The root-mean-square (rms) nuclear charge radius of 8 He, the most neutron-rich of all particlestable nuclei, has been determined for the first time to be 1.93(3) fm. In addition, the rms charge radius of 6 He was measured to be 2.068(11) fm, in excellent agreement with a previous result.The significant reduction in charge radius from 6 He to 8 He is an indication of the change in the correlations of the excess neutrons and is consistent with the 8 He neutron halo structure. The experiment was based on laser spectroscopy of individual helium atoms cooled and confined in a magneto-optical trap. Charge radii were extracted from the measured isotope shifts with the help of precision atomic theory calculations. * Electronic address: pmueller@anl.gov 1

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Production of Cs and Fr isotopes from uranium carbide targets of a high density has been investigated at IRIS (Investigation Radioactive Isotopes at Synchrocyclotron), Gatchina. The UC target material with a density of 12 g/cm3 was prepared in a form of pellets. Two targets were tested on-line under the same temperature conditions: (a) a reference small target with a thickness of 4.5 g/cm2; (b) a heavier (so called intermediate) target with a thickness of 91 g/cm2. Yields and release efficiencies of nuclides with half-lives from some minutes to some milliseconds produced by 1 GeV protons in these targets are presented. It is remarkable that yields, even those of very short-lived isotopes such as 214Fr (T1/2 = 5 ms) and 219Fr (T1/2 = 20 ms), increase proportionally to the target thickness. A one month off-line heating test of the 91 g/cm2 target at a temperature of 2000 °C has been carried out successfully. The yields and release efficiencies of Cs and Fr measured on-line before and after the heating test coincided within the limits of measurement errors, thereby demonstrating the conservation of the target unit parameters. Based on these very promising results, a heavier target with a mass about 0.7 kg is prepared presently at IRIS

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In the frame of the MICADO H2020 project, a passive and active neutron measurement system is being developed to estimate the nuclear material mass inside legacy waste drums of low and intermediate radioactivity levels. Monte-Carlo simulations have been performed to design a new modular and transportable neutron system, with the main objective to reach a good tradeoff between the performances in passive mode, i.e. neutron coincidence counting, and in active interrogation mode with the Differential Die-away Technique. Different designs are compared, which mainly differ in their moderation materials, graphite and polyethylene. This parametric study allowed us to define a prototype taking into account practical constraints in view of its final implementation in a wide range of in-situ locations and nuclear facilities. The total neutron detection efficiency of the prototype is 6.75%, as calculated for an empty drum, i.e. without waste matrix. The detection limit in terms of nuclear material equivalent mass have also been estimated based on assumptions for a homogeneous distribution of nuclear materials inside the drum, filled with four types of matrices covering the range of nuclear waste drums defined in the frame of the project. The most favorable matrix is made of stainless steel in passive mode and of polyethylene in active mode, with an apparent density of 0.7 g.cm -3 and 0.1 g.cm -3 , respectively. The calculated mass detection limits are respectively 68 mg of 240 Pu, 62 mg of 235 U and 39 mg of 239 Pu. The most penalizing matrix is made of polyethylene with an apparent density of 0.7 g.cm -3 , which leads to a mass detection limit of 519 mg of 240 Pu in passive mode, and 564 mg of 235 U or 349 mg of 239 Pu in active mode. Measurement time is 30 min for both passive and active modes. Next steps will be a complete investigation of matrix effects based on intensive Monte-Carlo calculations and an experimental design to figure out the appropriate corrections. Experiments will also be conducted at CEA Cadarache Nuclear Measurement Laboratory with the construction and the assembly of the neutron system prototype, and the measurement of mock-up drums filled with different matrices. I.