85Kr测厚源制备及焊接性能分析

为保证⁸⁵Kr测厚源的密封质量，通过⁸⁵Kr测厚源结构设计、焊接工艺参数优化，制备合格的⁸⁵Kr测厚源。铜管与壳体的连接采用真空钎焊工艺，钎焊温度约900 ℃，时间约30 min；源窗与壳体的连接采用电子束焊工艺，焊接电流7 mA，焊接转速13 mm/s；源后盖与壳体的连接采用激光焊工艺，焊接功率180~185 W，焊接速度2 mm/s。测厚源检验结果表明，所制备的85Kr测厚源，氦质谱检漏结果小于1.0×10^-9 Pa·m³·s^-1，放射性气体检验不超过4 kBq/24 h，符合GB/T 15849—1995中“其他射气检验方法”要求。金相实验结果表明，采用优化参数试样的焊缝中未发现明显的裂纹、未焊透、未熔合等缺陷，最大焊接熔深约0.73 mm。

The Preparation and Welding of 85Kr Thickness Gauge Source

In order to ensure the sealing quality of ⁸⁵Kr thickness gauge source, reasonable structural design, appropriate welding process and inspection processes are required. The connection between copper tube and shell is vacuum brazing, and the optimized vacuum brazing parameters are as follows: the temperature is about 900 ℃ and the time is about 30 min; the connection between source window and shell is electron beam welding, the optimized parameters are 7 mA and 13 mm/s for welding through experiment; the connection between source back cover and shell is laser welding, the parameters of laser welding are 180~185 W electric power and 2 mm/s speed. The inspection processes include helium mass spectrometry leak detection, radioactive active and leak method of radioactive gas. The results show that ⁸⁵Kr thickness gauge source has a leak mass detection rate of less than 1.0×10^-9 Pa·m³·s^-1, the radioactive gas inspection was not exceed 4 kBq /24 h, meeting the requirements of other radioactive gas inspection methods in GB/T 15849—1995. Through metallographic test analysis, no obvious welding defects such as crack, incomplete penetration and incomplete fusion were found in the welds with optimized parameters, and the maximum welding depth was about 0.73 mm.