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The neutron wavelength resolution, Bragg-edge measurement ability and future prospects regarding the neutron count rate were investigated at AISTANS. The wavelength resolution evaluated by Bragg-edge analysis using an iron powder sample is in reasonably good agreement with calculations at neutron wavelengths of 0.2–0.3 nm. Bragg-edge imaging was also performed on a steel plate sample with distinct regions of BCC and FCC crystallinity, and the different crystal structures were successfully discriminated. In addition, an aluminum sample containing a friction stir spot welding region was also measured and the 200 and 111 Bragg-edges at the two joining areas were observed. However, it was hard to characterize the difference in texture between the two areas. The neutron counting rate for Bragg-edge imaging is expected to increase by approximately a factor 50 in the near future thanks to the planned improvements of the electron beam power and the detection efficiency of the neutron detector.

A new electron accelerator has been designed and is now under construction at AIST, Tsukuba, Japan. The accelerator will be used to produce a pulsed neutron beam for materials analysis. The design maximizes the yield of slow neutrons with high pulse temporal resolution as described in a previous publication [K. Kino et al., Nuclear Inst. and Methods in Physics Research, A 927 (2019) 407–418]. The accelerator is composed of a thermal cathode type electron gun with S-Band buncher/accelerator cavity followed by three, 2.9 m long S-Band acceleration cavities. High power RF is supplied by three klystron units, with klystron No.1 supplying both the electron gun and the 1st cavity, and klystrons No.2 and No.3 connected to the 2nd and 3rd cavities respectively. The design parameters of the accelerator are; pulse rate: 100 Hz, pulse length: 10 μs, electron current: 250 mA, electron energy: 40 MeV. Operating at these parameters a maximum beam power of around 10 kW will be delivered to the water-cooled Ta target for neutron production. In this report we will describe the design and construction of the electron accelerator.

Kernel averaging misorientation (KAM) measurements and positron annihilation lifetime spectroscopy (PALS) were conducted to investigate the damage introduced by the tensile and fatigue testing of type 316L stainless steel. The fatigue tests were carried out at room temperature and at 550 °C under the strain controlled mode with total strain amounts, Δe of 0.4% and 1.5%. A number of different samples were prepared by interrupting the fatigue test at various ratios of fatigue cycle time to fatigue lifetime. Both KAM and PALS analyses indicated increasing damage as increasing misorientation average or number of vacancies with increasing strains in tensile- and fatigue-tested samples. Dislocations play an important role in the evolution of damage as they produce vacancies and form dislocation structures. In the fatigue test at high temperature, accelerated dislocation relaxation encourages formation of dislocation structures that result in an early increase in misorientation. Under the same conditions, the positron lifetime rather decreased because of the migration of defects at early stages of fatigue and rapidly increased at fracture. We observed different responses to mechanical straining that can be useful for evaluation of damage in 316L stainless steel.

We have designed and been constructing a compact accelerator-driven neutron facility for Bragg edge transmission imaging of structural materials to obtain position dependent crystallographic information. In order to combine a high neutron wavelength resolution, which is especially required for strain measurements, and an intense neutron beam flux at the sample position, which is required for obtaining high quality statistics within practical measurement times, the components of the neutron facility are optimized. To achieve a high wavelength resolution while maintaining an intense neutron beam flux at the sample position, a solid methane decoupled cold moderator at about 20 K coupled with neutron guide tubes is employed. The target–moderator system, especially the moderator thickness was optimized using the Monte-Carlo simulation code PHITS. Neutrons will be produced using a 35-MeV electron accelerator which is currently under construction. The accelerator has a design maximum beam power of 10 kW, a maximum repetition rate of 100 Hz and a maximum pulse width of 10 μ s . The combination of the flight path length of about 8 m and the repetition rate is suitable for efficient Bragg edge measurements. The pulse width of the electron beam is suitable to achieve a high wavelength resolution with the solid methane decoupled moderator. The estimated flux of the neutron beam at the sample position is 1.2 × 104 ∼ 4 . 5 × 104 /cm2/s depending on the usage of super mirror guide tubes. The wavelength resolution at the sample is 0.5 ∼ 0.7% in the wavelength region from 0.3 to 0.4 nm.

