Hudson Lawrence T, Glover Jack L, Minniti Ronaldo
National Institute of Standards and Technology, Gaithersburg, MD 20899.
J Res Natl Inst Stand Technol. 2014 Nov 6;119:540-53. doi: 10.6028/jres.119.021. eCollection 2014.
In recent times, ionizing radiation has been used around the world to screen persons for non-medical purposes, namely to detect bulk explosives or other contraband hidden on the body including materials not registered by metal detectors. In contrast to conventional transmission or projection imaging, backscatter and forward-scatter systems employ a "flying spot" of x rays and large-area detectors. A small spot is rastered across an individual and the Compton scatter signal collected by these detectors is quickly integrated and assigned to a pixel value in an image corresponding to the transient location of the small flying spot. These systems have been controversial due in part to possible radiation health risks, and lack of independent and accurate measurements of radiation exposures to the subjects, bystanders, and operators of such systems. In this paper we will outline the techniques and instrumentation used at the National Institute of Standards and Technology (NIST) to accurately determine the incident air kerma from a swept beam of x rays. We discuss in detail the response of a large-area free-air ionization chamber under the unusual temporal and spatial radiation fields delivered by commercial scanning systems and report typical values for air kerma levels as well as estimates of air kerma rates.
近年来，电离辐射在全球范围内被用于非医疗目的的人员筛查，即检测隐藏在身体上的大量爆炸物或其他违禁品，包括金属探测器无法检测到的物品。与传统的透射或投影成像不同，背散射和前散射系统采用X射线“飞点”和大面积探测器。一个小光斑在人体上进行光栅扫描，这些探测器收集到的康普顿散射信号会迅速积分，并分配给与小飞点瞬时位置相对应的图像中的像素值。这些系统一直存在争议，部分原因是可能存在辐射健康风险，而且缺乏对此类系统的受试者、旁观者和操作人员所受辐射暴露的独立且准确的测量。在本文中，我们将概述美国国家标准与技术研究院（NIST）所使用的技术和仪器，以精确测定X射线扫描束的入射空气比释动能。我们详细讨论了大面积自由空气电离室在商业扫描系统所产生的异常时空辐射场下的响应，并报告了空气比释动能水平的典型值以及空气比释动能率的估计值。
