation (sWA), this work demonstrates that the nonmesonic weak decay transition rates $\Gamma_{n}$ and $\Gamma_{p}$ can be expressed in all hypernuclei up to $^{29}_\Lambda $Si (and very likely in heavier ones too) in the same way as in the s-shell hypernuclei, i.e. as a linear combination of only three elementary transition rates. This finding leads to the analytic prediction that, independently of the transition mechanism, all hypernuclei that are on the stability line (N = Z), i.e. $^5_\Lambda $He, $^7_\Lambda $Li, $^9_\Lambda $Be, $^{11}_\Lambda$B, $^{13}_\Lambda $C, $^{17}_\Lambda $O, $^{29}_\Lambda $Si, etc should roughly have the same ratio $\Gamma_{n}/\Gamma_{p}$, the magnitude of which rapidly increases when one approaches the neutron drip-line (N >> Z), and opposite happens when one goes toward the proton drip-line (N << Z)., Comment: 7 pages, 1 figure

The nuclear gross theory, originally formulated by Takahashi and Yamada (1969 Prog. Theor. Phys. 41 1470) for the β-decay, is applied to the electronic-neutrino nucleus reactions, employing a more realistic description of the energetics of the Gamow-Teller resonances. The model parameters are gauged from the most recent experimental data, both for βand electron capture, separately for even-even, even-odd, odd-odd and odd-even nuclei. The numerical estimates for neutrino-nucleus cross-sections agree fairly well with previous evaluations done within the framework of microscopic models. The formalism presented here can be extended to the heavy nuclei mass region, where weak processes are quite relevant, which is of astrophysical interest because of its applications in supernova explosive nucleosynthesis., Facultad de Ciencias Exactas, Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Física La Plata

Besides exploring the Gamow-Teller response to the 2p2h excitations we also investigate the role of the 3p3h excitations in the final state, which become involved as soon as the ground-state correlations are considered. Both type of correlations in the final state are treated on the same footing. Particular emphasis is put on the conservation of the Ikeda sum rule in the framework of different approximations for the nuclear response. As an example we calculate the strength distribution in 48 Ca. We find that the combined effect of the ground state correlations and the 3p3h excitations produces a relatively small quenching of the low-lying strength compared with that generated by the 1p1h-2p2h coupling.

We explain the origin of the difficulties that appear in a straightforward application of the QRPA in 12C, and we demonstrate that it is imperative to use the projected QRPA (PQRPA). Satisfactory results, not only for the weak processes among the ground states of the triad {12B, 12C, 12N}, but also for the inclusive ones are obtained. We sketch as well a new formalism for the neutrino–nucleus interaction that furnishes very simple final formulae for the muon capture rate and neutrino induced cross sections., Facultad de Ciencias Exactas

A theory of weak hyperon non-leptonic decays is used to predict weak NNK vertices which appear in weak hypernuclear potentials. Comparison is made with other predictions.

15 págs.; 7 figs.; 1 tab.; 1 app. ; PACS number(s): 21.60.Jz, 23.40.Hc, 23.90.1w, The self-consistent quasiparticle random phase approximation (SCQRPA) within the O(5) model in the coupled proton-neutron representation is analyzed. The exact vacuum wave function is used to compute all involved matrix elements. A stability analysis of the stationary points is performed. A phase transition from the uncoupled to the coupled stable proton-neutron regime beyond the QRPA breakdown value of the particle-particle strength is evidenced. The excitation energies are close to the lowest stable exact eigenvalues given by the diagonalization procedure for all cases. The conditions for which the Ikeda sum rule is fulfilled for all values of the particle-particle strength are pointed out. ©2000 American Physical Society, One of us (D.S.D.) is grateful for the financial support given by CNRS during his stay in Grenoble, where the work was performed.

