Answer the following question given this paragraph: 

The alchemists were never successful in changing lead into gold. But modern nuclear physics can accomplish this task. Lead is subjected to nuclear bombardment in a particle accelerator. A small amount of gold can be obtained by this process. However, the cost of the procedure is far more than the amount of gold obtained. So the dream of the alchemists has never (and will never) come true.


Q: Which procedure helps modern nuclear physics convert lead into gold?


A:
nuclear bombardment