Monte Carlo simulation of Cherenkov light generated by underwater Co-60 source
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摘要: 随着核应用领域的不断拓宽，放射源丢失事故发生的概率也随之增加。机载伽马谱仪可有效搜寻地面放射源，然而对于放射源丢失于水域的情况，由于伽马射线经由水层屏蔽后可探测性降低，故利用放射源在水中产生的切伦科夫辐射对其进行搜寻显得十分重要。采用MCNP与Geant4相结合的方法，以及在Geant4程序中采用接续计算技巧，对Co-60源在水中的切伦科夫光产生以及传输进行了计算，计算表明，切伦科夫光经水中传播后，主要波段在300~600 nm，强度呈由边缘到中心渐强的特征分布，分布范围大致与放射源在水中的深度一致，在水中传输300 m后其光通量约为100 cm-2，可利用光谱特征和强度分布特征对其进行测量。
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关键词:
- 放射源丢失 /
- 切伦科夫辐射 /
- MCNP耦合Geant4计算 /
- Geant4接续计算 /
- 光学测量
Abstract: With wide application of nuclear techniques, accidents of lost radioactive sources increase. The airborne gamma spectrometer can be used for searching the lost radiation sources on the ground level. However, for radioactive sources lost in water, the use of gamma spectrometer is limited as a result of the shielding of gamma rays by water. So detection of underwater radioactive source based on Cherenkov light generated by the radioactive source is becoming important. With applications of combined simulation of Geant4 and MCNP, and continuation simulation method in Geant4, distributions and transmission of Cherenkov light generated by underwater Co-60 sealed source were simulated. The simulation reveals that wavelength of Cherenkov light is between 300~600 nm through transmission in water. The light intensity becomes stronger from the edge to the center, and the distribution range approximately equals to the depth of the radioactive source in water. The light flux is about 100 Cherenkov photons·cm-2 after 300 m transmission in water. The Cherenkov light can be detected by the characteristics of its wavelength spectrum and intensity distribution. -
图 3 Co-60在水中产生切伦科夫光通量分布
Figure 3. Flux distribution of Cherenkov light from Co-60 source
图 4 切伦科夫光在水中传播不同距离后光通量分布
Figure 4. Distributions of Cherenkov light flux after transmission through different distances in water
图 5 点源模型衰减计算与Geant4衰减计算光通量比较
Figure 5. Absorption simulation with Geant4 and point source assumption
图 6 衰减不同距离后切伦科夫光光谱变化
Figure 6. Variation of wavelength spectra of Cherenkov light through transmission in water
表 1 Co-60外壳表面伽马、电子源强
Table 1. Source intensity of gamma radiation and electrons
position gamma radiation
/(particles·s-1)electrons
/(particles·s-1)tube surface 1.358 4×1014 1.116 1×1012 top surface 6.822 4×1012 5.741 7×1010 bottom surface 2.126 1×1013 1.748 1×1011 
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