This demonstrated a high level of personal and social responsibility. He had made a mistake, causing danger to everyone, so his responsibility, as a moral person, was to put it right. This was described as "heroism in this case" but the morality involved is something "having the same anatomy the world over." This is something to aspire to, to be brave and make the right decision in any circumstances.
Michael Schulman, in his theory of 'How We Become Moral' (2002), stated that 'concern for others emerges spontaneously in very young children" and included empathy, moral connection to the goodness in others, and principles we all have about what is right and wrong. We do have the basic, innate ability to be moral. It seemed ironic that Slotin worked to create a bomb that destroyed many, but as Bronowski pointed out, people choose what they believe to be right, by following their conscience. Everybody develops an awareness of what is right for them, through upbringing, maybe religious or cultural belief, role models, learning and so forth. Moral integrity is when we look at how others would be affected by our actions; it is not about doing no harm, but about choosing to do good because others matter.
There are many examples to support this idea, as in the movie, 'Schindler's List', or those who helped the Jews during WW2, or the workers at the Twin Towers, on 9/11 - the list goes on. In caring about others, even when the consequences are not to our own advantage, we can try to make the right choices and achieve that level of moral integrity.