We have constructed a compact accelerator-based neutron facility at the National Institute of Advanced Industrial Science and Technology (AIST) in Japan aiming at development of structural materials of transportation vehicles for weight reduction. The facility consists of electron linear accelerator, neutron source, and a neutron beamline with a measurement hutch. Currently we are commissioning the accelerator and expecting a first neutron beam in 2019.

To comprehensively investigate the correlation between free volume properties (size and distribution) in the interior of polyamide (PA) active layer and mass transport mechanism, six polyamide thin film composite (TFC) membranes were characterized using positron annihilation lifetime spectroscopy (PALS). In case of pressurized filtration conditions, the rejection rate of boron across all PA membranes was found to be inversely proportional to the free volume size. The more boron transport occurred at the membrane containing larger free volume. In addition, the transition of the neutral boron transport mechanism from convection to diffusion was found to occur at a membrane free volume radius around 0.275 nm within the applied pressure range (2 and 10 bar), as verified by PALS and the dimensionless Peclet number. We believe that mass transport mechanism transition from convection to diffusion is caused by the compression of polyamide active layer due to applied hydraulic pressure (10 bar), resulting in lowering the convective mass transport pathway inside polyamide active layer. These membrane free volume size criteria and experimental filtration results may subsequently be used as new design guidelines for the development of high boron rejection polyamide TFC membranes having a low energy consumption.

We systematically investigate the pore structure of cellulose triacetate (CTA) and polyamide (PA) forward osmosis (FO) membranes with positron annihilation lifetime spectroscopy (PALS) and fractional rejection (FR) method to better understand the relationship between membrane pores (atomic-scale free volume) and separation performance. The results reported in this study suggest a range of membrane pore sizes and inner structures appropriate for the osmotic membrane process regardless of membrane materials. The PALS data suggest that the active layer of both FO membranes is mainly composed of generally uniform pores of larger size (0.29−0.30 nm) compared to seawater reverse osmosis (SWRO) (0.20−0.24 nm) membranes. The membrane pore size distribution (PSD) deduced by the FR method suggest that the PSD of both FO membranes are significantly shifted to smaller sizes under pressurized conditions, possibly due to the overall compression of the FO membranes. The effects of applied pressure on the structure and performance of active layer should be further investigated along with other properties such as thickness, swelling and sorption properties.

Positron annihilation lifetime measurements were performed on polyethylene films [low-density polyethylene and ultra-high molecular weight polyethylene (UHMWPE)] with a thickness of 15–2000 μm using a Na-22 positron source enclosed in a Kapton film. For thin films, some positrons will pass through the film and annihilate behind it. Using a single film in a commercial anti-coincidence system, by placing an annealed stainless steel (SUS304) cover behind the sample, it is possible to sufficiently measure the long-lifetime ortho-positronium (o-Ps) component even in thin films. Additionally, calculated intensities of the o-Ps component determined from the estimated film transmittance agreed well with the measured values. Furthermore, by applying this method to uniaxially stretched UHMWPE, we were able to observe structural changes owing to the stretching consistent with shorter measured o-Ps lifetime and increased o-Ps intensity.

Recently, we have found that the microvoid size in a-Si:H, determined via positron annihilation lifetime spectroscopy (PALS), is systematically correlated with the optical constant, the peak value of e 2 ;e 2 peak, obtained from spectroscopic ellipsometry. This indicates a possibility to establish a novel characterization method that allows the average size and density of microvoid to be estimated readily via spectroscopic ellipsometry. In this presentation, we demonstrate a new finding that the microvoid size and the e 2 peak of a-Si:H films deposited under different conditions, even including the sort of apparatus, are on an identical curve if a-Si:H films are prepared without doping.