The Gamow–Teller resonance in ²⁰⁸Pb is discussed in the context of a self-consistent RPA, based on the relativistic mean field theory. We inquire on the possibility of substituting the phenomenological Landau–Migdal force by a microscopic nucleon–nucleon interaction, generated from the rho-nucleon tensor coupling. The effect of this coupling turns out to be very small when the short range correlations are not taken into account, but too large when these correlations are simulated by the simple extraction of the contact terms from the resulting nucleon–nucleon interaction., Facultad de Ciencias Exactas

A general shell model formalism for the nonmesonic weak decay of the hypernuclei has been developed. It involves a partial wave expansion of the emitted nucleon waves, preserves naturally the antisymmetrization between the escaping particles and the residual core, and contains as a particular case the weak $\Lambda$-core coupling formalism. The Extreme Particle-Hole Model and the Quasiparticle Tamm-Dancoff Approximation are explicitly worked out. It is shown that the nuclear structure manifests itself basically through Pauli Principle, and a very simple expression is derived for the neutron and proton induced decays rates, $\Gamma_n$ and $\Gamma_p$, which does not involve the spectroscopic factors. We use the standard strangeness-changing weak $\Lambda N\to NN$ transition potential which comprises the exchange of the complete pseudoscalar and vector meson octets ($\pi,\eta,K,\rho,\omega,K^*$), taking into account some important parity violating transition operators that are systematically omitted in the literature. The interplay between different mesons in the decay of ${^{12}_\Lambda C}$ is carefully analyzed. With the commonly used parametrization in the One-Meson-Exchange Model (OMEM), the calculated rate $\Gamma_{NM}= \Gamma_n+\Gamma_p$ is of the order of the free $\Lambda$ decay rate $\Gamma^0(\Gamma_{NM}^{\rm th}\cong \Gamma^0)$ and is consistent with experiments. Yet, the measurements of $\Gamma_{n/p}=\Gamma_n/\Gamma_p$ and of $\Gamma_p$ are not well accounted for by the theory ($\Gamma_{n/p}^{\rm th}\lsim 0.42; \Gamma_p^{\rm th}\gsim 0.60 \Gamma^0$). It is suggested that, unless additional degrees of freedom are incorporated, the OMEM parameters should be radically modified., Comment: 44 pages, 2 eps figures, revtex, to appear in Phys. Rev. C

Convection in a cylindrical container of small aspect ratio is studied. It is known that when, in addition to buoyancy forces, thermocapillarity effects are taken into account, resonant interactions of two modes may appear. In the case of 1:2 resonance amplitude equations are derived, showing the existence of a stable heteroclinic orbit and rotating waves, until now not observed experimentally., Comment: 33 pages, latex, 14 figures, epsfig macro included. To appear in Physica D

We examine the contributions of odd-parity nuclear operators to the two-neutrino double beta decay $0^+\rightarrow 0^+$ amplitude, which come from the $P$-wave Coulomb corrections to the electron wave functions and the recoil corrections to the nuclear currents. Although they are formally of higher order in $\alpha Z/2$ or $v/c$ of the nucleon than the usual Fermi and Gamow-Teller matrix elements, explicit calculations performed within the QRPA show that they are significant when confronted with the experimental data., Comment: 9 pages, latex, no figures

We study the nonmesonic weak decay (NMWD) $\Lambda N \to nN$ of the ${}^{12}_{\Lambda} C$ hypernucleus induced by the nucleon $N=n,p$ with transition rate $\Gamma_N$. The nuclear process is described by the interplay of two models; one describing the NMWD of hyperon $\Lambda$ in the nuclear environment, and the other taking into account the Final State Interaction (FSI) of the two outgoing nucleons with the residual nucleus. The first one is done in the framework of the Independent-Particle Shell-Model (IPSM), with the decay dynamics represented by the exchange of $\pi+ \eta+ K+\rho+\omega+K^*$ mesons with usual parametrization. For the second one is used a time dependent multicollisional intranuclear cascade schema (implemented in the CRISP code - Collaboration Rio-Sao Paulo). The results obtained for inclusive and exclusive kinetic energy spectra, and the angular correlation are compared with recent data from KEK and FINUDA experiments. The calculated ratio $(\Gamma_n / \Gamma_p)^{\partial{\tiny FSI}}$, between the numbers of emitted back-to-back $nn$ and $np$ pairs, is in good agreement with the experimental data.

