Posted on behalf of Adam Mann
The growing concerns over radiation leaks at the damaged Fukushima Daiichi nuclear plant in Japan – a drama playing out against the wider scale disaster unfolding in the wake of the 11 March earthquake and tsunami – is having an impact in some of the most remote and sheltered corners of the scientific world.
Sensitive experiments in underground laboratories could be affected by the plant’s releases, physicists say, and in some cases measures are being taken to avoid radioactive contamination that would, in other circumstances, be considered negligible.
In a paper posted 25 March, a team at the University of Washington has made its initial measurements of airborne fission products originating from Fukushima. They analyzed the air filters of the university’s ventilation system and report the detection of small amounts of radioactive isotopes such as iodine-131 and cesium-137.
“These are well below health concern levels, but they could definitely impact experiments,” says Michael Miller, a co-author on the paper as well as a team member with MAJORANA, an experiment currently under construction in the Deep Underground Science and Engineering Laboratory (DUSEL) in Homestake, South Dakota. The project will look at double-beta decay in 1 metric ton of germanium crystals in an attempt to determine the mass of the neutrino.
MAJORANA may be particularly sensitive to fallout from Fukushima as its plans call for the construction of a detector with zero radioactive background interference. “A grain of dust would ruin the experiment, a fingerprint would be a disaster,” says Miller. The team had planned to bring copper used in the fabrication of their detector up from underground for machining this weekend. But since this would have exposed the metal to contamination, the move has been delayed.
Given the reported radioactivity levels, other collaborations sensitive to background should consider protecting themselves, says Harry Miley, a physicist at the Pacific Northwest National Laboratory (PNNL) in Richland, Washington, who previously worked on double-beta decay experiments during the 1986 Chernobyl disaster. Cesium-137 is of major concern for such experiments, given that it has a relatively long half-life of 30 years and a sharp energy peak at 662 KeV that could skew a low-energy detector’s results, he adds.
Experiments currently under construction need regular cleaning in labs that have good filtration systems, says Miley, while those in operation could use pressurized tents to prevent outside gas from contaminating their project.
Though the Coherent Germanium Neutrino Technology (CoGeNT) experiment, which sits in the Soudan mine in Minnesota and seeks to detect low-energy recoils from potential dark matter particles, is effectively isolated underground, team-leader Juan Collar of the University of Chicago isn’t taking any chances. “Let us just say that I am asking the crew at Soudan to make darned sure the gas purging system into our detector does not stop working during this downtime,” he writes in an e-mail. Experiments in Soudan have already suffered one potential difficulty recently, when a fire broke out in an elevator shaft.
Other collaborations are less worried. The Large Underground Xenon (LUX) experiment, which is currently building a 1-ton xenon tank to search for dark matter at DUSEL, has historically had to deal with contamination from another noble gas, krypton, says Richard Gaitskell, a physicist at Brown University in Providence, Rhode Island who leads LUX. Though krypton-85 in the atmosphere only comes from the venting of nuclear reactors, the team has already developed techniques to keep the krypton levels at the very low level of two parts per trillion, he adds. “Even if the krypton-85 levels go up significantly, we have processes to remove it,” he says.
For full coverage of the Fukushima disaster, go to Nature’s news special.
Image: CoGeNT collaboration