Presented by Dr. Amir H. Mohagheghi. Annual RMCC Workshop Middle East Scientific Institute for Security (MESIS) Amman, Jordan June 17-19, 2013

Transcription

1 Neutron Activation Analysis and Dosimetry based on reports by R. Burrows, A. Mohagheghi, and D. Ward: Personnel Nuclear Accident Dosimetry at Sandia National Laboratories SAND , SAND Presented by Dr. Amir H. Mohagheghi Annual RMCC Workshop Middle East Scientific Institute for Security (MESIS) Amman, Jordan June 17-19, 2013 S andia is a multiprogram laboratory operated by S andia Corporation, a Lockheed Martin Company, for the United States Department of Energy s National Nuclear S ecurity Administration under contract DE -AC04-94AL Presentation Outline Review of Basic Concepts neutron discovery interaction modes activation analysis neutron dosimetry Sandia Personnel Neutron Dosimeter Nuclear Accident Dosimeter Intercomparison Exercises 2

2 Review: Neutron Discovery 1920: Rutherford conceived the possible existence of the neutron 1920s: Model of the atomic nucleus as composed of protons and electrons development of quantum mechanics 1930: Ambartsumian and Ivanenko found that the nucleus cannot consist of protons and electrons a neutral particle must be present 1931: Bothe and Becker found that energetic alpha particles fell on certain light elements, an unusually penetrating radiation was produced gamma? 1932: Curie and Joliot showed that if this unknown radiation fell on paraffin, it ejected protons of very high energy 1932: Chadwick showed that the gamma ray hypothesis was untenable and suggested that the new radiation consisted of uncharged particles of approximately the mass of the proton Source: 3 Review: Interaction Modes Elastic and Inelastic Scattering - most common for fast neutrons Radiative capture with gamma emission (neutron activation) - most common for slow neutrons. Example: Co-59 + n Co-60 + γ Capture with charged particle emissions: (n,p), (n,d), (n, ), Fission 4

3 Review: Activation Analysis 5 Review: Activation Analysis - Example 6

4 Review: Neutron Dosimetry Dose is proportional to energy deposited in the body by radiation Target atoms: H, O, C, N, Na, Cl Interaction type and probability depend on neutron energy: 7 Presentation Outline Review of Basic Concepts neutron discovery interaction modes activation analysis neutron dosimetry Sandia Personnel Neutron Dosimeter (PNAD) Objectives Nuclear Accident Dosimeter Intercomparison Exercises 8

5 Determine Neutron Spectrum 9 Layout of the SNL PNAD 10

6 PNAD Elements Data 11 Determine Neutron Fluence 12

7 Absorbed Dose Neutron Dose = Neutron Fluence * Conversion Factor 13 Example Calculation: Activity Measurement Using a HPGe Detector 14

8 Example Calculation: Neutron Dose From table A-1, Spectrum #16 was selected as the best estimate of the incident neutron spectrum: Spectrum-weighted cross-section for In: 0.12 barns Fluence to dose conversion factor: 2.29 nrad/(n/cm 2 ) Reference Dose = 108 rad 15 Presentation Outline Review of Basic Concepts neutron discovery interaction modes activation analysis neutron dosimetry Sandia Personal Neutron Dosimeter Nuclear Accident Dosimeter Intercomparison Exercises 16

9 Los Alamos Neutron Accident Dosimetry Exercise 1996 Summary Performance Results 17 Los Alamos Neutron Accident Dosimetry Exercise Detailed Results for a Single Test 18

10 PNAD Quick Scan Procedure 19 PNAD Quick Scan Procedure: Example Measurement The PNAD was located on a 20 cm X 20 cm X 10 cm Lucite phantom and was exposed to a Godiva spectrum which passed through 20 cm of concrete. 20

11 CALIBAN Neutron Accident Dosimetry Exercise 2010 Example of Performance Results 21 References Turner, Atoms, Radiation, and Radiation Protection, Wiley. Evans, The Atomic Nucleus, McGraw Hill. Knoll, Radiation Detection and Measurement, Wiley. Brophy, Basic Electronics for Scientists, McGraw Hill. Martin, Physics for Radiation Protection, Wiley. Useful Web Sites: National Nuclear Database: Radionuclide Decay Data: 22

12 Thank you for your time شكرا 23