Target-ion source unit ionization efficiency measurement by a method of stable ion beam implantation

At the IRIS facility a rather precise method of the target-ion source unit ionization efficiency measurement has been developed. The method exploits an off-line mass-separator for the implantation of the ion beams of selected stable isotopes into a tantalum foil placed inside a Faraday cup in the focal plane of the mass-separator. After the implantation of the required amount of the investigated species, tantalum foil has been inserted into the volume of the target-ion source unit prepared for the on-line utilization at the IRIS on-line separator. The first tests have ensured the ionization efficiency values (90±10)% for Rb and (85±10)% for Cs in the empty combined target-ion source unit, which was used as a reference one. For the target-ion source unit with UC target material inside the measured value of the ionization efficiency of Rb was (52±20)%.     

Development of a RILIS ionisation scheme for gold at ISOLDE, CERN

At the ISOLDE on-line isotope separation facility, the resonance ionisation laser ion source (RILIS) can be used to ionise reaction products as they effuse from the target. The RILIS process of laser step-wise resonance ionisation of atoms in a hot metal cavity provides a highly element selective stage in the preparation of the radioactive ion beam. As a result, the ISOLDE mass separators can provide beams of a chosen isotope with greatly reduced isobaric contamination. With the addition of a new three-step ionisation scheme for gold, the RILIS is now capable of ionising 26 of the elements. The optimal scheme was determined during an extensive study of the atomic energy levels and auto-ionising states of gold, carried out by means of in-source resonance ionisation spectroscopy. Details of the ionisation scheme and a summary of the spectroscopy study are presented.     

Upgrade to the IGISOL laser ion source towards spectroscopy on Tc

A new method of optical pumping has been applied to increase the power of the Ti:Sapphire laser system of the FURIOS laser ion source, Jyväskylä. This upgrade has led to a factor of two improvement in the output power, and has been directly employed in the first off-line laser ionisation tests on the long-lived refractory isotope ⁹⁹Tc. In the future further studies will be done to determine the efficiency of this ionisation scheme and to employ it for on-line experiments.     

Resonant Ionization Laser Ion Source Project at TRIUMF

Resonant laser excitation and ionisation is one of the most successful tools for the selective production of radioactive ion beams (RIB) at on-line mass separator facilities. TRIUMF plans to augment the current ion sources with a resonant ionisation laser ion source (RILIS), to use the high production yields from the target, as shown by the delivery of 3*10⁴/s ¹¹Li ions from a standard target ion source with surface ionisation. The development and installation of TRIUMF's RILIS (TRILIS) is necessary to provide beams of short lived isotopes that conventional ion sources could not produce in sufficient intensity and purity for nuclear-, and nuclear astrophysics- experiments. A laser system consisting of three tunable titanium–sapphire (TiSa) lasers with frequency doubling and tripling was employed to demonstrate first off-line resonance ionisation of Ga, and is being installed for first on-line test and a run on ⁶²Ga in December 2004.     

Accurate masses of unstable rare-earth isotopes by ISOLTRAP

Direct mass measurements of neutron-deficient rare-earth isotopes in the vicinity of ¹⁴⁶Gd were performed with the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN. This paper reports on the measurement of more than 40 isotopes of the elements praseodymium, neodymium, promethium, samarium, europium, dysprosium and holmium, that have been measured with a typical accuracy of m 14 keV. An atomic mass evaluation has been performed taking into account other experimental mass values via a least-squares adjustment. The results of the adjustment are discussed. Received: 18 April 2000 / Accepted: 12 July 2000     

Independent fission yields of short-lived Br and I isotopes in thermal neutron fission of235U

Independent fission yields of^88–91Br and^138–141I produced in thermal neutron fission of²³⁵U were determined at the SOLIS on-line isotope separator. The measurements were made for the first time using a negative surface ionization integrated target-ion source.     

Atomic lines isotope shifts of short-lived radioactive Eu studied by high-sensitive laser resonance photoionization method in “on-line” experiments with proton beams

In “on-line” experiments the isotope shifts (IS) of ^141–144Eu have been measured at the mass-separator output. The overall detection efficiency of Eu atoms is equal to 3 x 10^-4. The accuracy of IS measurement is ±70 MHz and determined by laser linewidth.     

Target ion source and charge exchange cell development for the EXCYT facility

The EXCYT facility at the INFN-LNS is based on a K-800 superconducting cyclotron delivering stable ion beams on a Target Ion Source (TIS) assembly to produce the required nuclear species, and on a 15 MV Tandem for post-accelerating the radioactive beams. For some ion beams such as for Li, the extraction efficiency from the TIS is higher when obtained by positive ionisation, while the injection into the Tandem is possible only after a charge exchange to obtain negative ions. In this work we present the procedures together with the results of the production of ^6,7,8,9Li beams extracted at EXCYT during the last year. The production of the radioactive elements was performed by sending a ¹³C⁴⁺ primary beam of 45 MeV/u on a graphite target. The ionisation of the production species was achieved by a tungsten positive surface ioniser. The Li⁺ has been extracted from TIS at different energies to cross-check the transmission and the charge exchange efficiency. To perform the conversion from positive to negative ions we employed a Charge Exchange Cell (CEC) containing Cs vapours. The Li beam interacts with the latter in a two-step reaction, thus converting its charge from +1 to –1. The CEC was already characterised during off-line tests; the results obtained at EXCYT confirmed both the isotopic shift effect and the efficiency values at several given extraction energies. Future improvements of the TIS and the CEC are discussed.     

