Radiation Beams

Radiation beams emit beams of ionizing radiation, either charged particles or high energy photons. These pass through matter, and in the process knock off enough electrons as they go to heat the matter in the beam path and inflict radiation exposure.

Material strength is dependent on chemical bonds, which are interactions between the weakest-bound electrons. Radiation essentially ignore material strength, passing right through any matter and ionizing all chemical bonds so that the matter falls apart into highly ionized plasma. In game terms, all DR except for cover DR is ignored. However, the energy used to cause ionization is removed from the beam's energy. This is proportional to the amount of matter in the way, so that cover DR protects with its full DR.

As the radiation interacts with the matter it passes through, it can either lose energy continuously or via discrete processes. Continuous energy loss gives a well defined range to the particles - they can only go through so much stuff before they lose all their energy and stop. Discrete interactions remove some of the particles from the beam, but the amount is proportional to the amount of particles already in the beam, so as the beam gets less intense it loses energy more slowly. With only discrete interactions, the beam has no maximum range through matter and although it steadily loses intensity it never drops to exactly zero (although if it goes far enough it will be close enough to zero for all practical purposes). All charged particles suffer continuous energy loss - their electric field pulls the electrons and pushes on the nuclei if positively charged and vice versa if negatively charged. As the charged beam particles fly by, they give the matter electrons enough of a kick to knock them out of place. This heats the matter, but the energy to do so comes from the beam itself, whose particles will gradually slow down and eventually come to a stop. However, discrete processes may also occur which remove charged particles from the beam. Uncharged particles generally do not suffer from continuous energy loss but will usually experience some type of discrete interaction that can remove them from the beam.

When continuous energy loss is the major interaction with matter, the treatment of the beam is straightforward using GURPS mechanics - find the damage, and that is the amount of cover DR the beam can penetrate, ignoring all armor DR.
If discrete energy loss is the only mechanism operating, the penetrating ability of the particles is represented by the basic damage. Differences in ability to cause injury are represented by wounding multiples. A penetrating radiation beam will cause this basic damage at the full wounding multiple for their damage type (Pi++ is × 2, and so on). After the beam damage goes through as much cover DR as it can, the damage starts over with another full basic damage for the beam with only half the wounding multiple. This is then followed by another basic damage increment with half again the wounding multiple, and so on, ad infinitium. Each increment of damage starts going through armor and barriers where the previous increment left off. For example, a 3d Pi++ beam causes an initial 3d damage at ×2 injury, another 3d at ×1 injury, followed by 3d ×½, 3d ×¼, 3d ×¹⁄₈, and so on. It is important to use some form of blow-through mechanic and apply the wounding multiple after the blow through limit is reached, for example GURPS High-Tech pg. 162. This will be noted with a ⊗ symbol after the damage - for example a weapon with a 3d increment is listed as 3d⊗. For convenience, use the same damage roll for all damage increments.
If both discrete and continuous energy loss occurs, the beam acts like a beam suffering only discrete energy loss, but only causes a finite number of damage increments before it loses all of its energy and is spent. The last damage increment has its basic damage doubled (representing a second damage increment with the same wounding multiplier, because the beam is dumping the rest of its energy in that increment). This will be noted with an asterisk followed by the number of increments - for example, a weapon that delivers 4 increments of 10d (except for the doubled last increment) would be listed as 10d⊗4.

If the beam is incident on a superscience armor, screen, or barrier which can directly stop the beam particles; subtract the injury rather than the basic damage from the DR. That is, multiply the basic damage remaining in the current increment by the current wounding muliple. If this is more than the DR, subtract the DR from this, divide by the wounding multiple, and that is how much basic damage punches through. If the DR exceeds this, subtract the injury inflicted from the DR. If the remaining DR is more that the original damage for this damage increment, there is not enough remaining energy in the beam to punch through. Otherwise, apply the next damage increment with half the injury as before, and so on, until either the armor, screen, or barrier is penetrated or it is logically impossible to continue (mathematically, the injury from summing all damage increments including and after a given increment is exactly twice the injury from the starting increment. However, because of round-off error, this may not always hold true in a game. Don't sweat any discrepancies - if round-off error means the beam will not penetrate, neglect any further penetration). These subtractions from DR only apply to this hit - subsequent hits are at full DR except for that removed due to the ablative or semi-ablative nature of the armor or screen (which, again, should be based on injury rather than basic damage).

The heating caused by the passage of a beam of radiation through matter may flash the matter to vapor when it is still tightly focused in a very narrow beam. The explosive expansion of the heated material in the beam path will cause significant disruption to solid objects the beam passes through - including people. Even though the beam may be less than a millimeter wide, it will produce a large wound channel. At longer ranges, the beam expands. This heats a larger area but less violently. This will cause melting, thermal decomposition or degradation, or surface ignition. There comes a point where the beam is still intense enough to cook the flesh it passes through and perhaps melt wax or ice but cannot directly affect bulk materials that are relatively insensitive to heat such as rock or steel. Eventually, the beam will be diffuse enough that it can no longer substantially heat its target and it will stop causing direct thermal damage.

The direct heating damage is considered piercing. At long ranges where the heating due to the beam is enough to cook meat but insufficient to ignite flamables or melt rock or steel, the damage is limited only to living things or materials close to their melting temperature or an otherwise high sensitivity to heat. Beyond the distance at which injury can occur, the beam will still deliver radiation damage - roll damage for the beam, but do not apply any wounding except for the radiation effect. The range has three ranges listed - the maximum range for unconstrained piercing, the maximum range for piercing that only affects living beings, and finally the half-damage range for the radiation.

