Direct measurements of low-energy resonance strengths of the 23Na(p,γ)24Mg reaction for astrophysics

The NeNa and the MgAl cycles play a fundamental role in the nucleosynthesis of asymptotic giant branch stars undergoing hot bottom burning. The 23Na(p, \u3b3)24Mgreaction links these two cycles and a precise determination of its rate is required to correctly estimate the contribution of these stars to the chemical evolution of various isotopes of Na, Mg and Al. At temperatures of 50 <110 MK, narrow resonances at Ep=140and 251 keVare the main contributors to the reaction rate, in addition to the direct capture that dominates in the lower part of the temperature range. We present new measurements of the strengths of these resonances at the Laboratory for Underground Nuclear Astrophysics (LUNA). We have used two complementary detection approaches: high efficiency with a 4\u3c0BGO detector for the 140keV resonance, and high resolution with a HPGe detector for the 251keV resonance. Thanks to the reduced cosmic ray background of LUNA, we were able to determine the resonance strength of the 251keV resonance as \u3c9\u3b3=482(82)\u3bceVand observed new gamma ray transitions for the decay of the corresponding state in 24Mgat Ex=11931 keV. With the highly efficient BGO detector, we observed a signal for the 140keV resonance for the first time in a direct measurement, resulting in a strength of \u3c9\u3b3140=1.46+0.58 120.53neV(68% CL). Our measurement reduces the uncertainty of the 23Na(p, \u3b3)24Mgreaction rate in the temperature range from 0.05 to 0.1GK to at most +50% 1235%at 0.07GK. Accordingly, our results imply a significant reduction of the uncertainties in the nucleosynthesis calculations

Renal Transplants from Older Deceased Donors: Use of Preimplantation Biopsy and Differential Allocation to Dual or Single Kidney Transplant according to Histological Score Has No Advantages over Allocation to Single Kidney Transplant by Simple Clinical Indication

Background. Grafts from elderly donors (ECD) are increasingly allocated to single (SKT) or dual (DKT) kidney transplantation according to biopsy score. Indications and benefits of either procedure lack universal agreement. Methods. A total of 302 ECD-transplants in period from Jan 1, 2000, to Dec 31, 2015, were allocated to SKT (SKTpre) on clinical grounds alone (before Dec 2010, pre-DKT era, n=170) or according to a clinical-histological protocol (after Dec 2010, DKT era, n=132) to DKT (n=48), SKT biopsy-based protocol (“high-risk”, SKThr, n=51), or SKT clinically based protocol (“low-risk”, SKTlr, n=33). Graft and patient survival were compared between the two periods and between different transplant categories. Results. Graft and overall survival in recipients from ECD in pre-DKT and DKT era did not differ (5-year graft survival 87.7% and 84.2%, resp.); equal survival in the 2 ECD periods was shown in both donor age ranges of 60–69 and >70-years, and in low-risk or high-risk ECD categories. Within the DKT protocol SKThr showed worst graft and overall survival in the 60–69 donor age range; DKT did not result in significantly better outcome than SKT from ECD in either era. One-year posttransplant creatinine clearance in recipients did not differ between any ECD transplant category. At 3 and 5 years after transplantation there were significantly higher total dialysis-free recipient life years from an equal donor number in the pre-DKT era than in the DKT protocol. Conclusions. Use of a biopsy-based protocol to allocate grafts from aged donors to SKT or DKT did not result in better short term graft survival than a clinically based protocol with allocation only to SKT and reduced overall recipient dialysis-free life years in time

Advances in radiative capture studies at LUNA with a segmented BGO detector

Studies of charged-particle reactions for low-energy nuclear astrophysics require high sensitivity, which can be achieved by means of detection setups with high efficiency and low backgrounds, to obtain precise measurements in the energy region of interest for stellar scenarios. High-efficiency total absorption spectroscopy is an established and powerful tool for studying radiative capture reactions, particularly if combined with the cosmic background reduction by several orders of magnitude obtained at the Laboratory for Underground Nuclear Astrophysics (LUNA). We present recent improvements in the detection setup with the Bismuth GermaniumOxide (BGO) detector at LUNA, aiming to reduce high-energy backgrounds and to increase the summing detection efficiency. The new design results in enhanced sensitivity of the BGO setup, as we demonstrate and discuss in the context of the first direct measurement of the 65 keV resonance (Ex = 5672 keV) of the 17O(p, γ)18F reaction. Moreover, we show two applications of the BGO detector, which exploit its segmentation. In case of complex γ-ray cascades, e. g. the de-excitation of Ex = 5672 keV in 18F, the BGO segmentation allows to identify and suppress the beam induced background signals that mimic the sum peak of interest. We demonstrate another new application for such a detector in form of in-situ activation measurementsof a reaction with β+ unstable product nuclei, e. g., the 14N(p, γ)15O reactio