The search, which began immediately after the device was reported missing during work on the S7 expressway in Kraków's Nowa Huta district, has been extensive, state news agency PAP reported on Thursday.
Police have checked scrap collection points, secured available surveillance footage, conducted land searches, and deployed a police drone.
Residents in the vicinity have been questioned as part of these efforts.
The National Atomic Energy Agency, Poland's nuclear regulatory authority tasked with ensuring nuclear safety and radiological protection, is supporting the search with highly sensitive specialized equipment.
Its experts have warned against opening or tampering with the device, called the defectoscope, in any way. Even brief contact with the unprotected radioactive source inside the device poses a serious and direct threat to human life and health, they said.
A 33-year-old man responsible for supervising the device has been charged with mishandling radioactive material.
Equipment such as this one is routinely used in non-invasive testing of materials to detect defects such as cracks or corrosion. The company that owns the missing device has offered a reward of PLN 5,000 (EUR 1,150, USD 1,300) for information leading to its recovery.
Joanna Paździo, a spokeswoman for the regional administration, announced on Thursday that the reward would go to anyone who finds the defectoscope or contributes to its discovery.
The public is urged to report any information about the device to emergency numbers 112 and 997, the Regional Crisis Management Center at 987 or +48 12 39 21 300, the Radiation Incident Center of the National Atomic Energy Agency at +48 22 19 430, or the Kraków City Police Headquarters at +48 47 83 52 908.
(rt/gs)
Source: IAR, PAP, gov.pl