Absorption of light by stuff is frequency dependent. At the right frequency, stuff can be almost entirely transparent. Similar to how by detecting infrared lig

Absorption of light by stuff is frequency dependent. At the right frequency, stuff can be almost entirely transparent. Similar to how by detecting infrared light JWST can peer through the dust in galaxies to reveal detail that the couldn't see in optical light using Hubble[1]. Electron-positron annihilation releases photons with an energy of roughly 0.5MeV[2], and as you can see from this graph[3] the absorption is relatively low at those energy levels. Unless I got my math wrong, about 90% of those photons survive traveling through 1 cm of water or fat (which has roughly the same density as water). [1]: https://jwst.nasa.gov/content/about/comparisonWebbVsHubble.html https://jwst.nasa.gov/content/about/comparisonWebbVsHubble.h... [2]: https://en.wikipedia.org/wiki/Electron%E2%80%93positron_annihilation#Low-energy_case https://en.wikipedia.org/wiki/Electron%E2%80%93positron_anni... [3]: https://physics.nist.gov/PhysRefData/XrayMassCoef/ComTab/water.html https://physics.nist.gov/PhysRefData/XrayMassCoef/ComTab/wat...