With the advent of the atomic bomb in 1945, mankind had a terrible new weapon. It was obvious to most observers that a war fought with these devastating weapons, at its best, would regress humanity to the Paleolithic Era. Military strategies concerning the tactical usage of such weapons were those of "scorched earth"--total annihilation. Nuclear air-to-air missiles to down bomber formations (never seen since the end of the Second World War), nuclear depth charges to destroy submarine wolf packs (the same), nuclear artillery shells to totally eradicate massed armor and infantry charges (seen, but rarely). Strategically, atomic weaponry could be used to completely shatter a country's infrastructure and resolve. A people who's flesh is hanging from their bones in tatters and covered in lesions neither fights nor produces well.
The very nature of war was changed. The objective in a (defensive) war was no longer to conquer territory to force the enemy to stop fighting; the objective was to utterly destroy an enemy's capability to fight. Conquering became unneccesary, as conquered land would inevitably be pockmarked with nuclear-spawned craters and insidious radiation. Yet the major powers still maintained massive infantry and armor forces. The point of such forces is to take land. But if they take land aggressively and therefore start a nuclear war as a result, causing the Mutually Assured Destruction (MAD) of all parties involved, what was the point?
War required a weapon that held on to the killing power of atomics yet did not completely destroy the target. Something that would kill, but not destroy. Organisms would be wiped off the map, but buildings and infrastructure would be relatively unharmed and radiation would be minimized.
Thus entered the neutron bomb.
The neutron bomb operates on the same principle of other atomic weaponry--take a fissionable material and compress it until it explodes. However, a neutron bomb only produces a small explosion but has large amounts of neutron (hence the name) and gamma radiation. Radiation itself is when a fissionable material such as uranium or plutonium sheds small portions of its nuclei (the center bits) to become other, more stable materials. Radiation is an expulsion, not an explosion, because it occurs in small chunks, such as in these examples: alpha radiation, in which positively charged protons are expelled in groups of two, beta radiation, with negatively charged electrons are expelled, neutron radiation, where neutrally-charged neutrons are expelled, and gamma radiation, where particles are completely transformed into gobs of high-energy gamma rays. Neutron radiation is the same kind that the containment jar of a Battlemech's fusion engine is designed to contain, while gamma radiation is like X-rays on steroids.
Both neutrons and gamma rays zip through organisms and less-dense structural materials such as wood and drywall, playing havoc with genetic codes and bursting cells in the process. This radiation can even pass through metals such as aluminum and steel but are quickly stopped by denser materials such as concrete and lead. Neutrons fizzle away after about twelve minutes, and gamma rays are eventually transformed into heat as they pass through materials and are absorbed.
End result--anyone out in the open or in civilian buildings when the bomb goes off is fried through cell disruption and instantaneous genetic breakdown. Those in armored vehicles may not fare much better if the bomb is a big one, and those in reinforced bunkers are immune. The destructive blast effect is that of a nominal subatomic bomb with limited damage in an extremely limited area, but the radiation effect covers a much larger radius. After twelve minutes, the last of the radiation dissipates and the area is generally safe for occupation.
Of course, neutron weapons are stacked with other nukes in the political scheme of things. Bombing a city with neutrons is just as bad as wiping it off the map, and the MAD consequence will be the same.
TME Industries does not produce neutron weaponry, as it refuses to sell to a culture likely to use them. Admittedly, since neutron bombs are more useful tactically than nuclear weapons, they are used on rare occasion by both the Inner Sphere and the Clans. Both will use them in situations where conventional attacks would be both devastating and pyhrric. The Inner Sphere argues that the area is neither destroyed nor irradiated, which makes it better than all-out nuking. The Clans, addicted to their genetics, admit that neutron bombs pose only a minor threat of genetic abhorration as anyone close enough to have their DNA screwed with probably won't survive long enough to see the next PTA fundraiser.
GAME RULES
Neutron bombs work in this fashion: they are first given a point value like original Aerotech bombs. Unlike standard bombs, they only cause half the explosive damage of their standard counterparts. Ten-point bombs cause five points of damage; hundred-point bombs cause fifty.
The radiation effect expands in a blast radius, and is equal to the point value of the bomb. The target hex takes full radiation damage, the six adjacent hexes take twenty points less, the next ring takes twenty more points less, and so on until the bomb runs out of damage. For example, a ten-point bomb would cause only 10 radiation damage in the target hex (as the adjacent hexes would cause (20-10) -10 damage and that's just silly), while a hundred-point would cause 100 radiation damage in the target hex, 80 in the first ring, 60 in the second ring, 40 in the third ring, 20 in the fourth ring, and then no more damage further out. Making a bomb a neutron bomb either subtracts an additional .2 Safe Thrust (Aerotech 1) or counts as two bombs when figuring thrust loss and bomb limits (10-point neutron bombs only, Aerotech 2).
RADIATION EFFECTS
Unarmored infantry takes double damage. Unarmored infantry in Clear terrain, therefore, takes quadruple damage. Buildings absorb half as much damage as normal. Infantry directly behind Level 2 cliffs are protected from the blast.
Radiation does not actually damage armored vehicles and battle armor suits. However, if the armor would have been eliminated had the damage been explosive rather than radiation, the crew or armored infantryman is killed by intense radiation. The vehicle or battle armor suit is unharmed and may be salvaged. For example, a tank with 10 points of armor on its left side is hit by 10 or more points of radiation damage on that side. Had the 10 points come from, say, an autocannon, the armor would have been eliminated. Therefore, the crew is killed by the radiation from the neutron bomb but the armor is not actually harmed.
Battlemechs are also not actively damaged by radiation. Spread radiation damage into five-point groups as usual and apply. For each hit location where the armor would have been eliminated, roll one automatic critical hit and roll for the possibility of more. Ignore "limb blown off" effects and count as three critical hits instead. Ammunition critical hits do not explode but do make the ammunition unusable. Weapon, equipment, engine, actuator and gyro critical hits do have the standard effect but the hit item may be salvaged or quickly repaired after the battle as if it were undamaged. If the head armor would have been eliminated, the Mechwarrior dies instantly from radiation.