oa The Application of Experimental Microdosimetry to Mixed-Field Neutron-Gamma Dosimetry

Absorbed Dose Distributions In Lineal Energy For Neutrons And Gamma Rays Were Measured Using Both A Tissue-Equivalent Walled Counter (Tepc) And A Graphite-Walled Low Pressure Proportional Counter (Gpc) In The Am-Be Neutron Source Facility At Uoit. A Series Of Measurements Were Performed With The Counters Filled With Propane-Based Te Gas (55.1% C3H8, 39.5% Co2 And 5.4% N2) At Operating Gas Pressures Corresponding To Tissue Spheres 2.0 , 4.0 And 8.0 ?m In Diameter. The Results Of These Measurements Indicated Satisfactory Performance Of The Counters To Measure Microdosimetric Spectra Extending Down To Event-Sizes That Cover The Gamma Component Of A Mixed Field. An Assessment Of The Performance Of Different Size Tepc Has Been Done And Excellent Agreement Between Their Event Size Spectra Was Found With Differences In The Microdosimetric Parameters Yf And Yd Not Exceeding 3%, Which Is In The Region Of Counting Statistics. To Separate Neutron Dose From Gamma Dose A Simple Lineal Energy Threshold Technique Has Been Used In Addition To More Sophisticated Methods Using G-Fitting And Graphite-Walled Counter Measurements. The Results Of This Study Showed That The Absorbed Dose Gamma Fraction Of The Am-Be Source Was 34.5% As Determined By Gamma Fitting And Dual Chamber Methods. The Simple Threshold Technique Gave A Value Of The Gamma Fraction Of 48% Which Is Acceptable For Radiation Protection Monitoring, However, For Radiation Biology And Neutron Metrology The More Sophisticated Methods Of Determining The Gamma Fraction Of The Total Dose Should Be Used.