Abstract. The hadronic shift in pionic hydrogen has been redetermined to be 1s = 7.086 ± 0.007(stat) ± 0.006(sys) eV by X-ray spectroscopy of ground state transitions applying various energy calibration schemes. The experiment was performed at the high-intensity low-energy pion beam of the Paul Scherrer Institut by using the cyclotron trap and an ultimate-resolution Bragg spectrometer with bent crystals.

MOCABA is a combination of Monte Carlo sampling and Bayesian updating algorithms for the prediction of integral functions of nuclear data, such as reactor power distributions or neutron multiplication factors. Similarly to the established Generalized Linear Least Squares (GLLS) methodology, MOCABA offers the capability to utilize integral experimental data to reduce the prior uncertainty of integral observables. The MOCABA approach, however, does not involve any series expansions and, therefore, does not suffer from the breakdown of first-order perturbation theory for large nuclear data uncertainties. This is related to the fact that, in contrast to the GLLS method, the updating mechanism within MOCABA is applied directly to the integral observables without having to "adjust" any nuclear data. A central part of MOCABA is the nuclear data Monte Carlo program NUDUNA, which performs random sampling of nuclear data evaluations according to their covariance information and converts them into libraries for transport code systems like MCNP or SCALE. What is special about MOCABA is that it can be applied to any integral function of nuclear data, and any integral measurement can be taken into account to improve the prediction of an integral observable of interest. In this paper we present two example applications of the MOCABA framework: the prediction of the neutron multiplication factor of a water-moderated PWR fuel assembly based on 21 criticality safety benchmark experiments and the prediction of the power distribution within a toy model reactor containing 100 fuel assemblies.

The 5g − 4 f transitions in pionic nitrogen and muonic oxygen were measured simultaneously by using a gaseous nitrogen-oxygen mixture at 1.4 bar. Due to the precise knowledge of the muon mass the muonic line provides the energy calibration for the pionic transition. A value of (139.57077 ± 0.00018) MeV/c 2 (± 1.3ppm) is derived for the mass of the negatively charged pion, which is 4.2ppm larger than the present world average.

A set of 14 high-accuracy x-ray transition energies in the 2.4-3.1 keV range is presented, which can be used as x-ray standards. They were measured in two-to four-electron sulfur, chlorine, and argon ions produced in an electron-cyclotron resonance ion source, using a single spherically bent crystal spectrometer. The results include the first measurement of six transitions and improve the accuracy of six other experimental values. These measurements considerably extend the set of high-accuracy x-ray energies reported for highly charged ions. Their relative uncertainties range from 1 to 10 ppm. Theory only reaches such a precision in one-and two-electron ions. Our results thus have two distinct applications. On the one hand, they test predictions in two-electron ions [Artemyev, Shabaev, Yerokhin, Plunien, and Soff, Phys. Rev. A 71, 062104 (2005)], at the precision level of some two-photon QED contributions. We observe an agreement with theory for most of the transitions. On the other hand, the three-and four-electron ion transitions provide new benchmark energies for the calculation of missing theoretical contributions, such as Auger shifts or electronic correlations. Spectra were analyzed with an x-ray tracing simulation that contains all the relevant physics of the spectrometer.

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