I struggled to come up with a fair definition of nucleus. Indeed, some of these nucleon soups are more like mist than anything. And so my definition is: if a

I struggled to come up with a fair definition of nucleus. Indeed, some of these nucleon soups are more like mist than anything. And so my definition is: if a photon can traverse the width of the "nucleus" and the nucleus still exists by the time it gets to the other side, it's a nucleus. If it cannot hold together even that long, it doesn't count.