Which historical device used a gun-type assembly to combine two subcritical masses by firing one into the other?

Which historical device used a gun-type assembly to combine two subcritical masses by firing one into the other?

• A. Fat Man bomb
• B. Little Boy bomb
• C. Tsar Bomba
• D. Ivy Mike

Answer: (A)

A gun-type assembly achieves supercriticality by using a conventional explosive to shoot one subcritical piece of fissile material into another, forming a supercritical mass in a very brief moment. This straightforward approach is exactly what was used in the Little Boy device. It relied on uranium-235 and a simple mechanism to bring two subcritical pieces together. The other devices don’t fit this method. Fat Man used an implosion design that relies on explosive lenses to symmetrically compress a plutonium core into a supercritical state, rather than firing one piece into another. Tsar Bomba was a much later, large thermonuclear weapon built around staged fusion with no gun-type assembly. Ivy Mike was a test assembly for a hydrogen bomb using a different, more complex configuration focused on achieving fusion rather than simply assembling fissile mass. So, the device that used a gun-type method to join two subcritical masses is Little Boy.

A gun-type assembly achieves supercriticality by using a conventional explosive to shoot one subcritical piece of fissile material into another, forming a supercritical mass in a very brief moment. This straightforward approach is exactly what was used in the Little Boy device. It relied on uranium-235 and a simple mechanism to bring two subcritical pieces together.

The other devices don’t fit this method. Fat Man used an implosion design that relies on explosive lenses to symmetrically compress a plutonium core into a supercritical state, rather than firing one piece into another. Tsar Bomba was a much later, large thermonuclear weapon built around staged fusion with no gun-type assembly. Ivy Mike was a test assembly for a hydrogen bomb using a different, more complex configuration focused on achieving fusion rather than simply assembling fissile mass.

So, the device that used a gun-type method to join two subcritical masses is Little Boy.