The MiniBooNE experiment at Fermi National Accelerator Lab (Fermilab) is a search for neutrino oscillations. The goal is to either verify or disprove the results of the Los Alamos neutrino oscillation experiment called liquid scintillator neutrino detector (LSND) that indicated that such oscillations may occur. If they do occur, then neutrinos must have non-zero masses, a far-reaching result not accounted for in the current standard model of particle physics. MiniBooNE will use the 8-GeV protons from the Fermilab booster impinging on a beryllium target to produce pions, which in turn decay, producing, among other things, muon neutrinos.
Immediately downstream of the target is a magnetic focusing "horn," which will focus the pions. Thus, their decay products, the muon neutrinos, will be produced in a narrow cone and directed toward a detector after passing through a decay space designed to allow time for the pions to decay in flight. The focusing horn is, itself, a rather amazing piece of equipment. It will operate at 5 Hz, with each 170-kA pulse lasting for 150 microseconds for a desired lifetime of 100 million pulses. The most advanced horns prior to the MiniBooNE horn ran at 0.8 Hz for only 20 million 300-kA pulses. The horn is designed to maximize neutrino flux from 0.5 GeV to 1 GeV. Without the horn, the neutrino flux at the detector would be reduced by a factor of 10.
Following the decay space, the detector consists primarily of a 250,000 gal., spherical vessel consisting of highly purified mineral oil surrounded by 1550 large photomultiplier tubes that will be used to record events. The experiment has posted an informative and enjoyable MiniBooNE web site.
The focusing horn, as well as other components, will become highly radioactive. Especially because this device is physically large, its handling in the event of its failure is a matter of considerable concern. Procedures have been written to remotely disconnect a defunct horn, put it in a heavily shielded "coffin," and transport it to a safe storage place. Recently, a dry run was conducted, under the supervision of the radiation safety personnel, in which a brand new, unused horn was removed. Thus, this dry run was really a time and motion study used to estimate a total dose for the task. The dry run was very useful in better identifying the different steps involved and some new issues that were missed when the change-out procedure was written.
Full operation of this beamline are imminent as of this writing. Early on April 29, 2002, the Beams Division personnel and MiniBooNE collaborators successfully transported protons down the new 8-GeV beamline. The beam was transported into a temporary absorber placed just upstream of where the MiniBooNE target and horn will sit. This important milestone marks the beginning of the end of a large effort over several years in which the beamline and its enclosure were designed and built. Currently, the experimenters are getting ready for the second phase of commissioning, which is sending an 8-GeV beam, without the horn and target, to the 50-m beam absorber located at the end of the pion decay pipe. This effort, as can well be imagined, has generated a considerable amount of effort of safety analysis and safety review.