Measurements of the neutron dose near a 15 Mv medical linear accelerator

Abstract

In this work, simplified recombination methods for routine estimation of dose equivalent in mixed (gamma and neutrons) radiation field outside the irradiation field of linear medical accelerators is considered. The author's earlier reported method of H(10) measurements, involving determination of the recombination index of radiation quality, Q(4) by tissue-equivalent recombination chamber was combined with the new method for determination of the photon to neutron dose ratio D(X)/D(n) from the ratio of ion collection efficiencies measured in the investigated radiation field and in two reference fields of gamma and neutron radiations. The method is suitable when the neutron contribution to the total absorbed dose, D(n)/D, is >3%.

Fast method of determining the ambient dose equivalent at a depth of 10 mm of gamma-neutron fields based on recombination methods

“…A well-known recombination chamber of the REM-2 type was used in the study ( 1–5 , 7 ) . It is an ambient dose equivalent rate H * (10) detector in fields of unknown composition and a wide energy spectrum of particles.…”

“…direct measurement of the ambient absorbed dose rate described in Equation ( 1 ). ( 1 ) \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*} {D}^{\ast }(10)=\frac{I_S}{A} \end{equation*}\end{document} measurement of the ionisation current I S for voltage approximately equal to saturation U S with consideration of calibration coefficient A. Detector typically is calibrated in 137 Cs or 60 Co γ radiation source under saturation conditions; …”

“…In the context of radiation protection and biomedical engineering, gamma-neutron fields are the most common fields. Amongst the measurement methods of mixed radiation fields, a number of algorithms based on the initial gas recombination in the ionisation chamber can be distinguished ( 1 , 2 ) . Detectors that use the phenomenon of initial recombination in gases are linear energy transfer-dependent detectors, called recombination chambers.…”

Investigation of photoneutron contamination from the 18-MV photon beam in a medical linear accelerator

“…The threshold-energy values of a photoneutron production for Pb and W are 6.19 MeV and 6.17 MeV, respectively, while the respective values for Fe and Cu are 7.65 MeV and 9.91 MeV. [4][5][6][7][8] The probability of photonuclear reactions increases with the photon energy. Due to the fact that its maximum value in the radiotherapy was found to be 13-18 MeV, it can easily interact with a linac head including Pb, W, Fe and Cu.…”

On the role of LET-dependent parameters in the determination of the absorbed dose by in-phantom recombination chambers

“…Such an approach can be especially important in the case of in-phantom ionization chambers, which are mainly used to take measurements where the precise determination of the absorbed dose is required, e.g. in terms of beam dosimetry [30], dosimetric measurements at medical and research facilities [31,32], or for radiobiological studies [33].…”