POCATELLO — Physicists from the Idaho State University Idaho Accelerator Center and astronomers from the University of New Hampshire Space Science Center collaborated on a project to calibrate and test a prototype of a positron detector which could potentially be launched into space on a future NASA mission.
ISU physics professor Dan Dale explained that ordinary matter contains electrons. Positrons are their antimatter counterparts. Positrons are similar to electrons in that they have the same mass, but they have the opposite charge.
When a positron comes in contact with an electron, the two particles annihilate and turn into pure energy in the form of two or three photons.
Dale said a large amount of antimatter is believed to have existed in the early universe, however, most of it got “gobbled up” early on via these matter-antimatter annihilations. Any positrons detected in space now are likely to have been created in extremely energetic and violent processes. This is why they are of interest to scientists.
UNH Associate Professor James J. Connell, along with Research Associate Cliff Lopate and graduate student Dan Tran, have been working on the device for more than three years. A key motivation for testing the instrument with positrons generated here on Earth is to determine if it will effectively distinguish between positrons and protons in space.
“These studies are absolutely critical to perform before the device can be launched into space,” Dan said.
Connell and his associates traveled to ISU last week to test the device.
“This is the only place that could produce the positrons to test it,” Connell said. “Believe me, we looked for some place closer than Idaho.”
Dale said the accelerator used to produce the positrons for the UNH project was originally built to test detectors used for the U.S. nuclear weapons program.
“Converting this accelerator into a device to be used in fundamental science is kind of satisfying,” Dale said, “Kind of like converting swords into plowshares.”
High-energy electrons are produced inside the accelerator. A strong electric field accelerates electrons through 50 feet of stainless steel vacuum pipes at close to the speed of light. And when the electrons hit a tungsten metal sheet, high energy photons — about 10 million times the energy emitted by a light bulb — are created. These photons convert into pairs of electrons and their antimatter counterparts; the positrons are then directed by magnets through a 6-foot-thick concrete and earth wall, and then into the detector.
Tony Forest, with the ISU Physics Department, said four tons of lead blocks were moved into the Accelerator Center for the experiment. These were needed to shield the positron detector, which Forest described as being about the size of a bread box.
Forest explains that it is very expensive to put things in space, so the size and weight of the device are a critical part of its design.
If the prototype works, Connell said it will help scientists better understand how particles are accelerated in space and what impact that has on events such as solar flares.
“From a practical point of view, understanding the nature of these solar flares is important because these events can disrupt communication systems on Earth,” Connell said. “As a scientist, I see positrons as also providing an extremely important window on what are at present poorly understood phenomena in the universe.”
Connell said positrons do not make it through the Earth’s atmosphere and this will be the first technology capable of monitoring this energy in space.
The success of the project could mean an expansion in research programs for both universities, Connell said.
“The IAC is the only site that can deliver positrons of this energy,” Connell said. “If this works, we will try to contract with NASA to build one capable of going into space.”
Dale and Forest were quick to point out that this project is very much a team effort. The UNH team designed and built the detector. But the engineering team at the Idaho Accelerator Center — Kevin Folkman, Chad O’Neill, and Brian Berles — were crucial to its success, he said.
“In addition, undergraduate physics major Wayne Swigert put in long hours during the set-up phase of the experiment,” Dan said.
The IAC is the result of the Nuclear Science Application Project. This is an effort started by the ISU administration in the late 1980s to develop strength in nuclear-based applied research.
The NSAP was launched in 1988 when the ISU Physics Department established the Particle Beam Laboratory. The operation expanded with the addition of physics faculty and equipment, and the addition of the small accelerator facility in 1992. The organization became a state-approved research center in 1994.
Among the original projects was construction of a state-funded building to provide office and laboratory space for the former DOE Santa Barbara LINAC, a famous accelerator that was used to support nuclear weapons testing.
The IAC building was finished in October 1998 and by 2000 the IAC had about 20,000 square feet of laboratory space. Today the complex has 40,000 square-feet of laboratory and office space, along with 15 acres of open land for field testing.