FEATURE
Formation in the Field
| Why are granite slabs stacked incongruously in the middle of an open field four miles from Goddard? Could it be a half-finished monument or simply a storage area for unused construction materials?
Despite its remarkable lack of technological sophistication, the granite formation is actually a test site. Goddard scientist Ann Parsons plans to use it in the coming months to test an instrument she hopes NASA will one day land on the Moon, Mars, Venus, or even the rocky moons of the outer planets to survey the elements found as much as a foot beneath their surfaces — without ever digging or displacing one gram of material.
Her instrument, the Pulsed Neutron Generator-Gamma-Ray and Neutron Detector, combines different technologies to achieve this measurement feat. First, a generator pulses neutrons into a sample area. When the subatomic particles interact with an element’s nucleus, the nucleus becomes excited and emits a gamma ray, which a spectrometer then detects to reveal the identity of the element. The instrument also includes a neutron detector, which is effective for determining surface density and the presence of hydrogen atoms.
|
Ann Parsons (center) and her team pose with the granite formation, Goddard’s newest test site. From left to right: Sam Floyd, Richard Starr, Jack Trombka, Julia Bodnarik, Parsons, Min Namkung, Tim McClanahan, Larry Evans, and Lucy Lim.
|
Ideal for Inventorying Resources
“The nice thing about neutrons is that they go deep into the soil — a meter (nearly three feet) on average,” Parsons said. “To get a full elemental survey, the approach is effective down to about a half meter.” Her instrument also can measure over a relatively broad area — within a meter radius — making it ideal for inventorying resources and determining, for example, the location of potential water beneath the surface, she said. “The ability to make measurements at about 30 to 50 centimeters below the surface without having to drill is a revolutionary capability,” she said.
Parsons and her team, which includes Jack Trombka, a long-time Goddard scientist and recognized expert in gamma-ray instrumentation, has received Goddard Internal Research and Development and Headquarters funding to advance the concept.
Why Granite?
So why the granite placed in the middle of a field several hundred feet away from the road and the nearest building on the grounds of Goddard’s Geophysical and Astronomical Observatory?
It was a matter of necessity, Parsons said. Initially, she tested her instrument concept at a private research facility in New Jersey, but soon discovered that the generated neutrons interacted with “everything,” making the test results difficult to interpret. “The lesson learned from this experience led to the conclusion that the best way to perform these experiments is to have a very large, well-characterized test sample placed outdoors well away from other buildings and people.”
Granite, as it turns out, is ideal for testing the sensitivity of her instrument because it does not contain hydrogen and it does not absorb water like other potential test materials. This characteristic is important because it is hard to control the amount of moisture contained within most materials placed outdoors during a Maryland summer.
Hopes to Fly on Landed Mission
When she begins her tests in the next few weeks, she will place the neutron generator and detectors on top of the granite formation and pulse neutrons into the material. Through this testing, she hopes to advance the flight readiness of her instrument and in the future find a berth on a landed mission to another solar system body.
In the meantime, the granite formation will host other experimenters.
“Now that the facility is getting ready, we’re being asked by groups to test their instruments,” Trombka said. In a few months, the team will test and calibrate the Russian-built Dynamic Albedo of Neutrons instrument, which is flying on the Mars Science Laboratory. The team also could assist in calibrating a version of the Gamma-Ray and Neutron Spectrometer flying on the MESSENGER mission to Mercury.
“It’s going to be an amazingly busy summer,” Parsons said. |
