ACR CAPT DESCRIBED AN INCIDENT CLEARING CUSTOMS IN THE U.S. AND HEARING FROM THE CUSTOMS AGENT THAT THE F/O SEAT WAS SHOWING SOME RADIATION. THE CAPT IS CONCERNED ABOUT THE HEALTH IMPLICATIONS.

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ACFT X WAS PARKED ON THE US CUSTOMS RAMP AT ZZZ FOR THE PURPOSE OF CLRING US CUSTOMS AFTER A FLT FROM MEXICO. CUSTOMS AGENT INFORMED CREW THAT HER PDR WAS SHOWING LEVEL 3 RADIATION COMING FROM THE FO'S SEAT BACK. ALL MATERIAL WAS UNLOADED FROM THE SEAT BACK AND THE PDR STILL SHOWED LEVEL 3. SHE SUBSEQUENTLY CLRED THE FLT INTO THE US AND WHEN SHE WAS ASKED BY MYSELF (CAPT) IF THIS LEVEL 3 POSED A THREAT TO THE CREW; SHE STATED NO. SHE INFORMED US THAT IF IT HAD BEEN A LEVEL 6; THAT THIS NUMBER WOULD POSE A THREAT TO THE CREW AND IF IT HAD BEEN A LEVEL 9 SHE WOULD HAVE HAD TO CALL A RADIOLOGICAL HAZMAT TEAM TO DECONTAMINATE THE ACFT. SINCE WE HAD NO CARGO ON BOARD AND SINCE SHE HAD INDICATED THAT LEVEL 3 POSED NO SIGNIFICANT RISK AND SINCE SHE ALSO CLRED THE FLT; I HANDLED THE SITUATION BY MAKING A VERBAL RPT TO THE SENIOR DIRECTOR OF FLT OPS WHO ASSURED ME THAT HE WOULD HAVE THE SEAT CHKED OUT. AT THIS POINT; I HAD NO IDEA WHAT TYPE OF DEVICE THE AGENT USED; WHETHER IT WAS A GEIGER COUNTER OR OTHER DEVICE. SINCE WE HAD NOT HAD ANY RADIOLOGICAL FREIGHT ON BOARD AND DUE TO THE AGENT CLRING THE FLT; I FELT COMFORTABLE MAKING THE VERBAL RPT TO THE COMPANY BY TELEPHONE. THE ONLY QUESTION IN THE AGENT'S MIND WAS WHY THE READING WASN'T LOWER AND SINCE I VERBALLY TOLD HER I WAS MAKING A RPT TO THE COMPANY; SHE WAS NOT OVERLY CONCERNED EITHER.