Surface effect dosimeters

A new type of dosimeter was developed. The dosimeter which has been designated as a Surface Effect Dosimeter, contains phosphor on one surface for mass thicknesses of two or more mg cm-2. Phosphor content of the surface layer can be varied to about 30 percent by weight of matrix material. Samples of about 2 mg cm-2 thick CaSO4:Dy phosphor matrix material on plastic substrates were compared to standard dosimeters uniformly loaded to 25 weight percent phosphor with a physical thickness of about 85 mg cm-2. The apparent dosimeter evaluated alpha exposures, due to an electroplated 239Pu source, are 20 times larger per unit 137Cs exposure for the surface effect dosimeter as compared to standard dosimeters. Thermoluminescent light attenuation in the standard dosimeter reduces the effective thickness to about one-half of the physical thickness. Thus the 239Pu alpha improvement factor of 20 is mainly attributed to the reduced thickness of the surface effect dosimeter. Beta responses to 147Pm, 133Xe, and 85Kr are pending. Uranium-238 exposures show a 20 percent enhanced response for the surface effect dosimeter as compared to standard thickness dosimeters per unit 137Cs exposure. Improvement in beta exposure response to 133Xe and 85Kr are predicted for the surface effect dosimeter. Cesium-137 photon response of the surface effect dosimeter is about one-fifth of standard dosimeters. This provides minimum detectable doses, MDL, about five times higher than the standard dosimeter. For whole body monitoring, this represents an MDL of about 15 mrem and about 30 mrem for extremity dosimetry with present readout equipment