First PAC studies on the hydrogen diffusion in III-V semiconductors

We report on first experiments which observe on a microscopic scale the migration of isolated hydrogen in InP, InAs and GaAs. Using the radioactive acceptor 117Cd, Cd-H pairs have been formed in these III-V semiconductors. After the decay of 117Cd to 117In, H is no longer bound to 117In and can diffuse freely. This diffusion has been observed by perturbed gg angular correlation (PAC) spectroscopy. At 10 K, the occupation of two different lattice sites by hydrogen has been observed

Ground-state spin of 59^{59}Mn

Beta decay of $^{59}$Mn has been studied at PSB-ISOLDE, CERN. The intense and pure Mn beam was produced using the Resonance Ionization Laser Ion Source (RILIS). Based on the measured $\beta$-decay rates the ground-state spin and parity are proposed to be $J^{\pi}$ = 5/2$^{-}$. This result is consistent with the systematic trend of the odd-A Mn nuclei and extends the systematics one step further towards the neutron drip line

Studies of release properties of ISOLDE targets

Off-line release rates of Be, Mg, S, Mn and Kr from refractory materials were studied. Mn yields were determined from a ZrO2 target and Kr yields from a SrO and ZrO2 targets. A Monte Carlo code to optimize ISOLDE targets was introduced

In-source laser spectroscopy with the laser ion source and trap: first direct study of the ground-state properties of Po-217,Po-219

D. A. Fink et al.; 15 págs.; 17 figs.; 3 tabs.; Open Access funded by Creative Commons Atribution Licence 3.0A Laser Ion Source and Trap (LIST) for a thick-target, isotope-separation on-line facility has been implemented at CERN ISOLDE for the production of pure, laser-ionized, radioactive ion beams. It offers two modes of operation, either as an ion guide, which performs similarly to the standard ISOLDE resonance ionization laser ion source (RILIS), or as a more selective ion source, where surface-ionized ions from the hot ion-source cavity are repelled by an electrode, while laser ionization is done within a radiofrequency quadrupole ion guide. The first physics application of the LIST enables the suppression of francium contamination in ion beams of neutron-rich polonium isotopes at ISOLDE by more than 1000 with a reduction in laser-ionization efficiency of only 20. Resonance ionization spectroscopy is performed directly inside the LIST device, allowing the study of the hyperfine structure and isotope shift of 217Po for the first time. Nuclear decay spectroscopy of 219Po is performed for the first time, revealing its half-life, α- to-β-decay branching ratio, and α-particle energy. This experiment demonstrates the applicability of the LIST at radioactive ion-beam facilities for the production and study of pure beams of exotic isotopes. Published by the American Physical SocietyThis work was supported by the Bundesministerium für Bildung und Forschung (BMBF, Germany) within the Wolfgang- Gentner programme as well as through the consecutive project fundings of 06Mz9181I, 06Mz7177D, and 05P12UMCIA, by FWO-Vlaanderen (Belgium), by GOA/2010/010 (BOF-KULeuven), by the IUAP-Belgian State Belgian Science Policy (BRIX network P7/12), by the U.K. Science and Technology Facilities Council (STFC), by the European Union within FP7 (ENSAR No. 262010), by the Slovak Research and Development Agency (Contract No. APVV-0105-10), by the Slovak grant agency VEGA, and the Reimei Foundation of JAEA (Contract No. 1/0576/13). T. E. C. was supported by STFC Ernest Rutherford Grant No. ST/J004189/1.Peer Reviewe

The transverse and longitudinal beam characteristics of the phin photo-injector at Cern

International audienceThe laser driven RF photo-injectors are recent candidates for high-brightness, low-emittance electron sources. One of the main beam dynamics issues for a high brightness electron source is the optimization of beam envelope be- havior in the presence of the space charge force in order to get low emittance. Within the framework of the second Joint Research Activity PHIN of the European CARE pro- gram, a new photo-injector for CTF3 has been designed and installed by collaboration between LAL, CCLRC and CERN. Beam based measurements have been made dur- ing the commissioning runs of the PHIN 2008 and 2009 including measurements of the emittance, using multi-slit technique. The demonstration of the high charge and the stability along the long pulse train are between the goals of this photo-injector study as also being important issues for CTF3 and the CLIC drive beam. In this work the photo-injector will be described and the first beam mea- surement results will be presented and compared with the PARMELA simulations

