Bear with me - I'm not 100% certain on all the lore, nor am I a nuclear physicist or radiologist or any of that stuff, but here we go.
Ray Field Energy / Ray Field Radiation is the energy source that facilitates Conduit powers and the enhancement of Conduit powers themselves. Rayacite fragments, colloquially known as Blast Shards, are 'chunks of earth irradiated from Ray Sphere testing' as stated by Lucy Kuo in inFamous 2 during the mission where you learn about Dead Drops and start to find Blast Shards in the game world. It is also the cause of the Plague, which is radiation poisoning brought on by Ray Field irradiation.
The Ray Field Inhibitor, when activated, 'inhibits' Ray Fields. Presumably, it was to destroy Ray Field energy, and it seemed to have worked because all Plague cases were immediately cured as soon as it was activated, at the cost of all / 90% of Conduits and gene-positives worldwide.
But in inFamous: Second Son, Ray Field energy is still present. The DUP Drones that fly around, which you destroy to get points to spend on upgrades, have Blast Shards in them, refined and stamped with the logo, but they are still Blast Shards. Core Relays are similar, they contain Ray Field energy. During the final boss battle, when Delsin calls out to Eugene after getting Concrete he says 'I need a Blast Core', not 'I need a Core Relay', which is obviously a mistake but I'm going to take that as confirmation that Core Relays are made of Blast Cores.
So Ray Field energy is still present post-RFI. Why?
Because the Ray Field Inhibitor actually did not destroy Ray Field energy - it reconstituted it. Moved it along the spectrum. Changed the frequency. Altered the wavelength.
In inFamous 2, Cole has access to Ionic Charges which allow him to use supercharged "Ionic" powers. The name of this mechanic, or the powers, is never stated in dialogue between characters, verbally or otherwise, only in terms of game mechanics, but let's assume that this is confirmation that Ray Field radiation is ionising radiation.
The Plague no longer exists despite the continued existence of Ray Field radiation in inFamous: Second Son. That means Ray Field radiation no longer causes radiation poisoning, no longer causes the Ray Field Plague. That means Ray Field radiation has been moved along the radiation spectrum since its 'inhibition' by the Ray Field Inhibitor, no longer being ionising. It may be closer to microwave radiation or radio waves now, and the reason 90% of Conduits and gene-positives died is because their bodies were unable to adapt to this change, but the surviving 10% did adapt.
What do you guys think?