Alpha track density using a semiconductor detector

Abstract

Determination of the alpha track density in the cellulose nitrate (CN) dielectric version of solid state nuclear track detectors (SSNTD) has traditionally been tedious work which produced results that relied upon the person counting the film as well as the quality control associated with the etching process. Additionally, the constancy of the etch characteristics across an unexposed sample of film has proven to be questionable due to variability in manufacturing processes associated with SSNTD production. In the laboratory setting, when etching conditions are well controlled, the results obtained from etching samples of cellulose nitrate film, with different initial emulsion properties, are variable because the results of etching are dependent upon a number of factors including variation in the initial dielectric thickness, and other undefined parameters. In addition, the resultant radon concentration reading is dependent upon the calibration factor used to interpret the track density reading. Obtaining the etched dielectric thickness electro-optically, as a percent relative transmittance, in one reading that encompassed a major portion of the film area has proven to be efficient and statistically relevant. Such a quantity can be used to standardize the calibration factors used, regardless of the laboratory of origin, for the degree-of-etch as measured by the percent transmittance of the etched film. Therefore, the error in the calibration factor associated with different degrees of etching, or initial CN property differences, can be minimized. The CN from Kodak Path6 is a transparent deep red color. If blue light is projected through it, the intensity of the light exiting the CN is proportional to both the etched CN film thickness, and the number of holes in the film corresponding to the damage produced in the dielectric by alpha particle passage and etching enhancement. A xenon flash lamp was used as the blue light source (467nm) for a CN densitometer, and a cadmium sulfide (CdS) photoconductive semiconductor was used as the detector. The light leaving the film was filtered prior to reaching the detector; thus, the light incident upon the detector was proportional to the average CN thickness of the individual etched CN film sample.