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Abstract Carl Friedrich von Weizsäcker published two important papers on topics of nuclear astrophysics in 1937 and 1938 before he turned his attention elsewhere motivated by the discovery of fission and the outbreak of war in 1939. It seems, however, that he continued to actively think about issues related to astrophysics, namely the discussion and role of neutron stars and cosmology. Both are contemporary topics today. This paper presents the development of Weizsäcker’s thoughts in the years between 1935 and 1945, making use of his personal notes and letters. 

Abstract Nuclear beta decays provide an excellent probe of fundamental symmetries due to their mediation by the weak interaction. In particular, precise measurements of these decays provide constraints on the unitarity of the Cabbibo-Kobayashi-Maskawa (CKM) quark-mixing matrix. While superallowed pure Fermi decays currently set the most precise limits, the alternative suite of superallowed mixed mirror decays has been ill-studied. These nuclei can provide an important consistency check of calculation and measurement methods employed for the pure Fermi decays, more critically needed now in the wake of a 2.4σ deviation from unitarity of the CKM matrix. In order to remedy the gap in data for mirror decays, the Superallowed Transition Beta-Neutrino Decay Ion Coincidence Trap (St. Benedict) facility is being commissioned at the University of Notre Dame's Nuclear Science Laboratory (NSL). In this paper, we present first results of the commissioning of the St. Benedict facility on-line at the TwinSol radioactive beam facility. The results of initial commissioning experiments involving the St. Benedict gas catcher, RF carpet, RFQ ion guide and RFQ cooler-buncher will be presented. 

Abstract One of the most important stellar neutron sources is the²²Ne($$\alpha ,n$$ $\alpha ,n$)²⁵Mg reaction, which gets activated both during the helium intershell burning in asymptotic giant branch stars and in core helium and shell carbon burning in massive stars. The²²Ne($$\alpha ,n$$ $\alpha ,n$)²⁵Mg reaction serves as the main neutron producer for the weaks-process and provides a short but strong neutron exposure during the helium flash phase of the mains-process, significantly affecting the abundances at thes-process branch points. The cross section needs to be known at very low energies, as close as possible to the neutron threshold at$$E_\alpha =$$ $E_{\alpha }=$562 keV (Q= −478 keV), but both direct and indirect measurements have turned out to be very challenging, leading to significant uncertainties. Here we discuss the current status of the reaction, including recent and upcoming measurements, and provide a discussion on the astrophysical implications as well as an outlook into the near future. 

Abstract An in-beam gamma-ray spectroscopy study of the even–even nucleus⁹²Mo has been carried out using the³⁰Si +⁶⁵Cu,¹⁸O +⁸⁰Se reactions at beam energies of 120 and 99 MeV, respectively. Angular distribution from the oriented state ratio (R_ADO) and linear polarization (Δ_asym) measurements have fixed most of the tentatively assigned spin-parity of the high-energy levels. A large-scale shell-model calculation using the GWBXG interaction has been carried out to understand the configuration and structure of both positive and negative parity states up to the highest observed spin. The high-spin states primarily originate from the coupling of excited proton- and neutron-core structures in an almost stretched manner. The systematics of the energy required to form a neutron particle-hole pair excitation,νg_9/2→νd_5/2, is discussed. The lifetimes of a few high-spin states have been measured using the Doppler shift attenuation method. Additionally, a qualitative argument is proposed to explain the comparatively strong E1 transition feeding the 7310.9 keV level. 

Abstract Neutron-induced nuclear reactions play an important role in the Big Bang Nucleosynthesis. Their excitation functions are, from an experimental point of view, usually difficult to measure. Nevertheless, in the last decades, big efforts have led to a better understanding of their role in the primordial nucleosynthesis network. In this work, we apply the Trojan Horse Method to extract the cross section at astrophysical energies for the³He(n,p)³H reaction after a detailed study of the²H(³He,pt)H three-body process. Data extracted from the present measurement are compared with other published sets. The reaction rate is also calculated, and the impact on the Big Bang nucleosynthesis is examined in detail. 

Abstract The$$^{90}$$ $_{}^{90}$Zr(p,$$\gamma $$ $\gamma$)$$^{91}$$ $_{}^{91}$Nb reaction is one of the important reactions in the$$A\approx 90$$ $A\approx 90$mass region and part of the nucleosynthesis path responsible for production of$$^{92}$$ $_{}^{92}$Mo during the$$\gamma $$ $\gamma$-process. Discrepant data in the literature provide a cross section that varies up to 30% within the Gamow window for the$$^{90}$$ $_{}^{90}$Zr(p,$$\gamma $$ $\gamma$)$$^{91}$$ $_{}^{91}$Nb reaction. Thus, the cross section measurements of$$^{90}$$ $_{}^{90}$Zr(p,$$\gamma $$ $\gamma$)$$^{91}$$ $_{}^{91}$Nb reaction were revisited using the$$\gamma $$ $\gamma$-summing technique. The results are consistent with the lower-value cross sections found in the literature. Based on the new data an updated reaction rate for$$^{90}$$ $_{}^{90}$Zr(p,$$\gamma $$ $\gamma$)$$^{91}$$ $_{}^{91}$Nb is provided that is up to 20% higher than that obtained from thenon-smokercode. 

