Don’t know about airport x-ray scanners...
But they use X-rays on the conveyor belts of the diamond mines.
Surface diamonds will produce visible light when irradiated and other X-ray processes show diamonds buried in the mix.
And just last week my wife was asked to go into the security room the scanner showed a red dot on her shoulder?
They looked at the bare skin and rubbed it a bit, perhaps looking for hidden treasure?
She has a shoulder injury and googling around shows this to be a common occurrence.
Question?
Aren’t diamond sales to individuals usually at retail price and when you sell the best would be wholesale?
Diamonds in a carry on bag would certainly stand out especially if the airport scanner was capable of spectral x-ray. Humans are never put through x-ray scanners at airports the scanners for humans are passive millimeter wave scanners they see the radiation humans put off due to our heat in the MM wavelengths anything over our skin between out cloths shows up. Anything internal does not be it in the stomach or other orifice. In the USA you have the option of opting out of the MM wave scanners for a metal detector and or a physical pay down. Given how small a significant amount of diamond wealth would be one could fairly easily take millions out of the USA without declaring that.
Individual diamonds are retail if you buy them in bulk from a importer you can get them at wholesale the usual minimum for wholesale is $100,000 if you are stockpiling mobile wealth that’s nothing.