The polyamide skin layer of reverse osmosis (RO) membranes was characterised using advanced and complementary analytical techniques to investigate the mechanisms underlying the permeation of contaminants of emerging concern in potable water reuse ? N-nitrosodimethylamine (NDMA) and N-nitrosomethylethylamine (NMEA). This study used five RO membrane samples with similar membrane properties. The five RO membrane samples spanned over a large range of water permeance (0.9?5.8 L/m2 h bar) as well as permeation of NDMA (9?66%) and NMEA (3?29%). Despite these differences among the five RO membranes, characterisations of the skin layer using positron annihilation lifetime spectroscopy, atomic force microscopy and field emission scanning electron microscopy revealed almost no variation in their free-volume hole-radius (0.270?0.275 nm), effective surface area (198?212%) and thickness (30?35 nm) of the skin layer. The results suggest that there could be other RO skin layer properties, such as the interconnectivity of the protuberances within the polyamide skin layer additional to the free-volume hole-size and thickness of the skin layer, which can also govern water and solute permeation., Journal of Membrane Science, 554, pp.301-308; 2018

The electron emission properties of a coniferous carbon nano-structure (CCNS) based field emission electron gun have been measured. The CCNS was grown on a stainless steel substrate using chemical vapor deposition (CVD) and biased to about 50 kV. Stable, high-current-density electron emission (102 mA/cm 2 ) was measured continuously for more than 1300 h. This result compares favorably to printed and directly grown carbon nanotube (CNT) based emitters. A wide range of potential applications are foreseen for CCNS based electron emitters, such as high intensity X-ray sources.

A Zero-Boil-Off (ZBO) cryostat is designed to realize a compact, stand-alone cryogenic system for the AIST superconducting accelerator (SCA). Under normal operation there is no evaporative helium loss from the cryomodule and therefore operating costs associated with the supply of liquid helium can be eliminated. The only significant loss of helium from the module occurs during the initial cavity cool-down procedure or when the re-condensing cryostat is replaced. It takes about 3 h to cool down the cryostat head from room temperature (300 K) to 4 K. During this time around 100 L of liquid helium is lost due to evaporation. By pre-cooling the cryostat inside a low heat load vacuum tube before transfer to the cryomodule, this evaporative loss could be essentially eliminated, significantly reducing the volume of liquid helium required for the initial cryomodule cool-down. The pre-cooling system also provides an efficient method to test the cryostat prior to use.

The properties of materials involving polymer–solid interfaces are determined not only by the properties of the constituents but also by the interfacial region of the polymer near the solid, the so-called interphase. Here we report on positron annihilation lifetime spectroscopy (PALS) measurements of the free volume near the interface with a focused positron beam. The measurements were performed at an interface between a Teflon AF 1600 film and a 30 nm thick SiN membrane from the backside of a Si substrate which was locally etched away to expose the ultrathin SiN membrane. We were able to focus the positron beam onto the exposed region and to probe the SiN–Teflon AF 1600 interfacial region with low implantation energies, resulting in very narrow implantation profiles and excellent depth resolution. We found a pronounced decrease in orthopositronium lifetime close the interface. On the basis of modeling, we could estimate the interphase width and the average density increase in the interfacial region as ∼1...

A new photon-induced positron annihilation lifetime spectroscopy approach has been developed using an S-band compact electron linac at the National Institute of Advanced Industrial Science and Technology (AIST). The high energy ( 42 MeV ), intense (105 photons pulse−1), and ultra-short pulse (3 ps pulse width) photon beam creates positrons throughout an entire sample via pair production. A positron lifetime spectrum can be obtained by measuring the time difference between the accelerator's RF frequency and the detection time of the annihilation gamma rays. The positron lifetimes for lead and yttria-stabilized zirconia samples have been successfully measured.

We describe the recent installation of a new slow positron beamline at AIST and our plans to develop a dedicated superconducting accelerator for positron production. The new positron beamline is already installed and should be operational by the end of this fiscal year (March 2012). Initially positrons will be generated using a 70 MeV electron beam from the existing accelerator directed onto a newly installed converter and moderator assembly. The beamline has two experimental ports both dedicated to positron lifetime spectroscopy, one port with a focused beam (diameter ~ 30 microm) and the other unfocussed (~ 10 mm). A superconducting accelerator for positron production is currently under development. When completed, it will deliver a high frequency (~ MHz), high current (~ mA), short pulse length (< 100 ps) beam to the positron production target. We investigate the possibility of transporting the positron pulses thus produced directly onto samples for lifetime measurement. Such a scheme would remove the necessity for pulse stretching and chopping which is required with the existing LINAC and should allow for greatly increased slow positron transport efficiency.

