JOHANNESBURG, Nov. 14  This much is known: Just after midnight on Nov. 8, Anton Gerber was sitting with his fiancée in the control room of South Africa’s most secretive nuclear facility, the site at which this nation’s apartheid government conceived and delivered six atomic bombs, when four gunmen burst into the room. Mr. Gerber pushed his fiancée under a desk. The attackers shot him in the chest, grabbed a computer and fled, but abandoned their booty as they came under assault by guards.

Now, one week after the assault, the most serious on a nuclear installation in recent memory, the government is largely mum about who was behind it, how they broke in or why.

Already, the attack is raising questions among advocates and analysts about the wisdom of plans by South Africa and other African states to embrace nuclear energy as a solution to chronic power shortages and the looming problems of climate change.

The assault on the Pelindaba nuclear reactor and research center, one of South Africa’s most zealously guarded properties, is a severe embarrassment to the government. The four gunmen escaped cleanly, neither caught by guards nor identified on surveillance cameras. Mr. Gerber is still recovering.