Laser photodetachment of radioactive 128I−

S Rothe ,Reinhard Heinke,Κ Wendt ,T Day Goodacre ,R E Rossel ,K Johnston ,B A Marsh ,V N Fedosseev ,Dominik Studer,Jakob Welander,O Forstner ,C Seiffert ,Spyridon Fiotakis,J Sundberg ,Yuan Liu,T Kron ,K Chrysalidis ,A Ringvall-Moberg ,U Köster ,Dag Hanstorp

doi:10.1088/1361-6471/aa80aa

Abstract

The first experimental investigation of the electron affinity (EA) of a radioactive isotope has been conducted at the CERN-ISOLDE radioactive ion beam facility. The EA of the radioactive iodine isotope 128I (t1/2 = 25 min) was determined to be 3.059 052(38) eV. The experiment was conducted using the newly developed Gothenburg ANion Detector for Affinity measurements by Laser PHotodetachment (GANDALPH) apparatus, connected to a CERN-ISOLDE experimental beamline. 128I was produced in fission induced by 1.4 GeV protons striking a thorium/tantalum foil target and then extracted as singly charged negative ions at a beam energy of 20 keV. Laser photodetachment of the fast ion beam was performed in a collinear geometry inside the GANDALPH chamber. Neutral atoms produced in the photodetachment process were detected by allowing them to impinge on a glass surface, creating secondary electrons which were then detected using a channel electron multiplier. The photon energy of the laser was tuned across the threshold of the photodetachment process and the detachment threshold data were fitted to a Wigner law function in order to extract the EA. This first successful demonstration of photodetachment at an isotope separator on line facility opens up the opportunity for future studies of the fundamental properties of negatively charged radioactive isotopes such as the EA of astatine and polonium.

Highlights

IntroductionTraditional spectroscopic methods, which are used to identify and to determine the structure of atoms and positive ions, cannot be applied to negative ions
As a milestone on the way towards measuring the electron affinity (EA) of astatine we present here the first investigation of a radioactive negative ion: the measurement of the EA of 128I (t1/2 = 25 min)
We have demonstrated the first photodetachment study of a negatively charged radioactive isotope

Summary

Introduction

Traditional spectroscopic methods, which are used to identify and to determine the structure of atoms and positive ions, cannot be applied to negative ions. These weakly bound systems are abundant in many environments such as the solar atmosphere [3], the interstellar medium [4] and in plasmas [5]. Their presence is often extremely difficult to detect as a consequence of the scarcity of radiative transitions between bound states. Their unique properties provide valuable tools in many different applications, such as accelerator-based mass spectrometry [6] and fusion research [7]

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Discussion

Conclusion