A radioactive source is used to bombard the rocks surrounding the wellbore with gamma rays. By counting the backscattered gamma rays, the density of the subsurface rock can be computed.

利用放射性源的伽马射线轰击井眼周围的岩石，通过对反散射伽马射线计数，可以计算出地下岩石的密度。

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Interestingly, an April 18 paper in the journal Nature reported that upper limits for neutrinos measured from IceCube are low enough that gamma-ray bursts are unlikely to be the sole source of ultra-high energy cosmic rays.

CNN: Why gamma-ray burst shocked scientists