A neutron bomb is merely a mini-H bomb rigged to enhance the neutron output.
Neutrons are heavy uncharged particles, which means they can pass through thick armor or lead rather easily, unlike gamma rays.
Neutrons are selectively absorbed by light elements such as carbon which form living matter, whereas other forms of thermonuclear radiation ( alpha, beta, gamma ) are selectively absorbed by heavy elements.
Many years ago, one of the popular science magazines published a picture taken with a neutron camera, of a brass candelabra with candles, sitting inside a lead-brick enclosure. The neutrons went right through the lead and brass, which looked ghostly on the pictures -- but the neutrons were selectively absorbed by the organic material in the candle wax, which looked dense on the neutron photo.
In other words, energetic neutrons can pass through lead and brass without losing much energy or momentum. Having passed through the lead [or armor] unimpeded, the neutrons then expend their momentum and energy when they hit something organic, such as beeswax or human tissue, knocking loose electrons, ripping up molecular bonds, and basically disrupting the life-chemistry of anything living. When a neutron strikes an atom of a light element, the result is a shower of secondary ionizing radiation, which causes damage just like any other radiation.
Neutrons also have a nasty habit of traveling through the ground and reflect off the water table and off bedrock, killing anyone in an underground bunker. Other types of radiation ( alpha, beta and gamma ) don't have that capability. The tendency of neutrons to go right through armor and bounce around corners makes them attractive as bunker-busters, because modern bunker systems have blast doors at intervals, and dog-leg passages that can run for miles underground.
Unfortunately, bunker systems tend to be built under large civilian cities -- Saddam's bunker network was built under Baghdad ( pop. 7 million http://en.wikipedia.org/wiki/Baghdad
). If the US had had bunker-busting neutron bombs at the time they invaded Baghdad based on fabricated information about WMD, taking out the bunkers could have killed millions of Iraqi civilians through neutron flash and seismic shocks.
A neutron bomb does NOT ( as commonly mis-reported ) kill people and leave structures intact. A neutron bomb is a mini-hydrogen bomb; and produces all of the usual destructive effects of an H-bomb ( heat flash, gamma radiation flash, supersonic blast wave, over-pressure wave at greater distances, and radioactive fallout plume reaching high altitudes ). A neutron bomb actually produces MORE radioactive fallout than a 'regular' tactical-H-bomb of the same yield, because most of the radioactive fallout of a 'regular' mini-H-bomb comes from neutrons that induce persistent radioactivity in pulverized material.
A neutron bomb simply has 'enhanced kill' of living tissue hiding inside armor or inside bunkers or behind berms. The enhanced kill comes about because a higher percentage of the bomb's energy comes out as energetic neutrons, whereas in a 'normal' H-bomb more of the energy would come out as blast / heat / X-rays and whatnot. A normal H-bomb is surrounded by metals that reflect neutrons back into the bomb, to increase the yield. A neutron bomb is built without the neutron reflectors, so that the neutrons can get out. That would normally cause a lower yield, but extra tritium is added to bring the yield back up to par.
When a 'normal' tactical H-bomb goes off in mid-air ( "air burst" ), most of the energy gets absorbed by air within a half-mile radius of the detonation, turning that air into a "fireball" of extremely hot plasma. That fireball then does 2 things -- it emits a powerful flash of radiant energy all the way from the infrared to the X-ray region of the spectrum, and (
the fireball begins expanding at supersonic velocity, pushing aside millions of tons of air in the process. The displaced compacted air then flattens anything in its path. After a brief interval the fireball goes dark, because the scorched air within the fireball forms brown oxides of nitrogen. Displaced air then rushes back in, sweeping up pulverized material and ash into the fireball, which rises rapidly to the stratosphere and cooks a wider area with its heat and radiation as it rises.
The surplus of energetic neutrons emitted by a neutron bomb pass right through the forming fireball and keep going until they hit something solid made of light elements, such as people cowering behind a hardened wall.
Again, a neutron bomb is a matter of degree. All thermonuclear reactions produce neutrons, whether the reaction is fission ( A-bomb ) or fusion ( H bomb ). The tritium which 'powers' the H-bomb consists simply of heavy hydrogen which has 2 extra neutrons on every atom. That's necessary because an H-bomb turns hydrogen into helium. It takes 2 neutrons to make a helium atom, but a normal hydrogen atom has none, so heavy hydrogen is used to supply the required neutrons. Some of those extra neutrons get loose as neutron radiation. A neutron bomb is simply designed to let more neutrons out.
A neutron bomb can also kill electronics more effectively at short range, because some of the neutrons are stopped by silicon in the chips, which is a somewhat light element. It doesn't take much radiation damage to kill a chip, because silicon chips have to be near-perfect crystals in order to function as high-performance semiconductors. Anything that rips up the crystal structure even a little ruins the chip.
It's a myth that neutron bombs are clean, humane, or environmentally friendly. Their destructive effects are NO LESS than a tactical hydrogen bomb of equivalent yield. It's also a myth that neutron bombs can kill people in a WMD facility without releasing deadly spores, causing a nuclear meltdown or whatever. A neutron bomb might easily do both, especially if the targeting intel is sketchy or wrong. It takes an extremely high dose of radiation to kill anthrax, compared to what kills humans -- a strike near enough to crack open the containment and release the spores might not kill the spores.
A neutron bomb also might not stop someone with their finger on a retaliatory button. A person can receive many times the lethal dose of radiation and soldier on for several hours, until they start vomitting uncontrollably, bleeding internally and whatnot. http://en.wikipedia.org/wiki/Radiation_sickness
In other words, neutron bombs are not a 'magic bullet' to instantly wipe out terrorists who have a vial or a suitcase nuke or whatever. As with any tactical nuke, the radius of total destruction is limited, and the neutron kill radius isn't much higher. Neutron bombs aren't fully scalable, because neutrons are absorbed by atmosphere within several miles, regardless of how powerful the bomb is.
Because neutron bombs aren't a magic bullet and aren't at all 'surgical', they can have extreme political fallout when their use is provoked by disinformation or misdirection. A single neutron bomb could literally make tens of millions of enemies around the world, some of which might have access to a loose nuke or two to retaliate with -- making it hard to tell who was behind the loose-nuke attack because the former Soviets misplaced so many. For that reason, increased lethality needs to be matched by increasingly powerful intel, since modern opponents ( particularly Al Qaeda ) are adept at baiting the US into making enemies, using false trails of misinformation matching what the commander-in-chief wants to believe. This will remain a problem no matter who's the commander in chief or which party they're from. Congress has no constitutional power to rein in a US president once Congress approves a declaration of war, even if the president decides to use a nuclear weapon in response to an imagined threat. Congress has just signaled that they can only pass non-binding resolutions of opposition to whatever a president might choose to do. Several recent presidents have responded to situations with threats that no options were off the table [including nuclear], without needing approval from Congress to place the world on notice that a president was weighing unilateral use of a nuclear weapon.
None of the above information is classified -- it's all basic physics, because an H-bomb uses the same operating principle as a star. For quite a bit of additional information see the Wikipedia article at http://en.wikipedia.org/wiki/Neutron_bomb
"I don't know with what weapons World War 3 will be fought, but World War 4 will be fought with sticks and stones. -- Albert Einstein [ a guy who understood chain reactions. ]
""Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius -- and a lot of courage -- to move in the opposite direction." -- Albert Einstein.