Positron annihilation lifetime spectroscopy (PALS) is an experimental technique whereby the lifetime spectrum of positrons injected into a material is measured. Analysis of this spectrum can be used to characterize defects in the material. While radioisotope positron sources are often used for PALS, there are several advantages of using mono-energetic, slow positron beams. In order to measure lifetime spectra with such beams it is necessary to produce a pulsed beam with an extremely short pulse length (~ 200 ps). In this article we discuss the advantages of using pulsed, slow-positron beams, the various methods of beam production and pulsing methods. We focus in particular on intense beams generated by electron accelerators and describe the current status and future plans for the accelerator based facility at AIST.

A slow-positron beam system for in-situ positron lifetime measurements during ion beam irradiation is currently under development in order to obtain fundamental information on radiation-induced defects. The system uses a high-intensity positron beam generated through pair-creation by a 70 MeV electron beam from a linear accelerator. The system has typical pulsing electrodes for chopping and bunching positrons. The incident directions of positrons and ions are 0° and 45° to the surface normal of samples, respectively. H, He and inert-gas ions up to 150 keV can be introduced to a target chamber with the irradiation temperature variable from room temperature to 600 °C. In a preliminary examination of the beamlines, 150 keV Ar+, electrons from a photocathode and positrons from a radioisotope were successfully transported to the target chamber from their respective sources. In addition, in-situ lifetime measurements using the existing positron beamline were demonstrated.

Positron annihilation lifetime spectroscopy (PALS) using a low-energy positron microbeam extracted into air was applied to elucidating molecular-level pore structures formed in silicon-oxide-backboned microporous thin films under controlled humidity conditions; as a result, a direct observation of the interstitial spaces in the micropores filled with water molecules was achieved. It was demonstrated that PALS using a microbeam extracted into air in combination with water vapor adsorption is a powerful tool for the in-situ elucidation of both open and closed subnanoscaled pores of functional thin materials under practical conditions.

Sharp resonant structures in the cross section of the atomic electron-ion collision process of dielectronic recombination are exploited to study isotope shifts and hyperfine interaction of heavy highly-charged ions. This novel approach provides a conceptual alternative to existing methods. In this contribution, we present a series of measurements, which we performed at the heavy ion storage ring ESR of the GSI Helmholtzzentrum fur Schwerionenforschung, Darmstadt, Germany. In a first experiment the stable isotopes A = 142 and A = 150 of three-electron neodymium ANd57 + were studied. Isotope shifts of dielectronic resonances associated with 2s − 2pj (j = 1/2, 3/2) transitions were extracted from the measured data. The evaluation of the energy shift was performed within a full QED framework and yielded a change in the mean-square charge radius of \(^{142,150}\delta \langle r^2 \rangle = -1.36(1)(3)\) fm2. At GSI, in addition to the investigation of stable isotopes unstable species can be artificially synthesized and studied. Radioisotopes produced in-flight from fragmentation of a 238U primary beam were injected into the ESR and were subsequently separated by their mass-to-charge ratio. This enabled us to perform first DR experiments with the exotic nuclei 237U89 + (Z = 92 )and 234Pa88 + (Z = 91).

Decay dynamics of dielectronic recombination (DR) processes of H-like titanium ions was investigated with an electron beam ion trap. In the DR of H-like ions a K-shell vacancy is available even after the decay of the doubly excited state produced by the recombination. Therefore secondary X-ray emission is possible. An observed X-ray spectrum of DR obtained in the present experiment was well reproduced theoretically by taking into account the secondary X-rays.

Highly charged argon ions, Ar7+,8+ with kinetic energy of several keV, have been used to irradiate dodecanethiol self assembled monolayers. The irradiated samples were then imaged in situ by scanning tunneling microscopy. Comparisons between un-irradiated and irradiated surfaces showed the appearance of a number of small defects or ‘nanocraters’ in the regular domains of the monolayer after ion impact. Single nanocrater is produced by individual highly charged ion impact. The origin of the craters is analyzed by performing a time of flight study of desorbed positive ions.

