Case for an Improved Effective-Atomic-Number for the Electronic Baggage Scanning Program

Technical Report · Mon Nov 21 00:00:00 EST 2011

DOI:https://doi.org/10.2172/1033743· OSTI ID:1033743

Smith, Jerel A. ^[1]; Kallman, Jeffrey S. ^[1]; Martz Jr., Harry E. ^[1]

---

1. Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Z_eff, a parameter representing an 'effective atomic number' for a material, plays an important role in the Electronic Baggage Scanning Program (EBSP) to detect threats in dual-energy computed tomography (CT) baggage-scanning systems. We believe that Z_eff, as defined and used on this program, does not provide the accurate representation of a material's x-ray absorption properties that is needed by the EBSP. We present the case for a new method that defines an effective atomic number for compounds and mixtures, which we refer to as Z_e. Unlike Z_eff, Z_e is tied by definition to the x-ray absorption properties of each specific material. Use of this alternative will provide a more accurate scale for calibrating Micro-CT and EDS systems against standard reference materials and will provide a more accurate physical characterization of the x-ray properties of materials evaluated on those systems. This document: (1) Describes the current usage of the Z_eff parameter; (2) Details problems entailed in the use of the Z_eff parameter; (3) Proposes a well-defined alternative - Z_e; (4) Proposes and demonstrates an algorithm for optimally associating Z_e with any specified compound or mixture; (5) Discusses issues that can impact the usefulness of an effective-Z model; and (6) Recommends that, in order that the chosen effective-Z parameter not materially impact the accuracy of data produced by the EBSP program, the use of Z_eff be replaced by Z_e.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48; AC52-07NA27344
• OSTI ID: 1033743
• Report Number(s): LLNL--TR-520312
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
ABSORPTION
ACCURACY
ALGORITHMS
ATOMIC NUMBER
CALIBRATION STANDARDS
COMPUTERIZED TOMOGRAPHY
MIXTURES