  Most PoW blockchain protocols operate with a simple mechanism whereby a
threshold is set for each block and miners generate block hashes until one of
those values falls below the threshold. Although largely effective, this
mechanism produces blocks at a highly variable rate and also leaves a
blockchain susceptible to chain death, i.e. abandonment in the event that the
threshold is set too high to attract any miners. A recent innovation called
real-time block rate targeting, or RTT, fixes these problems by reducing the
target throughout the mining interval. RTT exhibits much less variable block
times and even features the ability to fully adjust the target after each
block. However, as we show in this paper, RTT also suffers from a critical
vulnerability whereby miners deviate form the protocol to increase their
profits. We introduce the Radium protocol, which mitigates this vulnerability
in RTT while retaining lower variance block times, responsive target
adjustment, and lowering the risk of chain death. We also show that Radium's
susceptibility to the doublespend attack and orphaned blocks remains similar to
Bitcoin.
