Characterization of the new free-air primary standard for medium-energy X-rays at CMI

TL;DR

This paper describes the development and characterization of a new free-air ionization chamber as a primary standard for medium-energy X-ray air kerma measurements, aiming to improve accuracy and reduce uncertainties.

Contribution

It presents the design, manufacturing, and initial performance evaluation of a new primary standard ionization chamber for medium-energy X-rays, including correction factors and uncertainty analysis.

Findings

Successful design and implementation of the FAC

Measured correction factors with uncertainty estimates

Preliminary performance tests confirm suitability

Abstract

In 2011 a decision was made by Czech Metrology Institute to build a free-air ionization chamber (FAC) intended to be used as a primary standard of air kerma rate for medium-energy X-rays (photon energy from 40 to 300 keV, including mammography X-ray qualities) in order to replace currently used secondary ionization chamber and to decrease the uncertainty of air kerma reference value. In period of 2013-2017, the FAC has been designed, manufactured and put into operation. Correction factors were measured or calculated by a Monte Carlo method. FAC performance was preliminary tested using a calibrated secondary chamber. Physical characteristics of the FAC are described and a summary of the correction factors with the uncertainty budget is presented.