Upcoming Events


Little Boy, the uranium gun–type atomic bomb developed at the Laboratory during World War II, was 9,700 pounds, 10-feet long and just over 2 feet in diameter.

On Thursday, July 14, at 1:10 p.m., join retired physicist Richard Malenfant for a classified talk: "Little Boy and the Hiroshima Dose Reconstruction.”

The talk is hosted by Director Thom Mason and Johnna Marlow of the Advanced Nuclear Technology (NEN-2) group. It takes place at the Pete V. Domenici Auditorium, National Security Sciences Building (03-1400, 1106).

This classified event is open to Q-cleared badge holders only (no foreign nationals).


Nearly all evaluations of the long-term effects of exposure to radiation for a human population have been derived from observations of the survivors of Hiroshima and Nagasaki during WWII. By observing differences in the effects between the two cities, it is possible in theory to derive a relative biological effectiveness, or quality factor, relating the damage from neutrons to those attributed to gamma rays.

The Hiroshima weapon, Little Boy, was never tested, unlike the more complicated plutonium implosion device, Fat Man, which underwent the Trinity test. No radiation measurements were made at either Hiroshima or Nagasaki.

An exact replica of Little Boy was constructed in 1981 at the Laboratory and operated as a radiation source of fissions so that doses could be estimated for comparison with calculations. In this talk, Malenfant will describe those findings at a classified level.


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Richard Malenfant

Richard (Dick) Malenfant retired in 1996 after 36 years at Los Alamos National Laboratory. Most of his time at the Lab was spent at Pajarito Canyon Site (TA-18), where he worked on the Rover nuclear-thermal rocket program and several critical experiments, including Sheba, a low-enriched uranium, uranyl nitrate solution reactor.

In the 1980s at TA-18, he participated in the construction of a replica of the Little Boy weapon and the operation of a criticality experiment on the replica, which was used to characterize the radiation doses to the survivors of Hiroshima.

His particular interests include the history of experiments conducted at TA-18, where the Manhattan Project National Historical Park has three buildings (the Pond Cabin, the Battleship Bunker and the Slotin Building).