National Aeronautics and Space Administration
shuttle accident investigation.
Scott Lassell, manager of nuclear services in the department, used N.C. State's
PULSTAR nuclear reactor
to conduct neutron activation analysis on 20 samples of reinforced carbon composite from the leading edge of the shuttle's left wing.
NASA investigators speculate that a hole or fissure in the left wing allowed hot gas to enter the wing, ultimately leading to the shuttle's breakup.
NASA officials contracted to have the analysis performed by N.C. State because the pieces have no physically distinguishable marks that would reveal their location on the wing's edge.
The analysis consists of exposing the samples to radiation, allowing time for radioactive decay and then measuring the gamma rays emitted by the samples, Lassell said.
Measuring those gamma rays provides clues to the elements inside the samples -- europium, for example -- which might shed light on the particular piece's manufacturing carbon fiber material lot, or the source of each particular piece.
NASA investigators know the locations of certain pieces from certain manufacturing lots. But they can't readily identify the source of all the pieces. If pieces of unknown origin have, for example, higher traces of a certain element, they may be part of the same manufacturing lot.
Figuring out which manufacturing lot a particular piece comes from might in turn reveal the piece's original location on the leading edge of the left wing.
Lassell and the N.C. State nuclear reactor program will continue working with NASA on another analysis on the shuttle samples later this summer.
Although the first analysis identifies elements present in each composite sample, Lassell said the subsequent analysis will entail extracting carbon fibers from the samples and determining relative concentrations of elements.
Reinforced carbon composite, according to Lassell, is a number of layers of carbon fibers woven together like a mat, separated by carbon dust. The ultra-hard surface can tolerate extremely high temperatures. It wraps around the edges of space shuttle wings to provide protection againstthe infernolike re-entry into the earth's atmosphere.
A breach of reinforced carbon composite on the leading edge of the left wing -- possibly caused by the impact of protective foam that fell off the exterior of a booster rocket 81 seconds after takeoff --allowed the extreme heat from re-entry to essentially melt the wing.
This is not the first time neutron activation analysis has been used to solve a forensic puzzle at N.C. State's nuclear reactor. Lassell has utilized the technique in a handful of criminal cases to ascertain the presence or lack of certain trace elements like arsenic and has testified during criminaltrials to report his findings.
N.C. State's nuclear reactor is one of a handful working reactors in the nation. A pioneer in nuclear research, N.C. State began operating the first reactor to be used for teaching, research and service to the public in 1953.
The current PULSTAR reactor became operational in 1972.
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