Dielectronic recombination (DR) has been studied in highly charged He-like Ti ions using an electron beam ion trap. X-rays emitted from radiative recombination (RR) and DR were observed as the electron beam energy was scanned through the resonances. Differential DR resonant strengths were determined by normalizing the DR x-ray intensity to the RR intensity using theoretical RR cross sections. KLn(2 ≤ n ≤ 5) resonant strengths were determined for He-like Ti ions. The differential resonant strengths were calibrated without reference to any theoretical DR calculations while the electron energy scale was derived with reference to the well-known energy for ionization of the He-like and H-like ions from the ground state. Calibration in this way facilitates a more exacting comparison between theory and experiment than has been reported previously. To facilitate this comparison, total and differential theoretical resonance strengths were calculated. These calculations were found to be in good agreement with the measured results.

The conceptual design of a new electron beam ion trap primarily intended for the study of electron–ion interactions is outlined along with some preliminary predictions regarding its capabilities.

We have determined resonant strengths of the KLn ð2 6 n 6 5Þ resonances for helium-like Ti ions and ð3 6 n 6 5Þ resonances for helium-like Fe ions. The results were obtained using the Tokyo electron beam ion trap. Characteristic X-rays from both dielectronic recombination and radiative recombination were detected as the electron beam energy was scanned through the resonances. 2003 Elsevier Science B.V. All rights reserved.

Electron beam trajectory simulations have been performed to design a new electron beam ion trap. The design of the magnet and electrode structures was optimized based on the results of the simulations.

We have measured electron impact ionization cross-sections of hydrogen-like iron and hydrogen-like molybdenum with an electron beam ion trap. The measurements were performed in the electron energy range between 13.5 and 40 keV for hydrogen-like iron and between 50 and 80 keV for hydrogen-like molybdenum.

A new method to realize Bose-Einstein condensation (BEC) of positronium (Ps) is proposed and a Monte-Carlo simulation was performed to evaluate the cooling efficiency of Ps atoms. Ps-BEC was found to be possible by a method including laser cooling of Ps. Laser specifications for Ps cooling are challenging and development is ongoing. A new temperature measurement method for cold Ps and development of an intense, pulsed, slow-positron microbeam are also necessary. They are under study as outlined in this contribution.

EUV, X-ray and EB mainly induce ionization in resist materials and its energy deposition process is different from ArF exposure. Linear energy transfer (LET) effect for resist sensitivity is very important issue from the viewpoint of radiation induced chemical reactions for high-volume nanofabrication. Therefore the knowledgebase of radiation chemistry is required for understanding the resist performances for EUV lithography. In order to acquire the knowledge of resist materials for EUV / EB lithography from a viewpoint of the free-volume, the positron annihilation lifetime spectroscopy was carried out using positron probe microanalyzer (PPMA) installed at AIST. The size of free-volume can be evaluated from the lifetime of ortho-Positronium (o-Ps). The lifetime and intensity of o-Ps in EB-exposed positive-tone non-chemically amplified (non-CA, ZEP) and CA (UV-III) EUV / EB resists were observed. Moreover, to evaluate the relationship between line edge roughness (LER) and free-volume, EB lithography was carried out, and then sensitivities (E0 and Esize) and LER were measured. For both non-CA and CA resist materials, the changes of free-volume due to evaporation of outgas, polarity change or chain scission would hardly influence on their LER and resolution.

The positron re-emission microscope (PRM) [1,2] images positrons that are re-emitted from surface after thermalization and diffusion of positrons implanted into material. By using PRM, it is able to nondestructively observe spatial distribution of vacancy-type defects at atomic levels below the detection limits of electron microscopy. Compared with scanning positron microscopy, PRM potentially has better lateral resolution with faster imaging time by more than one order of magnitude. However, in the previous studies of PRM [1-3], a long imaging time (more than 8 hours) was needed to acquire one image because radioisotope (RI) was used as a positron source. For practical use, a substantial reduction of the imaging time is required.

