In-Source Laser Spectroscopy with the Laser Ion Source and Trap: First Direct Study of the Ground-State Properties ofPo217,219

Abstract

A 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 217 Po for the first time. Nuclear decay spectroscopy of 219 Po 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.

Ion beam production and study of radioactive isotopes with the laser ion source at ISOLDE

“…Some key functionality (ion beam cooling and bunching) first proposed by Blaum has therefore been lost whilst the primary function of achieving orders-of-magnitude selectivity improvements has been demonstrated under normal on-line operating conditions with a UCx target [42]. So far the LIST has been successfully used for the production of pure Mg [19] and Po [42,43] beams. Table 2 is a summary of the LIST suppression factors that have been measured during off-line and on-line operation at ISOLDE.…”

“…Following the series of experiments on the study of nuclear spins and electromagnetic moments of Cu isotopes [56,[78][79][80] the in-source RIS collaboration has performed extensive laser and nuclear-spectroscopic studies of isotopes in the lead region, namely the Tl [81], Pb [70,[82][83][84], Hg [45], Bi [85], Po [43,77,86,87], At and Au chains [22,88]. Our recent activity in this field has revisited the neutron-deficient Au and Hg isotopes, which were first studied at ISOLDE approximately four decades ago: the very first optical spectroscopy experiments performed at an ISOL facility [89][90][91][92].…”

On-line implementation and first operation of the Laser Ion Source and Trap at ISOLDE/CERN

“…A fraction of the recoiling decay products of these atoms are captured inside the LIST to form a portion of the extracted ion beam. For a further discussion of these additional ionization mechanisms inside the LIST, we refer to our publications [25,30].…”

“…The radioactive magnesium ions were detected by the ISOLDE tape-station and the polonium ions were detected with the KU Leuven Windmill setup for the detection of a-emitters [33]. For more details of the setup of on-line run 2, we refer to our other publications [25,30].…”

“…After this successful demonstration of on-line operation, further off-line tests (off-line test 2) with a second newly constructed LIST (LIST 2) device were conducted for preparation of on-line run 2, the first on-line physics application of a LIST ion source attached to a uranium carbide (UC) target unit. This was used for the study of neutron-rich polonium [25,30]. Based on the results of the on-line run 1, the second LIST used during on-line run 2 was slightly modified, leading to an improvement of the ionization efficiency by a factor of 2.5.…”