Two-level lasers operating on the transitions to the ground state

We analyze in detail a model of two-level lasers with a thermal production of population inversion proposed by V. A. Gerasimov et al. (Phys. Rev. Lett., 2006, 96, 123902). We show that it is possible to obtain nine new laser lines on the transitions to the ground state in atoms of rare-earth metals (REMs) with an incomplete 4f shell (Pr, Nd, Sm, Eu, and Tb–Tm). The laser line wavelengths are from the UV (Eu) to the middle IR (Tb and Er) regions of the spectrum. Based on the estimates of the specific laser energy parameters (power, power density, and efficiency), we conclude that only Sm, Eu, and Tm (among the REMs under study) are suited for the experimental prototypes of these lasers. The estimated maximum efficiency and specific power density of continuous lasing can reach the values of >40% and ~10⁷÷10⁹ W/cm², respectively.     

Multifoil UCx target for the SPES project --An update

The target system is one of the key issues for the facilities aimed at the production of neutron-rich radioactive ion beams. In the framework of the SPES project (Study for the Production of Exotic Species), the possibility of using a target configuration with a proton beam (40MeV, 0.2mA) directly impinging on multiple uranium carbide disks is investigated. The ²³⁸U fission fragments constitute the source for the exotic beams and for this purpose the disks are placed inside a graphite box at 2000 ^°C. The target is split into several thin disks in order to allow the cooling of the system by thermal radiation. In this way about ∼ 10¹³ fissions s ^-1 are obtained with a relative simple system and with relative low costs. Further steps have been performed compared to previous publications and now all the main parameters of the system have been analysed by means of calculation codes: the fission rates and the fission fragment distribution; the power deposition and the thermal analysis; the thermo-mechanical behaviours of the disks; the effusive and diffusive extraction release properties of the target.     

Nuclear spins, magnetic moments and α-decay spectroscopy of long-lived isomeric states in 185Pb

Alpha-decay properties of the neutron-deficient isotope ¹⁸⁵Pb were studied at the PSB-ISOLDE (CERN) on-line mass separator using the resonance ionisation laser ion source (RILIS). The nuclei of interest were produced in a 1.4 GeV proton-induced spallation reaction of a uranium graphite target. In contrast to previous studies, two α-decaying isomeric states were identified in ¹⁸⁵Pb. The relative production of the isomers, monitored by their α-counting rates, could be significantly changed when a narrow-bandwidth laser at the RILIS setup was used to scan through the atomic hyperfine structure. Based on the atomic hyperfine structure measurements, along with the systematics for heavier odd-mass lead isotopes, the spin and the parity of these states were interpreted as 3/2^- and 13/2⁺ and their nuclear magnetic moments were deduced. The α-decay energy and half-life value for the I ^π = 13/2⁺ isomer are E _α = 6408(5) keV, T _1/2 = 4.3(2) s, respectively; while for the I ^π = 3/2^- isomer ( T _1/2 = 6.3(4) s) two α-decays with E _α1 = 6288(5) keV, I _α1 = 56(2)% and E _α2 = 6486(5) keV, I _α2 = 44(2)% were observed. By observing prompt α-γ coincidences new information on the low-lying states in the daughter isotope ¹⁸¹Hg was obtained. Received: 7 February 2002 / Accepted: 19 February 2002     

ISOL beams of hafnium isotopes and isomers

The production of ISOL beams of hafnium is described. Radioactive Hf isotopes were produced at ISOLDE by 1.4 GeV proton-induced spallation in Ta and W foils. Chemical evaporation in form of HfF₄ and mass separation in the molecular sideband HfF₃⁺ after electron impact ionization provided intense and pure beams. Beams of ^158-185Hf and short-lived isomers down to 1.1 s ^177mHf were observed, but the method could be extended to reach even more exotic isotopes: down to about ¹⁵⁴Hf (N=82) on the neutron-deficient side and up to neutron-rich ¹⁸⁸Hf.     

Sputtering yield of chromium by argon and xenon ions with energies from 50 to 500 eV

A radioactive tracer technique is described for the quantitative measurement of the sputtering yield of a target material electroplated on a copper substrate. Sputtering yields of chromium by argon and xenon ions with energies from 50 to 500 eV are reported. The ion beams, having a current density ranging from 0.01 to 0.1 mA/cm² at an operating pressure of 2×10^–5 Torr, were produced by a low-energy ion gun. The sputtered atoms were collected on an aluminum foil surrounding the target. ⁵¹Cr was used as the tracer isotope. The results indicate that the radioactive tracer technique is sensitive enough in measuring the extremely small amount of sputtered material at low ion currents and low ion energies.     

