The Power of the Atom

The Power of the Atom is a quest $$ It is also a PS3 trophy, and an Xbox 360 and PC achievement.

In the quest, the Lone Wanderer is given the choice of disarming or detonating an atomic bomb, thus deciding the fate of a town and its inhabitants.

Detailed walkthrough
This quest is given by:
 * Sheriff Lucas Simms: Wants the Lone Wanderer to disarm the nuclear bomb in the middle of Megaton. Lucas will at first offer 100 Caps, but Speech can be used to raise it to a total of 500 caps.
 * Mister Burke: Wants the bomb detonated, as his employer, Allistair Tenpenny, considers Megaton a blight on the landscape of the Capital Wasteland. Burke can be found in Moriarty's Saloon in Megaton, sitting in the corner. A Speech check can be used for a chance to increase the amount for detonating the bomb by 500 (total of 1,000) or the Black Widow perk (player character must be female) to guarantee a raise of 500 caps.
 * The quest can also be started by activating the bomb (25 Explosives Skill) and disarming it.

Rig Megaton's atomic bomb to explode
To rig the bomb, the Lone Wanderer has to place a fusion pulse charge, given to them by Burke, inside the bomb. This requires an Explosives skill of 25 or higher for a successful attempt. Mentats and/or the Raider blastmaster helmet can be used to boost the Explosives skill if the player character is within seven points of the required threshold.

The Lone Wanderer can warn Lucas Simms that they are planning on making the bomb explode. The sheriff takes the threat seriously and he and the whole town will turn hostile towards the player character. Deputy Weld and other NPCs that are outside the city remain outside and the citizens within the town remain inside.

In the Japanese version of Fallout 3, Mister Burke is absent and the fusion pulse charge is impossible to obtain. The only options are to disarm the nuke or ignore it.

Report to Mister Burke in Tenpenny Tower
After rigging the bomb, meet Burke at Tenpenny Tower, which is southwest of Megaton near the RobCo facility. There, the explosion can be observed from a safe distance together with Burke and Tenpenny.

Mister Burke will give the player character the 'privilege' to push the button to detonate the bomb. Doing so instantly lowers the player character's Karma by 1000 points. If Karma before detonation was 0 or negative, a change of -1000 Karma will instantly lead to the lowest possible Karma in the game.

After helping Roy Phillips take over Tenpenny Tower in the Tenpenny Tower quest prior to completing Power of the Atom, the player character may still complete Power of the Atom. When returning to the top floor penthouse, the player character will stumble onto Roy Phillips and Mister Burke having a conversation. Roy is intimidated by Mister Burke and the fact that he made his way to the top floor. Roy agrees with Burke on the matter of blowing up Megaton and also states that he could use a man like Burke, thus Burke begins a new partnership with Roy.

Disarm Megaton's atomic bomb
Lucas Simms wants the Lone Wanderer to disarm Megaton's bomb. The player character's Explosives skill must be at least 25 to attempt this. Taking some Mentats and/or equipping the raider blastmaster helmet can temporarily increase it to the necessary level unless it was very low, to begin with. If successful, the player character will get the reward and the keys to a personal Megaton house. The reward is usually 100 caps, but with the successful use of the Speech skill on Lucas (before actually disarming the bomb) the reward can be upped to 500 caps. If the player character declines payment, they will typically gain 200 Karma instead. If the bomb is disarmed before speaking to Simms, he will give the player character 100 caps if it is brought up in further conversation.

Mister Burke will leave Megaton once the bomb is defused, and send Talon Company mercenaries that will randomly appear and attempt to kill the Lone Wanderer.

Optional: Deal with Mister Burke
The player character can kill Burke after speaking to him, without talking to Simms first. Killing him will result in good Karma and avoid risking Simms possibly getting killed. The player character can also accept the quest to blow up Megaton, and then kill Mister Burke, without penalty.

Optional: Leo Stahl's drug stash
If the Explosives skill is insufficient (below 25), the player character will be unable to rig or disarm the Megaton bomb. If Perception is at least 5 and/or the Explosives skill is at least 20, it can be sufficiently raised by consuming Mentats. One nearby source of Mentats is Leo Stahl's drug cache, which is hidden inside a desk within the water processing plant. One can gain access via the Leo's Drug Habit quest, by picking the lock on the desk (Very Hard), or by speaking to Doc Church.

Report Mister Burke to Lucas Simms
After speaking to Burke, a new dialogue option will become available when speaking with Lucas Simms, which can result in him confronting Burke about his plot to destroy Megaton, as long as one's Karma is low enough. Mentioning the fusion pulse charge to Simms results in him confiscating it before he proceeds. Simms tells the Lone Wanderer to follow him, after informing them that they will see "wasteland justice" first hand.

He will then attempt to arrest Burke, who will deny the allegations, but eventually agrees to be detained and suggests that Simms leads the way. Burke then proceeds to shoot him with a silenced 10mm pistol, threaten the Lone Wanderer for their betrayal, and disappears.

Options to save Simms include shooting Burke's pistol out of his hand in V.A.T.S., killing him after the conversation or at any point before it. Whichever option is chosen, the sheriff will be thankful afterward. If he dies, the quest can still be completed after disarming the bomb, by talking with his son Harden. If Simms is attacked on accident, the whole turn turns hostile toward the Lone Wanderer.

Seducing Mister Burke
A female character with the Black Widow perk can seduce Burke and persuade him to spare Megaton. He will then leave the city, with the promise of sending for the player character later. He will even send love letters, which can be picked up at Moriarty's Saloon. Another possibility is persuading him to give the Lone Wanderer 1,000 caps upon detonation of the bomb, as opposed to the 500 normally given. Using the Black Widow perk to seduce Burke still results in him putting a hit out on the Lone Wanderer if the bomb is disarmed later.

If the bomb is disarmed

 * Bottle caps
 * 500 - If Speech was successful at the start of the quest
 * 100 - If the offer is accepted, Speech failed, or unemployed at the start of the quest
 * My Megaton house key
 * Deed: My Megaton house
 * 300 XP
 * Karma [+200]: If the bomb is disarmed for free
 * A contract for extermination will be put out by Mister Burke or Allistair Tenpenny and Talon Company will start hunting the player character.

If Megaton is destroyed

 * Bottle caps
 * 1000 - If Speech was successful at the start of the quest, or if the Black Widow perk was taken and unique dialogue is chosen
 * 500 - If the offer is accepted or Speech failed
 * My Tenpenny Tower suite key
 * Deed: Tenpenny Tower suite
 * 300 XP
 * Karma [-1,000]: If Megaton is destroyed
 * Regulators will start hunting the player character. It is also possible to be ambushed by angry former Megaton citizens.

Behind the scenes

 * The coordinates displayed on the remote detonator at Tenpenny Tower (-01,-07), are the actual coordinates of the game cell which contains the bomb.
 * In the Japanese version of the game, Mister Burke is absent from the game, disabling the option to rig the bomb to explode.
 * Characters have dubbed voice lines related to the bomb's pre- and post-detonation.