title: The role of activator concentration and precipitate formation on optical and dosimetric properties of KCl:Eu(2+) storage phosphor detectors.
abstract: OBJECTIVE
  The activator ion (Eu(2+) in KCl:Eu(2+)) plays an important role in the photostimulated luminescence (PSL) mechanism of storage phosphor radiation detectors. In order to design an accurate, effective, and robust detector, it is important to understand how the activator ion concentration affects the structure and, consequently, radiation detection properties of KCl:Eu(2+).
  
  
  METHODS
  Potassium chloride pellets were fabricated with various amounts of europium dopant (0.01-5.0 mol.% Eu(2+)). Clinical radiation doses were given with a 6 MV linear accelerator. Radiation doses larger than 100 Gy were given with a (137)Cs irradiator. Dose response curves, radiation hardness, and temporal signal stability were measured using a laboratory PSL readout system. The crystal structure of the material was studied using x ray diffraction and luminescence spectroscopy.
  
  
  RESULTS
  The most intense PSL signal was from samples with 1.0 mol.% Eu. However, samples with concentrations higher than 0.05 mol.% Eu exhibited significant degradation in PSL intensity for cumulated doses larger than 3000 Gy. Structural and luminescence spectroscopy showed clear evidence of precipitate phases within the KCl lattice, especially for high activator concentrations. Analysis of PL emission spectra showed that interactions between Eu-Vc dipoles and Eu-Vc trimers could explain trends in PSL sensitivity and radiation hardness observations.
  
  
  CONCLUSIONS
  The concentration of the activator ion (Eu(2+)) significantly affects radiation detection properties of the storage phosphor KCl:Eu(2+). An activator concentration between 0.01 and 0.05 mol.% Eu in KCl:Eu(2+) storage phosphor detectors is recommended for linear dose response, good PSL sensitivity, predictable temporal stability, and high reusability for megavoltage radiation detection.
authors.affiliation: Department of Radiation Oncology, Washington University School of Medicine, 4921 Parkview Place, Campus Box 8224, St. Louis, Missouri 63110, USA.
authors.forename: Rachael A
authors.initials: RA
authors.lastname: Hansel
authors.forename: Zhiyan
authors.initials: Z
authors.lastname: Xiao
authors.forename: Yanle
authors.initials: Y
authors.lastname: Hu
authors.forename: Olga
authors.initials: O
authors.lastname: Green
authors.forename: Deshan
authors.initials: D
authors.lastname: Yang
authors.forename: H
authors.initials: H
authors.lastname: Harold Li
mesh_terms: D011232:Chemical Precipitation; D005063:Europium / Q000737:chemistry*; D008163:Luminescent Measurements; D055620:Optical Phenomena; D011189:Potassium Chloride / Q000737:chemistry*; D011874:Radiometry / Q000379:methods*; D013997:Time Factors; D014961:X-Ray Diffraction
chemical_list: D005063:Europium; D011189:Potassium Chloride