I have to referee a paper not really in my field and need some answers concerning the prime radical of a ring and nilpotent ideals.

The definition of a strong nilpotent element already have appeared in this question:

Recall that an element x in a noncommutative ring R is strongly nilpotent if any chain $x_1=x, x_2, ... $, with $x_{n+1}\in x_n R x_n$ terminates at zero.

My question is the following: is this definition equivalent to $RxR$ to be a nilpotent ideal of R?

Could you also please give a precise reference for the statement that the prime radical coincides to the set of all strong nilpotent elements?

From my understanding, in non commutative rings, an ideal is called locally nilpotent if any finitely generated sub-ideal of it is nilpotent.

- Is the prime radical $P(R)$ the largest locally nilpotent ideal of $R$? If yes can someone provide a reference for this to me.

Thank you in advance for your help!