Shapes of the 192,190^{192,190}Pb ground states from beta decay studies using the total absorption technique

The beta decay of $^{192,190}$Pb has been studied using the total absorption technique at the ISOLDE(CERN) facility. The beta-decay strength deduced from the measurements, combined with QRPA theoretical calculations, allow us to infer that the ground states of the $^{192,190}$Pb isotopes are spherical. These results represent the first application of the shape determination method using the total absorption technique for heavy nuclei and in a region where there is considerable interest in nuclear shapes and shape effects

Decay-assisted collinear resonance ionization spectroscopy: Application to neutron-deficient francium

This paper reports on the hyperfine-structure and radioactive-decay studies of the neutron-deficient francium isotopes $^{202-206}$Fr performed with the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at the ISOLDE facility, CERN. The high resolution innate to collinear laser spectroscopy is combined with the high efficiency of ion detection to provide a highly-sensitive technique to probe the hyperfine structure of exotic isotopes. The technique of decay-assisted laser spectroscopy is presented, whereby the isomeric ion beam is deflected to a decay spectroscopy station for alpha-decay tagging of the hyperfine components. Here, we present the first hyperfine-structure measurements of the neutron-deficient francium isotopes $^{202-206}$Fr, in addition to the identification of the low-lying states of $^{202,204}$Fr performed at the CRIS experiment.Comment: Accepted for publication with Physical Review

Generation of 10-m-lengthscale plasma columns by resonant and off-resonant laser pulses

Creating extended, highly homogeneous plasma columns like that required by plasma wakefield accelerators can be a challenge. We study the propagation of ultra-short, TW power ionizing laser pulses in a 10-meter-long rubidium vapor and the plasma columns they create. We perform experiments and numerical simulations for pulses with 780 nm central wavelength, which is resonant with the D$_2$ transition from the ground state of rubidium atoms, as well as for pulses with 810 nm central wavelength, some distance from resonances. We measure transmitted energy and transverse width of the pulse and use schlieren imaging to probe the plasma column in the vapor close to the end of the vapor source. We find, that resonant pulses are more confined in a transverse direction by the interaction than off-resonant pulses are and that the plasma channels they create are more sharply bounded. Off-resonant pulses leave a wider layer of partially ionized atoms and thus lose more energy per unit propagation distance. Using experimental data, we estimate the energy required to generate a 20-meter-long plasma column and conclude that resonant pulses are much more suitable for creating a long, homogeneous plasma.Comment: 12 pages, 14 figure

Laser spectroscopy of francium isotopes at the borders of the region of reflection asymmetry

The magnetic dipole moments and changes in mean-square charge radii of the neutron-rich $^{218m,219,229,231}\text{Fr}$ isotopes were measured with the newly-installed Collinear Resonance Ionization Spectroscopy (CRIS) beam line at ISOLDE, CERN, probing the $7s~^{2}S_{1/2}$ to $8p~^{2}P_{3/2}$ atomic transition. The $\delta\langle r^{2}\rangle^{A,221}$ values for $^{218m,219}\text{Fr}$ and $^{229,231}\text{Fr}$ follow the observed increasing slope of the charge radii beyond $N~=~126$. The charge radii odd-even staggering in this neutron-rich region is discussed, showing that $^{220}\text{Fr}$ has a weakly inverted odd-even staggering while $^{228}\text{Fr}$ has normal staggering. This suggests that both isotopes reside at the borders of a region of inverted staggering, which has been associated with reflection-asymmetric shapes. The $g(^{219}\text{Fr}) = +0.69(1)$ value supports a $\pi 1h_{9/2}$ shell model configuration for the ground state. The $g(^{229,231}\text{Fr})$ values support the tentative $I^{\pi}(^{229,231}\text{Fr}) = (1/2^{+})$ spin, and point to a $\pi s_{1/2}^{-1}$ intruder ground state configuration.Comment: Accepted for publication with Physical Review