A Q400 AT FL240 8 NM IN TRAIL OF AN MD80 EXPERIENCED WAKE TURBULENCE.

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FLT WAS ENRTE TO ZZZ LEVEL AT FL240. WE WERE ON THE XYZ ARR. WE WERE IN AND OUT OF VERY THIN CIRRUS TYPE CLOUDS AND SMOOTH AIR. WE STARTED TO EXPERIENCE LIGHT CHOP THAT INCREASED SLIGHTLY IN INTENSITY. I NOTICED AT THAT TIME THE ACFT WAS ROLLING TO THE L AND THE CTL YOKE WAS AT APPROX 25 DEGS DEFLECTED TO THE R. I TURNED THE AUTOPLT OFF AND THE ACFT CONTINUED TO ROLL L TO 25 TO 30 DEGS. IN AN ATTEMPT TO REGAIN CTL I LOWERED THE NOSE AND CONTINUED THE CTL INPUT TO STOP THE ROLL. I STABILIZED THE ROLL AND DSCNT AND BEGAN CLBING BACK TO THE CLRNC ALTITUDE. WHEN WE STARTED THE DSCNT A CALL WAS IMMEDIATELY MADE TO ATC DECLARING OUR ACTIONS. THIS CALL WENT UNANSWERED. AS WE DSNDED WE COULD SEE THAT THE CLOUDS WE WERE IN WAS ACTUALLY A CONTRAIL FROM ANOTHER ACFT AND THE TURBULENCE WE FELT WAS THEIR WAKE TURBULENCE. I ASKED ATC WHAT WE WERE FOLLOWING AND AFTER 2 CALLS HE TOLD US WE WERE 8 MILES BEHIND AN MD80 ALSO AT FL240 AND TO RETURN TO FL240 AND APOLOGIZED FOR THE SITUATION. WE SAID WE WOULD COMPLY BUT WE WOULD OFFSET THE COURSE TO AVOID FURTHER WAKE TURBULENCE. THE REST OF THE FLT WAS UNEVENTFUL. I CAN ONLY COME TO THE CONCLUSION THAT THE SEPARATION BETWEEN ACFT WAS NOT ADEQUATE. IT MIGHT BE POSSIBLE THAT UNIQUE ATMOSPHERIC CONDITIONS WERE PRESENT TO CAUSE THE WAKE TURBULENCE FROM THE MD80 TO REMAIN AT THE ALTITUDE. I DON'T THINK ANYONE IS AT FAULT FOR THE SITUATION AND THE ALTITUDE EXCURSION WAS A RESULT OF THE ACFT UPSET.