We report synthesis and characterization of a batch of three cesium potassium antimonide photocathodes that have been grown on pure copper substrates via a ternary co-deposition method whose ...procedure is described herein. A deposition system that was designed for synthesis of two-element photocathodes has been utilized for synthesis of the aforementioned three-element photocathodes with slope of the in situ photocurrent as the driver for the growth process. A variation of substrate temperature and deposition parameters among the three photocathodes during synthesis has yielded a maximum quantum efficiency of 6% for 140°C substrate temperature. Lifetime studies performed in a 65-kV DC electron gun on two of the photocathodes, but under oxidized states, at tens of μA average currents (ampere-level peak currents) extracted utilizing a 532-nm wavelength, 1-kHz repetition rate laser, have resulted in charge-lifetimes of 6.13 C and 13.78 C, respectively. X-ray photoelectron spectroscopy analysis of the photocathode with the highest quantum efficiency has revealed a nearly impurity-free surface with stoichiometry Cs1.3K1.8Sb1.0 when pristine. Furthermore, it has been found that oxidation of the alkali surface atoms as well as carbon adsorption from hydrocarbons and minor fluorine uptake are the causes of quantum efficiency reduction during laser illumination in the utilized experimental set-up.
New technical developments have led to a 2 orders of magnitude improvement of the resolution of the collinear resonance ionization spectroscopy (CRIS) experiment at ISOLDE, CERN, without sacrificing ...the high efficiency of the CRIS technique. Experimental linewidths of 20(1) MHz were obtained on radioactive beams of francium, allowing us for the first time to determine the electric quadrupole moment of the short lived t_{1/2}=22.0(5) ms ^{219}Fr Q_{s}=-1.21(2) eb, which would not have been possible without the advantages offered by the new method. This method relies on a continuous-wave laser and an external Pockels cell to produce narrow-band light pulses, required to reach the high resolution in two-step resonance ionization. Exotic nuclei produced at rates of a few hundred ions/s can now be studied with high resolution, allowing detailed studies of the anchor points for nuclear theories.
The presented paper discusses the production of radioactive ion beams of francium, radium, and actinium from thick uranium carbide (UC
) targets at ISOLDE, CERN. This study focuses on the release ...curves and extractable yields of francium, radium and actinium isotopes. The ion source temperature was varied in order to study the relative contributions of surface and laser ionization to the production of the actinium ion beams. The experimental results are presented in the form of release parameters. Representative extractable yields per
C are presented for
Ac, several Ra and Fr isotopes in the mass ranges 214
A
233 and 205
A
231 respectively. The release efficiency for several isotopes of each of the studied elements was calculated by comparing their yields to the estimated in-target production rates modeled by CERN-FLUKA. The maximal extraction efficiency of actinium was calculated to be 2.1(6)% for a combination of surface ionization using a Ta ion source and resonant laser ionization using the two-step 438.58 nm, and 424.69 nm scheme.
The applications of the laser resonance ionization method in nuclear research are reviewed. Investigation of radioactive isotopes using resonance ionization techniques provides a valuable combination ...of high selectivity, efficiency and spectral resolution. The majority of radioactive ion beams produced at on-line isotope separator facilities profit from the selectivity and universal applicability of laser ion sources. Numerous ultra-sensitive and high-resolution techniques of laser spectroscopy based on resonance ionization of atoms have been developed for the study of rare and radioactive isotopes. A summary of ionization schemes applied to radioactive isotopes is given in table form.
Polonium (Po) is one of the rarest elements in Earth's crust. None of its isotopes are stable and sufficient amounts for systematic experimental studies of its most fundamental properties are only ...available by artificial production. At the radioactive ion beam facility ISOLDE at CERN, 208Po was produced by proton-induced spallation of uranium. Using the technique of in-source Resonance Ionization Spectroscopy the ionization threshold was probed with a tunable dye laser. A spectrum of 110 previously undocumented odd-parity Rydberg states was observed. Applying the Rydberg formalism to the data enabled the determination of the first ionization energy of polonium as 67896.310(14)(30) cm−1 or 8.4180700(18)(37) eV. This is a precision improvement of more than 600 over the existing literature value. A comparison with the homologous elements sulfur, selenium and tellurium enabled the assignment of the electron configuration of the resonances found in the spectrum.
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•Resonance Ionization Spectroscopy of polonium performed at CERN-ISOLDE.•110 previously undocumented odd-parity Rydberg states of polonium observed.•Ionization energy of polonium is 67896.310(14)(30) cm−1 or 8.4180700(18)(37)eV.•More than 600-fold precision improvement over existing literature values of polonium IE
The magnetic moments and isotope shifts of the neutron-deficient francium isotopes (202-205)Fr were measured at ISOLDE-CERN with use of collinear resonance ionization spectroscopy. A ...production-to-detection efficiency of 1% was measured for (202)Fr. The background from nonresonant and collisional ionization was maintained below one ion in 10(5) beam particles. Through a comparison of the measured charge radii with predictions from the spherical droplet model, it is concluded that the ground-state wave function remains spherical down to (205)Fr, with a departure observed in (203)Fr (N=116).
The SPES laser ion source has been tested at ISOLDE Offline 2, CERN. A two-step single resonance photo-ionization scheme has been used to ionize gallium atoms in the SPES tantalum hot-cavity ion ...source. The ion beam time structure, laser enhancement of ion yield, and ionization efficiency are investigated in relation to the ion source temperature and ion load. From the time structures, it is inferred that a significant fraction of the extracted ions are generated in the transfer line rather than just in the hot cavity. The effect of the electrostatic axial field on the movement of ions inside the ion source is discussed. Generally, there is an inverse relationship between total ion load and the laser enhancement factor. This dependency is enhanced at lower operating temperature of the ion source. This is explained by the influence of thermionic electron emission and ion density on the transverse laser-ion confinement, and therefore the survival of ions as they drift towards the extraction region of the ion source. At 2200 °C, the nominal temperature for on-line operation of the ion source, the ratio of laser-ionized to surface-ionized gallium was stable around 55 during the measurement campaign, and independent of the total extracted ion current up to the measured value of 1.1 μA. A resonance laser ionization efficiency value of 27.2% for gallium has been measured.
This article summarizes the current specifications and the latest features of the CERN-ISOLDE resonance ionization laser ion source (RILIS). This includes a description of the optical layout and the ...newly designed reference system. The ionization schemes for the laser ionized beams at ISOLDE are tabulated, including six new elements. All RILIS schemes are also made publicly available in the RILIS elements on-line database. Finally, we announce a paradigm shift in RILIS operation – the combination of a machine protection and a monitoring and control system has enabled on-call operation of the laser ion source for selected beams in 2014 and has become the standard mode of operation in 2015.
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