Domen Steve R
National Bureau of Standards, Washington, D.C. 20234.
J Res Natl Bur Stand (1977). 1982 May-Jun;87(3):211-235. doi: 10.6028/jres.087.016.
Two calibrated thermistors sandwiched between two insulative polyethylene films were immersed in a 30 cm cube of water having a low thermal diffusivity. The product of the specific heat of water and temperature rise gave the combined effect of the local absorbed dose and any heat defect at a position along a temperature profile produced by cobalt-60 irradiation. The dose rate was near 18 mGy/s and exposure times were 3 min. The standard deviation for a daily set of measurements was about 0.6 percent. Calculations showed that conductive heat transfer produced a negligible effect at the position of measurement along the beam axis. Tests showed the absence of convection. Temperature drifts before irradiation were quickly controlled by changing the power dissipated in the water between two immersed electrodes. Reproducible measurements were obtained in distilled water supplies that had a wide range of impurities. Measurements, after saturating the water with nitrogen or oxygen, showed no difference. A difference of 0.6 percent would have been easily detectable. Tests with several chemicals added to water showed some unexpected results and changes in the measured absorbed dose rate versus accumulated dose. The measured absorbed dose rate in distilled water under the conditions described was 3.5 percent higher than that determined from measurements with a graphite calorimeter.
将夹在两片绝缘聚乙烯薄膜之间的两个校准热敏电阻浸入一个热扩散率较低的30厘米见方的水中。水的比热容与温度上升的乘积给出了钴-60辐照产生的温度分布曲线上某一位置处局部吸收剂量和任何热缺陷的综合效应。剂量率接近18 mGy/s，照射时间为3分钟。每日一组测量的标准偏差约为0.6%。计算表明，在沿束轴的测量位置处，传导热传递产生的影响可忽略不计。测试表明不存在对流。通过改变两个浸入电极之间水中耗散的功率，可快速控制辐照前的温度漂移。在含有各种杂质的蒸馏水供应中获得了可重复的测量结果。用水饱和氮气或氧气后进行测量，结果没有差异。0.6%的差异很容易被检测到。向水中添加几种化学物质进行的测试显示了一些意想不到的结果，以及测量的吸收剂量率与累积剂量的变化。在所述条件下，蒸馏水中测量的吸收剂量率比用石墨量热计测量确定的值高3.5%。
