Lifetime measurements of yrast states in $$^{\mathbf {178}}$$Pt using the charge plunger method with a recoil separator

Lifetime measurements in $$^{178}$$ 178 Pt with excited states de-exciting through $$\gamma $$ γ -ray transitions and internal electron conversions have been performed. Ionic charges were selected by the in-flight mass separator MARA and measured at the focal plane in coincidence with the $$4_1^+\rightarrow 2_1^+$$ 4 1 + → 2 1 + $$257\,$$ 257 keV $$\gamma $$ γ -ray transition detected using the JUROGAM 3 spectrometer. The resulting charge-state distributions were analysed using the differential decay curve method (DDCM) framework to obtain a lifetime value of 430(20) ps for the $$2_1^+$$ 2 1 + state. This work builds on a method that combines the charge plunger technique with the DDCM analysis. As an alternative analysis, ions were selected in coincidence with the $$^{178}$$ 178 Pt alpha decay ($$E_{\mathrm {alpha}} = 5.458(5)$$ E alpha = 5.458 ( 5 ) MeV) at the focal plane. Lifetime information was obtained by fitting a two-state Bateman equation to the decay curve with the lifetime of individual states defined by a single quadrupole moment. This yielded a lifetime value of 430(50) ps for the $$2_1^+$$ 2 1 + state, and 54(6) ps for the $$4_1^+$$ 4 1 + state. An analysis method based around the Bateman equation will become especially important when using the charge plunger method for the cases where utilising coincidences between prompt $$\gamma $$ γ rays and recoils is not feasible.

The Ionospheric Source of the Plasma Sheet During Storm Main Phase

<p>The ionospheric and solar wind contributions to the magnetosphere can be distinguished by their composition.  While both sources contain significant H+, the heavy ion species from the ionospheric source are generally singly ionized, while the solar wind consists of highly ionized ions. Both the solar wind and the ionosphere contribute to the plasma sheet.  It has been shown that with both enhanced geomagnetic activity and enhanced solar EUV, the ionospheric contribution, and particularly the ionospheric heavy ions contribution increases.  However, the details of this transition from a solar wind dominated to more ionospheric dominated plasma sheet are not well understood.  An initial study using AMPTE/CHEM data, a data set that includes the full charge state distributions of the major species, shows that the transition can occur quite sharply during storms, with the ionospheric contribution becoming dominant during the storm main phase.  However, during the AMPTE time-period, there were no continuous measurements of the upstream solar wind, and so both the simultaneous solar wind composition and the driving solar wind and IMF parameters were not known.  The HPCA instrument on MMS and both the LEPi and MEPi instruments on Arase are able to measure He++.   With these data sets, the He++/H+ ratio can be compared to the simultaneous He++/H+ ratios in the solar wind to more definitively identify the solar wind contribution to the plasma sheet.  This allows the ionospheric contribution to the H+ population to be determined, so that the full ionospheric population is known. We find that when the IMF turns southward during the storm main phase, the dominant source of the hot plasma sheet becomes ionospheric.  This composition change explains why the storm time ring current also has a high ionospheric contribution.</p>

xcalib: a focal spot calibrator for intense X-ray free-electron laser pulses based on the charge state distributions of light atoms

The xcalib toolkit has been developed to calibrate the beam profile of an X-ray free-electron laser (XFEL) at the focal spot based on the experimental charge state distributions (CSDs) of light atoms. Characterization of the fluence distribution at the focal spot is essential to perform the volume integrations of physical quantities for a quantitative comparison between theoretical and experimental results, especially for fluence-dependent quantities. The use of the CSDs of light atoms is advantageous because CSDs directly reflect experimental conditions at the focal spot, and the properties of light atoms have been well established in both theory and experiment. Theoretical CSDs are obtained using xatom, a toolkit to calculate atomic electronic structure and to simulate ionization dynamics of atoms exposed to intense XFEL pulses, which involves highly excited multiple core-hole states. Employing a simple function with a few parameters, the spatial profile of an XFEL beam is determined by minimizing the difference between theoretical and experimental results. The optimization procedure employing the reinforcement learning technique can automatize and organize calibration procedures which, before, had been performed manually. xcalib has high flexibility, simultaneously combining different optimization methods, sets of charge states, and a wide range of parameter space. Hence, in combination with xatom, xcalib serves as a comprehensive tool to calibrate the fluence profile of a tightly focused XFEL beam in the interaction region.