A new slow positron beamline with two measurement ports has been installed at AIST. Positrons are generated using the 70 MeV AIST LINAC and are guided to the measurement ports using a solenoid magnetic field. Both beam ports are arranged vertically with the positron beam incident on the sample from above and samples loaded horizontally. Port No. 1 is designed for positron annihilation lifetime spectroscopy (PALS) and Doppler broadening of annihilation radiation (DBAR) measurements with a ∼10 mm diameter positron beam. The beamline on port No. 2 contains a transmission type remoderator for a brightness enhanced positron microbeam, similar to the existing positron probe microanalyzer (PPMA) at AIST.

We have studied the dielectronic recombination process in He-like Fe ions and have obtained the resonant strengths of the KLn (3 n 5) resonances. This measurement was performed with the use of an electron beam ion trap by measuring the x-ray energy emitted from highly charged ions simultaneously with the electron beam energy scanned during the measurement. The total resonant strengths obtained are 5.0×10 −19 ,2 .1×10 −19 and 1.1×10 −19 cm 2 eV, for KLM, KLN and KLO, respectively.

Electron-impact ionization cross sections have been determined for hydrogen-like iron ions at selected electron energies between 1.45 and 4.3 times the threshold energy. The cross sections were obtained by measuring the equilibrium ionization balance in an electron beam ion trap. This ionization balance is obtained from x-ray measurements of radiative recombination into the K-shell of hydrogen-like and bare iron ions. The measured cross sections are compared with distorted-wave calculations and several semiempirical formulations.

An electron beam ion trap (EBIT) has been designed and is currently under construction for use in atomic physics experiments at the Queen's University, Belfast. In contrast to traditional EBITs where pairs of superconducting magnets are used, a pair of permanent magnets will be used to compress the electron beam. The permanent magnets have been designed in conjunction with bespoke vacuum ports to give unprecedented access for photon detection. Furthermore, the bespoke vacuum ports facillitate a versatile, reconfigurable trap structure able to accommodate various in-situ detectors and in-line charged particle analysers. Although the machine will have somewhat lower specifications than many existing EBITs in terms of beam current density, it is hoped that the unique features will facilitate a number of hitherto impossible studies involving interactions between electrons and highly charged ions. In this article the new machine's design is outlined along with some suggestions of the type of process to be studied once the construction is completed.

An electron-beam ion trap (EBIT) has been designed for atomic physics experiments at the Queen’s University of Belfast. A pair of permanent magnets will be used to produce an axial magnetic field to compress an electron beam, whereas pairs of superconducting magnets have been used for traditional EBITs. The design of the new EBIT is detailed and possible experiments are explained to show the feasibility of the EBIT.

To clarify the free volume size distributions of the cardo-based polymer membranes, where ortho-positronium (o-Ps) undergoes pick-off annihilation, the o-Ps lifetime distributions were analyzed by the LT9 programme. It was found that the cardo-based polysulfone membrane has much narrower o-Ps lifetime/hole size distributions than the cardo-based polyimide membranes with the 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) moiety. Further, the lifetime/hole size distributions of the cardo-based polymer membranes are appreciably broadened with increasing temperature. This suggests that in these membranes there are holes not only of different sizes but also of different thermal expansion coefficients. It is also shown that in a membrane with a wider hole size distribution the average o-Ps lifetime tends to be longer than would be expected from the correlation between the o-Ps lifetime and the total free volume for common polymers.

A technique for investigating atomic-scale defects and/or nanometer (sub-nanometer)-order pores near the surface of samples mounted in air (without vacuum) by positron annihilation spectroscopy (PAS) has been developed. The method relies on the extraction of slow positron beams from the vacuum chamber to air through a thin SiN membrane vacuum window. Using a positron beam with an injection energy of 2.6 keV and a vacuum window with a thickness of 30 nm, samples mounted in air can be investigated by PAS to a depth of ~100 nm.

