Conversion and Quality Factors Relating Neutron Fluence and Dosimetric Quantities

High-Accuracy Relative Biological Effectiveness Values Following Low-Dose Thermal Neutron Exposures Support Bimodal Quality Factor Response with Neutron Energy

“…This RBE M value of 15.5 ± 2.2 is also similar to the quality factor of 18.4 ± 0.8 simulated by Ali et al [12] for the current experimental setup. Furthermore, all RBE M values presented here support the bimodal quality factor distribution put forward by Cross and Ing [13] and Stinchcomb and Borak [14] that describes one peak in quality factor within, or nearing, the thermal range and a second peak in the fast-neutron energy range (Figure 1). Cross and Ing's quality factor results were obtained by first-principles calculations for tissue [13], whereas the data trend of Stinchcomb and Borak was acquired using microdosimetry [14].…”

“…Consequently, knowledge and understanding of this bimodal trend of the neutron quality factor and, subsequently, of the RBE means that radiation protection aspects that specifically acknowledge a thermal neutron peak warrant further consideration. [1], CANDU reactor environments [4], and at high altitudes [7] (originally normalized and presented by Ali et al [12]) and the bimodal quality factor distribution presented by Cross and Ing [13].…”

“…Other high-LET particles, such as alpha particles, fission fragments, and heavy nuclei have also been ascribed a w R of 20 [10]. Monte Carlo simulations have indicated that the quality factor for thermal neutrons may be closer to 20 [11,12], and previous first-principles calculations and microdosimetric evaluations have demonstrated that the energy-dependent neutron quality factor follows a bimodal distribution with a peak near the thermal-neutron energy range and another in the fast-neutron energy range [13,14] (Figure 1). To investigate the discrepancy between the ICRP radiation weighting factor, w R and the reported quality factors, we experimentally evaluated the relative biological effectiveness (RBE) of low-dose, low-energy thermal neutrons in human peripheral blood lymphocytes.…”

“…As a result, RBE and w R values are similar but not necessarily equal. [10], and smoothed quality factor distributions calculated by Cross and Ing (blue dotted line) [13] and by Stinchcomb and Borak (blue solid line) [14], and thermal neutron quality factors calculated by Schuhmacher and Seibert (blue square) [11] and Ali et al (blue circle) [12].…”

Quality Factors

“…A major objection to the use of maximum values in neutron protection is that they are nonadditive when applied to a broad spectrum of neutron energies (Cross and Ing 1985) and therefore overestimate the dose equivalent at any depth in the body. For neutron energies between 100 keV and 15 MeV, the maximum dose equivalent occurs within 1 cm of the body surface (on the beam side), but for other neutron energies, it occurs deeper within the body (i.e., 3-5 cm for neutron energies less than 100 keV).…”