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The sandbox and the moon Experimenters are certainly inventive. Give them a sandbox and pretty soon they want the moon. A group at DOE's Stanford Linear Accelerator Center (SLAC) has used a sandbox to test a theory about microwave signals from neutrinos that could eventually become an experiment using the moon.
Astronomer Peter Gorham from Cal Tech's Jet Propulsion Lab (JPL) in Pasadena; physicist David Saltzberg from UCLA, graduate student Dawn Williams, and SLAC physicists Al Odian, Clive Fields, Rick Iverson and Dieter Walz have sent a beam of gamma rays into a sandbox. Dipole antennas were buried in the sand and microwave antennas were mounted along one side of the sandbox. They were used to observe and measure signals emitted when the energetic gamma rays (photons) generated electromagnetic cascade showers in a dielectric medium like dry sand. The technique and the results should help in the observation of energetic neutrino showers using the moon as an emitter. Neutrinos are difficult particles to detect. They have a very small mass, no charge and only weak interactions. Like photons, neutrinos travel in fairly straight lines from their source to the point of detection. In addition, the neutrino will go through almost anything, hardly noticing that something is in their way. So to detect and observe neutrinos requires emitters and detectors with lots of material. Enter the moon, nature's own emitter with lots of material. In 1988 a theory was proposed that large antennas used in ground-based radio astronomy should be able to detect radio pulses from neutrinos interacting in the moon's surface layers. Energetic neutrinos in the universe form a steady stream of particles and some of those pass through the moon's mass and a few interact. Those interactions will create a type of radiation known as coherent Cherenkov microwave radiation. If the interaction is close enough to the moon's sandy and dusty surface, then microwave signals might be detectable on earth. All that's needed are some radio telescopes to receive those signals, which could be provided by NASA scientists working at JPL, and of course, the ability to understand the nature of the signals. David Saltzberg was thrilled to test the theory at SLAC. According to the UCLA scientist, it was like building a scale model. "We could not have done this without the help of so many people at SLAC. I am extremely pleased that we could propose an experiment in April and have it completed by August. This result would have been impossible without the incredible precision and stability of the beams at SLAC." SLAC's Final Focus Test Beam is uniquely suitable for this test since the combination of its energy and current creates showers comparable to those expected from very energetic cosmic neutrinos. According to Peter Gorham, "The results of this experiment at SLAC will be hugely important to current efforts to detect ultra-high energy cosmic neutrinos. This remarkably large effect went undetected for almost 40 years." Results will be published in the fall. Submitted by DOE's Stanford Linear Accelerator Center |
