The identification of autoionizing states of atomic chromium for the resonance ionization laser ion source of the ISOLDE radioactive ion beam facility

T Day Goodacre,K Chrysalidis,D.V Fedorov,V.N Fedosseev,B.A Marsh,P.L Molkanov,R.E Rossel,S Rothe,C Seiffert

doi:10.1016/j.sab.2017.01.001

Abstract

This paper presents the results of an investigation into autoionizing states of atomic chromium, in the service of the resonance ionization laser ion source (RILIS): the principal ion source of the ISOLDE radioactive ion beam facility based at CERN. The multi-step resonance photo-ionization process enables element selective ionization which, in combination with mass separation, allows isotope specific selectivity in the production of radioactive ion beams at ISOLDE. The element selective nature of the process requires a multi-step “ionization scheme” to be developed for each element. Using the method of in-source resonance ionization spectroscopy, an optimal three-step, three-resonance photo-ionization scheme originating from the 3d5(6S)4s a7S3 atomic ground state has been developed for chromium. The scheme uses an ionizing transition to one of the 15 newly observed autoionizing states reported here. Details of the spectroscopic studies are described and the new ionization scheme is summarized.

Highlights

The resonance ionization laser ion source (RILIS) [1], of the ISOLDE radioactive ion beam facility [2], utilizes the technique of multi-step resonance photo-ionization for the element selective ionization of ISOLDE reaction products
We present here a new RILIS “ionization scheme” for atomic chromium, which will enable multiple experiments to take place at ISOLDE, in fields ranging from solid state physics to fundamental nuclear physics
The 532 nm laser beam was replaced with the tunable dye laser beam to excite from the 3d5(6S)4d e7D5 level at 42,261.226 cm−1 and scan above the ionization potential. 15 transitions to new autoionizing states were observed in the scans between 16,526 cm−1 and 17,854 cm−1 (560–605 nm)

Summary

Introduction

The resonance ionization laser ion source (RILIS) [1], of the ISOLDE radioactive ion beam facility [2], utilizes the technique of multi-step resonance photo-ionization for the element selective ionization of ISOLDE reaction products. We present here a new RILIS “ionization scheme” for atomic chromium, which will enable multiple experiments to take place at ISOLDE, in fields ranging from solid state physics to fundamental nuclear physics. ISOLDE is an isotope separator on-line (ISOL) type radioactive ion beam facility, connected to the CERN accelerator complex. Reaction products, created via fragmentation, spallation and fission, are stopped and thermalized within the target material. The target is heated to enable sufficiently volatile elements to diffuse through the target material and effuse, via a transfer line, to an ion source typically for 1+ ionization

Methods

Results

Conclusion