We study the nonmesonic weak decay (NMWD) ?N ? nN of hypernucleus induced by one nucleon N = n, p. The whole process is described by two coupled models: one for the primary NMWD of ? hyperon in the nuclear environment, and the other taking into account the final state interactions (FSI) of the two outgoing nucleons within the residual nucleus. The NMWD dynamics is represented by the one-meson-exchange potential with usual parametrization, while the independent-particle shell model is used as the nuclear structure framework. The FSI are accounted for by a time-dependent multicollisional Monte Carlo cascade scheme, implemented within the CRISP code (Collaboration Rio-S?o Paulo), which describes in a phenomenological way both the nucleon?nucleon scattering inside the nucleus and the escaping of nucleons from the nuclear surface. An evaporation phase is included to cool down the cascade residual nucleus as well. We analyze the single-nucleon kinetic energy spectra, and the two-nucleon coincidence spectra as a function of both: (i) the sum of the kinetic energies and (ii) the opening angle. The theoretical results are compared with recent data from KEK and FINUDA experiments, obtaining fairly good agreement for inclusive and exclusive kinetic energy spectra. Further theoretical improvements are required to explain angular distributions.

The nuclear levels in $^{197}\mathrm{Pt}$ have been studied from the decay of 95.4 min $^{197}\mathrm{Pt}^{m}$. The isomeric state was produced by ($n$,$\ensuremath{\gamma}$) reaction on the enriched $^{196}\mathrm{Pt}$. The $\ensuremath{\gamma}$-ray spectra have been observed with a hyperpure Ge detector and a large volume Ge(Li) detector. The half-lives of the 399 keV and the 53 keV states were determined with improved precision. The results are ${T}_{\frac{1}{2}}$ (399 keV) =95.41\ifmmode\pm\else\textpm\fi{}0.18 min and ${T}_{\frac{1}{2}}$ (53 keV)=16.58\ifmmode\pm\else\textpm\fi{}0.17 ns. The $g$ factor of the 53 keV ${\frac{5}{2}}^{\ensuremath{-}}$ state has been measured by the gamma-gamma time differential perturbed angular correlation method in an external magnetic field of 25.1 kG using the 346-53 keV gamma cascade. The value of the $g$ factor was obtained to be +0.335\ifmmode\pm\else\textpm\fi{}0.010. This result is compared with the known $g$ factors of the similar states in $^{195}\mathrm{Pt}$, and in $^{197}\mathrm{Hg}$ and $^{199}\mathrm{Hg}$, and also with theoretical calculations based on the quasiparticle-phonon coupling scheme. The possibility of using the 346-53 keV gamma cascade in $^{197}\mathrm{Pt}$ in the future time differential perturbed angular correlation studies is discussed.RADIOACTIVITY $^{197}\mathrm{Pt}^{m}$ [from $^{196}\mathrm{Pt}$$(n,\ensuremath{\gamma})^{197}\mathrm{Pt}^{m}$]; measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}(t)$, $\ensuremath{\gamma}\ensuremath{\gamma}(t)$, $\ensuremath{\gamma}\ensuremath{\gamma}(\ensuremath{\theta},T,H)$, ${T}_{\frac{1}{2}}$; deduced $B(E2)$, $\ensuremath{\mu}$; calculated $B(E2)$, $\ensuremath{\mu}$; Ge(Li), Ge hyperpure, NaI(T1) detectors. Enriched target.

The influence of collective effects associated with spin-isospin-dependent modes upon unique first-forbidden β-decay transitions is studied. The ft values for the 0 − → 0 + and 2 − → 0 + transitions, in the mass region 70 ≤ A ≤ 214, are calculated and compared with the experimental data.

The relevance of the quenching effects induced by charge-exchange collective fields and Δ-isobar-hole excitations is discussed in the case of the β-γ angular correlations in the decay of 208 Tl to the 5 − 1 , 4 − 1 and 5 − 2 levels in 208 Pb. It is found that, although these effects give rise to a large hindrance of the β-moments, they influence the anisotropy factor only very weakly. Satisfactory agreement between theoretical predictions and experimental data is obtained for all the transitions.

The core polarization effects induced by the low-lying charge-conserving vibrational fields on the axial-vector coupling constant are analyzed in terms of the particle-vibration coupling model. As a consequence of the strong incoherent competition among the partial contributions, the resulting quenching for transitions in the lead region is found to be considerably smaller than the quenching induced by the Δ -resonance.