Abstract The evolutionary path of massive stars begins at helium burning. Energy production for this phase of stellar evolution is dominated by the reaction path 3$$\alpha \rightarrow ^{12}$$ $\alpha {\to }^{12}$C$$(\alpha ,\gamma )^{16}$$ ${(\alpha ,\gamma )}^{16}$O and also determines the ratio of$$^{12}$$ $_{}^{12}$C/$$^{16}$$ $_{}^{16}$O in the stellar core. This ratio then sets the evolutionary trajectory as the star evolves towards a white dwarf, neutron star or black hole. Although the reaction rate of the 3$$\alpha $$ $\alpha$process is relatively well known, since it proceeds mainly through a single narrow resonance in$$^{12}$$ $_{}^{12}$C, that of the$$^{12}$$ $_{}^{12}$C$$(\alpha ,\gamma )^{16}$$ ${(\alpha ,\gamma )}^{16}$O reaction remains uncertain since it is the result of a more difficult to pin down, slowly-varying, portion of the cross section over a strong interference region between the high-energy tails of subthreshold resonances, the low-energy tails of higher-energy broad resonances and direct capture. Experimental measurements of this cross section require herculean efforts, since even at higher energies the cross section remains small and large background sources are often present that require the use of very sensitive experimental methods. Since the$$^{12}$$ $_{}^{12}$C$$(\alpha ,\gamma )^{16}$$ ${(\alpha ,\gamma )}^{16}$O reaction has such a strong influence on many different stellar objects, it is also interesting to try to back calculate the required rate needed to match astrophysical observations. This has become increasingly tempting, as the accuracy and precision of observational data has been steadily improving. Yet, the pitfall to this approach lies in the intermediary steps of modeling, where other uncertainties needed to model a star’s internal behavior remain highly uncertain. 

Abstract Low-lying states in$$^{54}$$ $_{}^{54}$Cr have been investigated via the$$\alpha $$ $\alpha$-transfer reaction$$^{50}$$ $_{}^{50}$Ti($$^{7}$$ $_{}^7$Li,t) at a bombarding energy of 20 MeV. The exclusive$$\alpha $$ $\alpha$-transfer channel is separated from other reaction channels through the appropriate energy gate on the complementary particle, triton. Levels of$$^{54}$$ $_{}^{54}$Cr populated exclusively by the$$\alpha $$ $\alpha$-transfer process could be identified up to$$\approx $$ $\approx$5 MeV excitation energy and angular momentum up to$$(8)^{+}$$ ${\left(8\right)}^{+}$, by identifying the corresponding known$$\gamma $$ $\gamma$-rays. These include multiple low-lying non-yrast 2$$^+$$ $_{}^{+}$and 4$$^+$$ $_{}^{+}$states, which would otherwise be unfavorable via fusion evaporation reactions. The feeding-subtracted$$\gamma $$ $\gamma$-ray yields have been extracted to estimate the population of various excited states through the transfer process. The measured integrated transfer cross sections for all the observed yrast and non-yrast states are compared with Coupled Channels calculations usingfrescoto extract the$$\alpha $$ $\alpha$+$$^{50}$$ $_{}^{50}$Ti core spectroscopic factors. For the yrast states, a higher$$\alpha $$ $\alpha$+core overlap is seen for the$$2^+$$ $2^{+}$and$$4^+$$ $4^{+}$states, while it is seen to be less favorable for the$$6^+$$ $6^{+}$and$$(8)^+$$ ${\left(8\right)}^{+}$states when$$\alpha $$ $\alpha$-transfer is considered to occur predominantly as a direct one-step process to the$$^{50}$$ $_{}^{50}$Ti core ground state. The yrast$$2^+$$ $2^{+}$, and$$4^+$$ $4^{+}$states are predominantly populated by single-step transfer, while for the states with spin$$\ge $$ $\ge$5, the possibility of core excitation followed by$$\alpha $$ $\alpha$-transfer shows a larger$$\alpha $$ $\alpha$-core overlap. For the non-yrast$$0^+$$ $0^{+}$,$$2^+$$ $2^{+}$, and$$4^+$$ $4^{+}$states, single-step transfer shows moderate to small$$\alpha $$ $\alpha$-core overlap. No higher spin non-yrast states are observed. 

Abstract A new type of radio frequency (RF) timing technique is presented. It is based on a helical deflector, which performs circular or elliptical sweeps of photo- or secondary electrons, accelerated to keV energies, by means of RF fields in the 500–1000 MHz range. By converting a time distribution of the electrons to a hit position distribution on a circle or ellipse, this device achieves extremely precise timing, similar to streak cameras. Detection of the scanned electrons, using a position sensitive detector based on microchannel plates and a delay line anode, resulted in a timing resolution of 10 ps, which can be potentially improved to 1 ps. RF-Timer-based single photon and heavy ion detectors have potential applications in different fields of science and industry, which include high energy nuclear physics and imaging technologies. This technique could play a crucial role in developing of sub 10 ps Time-of-Flight Positron Emission Tomography. 

Abstract The Istituto Nazionale di Fisica Nucleare—Laboratori Nazionali del Gran Sasso (LNGS) is one of the largest underground physics laboratory, a very peculiar environment suited for experiments in Astroparticle Physics, Nuclear Physics and Fundamental Symmetries. The newly established Bellotti Ion Beam facility represents a major advance in the possibilities of studying nuclear processes in an underground environment. A workshop was organized at LNGS in the framework of the Nuclear Physics Mid Term Plan in Italy, an initiative of the Nuclear Physics Division of the Instituto Nazionale di Fisica Nucleare to discuss the opportunities that will be possible to study in the near future by employing state-of-the-art detection systems. In this report, a detailed discussion of the outcome of the workshop is presented.