Campi F, Edwards R A, Ossiri A, Pacenti P, Terrani S
Department of Nuclear Engineering, Polytechnic of Milan, Milano, Italy.
Health Phys. 1998 Aug;75(2):179-82. doi: 10.1097/00004032-199808000-00009.
Tritium is presently used in large quantities in laboratories for technological studies, as fuel for the process of nuclear fusion, and in the manufacture of radio-luminescent items. It is also produced in fission nuclear plants (with a yield of 10(-4) if the fuel is 235U and twice as much if the fuel is 239Pu), particularly in those which use D2O as moderator. The weak energy of beta particles (Emean=5.7 keV) produced by tritium implies that it is only harmful if internalized. In nature tritium in air is mainly present under two different chemical forms: elementary (HT, DT, T2) and oxidized (HTO, DTO, T2O). The latter is extremely more dangerous than the former as far as radioprotection is concerned; for this reason the derived air concentration limit (8 x 10(5) Bq m(-3)) for the gaseous form is 25,000 times higher than the value for the oxidized one. The purpose of the work presented here is to realize an area monitor that is able to discriminate in real time between the two chemical forms. Using the properties of zeolite as an absorber and scintillator, it was possible to construct such a detector. In 1 h the instrument can reveal HTO concentrations 40 times below the derived air concentration. A concentration equal to the derived air concentration can be revealed within the first minute of counting and the performance may be further improved. Moreover, the prototype realized is able to work automatically and continuously for 5 h. The capability of discriminating the oxidized chemical form, the sensitivity, and the possibility of obtaining real time information make this instrument a good monitor in those cases where there is a real risk of tritium air contamination.
目前，氚在实验室中大量用于技术研究、作为核聚变过程的燃料以及用于制造放射性发光物品。它也在裂变核电站中产生（如果燃料是235U，产率为10^(-4)，如果燃料是239Pu，产率则是前者的两倍），特别是在那些使用重水作为慢化剂的核电站。氚产生的β粒子能量较弱（平均能量Emean = 5.7 keV），这意味着只有当它被摄入体内时才具有危害性。在自然界中，空气中的氚主要以两种不同的化学形式存在：单质形式（HT、DT、T2）和氧化形式（HTO、DTO、T2O）。就辐射防护而言，后者比前者极其危险得多；因此，气态形式的导出空气浓度限值（8×10^5 Bq m^(-3)）比氧化形式的值高25000倍。本文所介绍工作的目的是实现一种能够实时区分这两种化学形式的区域监测器。利用沸石作为吸收剂和闪烁体的特性，有可能构建这样一种探测器。该仪器在1小时内能够检测到比导出空气浓度低40倍的HTO浓度。在计数的第一分钟内就能检测到等于导出空气浓度的浓度，并且性能还可以进一步提高。此外，所实现的原型能够自动连续工作5小时。能够区分氧化化学形式、具有灵敏度以及能够获取实时信息，使得该仪器在存在氚空气污染实际风险的情况下成为一种良好的监测器。