A detailed study of the results of correcting BCS approximation for the effects of particle-number projection and blocking has been carried out. A low-seniority shell-model approximation was used as the frame of reference for investigating the mixing of one- and three-quasiparticle states in odd-mass Ni isotopes and in odd-mass N = 82 isotones. We discuss the results obtained for the energy spectra and electromagnetic decay properties. Effects of seniority-five configurations on the low-lying states have also been studied through the comparison of the low-seniority shell-model results with those which arose from the corresponding full shell-model calculations.

The method developed previously for the treatment of a charge-independent hamiltonian with wave functions having isospin as a good quantum number has been carried further, giving explicit results for the matrix elements and transition probabilities. As an example of application of the formalism we performed a calculation of the well-known Gamow-Teller giant resonances.

We show that the nuclear polarizability plays a very important role in establishing the magnitude of the Δ-hole polarization effect on the axial-vector coupling constant.

Angular distributions of the cross section for the elastic and inelastic scattering of protons have been measured at four isobaric analog resonances of the /sup 144/Sm+p system and at two off-resonance energies. Spectroscopic information about the (7/2)/sub 1//sup -/, (3/2)/sub 1//sup -/, (1/2)/sub 1//sup -/, and (5/2)/sub 1//sup -/ states of the parent nucleus /sup 145/Sm is extracted, with the core /sup 144/Sm in the states 0/sub 1//sup +/, 2/sub 1//sup +/, 3/sub 1//sup -/, 4/sub 1//sup +/, and 2/sub 2//sup +/. The analysis includes direct and fluctuating nonresonant processes. The direct scattering amplitude is obtained from a coupled channel treatment. Different methods for the calculations of the single-particle widths have been employed. The experimental spectroscopic amplitudes were compared with nuclear structure calculations based on the particle-vibrator model. Both the liquid drop model and the quasi-particle random phase approximation were used to describe the vibrator. The calculations based on the latter model show good agreement with the experimental results.

In the lead region a theoretical study of two-nucleon transfer processes is made with the help of the generator coordinate method. Both two-proton and two-neutron transfer reactions are described. The two-phonon pairing vibrational states in 208 Pb are especially considered. Energies, relative cross sections and angular distributions are presented and compared, when possible, with experiments.

Angular-distribution data are presented of single relativistic charged particles produced in inelastic and incoherent negative-pion interactions with emulsion nuclei heavier than hydrogen at 300 GeV/c. The obtained results are compared with data from proton nuclei interactions at the same energy.

We study the introduction of the internal dynamical variables for constituent quarks. These variables are related to the center-of-mass of a nucleon. The problem is connected with the description of spinorial properties of the quarks. The spinors must be artificially introduced in a harmonic oscillator (HO) model. Experimental values of the magnetic moment and the axial-vector coupling constant of a nucleon can be easily reproduced. The theoretical results are not sensitive to the theoretical details; they follow from the general properties of the quark structure of baryons. The connections with the relativistic HO models are also discussed. The case of a very small confinement radius is explored in the Appendix.

Scattering of the radiation emitted in a radioactive decay at the constructional components of a magnetic spectrometer will give rise to a background which usually is not eliminated by coincidence techniques. The background spectrum depends upon the features of the decay under investigation, the instrumental settings and the design parameters of the spectrometer. We investigated origin and intensity of various types of background signals observed in a magnetic lens spectrometer. Quantitative representative results are given which can provide an order of magnitude estimate for the background intensity to be expected in a certain decay. Significant background intensities are caused by γ-radiation as well as by electrons emitted in the decay. It was found that scattered conversion electrons can give rise to sharp structures in the apparent electron spectrum, which are comparable to or even narrower than the instrumental resolution. It is shown by which counter measures the various types of backgrounds can be minimized.

The pairing vibrational states and the two-neutron transfer cross sections between these states are calculated in Ni, Sn and Pb isotopes by the generator coordinate method (GCM). The particle number fluctuation of the BCS functions is handled by projecting in a good approximation on sharp particle numbers. The results agree quite well with the experimental data.

A qualitative description of the low-lying states of odd-mass iodine nuclei is proposed in terms of a three-proton cluster coupled to a harmomic- quadrupole vibrational field. Using reasonable values for the parameters involved, the calculated spectrum of /sup 131/I is in good agreement with experimental data. The comparison with experiments is also satisfactory for the one-body stripping strengths, B(E2) transition probabilities, and magnetic-dipole and electric-quadrupole moments. We do not obtain good results concerning the energies of the lightest I isotopes, (auth)