Hope College Department of Physics and Engineering
Research Experiences for Undergraduates
Summer 2001
Project Summary

Project Title: Optically Stimulated Luminescence Dating at Hope College
Student Name: Matthew J. Goupell
Studentís Home Institution: Hope College
Research Advisor: Dr. Paul DeYoung
Source of Support: NSF-RUI

Dune sand sediments consist of 90% quartz, 9% feldspar, and 1% other material. Unable to be dated by 14C techniques because of the relatively young age (~1000 yrs), dune sand sediments can be dated by the technique known as Optically Stimulated Luminescence (OSL). This technique is of particular importance to the Hope College Geology Department whom frequently date dune sand sediments with ages of this order of magnitude. A collaborative effort with the Department of Physics and Engineering was enacted to setup the instrumentation of an OSL laboratory to date samples at Hope College. This would be of particular convenience because there are only a few dozen luminescence laboratories around the world. A long-term goal may include dating samples for outside parties.

The mechanism responsible for the luminescence of a sediment sample is negative-ion vacancies in the ionic structure of the sand. Natural radiation from the surrounding area causes the negative-ion vacancies to occur, in which they have the ability to capture electrons from the material. If an electron is trapped in a negative-ion vacancy, it will be released along with visible light of a blue wavelength if exposed to heat or light. However, if the sample is buried during natural geological evolution, the sediment will maintain the number of electrons in negative-ion traps. To summarize, the amount of light released from a sediment sample is proportional to the number of trapped electrons, which is proportional to the amount of radiation received from the surroundings since it was last exposed to sunlight.

Knowing the proportionality between the light emitted and the radiation received, it is possible to calculate the age of the sediment sample since it had last been exposed to sunlight. This is done by the equation:

Age = Paleodose / Annual Dose, (1) where the paleodose is the total radiation received since the sample has been buried and the annual dose is the radiation received per year.

Experimental Procedure
An IR Laser (880 ± 20 nm) illuminates the natural sediment sample. The following luminescence, which is emitted when the trapped electrons return to the ground state, is measured on a Hamamatsu R878 photomultiplier tube (PMT). The infrared wavelengths from the laser are filtered out by a combination of BG3 and BG39 Schott filters. The PMT is connected to an integrator and rate counter. This process is repeated with a sample with an added amount of radiation (h ). This radiation is delivered by any b or g source. Another sampleís luminescence is measured after double this amount of radiation (2h ). With three data points, a line can be extrapolated back to the x-intercept on a luminescence versus additive dose plot. The distance from the intercept to the y-axis is the measured paleodose.

To find the annual dose, the second part of the age equation, several techniques can be used. In all the techniques, the abundance of radioactive elements (K, Rb, U, Th) in the sample is found. Therefore, the amount of activity of the elements can be found, which is converted into energy delivered per year. Techniques to find the abundances include neutron activation analysis, a -particle counting pairs technique, luminescence dosimetry, portable g -spectrometer, and

portable g -scintillometer. Although all these methods are valid, the easiest to perform at Hope College is the neutron activation analysis.

Future Work
The present direction of this work is to observe a luminescent signal with our equipment and determine whether an age can be resolved from it. If so, a comparison between the age of a predated sample from the Geology Department and our dating technique will be performed.

Slide show of Matthew Goupell's work
___________________________________________________________________________________________________________________________________________________________ Publications and Presentations:
“Alpha particle emission from 6He+209Bi.” D. Lizcano. E.F. Aguilera, E. Martinez-Quiroz, J.J. Kolata, V. Guimaraes, D. Peterson, P. Santi, R. White Stevens, P.A. DeYoung, G.F. Peaslee, M. Goupell*, B. Hughey*, A. Nowlin*, F.D. Becchetti, T. O’Donnell, M.Y. Lee, and F. M. Nunez. Rev. Mex. Fis. 46, Supl. 1, 116-120 (2000). XXIII Oaxtepec Symposium on Nuclear Physics, Oaxtepec. Mor. Mex. Jan. 10-13, 2000.
“Alpha particle emission from 6He+209Bi.” D. Lizcano, E.F. Aguilera, E. Martinez-Quiroz, J.J. Kolata, V. Guimaraes, D. Peterson, P. Santi, R. White Stevens, P.A. DeYoung, G.F. Peaslee, M. Goupell*, B. Hughey*, A. Nowlin*, F.D. Becchetti, T. O’Donnell, M.Y. Lee, and F.M. Nunez. Rev. Mex. Fis. 46, Supl. 1, 116-120 (2000).
“Transfer/Breakup Modes in the 6He+209Bi Reaction Near and Below the Coulomb Barrier.” E.F. Aguilera, J.J. Kolata, F.M. Nunes, F.D. Becchetti, P.A. DeYoung, M. Goupell*, V. Guimaraes, B. Hughey*, M.Y. Lee, D. Lizcano, E. Martinez-Quiroz, A. Nowlin*, T.O. O’Donnell, G.F. Peaslee, D. Peterson, P. Santi, and R. White-Stevens. Phys. Rev. Lett. 84, 5058 (2000).
“ Evidence of Non-Equilbrium Proton Emission in a Low-Energy Heavy-Ion Reaction.” P.A. DeYoung, M.J. Goupell*, B.V. Atallah*, J.A. Haglund*, P.L. Jovivette, M.K. MacDermaid*, G.F. Peaslee, J.J. Kolata, E.D. Bereners, D. Peterson, J. vonSchwarzenbert, and J.D. Hinnefeld. Phys.Rev. C 61, 024603 (2000).
“Transfer and Breakup in the 6He+209Bi Reaction.” J.J. Kolata, V. Guimaraes, D. Peterson, R. White-Stevens, E.F. Aguilera, E. Martinez-Quiroz, D. Lizcano, P.A. DeYoung, G.F. Peaslee, M. Goupell*, B. Hughey*, A. Nowlin*, F.D. Becchetti, T. O’Donnell, and M.Y. Lee. Paper IC.03. Division of Nuclear Physics meeting. Pacific Grove, CA, October 20-23 1999.
“Angular Dependence of Light charged Particle Correlations.” M Goupell*, P.A. DeYoung, G.F. Peaslee, and P.L. Jolivette. 1998 Division of Nuclear Physics student poster session, Santa Fe, NM.