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The 12C+12C fusion reaction was studied in the range of E c.m.=8.9 to 21 MeV using the active-target Time Projection Chamber. With full information on all tracks of the reaction products, cross sections of the 12C(12C,8Be)16Og.s. channel and the 12C(12C,3α)12C channel could be measured down to the level of a few milibarns. The 12C(12C,8Be)16Og.s. reaction channel was determined to be 10 mb at E c.m.=11.1 MeV, supporting the direct α transfer reaction mechanism. The 12C(12C,3α)12C reaction channel was studied for the first time using an exclusive measurement. Our result does not confirm the anomaly behavior reported in the previous inclusive measurement by Kolata et al. [Phys. Rev. C 21, 579 (1980)]. Our comparisons with statistical model calculations suggest that the 3α channel is dominated by the fusion evaporation process at E c.m. > 19 MeV. The additional contribution of the 3α channel increases the fusion reaction cross section by 10% at energies above 20 MeV. We also find that an additional reaction mechanism is needed to explain the measured cross section at E c.m. < 15 MeV at which point the statistical model prediction vanishes.

The 12C(12C,n) reaction (Q=-2.6 MeV) is a potential neutron source for the weak s-process occurring in shell-carbon burning of massive stars. The uncertainty in this reaction rate limits our understanding of the production of elements in the range 60 < A < 110. Current stellar models must rely on the smooth extrapolation of a dubious statistical model calculation based on experimental data taken at energies well above the Gamow window which lies below 3.2 MeV. At Notre Dame, this reaction cross section has been measured in finer steps at energies above 3.5 MeV, while successful measurements down to 3.1 MeV have just recently been achieved. In addition, a new extrapolation based on measurements of the mirror system has been developed which predicts a number of low-energy resonances while accounting well for the high-energy resonances. An overview of this work along with the most recent results and astrophysical implications are presented.

The 12C+12C fusion reaction plays a crucial role during stellar evolution. The astrophysically important energy range spans from 1 MeV to 3 MeV. However, its cross section has not been determined with enough precision, despite numerous studies, due to the extremely low reaction cross sections and the large experimental background. To allow measurements of the 12C+12C fusion at astrophysical energies, we developed an efficient thick-target method using large-area silicon strip detectors. Further measurements at even lower energies will be performed using coincidences between a silicon-detector and a Ge-detector array, at the high-current accelerator under construction at the University of Notre Dame. Since the coincidence method does not allow obtaining information about the channels without gamma-ray emission, a solenoid spectrometer has been constructed for complementary measurements. Meanwhile, we are also investigating the 24Mg(α, α') reaction using the Grand Raiden Spectrometer at RCNP to search for potential resonances in the 12C+12C fusion reaction. Preliminary results from these measurements will be presented.

The elements between iron and strontium are largely produced by the weak s-process occurring in massive stars during the late stages of convective core He burning and the convective shell carbon burning with the primary source of neutrons coming from the reaction 22Ne(α,n)25Mg. However, shell carbon burning may produce hot enough temperatures to activate 12C(12C,n)23Mg as a significant neutron source. Few studies have been done on this reaction, and the extrapolation from experimental data down to the relevant astrophysical energies is uncertain. Recent studies performed at the Nuclear Science Laboratory of Notre Dame aim to improve the existing reaction data using new experimental techniques as well as provide a more reliable extrapolation to the low energies not accessible by experiment. Preliminary results will be presented and the astrophysical implications will be discussed.

Superbursts are long, energetic, rare explosions, probably triggered by the 12C+12C burning in the crust of neutron stars. However, with the current adopted 12C+12C fusion reaction rate, it is impossible for the current model to explain observations. Therefore, a strong resonance at Ec.m.=1.5 MeV has been proposed to enhance the carbon fusion reaction rate. By comparing the cross sections of the three carbon isotope fusion reactions, 12C+12C, 12C+13C and 13C+13C, we have established an upper limit for the 12C+12C fusion reaction rate. Our preliminary results show that the proposed strong resonance might not be realistic. The superburst puzzle is still unsolved.

Since the first observation of hindrance in heavy-ion fusion, many extrapolated cross sections for astrophysically interesting fusion reactions, such as 12C + 12C, 12C + 16O, 16O + 16O, 24O etc. need to be reexamined. In this contribution, the effects of fusion hindrance at extreme low energies are discussed.

Long multifilamentary Nb3Sn strands for ITER (International Thermonuclear Experimental Reactor) have been successfully fabricated by internal Sn and bronze processes, respectively. To improve the bonding of Nb and Cu and the diffusion between Sn and Cu for the internal tin process, the traditional RIT (rod-in-tube) and new hot extrusion (HE) processes have been employed to manufacture the Cu/Nb rods. The final internal tin process strand with a unit length of 3000–5000 m comprises a Cu stabilizer, a Cu/Ta barrier and 19 subfilaments. Every subfilament consists of about 280–330 Nb filaments in a Cu matrix surrounding an Sn–Ti core. The bronze process Nb3Sn strands with 11581 and 9805 filaments of Nb7.5Ta with an unit length of more than 3 km have been produced, respectively. The Ta or Nb barriers were used to compare the influence of different barrier materials on the fabrication process and superconducting properties of Nb3Sn strands. The microstructure details of two kinds of strands before and after heat treatment have been investigated by scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX). The non-Cu Jc (12 T, 4.2 K) value of 812 A mm − 2 with hysteresis loss of 760 mJ cm − 3 for the bronze-process strand and 1069 A mm − 2 with hysteresis loss of 956 mJ cm − 3 for the internal tin-process strand have been obtained. The influence of microstructure on the transport property and hysteresis loss of strands has been discussed.

We are developing a technique of ultra-sensitive detection of the p-process 146Sm nuclide by accelerator mass spectrometry. 146Sm was produced via the reactions (γ,n), (p,2ne) and (n,2n) on 147Sm. Preliminary results demonstrate for the first time the capability of identifying unambiguously 146Sm through separation and discrimination of its stable 146Nd isobar and other background ions. We consider applying the detection method to an independent determination of 146Sm half-life and to the measurements of cross sections of low-energy nuclear reactions producing long-lived nuclides in the vicinity of 146Sm.