What it’s like to carry your Nobel Prize through airport security

Scientific American:

“When I won this, my grandma, who lives in Fargo, North Dakota, wanted to see it. I was coming around so I decided I’d bring my Nobel Prize. You would think that carrying around a Nobel Prize would be uneventful, and it was uneventful, until I tried to leave Fargo with it, and went through the X-ray machine. I could see they were puzzled. It was in my laptop bag. It’s made of gold, so it absorbs all the X-rays—it’s completely black. And they had never seen anything completely black.

My question is, why didn’t they notice it when he was going to North Dakota?