Monte Carlo simulations of slow positron production via energetic electron interaction with a solid target have been performed. The aim of the simulations was to determine the expected slow positron beam intensity from a low energy, high current electron accelerator. By simulating (a) the fast positron production from a tantalum electron-positron converter and (b) the positron depth deposition profile in a tungsten moderator, the slow positron production probability per incident electron was estimated. Normalizing the calculated result to the measured slow positron yield at the present AIST LINAC the expected slow positron yield as a function of energy was determined. For an electron beam energy of 5 MeV (10 MeV) and current 240 $\mu$A (30 $\mu$A) production of a slow positron beam of intensity 5 $\times$ 10$^{6}$ s$^{-1}$ is predicted. The simulation also calculates the average energy deposited in the converter per electron, allowing an estimate of the beam heating at a given electron energy and current. For low energy, high-current operation the maximum obtainable positron beam intensity will be limited by this beam heating., Comment: 11 pages, 15 figures, submitted to Review of Scientific Instruments

This paper reports a systematic study of the dependence on atomic number of the dielectronic recombination resonance strengths for He-like, Li-like and Be-like ions. Recent measurements of dielectronic recombination resonance strengths for the KLL and KLM manifolds for iron, yttrium, iodine, holmium, and bismuth are also described. The resonance strengths were normalized to calculated electron impact ionization cross sections. The measured resonance strengths generally agree well with theoretical calculations using the distorted wave approximation. However, KLM resonance strength measurements on high atomic number open-shell ions gave higher values than those suggested by calculations. Using recently measured data, along with existing results, scaling laws have been generated as a function of atomic number for He-like, Li-like, and Be-like ions in the KLL and KLM manifolds.

International audience; Recent advances in the development of 2D microstrip detectors open up new possibilities for hard x-ray spectroscopy, in particular for polarization studies. These detectors make ideal Compton polarimeters, which enable us to study precisely the polarization of hard x-rays. Here, we present recent results from measurements of Radiative Electron Capture into the K-shell of highly-charged uranium ions. The experiments were performed with a novel 2D Si(Li) Compton polarimeter at the Experimental Storage Ring at GSI. Stored and cooled beams of U91+ and U92+ ions, with kinetic energies of 43 MeV/u and 96 MeV/u respectively, were crossed with a hydrogen gasjet. The preliminary data analysis shows x-rays from the K-REC process, emitted perpendicularly to the ion beam, to be strongly linearly polarized.

The study of isotope shifts and hyperfine effects in dielectronic recombination (DR) resonance spectra strikes a conceptually new path for investigations of nuclear properties such as charge radius, spin, magnetic moment of nuclei or lifetimes of long-lived excited nuclear states. A series of DR experiments with heavy three-electron ions (Li-like) was performed at the heavy-ion storage ring ESR of the GSI Helmholtzzentrum fur Schwerionenforschung, Darmstadt, Germany. In a pilot experiment the two stable isotopes A=142 and A=150 of neodymium ANd57+ were investigated. From the displacement of DR resonances the isotope shifts δE142,150(2s – 2Pl/2) = 40.2(3)(6) meV and δE142,150(2s – 2p3/2) = 42.3(12)(20) meV for 2s – 2Pj transitions of the Li-like ions have been obtained. An evaluation within a full QED framework yielded a change in the mean-square charge radius of 142,150δ(r2) = −1.36(1)(3) fm2. At GSI, in addition to stable isotopes, in-flight synthesized radioisotopes can be studied as well. The production of radioisotopes of interest, the subsequent separation in the storage ring ESR and first DR experiments with the exotic nuclei 237U89+ and 234Pa88+ (Z=91) are presented. The paper is concluded with a brief outlook at future DR experiments with heavy radioisotopes at the ESR.

In dielectronic recombination of hydrogenlike ions an intermediate doubly excited heliumlike ion is formed. Since the $K$ shell is empty, both excited electrons can decay sequentially to the ground state. In this paper we analyze the x-ray radiation emitted from doubly and singly excited heliumlike titanium ions produced inside the Tokyo electron beam ion trap. Theoretical population densities of the singly excited states after the first transition and the transition probabilities of these states into the ground state were also calculated. This allowed theoretical branching ratios to be determined for each manifold. These branching ratios are compared to the experimentally obtained x-ray distribution by fitting across the relevant peak using a convolution of the theoretically obtained resonance strengths and energies. By taking into account $2E1$ transitions which are not observed in the experiment, the measured and calculated ratios agree well. This method provides a valuable insight into the transition dynamics of excited highly charged ions.