Editing Nuclear weapon design (section)

===Two-point linear implosion===
[[File:Linear implosion schematic.svg|right|350 px]]
In the two-point linear implosion, the nuclear fuel is cast into a solid shape and placed within the center of a cylinder of high explosive. Detonators are placed at either end of the explosive cylinder, and a plate-like insert, or ''shaper'', is placed in the explosive just inside the detonators. When the detonators are fired, the initial detonation is trapped between the shaper and the end of the cylinder, causing it to travel out to the edges of the shaper where it is diffracted around the edges into the main mass of explosive. This causes the detonation to form into a ring that proceeds inward from the shaper.<ref>[https://nuclearweaponarchive.org/Nwfaq/Nfaq4-1.html#Nfaq4.1.6.3 Nuclear Weapons FAQ: 4.1.6.3 Hybrid Assembly Techniques] {{webarchive |url=https://web.archive.org/web/20160419071500/https://nuclearweaponarchive.org/Nwfaq/Nfaq4-1.html#Nfaq4.1.6.3 |date=April 19, 2016}}, accessed December 1, 2007. Drawing adapted from the same source.</ref>

Due to the lack of a tamper or lenses to shape the progression, the detonation does not reach the pit in a spherical shape. To produce the desired spherical implosion, the fissile material itself is shaped to produce the same effect. Due to the physics of the shock wave propagation within the explosive mass, this requires the pit to be a [[prolate spheroid]], that is, roughly egg shaped. The shock wave first reaches the pit at its tips, driving them inward and causing the mass to become spherical. The shock may also change plutonium from delta to alpha phase, increasing its density by 23%, but without the inward momentum of a true implosion.{{Citation needed|date=June 2021}}

The lack of compression makes such designs inefficient, but the simplicity and small diameter make it suitable for use in artillery shells and atomic demolition munitions – ADMs – also known as backpack or [[suitcase nuke]]s; an example is the [[W48]] artillery shell, the smallest nuclear weapon ever built or deployed. All such low-yield battlefield weapons, whether gun-type U-235 designs or linear implosion Pu-239 designs, pay a high price in fissile material in order to achieve diameters between six and ten inches (15 and 25&nbsp;cm).{{Citation needed|date=June 2021}}