Frequency domain fluorimetry using a mercury vapor lamp

Matthew J. Bohn
2009 Journal of Applied Remote Sensing  
Frequency Domain (FD) fluorimetry, capitalizes on the frequency response function of a fluorophore and offers independence from light scatter and excitation/emission intensity variations in order to extract the sample's fluorescent lifetime. Mercury vapor lamps, a common source of industrial facility lighting, emit radiation that overlaps the UV/blue absorption spectrum of many fluorophores and may be used as an efficient and portable excitation source. The AC power modulation of mercury vapor
more » ... n of mercury vapor lamps modulates the lamp's intensity at 120 Hz (in the United States) and higher harmonics. The fluorescent lifetimes for 3 different materials (willemite, uranium doped glass and U 3 O 8 ) are measured with conventional techniques and compared with the FD technique using the power harmonics from a mercury vapor lamp. The mercury lamp measurements agree to within 25% of the conventional methods. Keywords: frequency domain fluorimetry, phase fluorimetry, remote sensing. INTRODUCTION Remote detection of minerals has been demonstrated using solar reflectance spectroscopy; however, trace quantities from small nuclear spills [1] is an important problem that is impossible to detect using this method. Uranium quickly oxidizes to form uranyl compounds, UO 2 2+ , (the +6 oxidation state of uranium) that fluoresce brightly in the green under blue/ultraviolet radiation. The spectral fluorescence can be a good indicator of the presence of uranium. An additional marker is the tell-tale lifetime of this fluorescence, which is extremely long lived ~ 0.6 milliseconds. UV laser induced fluorescence fluorimetry has been previously demonstrated for uranium prospecting [2] . This method measured both the fluorescence spectrum and the fluorescent lifetime in order to identify the uranium minerals; however, the disadvantage is that it requires high power UV radiation on the target when used for remote sensing. This report details a new method of remote sensing long lived UV-active fluorophores by exploiting ambient mercury vapor lamps that occur at the target sight. Mercury vapor lamps are prevalent throughout the world for parking lots and security lighting surrounding facilities and can provide up to 500 W in the UV/blue spectrum. This research effort explores the use of mercury vapor lamps modulated at facility power in order to determine fluorophore's lifetime using Frequency Domain (FD) fluorimetry as a new method of remote sensing UV-active fluorophores such as uranyl compounds. Clear, or uncoated, mercury vapor lamps emit approximately 50% of their optical output (see Fig. 1 ) in the UV/blue region of the spectrum in emission lines at 365, 405 and 436 nm. Downloaded from SPIE Digital Library on 05 Jan 2010 to 131.84.11.215. Terms of Use: http://spiedl.org/terms Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. Same as Report (SAR) 18. NUMBER OF PAGES 12 19a. NAME OF RESPONSIBLE PERSON a. REPORT unclassified b. ABSTRACT unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98)
doi:10.1117/1.3117448 fatcat:4a773s3o65bdvcowpqg3mat3ny