I'm not sure if nuclear science involves radioactive. But if you have something to do with radioactives, you can try for the NDT (Non Destructive Test). Some use radioactives to inspect pipeline. (Right?) At least, I know one such company that does.
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Btw, I'm still new in the OnG industry. I'm actually from the electronics degree background. I jumped into a OnG supplier company recently (since that was the only company that offered) from RnD company. Got a position as sales engineer. My salary cut was quite huge but I was fired up to work in OnG at that time and was willing to start from beginning (reealy wanted to feel how it is to go offshore).

Do you think there is any possibility for me to move towards technical position later on? I am hoping to get a position that does field work. Does my experience in OnG doing sales count, to allow me to move towards me being able to do field work?

Thanks for any feedback. I really am lost in my career direction in OnG since my background is in electronics. There does not seem to be much options but they say it exists.

In the O&G, there're lots of vendors that requires Sales Engineer. If you search at the online job agency like jobstreet, you'll find several sales position are open for O&G companies.