Team admits a mix-up with one of their neutron detectors.
Eugenie Samuel Reich
Rusi Taleyarkhan with his table-top fusion equipment in a lab at Oak Ridge, Tennessee, where he conducted research before coming to Purdue.
Credit: U.S. Department of Energy file photo/Lynn Freeny
A group of researchers making high-profile claims about fusion energy has admitted to accidentally using equipment different from that reported in their most recent paper.
An erratum providing details of the mistake by Rusi Taleyarkhan of Purdue University and colleagues has been published in Physical Review Letters1. Critics interpret the admission as a sign that the group's fusion claims2 are unravelling, because it comes in the wake of serious questions about the original work's validity (see 'Is bubble fusion simply hot air?').
"Confusing detectors in a discovery of this magnitude is an embarrassing mistake," says Seth Putterman of the University of California, Los Angeles. But Taleyarkhan and colleagues say that their data, analysis and conclusions are not affected by the error.
In January, Taleyarkhan published the most recent of a series of papers in respected journals that claimed to see neutrons characteristic of fusion reactions coming from collapsing bubbles in organic fluids.
If validated, such work could pave the way for cheap, green energy. Taleyarkhan claimed to have deployed three independent methods of detecting these neutrons, one of which was a boron trifluoride gas proportional tube with a polyethylene covering. His erratum notes that this actually turned out to be a lithium iodide crystal scintillation detector, also with a polyethylene covering.
According to the erratum, the error was discovered "upon disassembly of the outer coverings" of the detector and is due to "an oversight which was based on incorrect information from a person's recollection who loaned this apparatus for the study".
Knowing what you're working with
The mistake does not in itself invalidate the experiment's conclusions, but experts say it casts further doubt over the results. Neutron expert Mike Saltmarsh of Oak Ridge National Laboratory in Tennessee, where Taleyarkhan previously worked, points out that doing a good technical job involves knowing what detector is in use.
"If you don't know what you're working with, you can easily make mistakes," says Saltmarsh.
Manuals provided by Ludlum Measurements, which manufactures both types of detector, confirm that different operating voltages and different calibration checks are recommended for the two, for example.
Source of confusion
Brian Naranjo of the University of California, Los Angeles, claimed in March that Taleyarkhan's observed neutrons probably came from a standard lab source rather than fusion reactions3. Naranjo based his study on results from a different detector in Taleyarkhan's setup.
Saltmarsh points out that the data from the lithium iodide detector, as it is now known to be, are consistent with Naranjo's claim. In Taleyarkhan's experiment, the 'boron trifluoride' detector observed high levels of gamma rays (gamma-rays) alongside the neutrons, despite the fact that boron trifluoride detectors are not very sensitive to gamma-rays. Taleyarkhan and his colleagues suggest that neutrons from fusion were interacting with the detector's polyethylene coating to produce a slew of rays.
But the lithium iodide detector is more sensitive to gamma-rays, says Saltmarsh, and the lab source posited by Naranjo could easily have provided enough for the levels observed.
Taleyarkhan's co-author Robert Block, of Rensselaer Polytechnic Institute in New York, disagrees. Block says he and Taleyarkhan still think the observed gamma-rays are produced by fusion neutrons colliding in the polyethylene covering, no matter what the detector.
A university review of Taleyarkhan's work is under way and due to finish by 1 June.
Eugenie Samuel Reich
Rusi Taleyarkhan with his table-top fusion equipment in a lab at Oak Ridge, Tennessee, where he conducted research before coming to Purdue.
Credit: U.S. Department of Energy file photo/Lynn Freeny
A group of researchers making high-profile claims about fusion energy has admitted to accidentally using equipment different from that reported in their most recent paper.
An erratum providing details of the mistake by Rusi Taleyarkhan of Purdue University and colleagues has been published in Physical Review Letters1. Critics interpret the admission as a sign that the group's fusion claims2 are unravelling, because it comes in the wake of serious questions about the original work's validity (see 'Is bubble fusion simply hot air?').
"Confusing detectors in a discovery of this magnitude is an embarrassing mistake," says Seth Putterman of the University of California, Los Angeles. But Taleyarkhan and colleagues say that their data, analysis and conclusions are not affected by the error.
In January, Taleyarkhan published the most recent of a series of papers in respected journals that claimed to see neutrons characteristic of fusion reactions coming from collapsing bubbles in organic fluids.
If validated, such work could pave the way for cheap, green energy. Taleyarkhan claimed to have deployed three independent methods of detecting these neutrons, one of which was a boron trifluoride gas proportional tube with a polyethylene covering. His erratum notes that this actually turned out to be a lithium iodide crystal scintillation detector, also with a polyethylene covering.
According to the erratum, the error was discovered "upon disassembly of the outer coverings" of the detector and is due to "an oversight which was based on incorrect information from a person's recollection who loaned this apparatus for the study".
Knowing what you're working with
The mistake does not in itself invalidate the experiment's conclusions, but experts say it casts further doubt over the results. Neutron expert Mike Saltmarsh of Oak Ridge National Laboratory in Tennessee, where Taleyarkhan previously worked, points out that doing a good technical job involves knowing what detector is in use.
"If you don't know what you're working with, you can easily make mistakes," says Saltmarsh.
Manuals provided by Ludlum Measurements, which manufactures both types of detector, confirm that different operating voltages and different calibration checks are recommended for the two, for example.
Source of confusion
Brian Naranjo of the University of California, Los Angeles, claimed in March that Taleyarkhan's observed neutrons probably came from a standard lab source rather than fusion reactions3. Naranjo based his study on results from a different detector in Taleyarkhan's setup.
Saltmarsh points out that the data from the lithium iodide detector, as it is now known to be, are consistent with Naranjo's claim. In Taleyarkhan's experiment, the 'boron trifluoride' detector observed high levels of gamma rays (gamma-rays) alongside the neutrons, despite the fact that boron trifluoride detectors are not very sensitive to gamma-rays. Taleyarkhan and his colleagues suggest that neutrons from fusion were interacting with the detector's polyethylene coating to produce a slew of rays.
But the lithium iodide detector is more sensitive to gamma-rays, says Saltmarsh, and the lab source posited by Naranjo could easily have provided enough for the levels observed.
Taleyarkhan's co-author Robert Block, of Rensselaer Polytechnic Institute in New York, disagrees. Block says he and Taleyarkhan still think the observed gamma-rays are produced by fusion neutrons colliding in the polyethylene covering, no matter what the detector.
A university review of Taleyarkhan's work is under way and due to finish by 1 June.
