Los Alamos scientists Alexander Malyzhenkov and Alonso Castro demonstrate levitating uranium particles with laser beams. (Credit: Los Alamos National Laboratory)

Nuclear forensics aims to determine the movements and source of the world’s most dangerous weapons and material. But according to experts, it can take weeks or months to get answers in situations where investigators can only spare hours—or minutes.

Nuclear forensics may get a big speed boost with a new Los Alamos National Laboratory-devised analytical methodology.

“Optical tweezers,” using lasers to lift microscopic plutonium and uranium particles, shows measurements of recoil of the material during radioactive decay—thereby allowing investigators to “fingerprint” substances in relatively short time, according to a new paper in the journal Physical Review A.

“The proposed technique does not require the use of specific detectors for each type of emitted radiation, because it does not rely on the detection of emitted particles, as in conventional alpha, beta, or gamma spectrometry,” write the authors.

The optical tweezers allows a sample particle to be levitated in the laser-powered “trap.” The kinetic energy of the emitted daughter particle can be determined by measuring the recoil of the hovering particle, since it absorbs the momentum, creating an oscillation.

That harmonic reaction can be relatively easily and quickly measured by the scientists, according to the paper. And those measurements can provide a wide variety of data, including isotopic and other criteria.

“Nuclear decay recoil can be observed within small particles levitated in an optical trap with high positional resolution,” the authors write. “Precise measurements of the magnitude of each recoil as well as their rate of occurrence can provide accurate information about the isotopic composition of a radioactive sample. We expect that this technique for nuclear material characterization will be especially useful in the area of nuclear forensic analysis.”

The nuclear forensic scenarios, involving the tiniest traces of nuclear material, would be ideal for such an exacting method, added Alonso Castro, lead author, from Los Alamos.

“The impact of our approach is that it can very quickly determine the isotopic composition of the types of nanometer and micrometer-seized particles found in nuclear forensic scenarios,” added Castro, in a laboratory statement.

The new nuclear recoil spectroscopy method could speed crucial steps in nuclear forensics.

Currently, methodologies employed in nuclear forensics are alpha spectrometry, gamma spectrometry, beta detection, scintillation counting, cloud chamber detection and the general use of mass spectrometry to conduct isotopic analysis based on their mass-to-charge ratios.

But all of it is time-consuming. Effective intelligence analysis in the wake of a nuclear terrorist attack could take between three weeks and three months, if at all, according to the Federation of American Scientists

The “optical tweezers” tool was the creation that won part of this year’s Nobel Prize for Physics, announced last month for American Arthur Ashkin, the oldest-ever recipient of a Nobel, at the age of 96. Ashkin developed the tool in the 1980s at Bell Laboratories in New Jersey.

“It is only fitting that Arthur Ashkin’s invention is still yielding novel science even after 30 years,” said Castro.