What is the ruling of Islamic law on a relative who works in food irradiation analysis and divides the leftover materials after analysis instead of returning them to their owners?

If the owners of the food relinquish it, then you are permitted to benefit from it with the permission of the responsible authority. However, if the owners request it, then it is a trust to be given as charity under certain conditions, and you are permitted to take from it if you are in need.