CW laser oscillation on transitions of Tl+ in a hollow-cathode Ne-Tl-halide discharge

CW laser oscillation on Tl⁺ transitions (594.9 nm and 695.1 nm) at low operating temperatures is obtained. As a source of Tl atoms the volatile salt TlCl is used. The compound is evaporated due to selfheating by the discharge current. Maximum laser intensity is obtained at neon pressure of 10–13 Torr and cathode temperature ≈ 320°C.     

Investigation on Mössbauer spectra of151Eu double rare-earth oxides

The¹⁵¹Eu double rare-earth oxides (EuR)O₃(R=Gd, Dy, and other rare-earth elements except for Eu) which synthesized by means of high pressure and high temperature, were investigated using Mossbauer spectroscopy. Owing to that the asymmetry parameter of EFG 0, each experimental spectrum was fitted by twelve transitional lines. The results show that the isomer shift depends on atomic number of the second rare-earth element and in linear relationship with unit-cell volume V^1/3.     

Silicon interaction with the (0001) surface of La and Gd layers

A study is reported on a system consisting of a Si layer on the surface of rare-earth metals (REMs), which is the reverse of a rare-earth metal on silicon, the system of current widespread interest. Interaction of silicon with the (0001) surface of trivalent La and Gd single-crystal layers grown on a W(110) surface is studied by Auger spectroscopy combined with layer-by-layer argon-ion etching of the system and photoelectron spectroscopy. It is found that silicon interacts with the La(0001) and Gd(0001) surfaces even at room temperature with the formation of silicide, but no mutual mixing of the silicon and substrate atoms occurs. When the Si/La(0001) and Si/Gd(0001) systems are heated at 400°C, silicon does not diffuse into the bulk of the metal substrate or to the REM/W(110) interface.     

Preparation of Y2O3:Eu thin films by excimer-laser-assisted metal organic deposition

Europium-doped yttrium oxide (Y₂O₃:Eu) thin films were successfully deposited on quartz and ITO/glass substrates by excimer-laser-assisted metal organic deposition (ELAMOD) at low temperatures. The effects of laser wavelength and thermal temperature on the films’ crystallinity and photoluminescence properties were investigated. Films irradiated by an ArF laser at 80 mJ/cm² and 400–500°C were highly crystallized compared with those prepared by thermal MOD. In contrast, when the film was irradiated by a KrF laser at 500°C, no crystalline Y₂O₃:Eu was formed. The Y₂O₃:Eu film irradiated by the ArF laser at 80 mJ/cm² and 500°C showed typical PL spectra of Eu³⁺ ions with cubic symmetry and a ⁵D₀→⁷F₂ transition at ∼612 nm. The PL intensity at 612 nm was much higher for the film prepared with ELAMOD than for that prepared by the thermal-assisted process, and the photoemission intensity of the film prepared with ELAMOD strongly depended on the substrate material.     

Production of a highly polarized sodium atomic beam

Two experimental techniques for preparing atoms in selected states were combined in order to obtain a highly polarized sodium beam: Firstly state selection by an inhomogeneous magnetic field and secondly optical pumping with laser light. This results in a dominating population of the 3s ² S _1/2 ground state levelF=2M _F=+2 (or alternativelyF=2M _F=−2) corresponding to high electron as well as nuclear spin polarization. Polarization values of 0.85±0.05 were easily obtained. The sign of the polarization can be reversed by changing the light polarization. The method can also be applied to other atoms. In addition, it is demonstrated that the optical pumping process allows a determination of the spin-selectivity of hexapole magnets.     

Recent developments and on-line tests of uranium carbide targets for production of nuclides far from stability

The capacity of uranium carbide target materials of different structure and density for production of neutron-rich and heavy neutron-deficient nuclides have been investigated. The yields of Cs and Fr produced by a 1 GeV proton beam of the PNPI synchrocyclotron and release properties of different targets have been measured. Yields and release efficiencies of Cs and Fr produced from a high density UC target material and from low density UCx prepared by the ISOLDE method at IRIS in the collaboration with PARRNe group from Orsay are compared. The yields from ISOLDE original target are presented for comparison as well.     

A modified electron bombardment type ion source for the study of solids

A modified electron bombardment type ion source suitable for use with mass spectrometer is described. Ion formation occurs throughout a relatively large volume in the ionisation box, since no magnetic field is used to collimate the ionising electrons. A sensitivity of 2 × 10⁻⁵ amp/torr is obtained for an ion extraction energy of 2 keV and 200 mass resolution. Trajectory tracing has been used to study the operation of the ion source. Capability of the ion source to analyse solid samples in microgram quantity was tested by studying evaporation of BaO from tungsten.