裂变中子照射对小鼠胸腺淋巴细胞亚群的影响 Ⅱ.小鼠经裂变中子照射后胸腺淋巴细胞及亚群的动力学变化

目的：研究小鼠胸腺细胞及其亚群在裂变中子照射后损伤和修复的规律，并与大约相同致死效应的６０Ｃｏγ射线照射后的规律进行比较。方法：测定照后不同时间小鼠胸腺细胞总数和胸腺重量指数，并采用间接免疫荧光法，测定照后不同时间小鼠胸腺淋巴细胞Ｌｙｔ＋２和Ｌ３Ｔ＋４细胞亚群的百分数。结果和结论：裂变中子和６０Ｃｏγ射线照射后小鼠胸腺重量指数均在照后第３天降至最低，而后的恢复速度差不多，但恢复水平前者一直低于后者，３１ｄ时的水平二者无显著差异。两种辐射照射后第３天胸腺细胞数几乎降至为０，随后的恢复中子照射稍逊于γ射线照射，３１ｄ的恢复水平基本一致。小鼠经裂变中子２．３Ｇｙ和６０Ｃｏγ射线４．５Ｇｙ照射后，第１天Ｌｙｔ＋２和Ｌ３Ｔ＋４细胞百分率均下降，水平基本一致。中子照射第３天的Ｌｙｔ＋２和Ｌ３Ｔ＋４细胞百分率降至更低（７０％以下），而γ射线照射的Ｌｙｔ＋２和Ｌ３Ｔ＋４细胞百分率则开始恢复。中子照射后经第７天明显恢复后，又出现第２次下降，３１ｄ仍未恢复至照前水平。γ射线照射后第３１天，Ｌｙｔ＋２细胞已恢复至照前水平，Ｌ３Ｔ＋４细胞则仍低于照前水平。

局部屏蔽对裂变中子照射狗的防护作用 Ⅰ.屏蔽部位对防护效果的影响

狗在受到2Gy 裂变中子照射时,用含硼橡胶屏蔽身体的不同部位,可以减轻其辐射损伤。屏蔽狗的头颈部,可减轻由于中子对口腔粘膜直接损伤作用而产生的大片溃疡。屏蔽腹部可使早期胃肠反应症状消失、早期白细胞水平升高。屏蔽骨盆部或下腹+骨盆部,使受照射动物多数临床症状和外周血像改善,病情减轻最明显,活存率最高。屏蔽腹部、骨盆部及下腹+骨盆部,可使无屏蔽时的重度骨髓型急性放射病减轻为中度骨髓型急性放射病。

局部屏蔽对裂变中子照射狗的防护作用——Ⅱ.照射剂量对防护效果的影响

在使狗产生轻度肠型(3Gy 照射)、极重度骨髓型(3和2.65Gy 照射)和重度骨髓型(2Gy 照射)中子急性放射病的全身照射剂量条件下,使用含硼橡胶屏蔽狗的下腹+骨盆部,均可使病情减轻。3Gy 和2.65Gy 时减轻为重度骨髓型放射病,2Gy 时减轻为中度骨髓型放射病。从屏蔽狗的活存率、临床症状及外周血白细胞数看,剂量低时比剂量高时的屏蔽效果明显。

Insufficient thermalization effects on determining fission-track ages

Fission-Track Dating (FTD) has been developed as a useful technique for geological studies. Parent elements are measured by counting 235 U tracks induced by thermal neutrons. If insufficient thermalization occurs, fission of 238 U and 232 Th will be induced, and further measurement error will be introduced. Therefore, whether the neutrons are well thermalized or not will affect the FTD results. Due to requirement of safe operation, the 101 reactor was terminated in 2007. By using the 492 reactor as the new thermal neutron reactor, our present paper will attempt to study the feasibility and the potential influence on FTD. By irradiating monitor glass SRM612 and CN5 in pairs, we will study the thermalization situation of the 492 reactor. Irradiated data show that thermal neutrons are not evenly distributed either in horizontal or in vertical dimension. Especially, horizontal heterogeneity is obvious. But we discovered that proper irradiation position in the reactor can meet the requirement of FTD. Under the current irradiation condition, we calculated and assessed the insufficient thermalization effects on determining fission-track ages. We found that the difference between the 232 Th/ 238 U ratios of samples and standards is the main factor to the experiment results. The results will not be affected if the 232 Th/ 238 U value of samples is equal to the standard samples. However, if the 232 Th/ 238 U ratio is larger than that of the standards, the results will be smaller than actual ages. Comparatively, the ages will be more than expected if the 232 Th/ 238 U ratio is less. Therefore, to reduce the irradiation error, we suggest either locating the position of irradiation strictly, or minimizing the influence of lateral heterogeneity by reducing the amount of each sample package. Additionally, accuracy of the experimental results can be improved by increasing standard samples to adjust ζ value and using the monitor of standard glass SRM612 and CN5 together.