Ultrasensitive Resonance Ionization Mass Spectrometry of Plutonium

Dr Alfredo Galindo-Uribarri1

1Oak Ridge National Laboratory, Oak Ridge, United States

The monitoring and quantification of actinides such as thorium, uranium, and plutonium at ultra-low levels is a challenge in many fields of science: neutrino physics, dark matter searches, nuclear astrophysics, environmental science, etc. These fields are pushing the limits of conventional techniques for ultra-trace analysis, demanding more sensitive and more efficient techniques. Ultra-trace analytical techniques such as Accelerator Mass Spectrometry (AMS) have been used to measure the abundance of 244Pu in deep-sea reservoirs on Earth. However, this technique using Cs-sputtering sources has relatively low efficiency for actinides.
Resonance ionization mass spectrometry (RIMS) is one of the most sensitive techniques for ultra-trace analysis of long-lived radionuclides such as the isotopes of actinides. In RIMS, ions are formed by stepwise resonant absorption of two or three photons through allowed atomic levels to photoionization. The multistep resonance process is extremely selective for the specific element of interest. Thus, in comparison with the commonly used mass spectrometry techniques RIMS is superior in suppressing the isobaric interferences in the subsequent mass separation and promises high detection efficiencies and thus high sensitivities.
The Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory (ORNL) provided beams of Radioactive Ion Beams for over 15 years. The two fields of research – AMS and RIBs – complement each other in techniques. With a setup consisting of a Resonant Ionization Laser Ion Source (RILIS), a mass spectrometer based on a radioactive beam platform and a single counter detector (Channeltron) we performed sensitivity studies in Pu. We present the studies of efficient resonance ionization schemes for ultra-trace analysis of Pu isotopes by RIMS. We have identified several highly efficient three-step resonant ionization schemes for Pu. The total efficiency of the method was investigated and a total efficiency above 50% was reached. These unique outstanding results compare very favorably with the efficiencies obtained in AMS for actinides and is an order of magnitude improvement over the previously reported laser ionization efficiency for Pu. We describe the experimental setup, and a path forward to apply this technique for ultrasensitive analytical work of actinides and potential applications.


Senior Scientist at the Physics Division, at ORNL and Professor Adjunct (Physics) at UT-Knoxville. I am a grant, manuscript, and personnel reviewer for agencies, journals, and institutions worldwide. I received my B.Sc. at UNAM, my M.Sc. in AMS and my Ph.D. in Nuclear Physics from Toronto and began my career at Chalk River. More recently, I have been pursuing a broad research program in nuclear, and particle physics with emphasis on weak interactions and fundamental interactions. Over the years I have been committed to mentoring and developing highly skilled young talent. I have been active in fostering inter-disciplinary scientific activities.

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Nov 17 2021


10:00 am - 10:55 am