{"id":1127,"date":"2020-03-12T11:05:54","date_gmt":"2020-03-12T15:05:57","guid":{"rendered":"http:\/\/www.nuclearphysicslab.com\/npl\/?page_id=1127"},"modified":"2020-03-20T18:46:27","modified_gmt":"2020-03-20T22:46:27","slug":"nas-mystery","status":"publish","type":"page","link":"http:\/\/www.nuclearphysicslab.com\/npl\/npl-home\/spectroscopy\/gamma-ray-spectroscopy\/nas-mystery\/","title":{"rendered":"NAS Wildwood Mystery"},"content":{"rendered":"\n

Author: Tim<\/em><\/p>\n\n\n\n

\"\"<\/a>
The museum at NAS Wildwood – a must see!<\/figcaption><\/figure>\n\n\n\n

During a trip to Cape May NJ , my family toured the Naval Air Station Wildwood Aviation museum for an afternoon. It is a climb-in, hands-on, bump-your-head-on kind of place. My father-in-law and I climbed into a Vietnam era aircraft loaded with authentic radium bearing meters and dials. To demonstrate the large gamma field that I could almost smell the ozone from, I went back to the truck to retrieve my Ludlum model 19 micro-R meter. As I walked backing into the museum a with the radiation meter something else in the hangar diverted my attention! The micro-R meter quickly escorted me to a jet engine some twenty feet away. Maximum gamma activity was on the order of 5 mr\/hr on contact. None of the museum staff knew the engine was radioactive or what in it might be. I promised I would return with my portable HPGe gamma ray spectrometer to get to solve this mystery.<\/p>\n\n\n\n

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An engine on display.<\/figcaption><\/figure>\n\n\n\n

It took a year, but I did return. Leading up to the return visit required several days of planning, gathering the detector and necessary supporting electronics, and a full 30 liter Dewar of liquid nitrogen. I forgot the extension cord!<\/p>\n\n\n\n

About a foot away the filed was still about 1\/2 mr\/hr.<\/p>\n\n\n\n

\"\"<\/a>
Demonstrating the gamma field around the engine.<\/figcaption><\/figure>\n\n\n\n

In the elapsed year between visits, the museum rearraged their collection and the original engine was gone! But now two new ones that were radioactive had showed up.<\/p>\n\n\n\n

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The portable HPGe setup ready to acquire the spectra.<\/figcaption><\/figure>\n\n\n\n

I cannot tell you what type of engines these are as there were no identifying marks on the first engine. With the High Purity Germanium (HPGe) detector, however, I can now identify the radioactive material the engines are is composed of. Two 600-second live-time counts were run. The detector was first set near to the engine to gather its spectrum and then removed to acquire a background count, and finally a third count with three known standard sources for calibration.<\/p>\n\n\n\n

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Due to the high count rate, had to back the portable away from the engine.<\/figcaption><\/figure>\n\n\n\n

Analysis of the data revealed several dominating gamma ray lines, the most prominent at 238.62, 338.35, 583.25, and 969.04 keV. These match the software’s Thorium-232 spectrum library. The relative counts between the measured lines of 911 and 969 keV peaks are also consistent with Thorium. The Th-232 decay chain the Ac-228 decays into Th-228 with the two gamma rays of relative branching ratio at 64% which perfectly matches the measured to be 64%.<\/p>\n\n\n\n

\"\"<\/a>
The first spectrum.<\/figcaption><\/figure>\n\n\n\n

Next, I moved to the second radioactive engine. Here, I took just one ten minute count. This engine was marked as a Cobra helicopter jet engine. The collected spectrum was identical to the first engine, clearly the unknown radioactive material is common to the construction of various jet engines.<\/p>\n\n\n\n

\"\"<\/a>
Gathering the spectra from the second engine.<\/figcaption><\/figure>\n\n\n\n
\"\"<\/a>
Gathering the spectra from the second engine.<\/figcaption><\/figure>\n\n\n\n

In doing a little bit of on-line homework, I found that these engines use an a high temperature and high strength alloy called MagThor \u2013 and the Thor is in fact thorium, which is the source of the detectable radiation.<\/p>\n\n\n\n

\"\"<\/a>
Spectra of MagThor (magnesium thorium alloy).<\/figcaption><\/figure>\n","protected":false},"excerpt":{"rendered":"

Author: Tim During a trip to Cape May NJ , my family toured the Naval Air Station Wildwood Aviation museum for an afternoon. It is a climb-in, hands-on, bump-your-head-on kind of place. My father-in-law and I climbed into a Vietnam era aircraft loaded with authentic radium bearing meters and dials. To demonstrate the large…<\/p>\n

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