This is an accepted version of a paper published in Nature. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination.Citation for the published paper: Hinke, C., Boehmer, M., Boutachkov, P., Faestermann, T., Geissel, H. et al. (2012) "Superallowed Gamow-Teller decay of the doubly magic nucleus 100 Sn" Nature, 486 (7403): [341][342][343][344][345] Access to the published version may require subscription.

The antineutrino spectra measured in recent experiments at reactors are inconsistent with calculations based on the conversion of integral beta spectra recorded at the ILL reactor. 92 Rb makes the dominant contribution to the reactor antineutrino spectrum in the 5-8 MeV range but its decay properties are in question. We have studied 92 Rb decay with total absorption spectroscopy. Previously unobserved beta feeding was seen in the 4.5-5.5 region and the GS to GS feeding was found to be 87.5(25)%. The impact on the reactor antineutrino spectra calculated with the summation method is shown and discussed.

Total absorption γ-ray spectroscopy of the β-delayed neutron emitters ^{87}Br, ^{88}Br, and ^{94}Rb We investigate the decay of 87,88 Br and 94 Rb using total absorption γ-ray spectroscopy. These important fission products are β-delayed neutron emitters. Our data show considerable βγ-intensity, so far unobserved in high-resolution γ-ray spectroscopy, from states at high excitation energy. We also find significant differences with the β intensity that can be deduced from existing measurements of the β spectrum. We evaluate the impact of the present data on reactor decay heat using summation calculations. Although the effect is relatively small it helps to reduce the discrepancy between calculations and integral measurements of the photon component for 235 U fission at cooling times in the range 1 − 100 s. We also use summation calculations to evaluate the impact of present data on reactor antineutrino spectra. We find a significant effect at antineutrino energies in the range of 5 to 9 MeV. In addition, we observe an unexpected strong probability for γ emission from neutron unbound states populated in the daughter nucleus. The γ branching is compared to Hauser-Feshbach calculations which allow one to explain the large value for bromine isotopes as due to nuclear structure. However the branching for 94 Rb, although much smaller, hints of the need to increase the radiative width Γγ by one order-of-magnitude. This increase in Γγ would lead to a similar increase in the calculated (n, γ) cross section for this very neutron-rich nucleus with a potential impact on r process abundance calculations.

Cs [5], 95 Rb [6], 94 Rb [7], 77 Cu [8], and 75 Cu [9]. The paucity of information is related to the difficulty of detecting weak high-energy γ-ray cascades with the germanium detectors that are usually employed in β-decay studies. This problem has become known as the Pandemonium effect [10] and it also affects the accuracy of the data. There is an analogy [11] between this decay process and neutron capture reactions which populate states in the compound nucleus that re-emit a neutron (elastic channel) or de-excite by γ rays (radiative capture). Indeed the reaction cross section is parametrized in terms of neutron 40 and γ widths, Γ n and Γ γ respectively, which also deter-41 mines the fraction of β intensity above S n that proceeds 42 by neutron or γ emission. Radiative capture (n, γ) cross 43 sections for very neutron-rich nuclei are a key ingredient 44 in reaction network calculations used to obtain the yield 45 of elements heavier than iron in the rapid (r) neutron 46 capture process occurring in explosive-like stellar events. 47 It has been shown [12-14] that the abundance distribu-48 tions in different astrophysical scenarios are sensitive to 49 (n, γ) cross sections. In the classical "hot" r process late 50 captures during freeze-out modify the final element abun-51 dance. In the "cold" r process the competition between 52 neutron captures and β decays determines the forma-53 tion path. Cross section values for these exotic nuclei 54 are taken from Hauser-Feshbach model calculations [15], 55 which are based on a few quantities describing average 56 nuclear properties: nuclear level densities (NLD), pho-57 ton strength functions (PSF) and neutron transmission 58 coefficients (NTC). Since these quantities are adjusted to experiment close to β stability it is crucial to find means 60 to verify the predictions for very neutron-rich nuclei. 61 The Total Absorption Gamma-ray Spectroscopy (TAGS) technique aims at detecting cascades rather than 63 individual γ rays using large 4π scintillation detectors. The superiority of this method over high-resolution ger-65 manium spectroscopy to locate missing β intensity has 66 been demonstrated before [16, 17]. However its appli-67 cation in the present case is very challenging, since the 68 expected γ-branching is very small and located at rather 69 high excitation energies. As a matter of fact previous 70 attempts at LNPI [7] with a similar aim did not lead to 71 clear conclusions. In this Letter we propose and demon-72 strate for the first time the use of the TAGS technique 73 to study γ-ray emission above S n in β-delayed neutron 74 emitters and extract accurate information that can be 75 used to improve (n, γ) cross section estimates far from β 76 stability. 77 Neutron capture and transmission reactions have been 78 extensively used [18] to determine neutron and γ widths 79 (or related strength functions). An inspection of Ref. [18] 80 shows that in general Γ n is orders-of-magnitude larger 81 than Γ γ. In the decay of 87 Br, which is the best stud-82 ied case [1, 19-...

Neutron-rich isotopes around lead, beyond N=126, have been studied exploiting the fragmentation of an uranium primary beam at the FRS-RISING setup at GSI. For the first time β-decay half-lives of 219 Bi and 211,212,213 Tl isotopes have been derived. The half-lives have been extracted using a numerical simulation developed for experiments in high-background conditions. Comparison with state of the art models used in r-process calculations is given, showing a systematic underestimation of the experimental values, at variance from close-lying nuclei.