Large Transport
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 1.5
Distraction; Troubleshooting
Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Human Factors; Procedure
The southwest arrival gate was shut-off due to weather.  Their arrivals were routed tower-en-route via PUB..BRK..FQF..KDEN.  This took all the southwest arrivals head-on with all the south departures (as they were coming out via SPAZZ/STAKR/PUB due to weather).  Towards the tail end of the arrival push; Aircraft X was approximately 5 miles in front of Aircraft Y a APA arrival deviating.  R2601 was active FL349 and below complicating matters.  After Aircraft Y was no longer deviating north (toward R2601); I assigned present heading.  At this time; both Aircraft X and Aircraft Y were descending 170.  Aircraft X had been a few thousand feet lower the entire time.  I turned Aircraft X direct BRK thinking Aircraft Y would stay behind still.  I slowed Aircraft Y to 250kt.  The turn to BRK was enough to where I was going to loose lateral separation.  At this time; Aircraft Y was descending through FL230 and Aircraft X was leaving FL220.  I stopped Aircraft Y at FL220; and expedited Aircraft X to 170.  I believe Aircraft X did not descend at a rate quickly enough to keep separation.  I noticed while Aircraft Y was on the edge of the bubble; Aircraft X was leaving FL212 and Aircraft Y was leveling off at FL220.  There was also an ALS arrival; and an ALS departure while all of this was going on.  I should have used vertical separation until I was sure lateral would work.
ZDV Controller reports of a loss of separation due to a slow descent rate of the lower aircraft.