The US oilfield services company Halliburton has found a seven-inch radioactive rod it lost in the Texas desert almost a month ago.

The company lost the rod, which contains americium-241/beryllium, during a 130-mile journey between oil well sites in Pecos and Odessa on 11 September.

A spokesman for Halliburton said the device was found late on Thursday night on a road about seven miles from the well site in Pecos, where the rod was last used.

Midland County sheriff Gary Painter said an oilfield pumper recognised the device from fliers that had been handed out in the area.

Halliburton workers, police officers and the national guard had been involved in searching for the rod, which is stamped with a radiation symbol and the words "Danger Radioactive: Do not handle. Notify civil authorities if found."

The US Nuclear Regulatory Commission (NRC) had warned that the radioactive materials "could cause permanent injury to a person who handled them".

The agency said americium-241/beryllium, known as Am-241, is a "category 3" source of radiation and would normally have to be held for some hours before causing health problems. But the NRC still warned that "it could possibly – although it is unlikely – be fatal to be close to this amount of unshielded radioactive material for a period of days to weeks".

It is the first time the loss of a radioactive rod has been recorded by the NRC in at least five years, a spokesman for the agency said.

The three-man Halliburton crew who lost the rod had been using it to identify oil and gas deposits suitable for fracking.

Halliburton, which was once run by former vice president Dick Cheney, has previously attracted controversy for its role in BP's Deepwater Horizon oil spill disaster, building Guantánamo Bay and for working in Iraq, Iran and Libya.