MEDAPP: Fission neutron beam for science, medicine, and industry

The instrument MEDAPP Medical Applications), operated by the Technische Universität München, and the respective irradiation position are located at the world-wide unique fast neutron beam tube SR10 to which a uranium converter is attached. Thus, the instrument is operated with unmoderated fission neutrons and can be used for a broad variety of applications. For selected tasks, an alternative use with thermal neutrons is possible

Partial Neutron Capture Cross Sections of Actinides using Cold Neutron Prompt Gamma Activation Analysis

Nuclear waste needs to be characterized for its safe handling and storage. In particular long-lived actinides render the waste characterization challenging. The results described in this thesis demonstrate that Prompt Gamma Neutron Activation Analysis (PGAA) with cold neutrons is a reliable tool for the non-destructive analysis of actinides. Nuclear data required for an accurate identification and quantification of actinides was acquired. Therefore, a sample design suitable for accurate and precise measurements of prompt $\gamma$-ray energies and partial cross sections of long-lived actinides at existing PGAA facilities was presented. Using the developed sample design the fundamental prompt $\gamma$-ray data on $^{237}$Np, $^{241}$Am and $^{242}$Pu were measured. The data were validated by repetitive analysis of different samples at two individual irradiation and counting facilities – the BRR in Budapest and the FRM II in Garching near Munich. Employing cold neutrons, resonance neutron capture by low energetic resonances was avoided during the experiments. This is an improvement over older neutron activation based works at thermal reactor neutron energies. 152 prompt $\gamma$-rays of $^{237}$Np were identified, as well as 19 of $^{241}$Am, and 127 prompt $\gamma$-rays of $^{242}$Pu. In all cases, both high and lower energetic prompt $\gamma$-rays were identified. The most intense line of $^{237}$Np was observed at an energy of E$_{\gamma}$ = 182.82(10) keV associated with a partial capture cross section of $_{\sigma_\gamma}$= 22.06(39) b. The most intense prompt $\gamma$-ray lines of $^{241}$Am and of $^{242}$Pu were observed at E$_{\gamma}$ = 154.72(7) keV with $\sigma_{\gamma}$= 72.80(252) b and E$_{\gamma}$ = 287.69(8) keV with $\sigma_{\gamma}$= 7.07(12) b, respectively. The measurements described in this thesis provide the first reported quantifications on partial radiative capture cross sections for $^{237}$Np, $^{241}$Am and $^{242}$Pu measured simultaneously over the large energy range from 45 keV to 12 MeV. Detailed uncertainty assessments were performed and the validity of the given uncertainties was demonstrated. Compared to existing literature data on prompt $\gamma$-ray energies and emission probabilities the uncertainties of the data were improved. In addition to the basic nuclear data necessary for PGAA, the thermal radiative neutroncapture cross sections of $^{237}$Np and of $^{241}$Am were determined from decay measurements after neutron irradiation. The thermal radiative neutron capture cross section of $^{237}$Np was determined as $\sigma^{0}_{c}$ = 176.3(47) b. The thermal radiative neutron capture cross sectionof $^{241}$Am was determined as $\sigma^{0}_{c}$ = 667.7(312) b. The thermal radiative neutron capture cross section of $^{242}$Pu was calculated as $\sigma^{0}_{c}$ = 21.9(15) b using nuclear structure simulations with the statistical decay code DICEBOX, constraint by the measured prompt $\gamma$-ray data. In the corresponding simulation the total radiative width of the capture state was found to be 28(1) meV. Also, the neutron separation energies of $^{238}$Np and of $^{243}$Pu were derived. The neutron separation energy of $^{238}$Np was calculated as S$_{n}$ = 5488.02(17) keV. The neutron separation energy of $^{243}$Pu was calculated as S$_{n}$ = 5036.33(59) keV. Detection limits for PGAA at FRM II were calculated for $^{237}$Np as 0.056 $\mu$g, for $^{241}$Am as 0.017 $\mu$g and for $^{242}$Pu as 0.20 $\mu$g

Oxygen hole formation controls stability in LiNiO2 cathodes

Ni-rich lithium-ion cathode materials achieve both high voltages and capacities but are prone to structural instabilities and oxygen loss. The origin of the instability lies in the pronounced oxidation of O during delithiation: for LiNiO2, NiO2, and the rock salt NiO, density functional theory and dynamical mean-field theory calculations based on maximally localized Wannier functions yield a Ni charge state of ca. +2, with O varying between −2 (NiO), −1.5 (LiNiO2), and −1 (NiO2). Calculated X-ray spectroscopy Ni K and O K-edge spectra agree well with experimental spectra. Using ab initio molecular dynamics simulations, we observe loss of oxygen from the (012) surface of delithiated LiNiO2, two surface O⋅− radicals combining to form a peroxide ion, and the peroxide ion being oxidized to form O2, leaving behind two O vacancies and two O2− ions. Preferential release of 1O2 is dictated via the singlet ground state of the peroxide ion and spin conservation

Standard for Synthesis of Customized Peptides by Non-Ribosomal Peptide Synthetases

The purpose of this RFC is to introduce a standardized framework for the engineering of customizable non-ribosomal peptide synthetases (NRPS) and their application for in vivo and in vitro synthesis of short non-ribosomal peptides (NRPs) of user-defined sequence and structure

Developments in Capture- γ Libraries for Nonproliferation Applications

The neutron-capture reaction is fundamental for identifying and analyzing the γ-ray spectrum from an unknown assembly because it provides unambiguous information on the neutron-absorbing isotopes. Nondestructive-assay applications may exploit this phenomenon passively, for example, in the presence of spontaneous-fission neutrons, or actively where an external neutron source is used as a probe. There are known gaps in the Evaluated Nuclear Data File libraries corresponding to neutron-capture γ-ray data that otherwise limit transport-modeling applications. In this work, we describe how new thermal neutron-capture data are being used to improve information in the neutron-data libraries for isotopes relevant to nonproliferation applications. We address this problem by providing new experimentally-deduced partial and total neutron-capture reaction cross sections and then evaluate these data by comparison with statistical-model calculations