All beams of penetrating radiation are made of ionizing radiation. Some of the particles will inevitably scatter out of the beam, and the interaction of the beam with matter typically creates other forms of ionizing radiation as well. This will cause radiation exposure with the subsequent acute radiation poisoning and chronic radiation sickness. Radiation exposure is also caused when the beam passes through living tissue at too low of an intensity to cook the tissue. Radiation exposure from a given beam will be a multiple of the basic damage delivered to the target (or damage absorbed, for barriers or other intervening objects) times the square of the wound modifier as toxic rad exp damage type, approximating ×1.5² as ×2 (i.e. Pi- causes ¼ as much radiation, Pi causes the basic amount of radiation, Pi+ causes twice as much radiation, and Pi++ causes four times as much radiation). As usual with explosive damage, internal damage (in this case radiation dose) resulting from damage absorbed by a direct hit is multiplied by 3. Unlike normal explosions, radiation dose falls off as the square of the distance from the source to the victim. A target will take the full dose produced from damage absorbed by armor or any other interposing matter he was wearing. Because of the explosive modifier, bystanders near the point of incidence or intended targest that got lucky with a near miss can be irradiated by the radiation escaping from the point of incidence. This includes the gunner, if he is standing too close to his target! Against most biological beings, any direct hit will deliver a lethal dose.

Even damage absorbed by the air en route to the target will emit radiation, according to how much damage was absorbed by the air. This will end up irradiating the gunner as well. Rather than adding up all the radiation exposure from each point along the beam, figure anyone affected will take an exposure equal to the square of the wounding multiple × the cover DR/m of the air times the radiation multiplier divided by the distance from the beam (for a gunner using a handheld weapon, this will be his Reach. Assume Reach C is 0.5 m). The dose per shot may be small, but after emptying a power cell the gunner may end up very sick. For this reason, radiation beamers are usually only used by rad-hardened automated systems, by vehicles whose crews are protected by heavy shielding, or in vacuum. (Note - this is the distance from the beam, not the square of the distance from the beam. Dose from line sources goes as 1/distance, as opposed to the 1/distance² of point sources.)

Example: Jed the Space Marine is guarding an asteroid space depot in his Dreadnought battlesuit (5 points cover DR). He is shot by a p-beamer from an enemy spacecraft that inflicts 10d⊗4 Pi+2 damage. The initial damage roll is 28 points. The first 5 of these are absorbed by the armor, producing 5×100 points of radiation, multiplied by 4 because the damage type is Pi++, for a total of 2000 points of radiation damage. This is divided by the battlesuit's PF of 20 for 100 points delivered to Jed. Next, Jed with his 11 HP takes 11 points of basic damage before blow-through, with injury increased to 22 points due to the wound multiple as a cylinder of meat in his torso is heated to the point that it cooks. The 11 points of basic damage are multiplied by 100 to get the base radiation, and then by 4 for the radiation wounding multiple, and then by 3 because the dose is internal, to give Jed 13200 points of radiation damage. As the beam exits, it spits off another 100 points of radiation from Jed's suit. Jed is badly injured, and is unlikely to survive the radiation exposure.
Jed's squadmate Ned is in an underground room in the depot. A stray beam pierces the meter of overhead rock (cover DR 100) and four centimeters of steel plate for the armored pressure walls (cover DR 12) and goes through Ned. The damage roll is is 40. The initial 40 points Pi++ are absorbed by the rock, as are the next 40 points where the beam injury is equal to the damage absorbed, and 32 of the next 40 where injury is halved. This leaves 8 points of basic damage in this increment to go through Ned and his battlesuit. The battlesuit absorbs 5 of this, producing 5×100×0.25 = 125 points of radiation, which rounds to 6 after the suit's PF is applied. Ned has 12 HP and can take 12 points of basic damage from this attack before it blows through. Ned takes the remaining 3 from this damage increment, and 9 of the 40 points from the next damage increment where injury is quartered. This evaluates to 3×0.5+9×0.25 = 4 points of injury, and 3×100×0.5²+9×100×0.25² = 131 points of radiation exposure. Finally, Ned takes the additional 6 points of radiation exposure from the beam going out the back of his suit. Ned is in pain with deep burns going through his body, but is likely to survive both the injury and radiation exposure.

The range listed for radiation damage is the range where SM 0 targets take the full radiation exposure. This is the range where the entire focused spot of the beam can be expected to pass through the target. For longer ranges, the beam is wide enough that much of the radiation passes by the target. Divide the radiation damage by the square of the number of multiples of the listed range, rounding all fractions up (for example, between the listed range and twice the listed range, damage is divied by 4. Between twice the listed range and three times the listed range, damage is divided by 9). Targets with different size modifiers have the half-damage range multiplied by half the Linear Measurement value from the Speed/Range table (pg. B550) corresponding to their size.

Radiation beams are very obvious. At ranges close enough to cause flash-vaporization, they produce a blazing blue-white streak along the beam path flashing instantly and momentarily from the gun to the target with the sound of a thunderclap; and an actinic flash, explosive bang, and shower of sparks and debris where the beam is incident. The beam streak clearly shows the position of anyone using one of these weapons. Beyond this range, the beam causes the air it passes through to fluoresce blue for an instant along the path of the beam, and may make the target glow from its heat or burst into flames.

There are various ways of producing radiation beams:

Electron Beamers (TL 11).
Relativistic Plasma Beamers (TL 11) (TL 12).
Gamma-Beamers (TL 12).
Neutron Beamers (TL 11^) (TL 12^).
Muon beams are an example of a marginal technology. They would be extremely penetrating, so although they would go through just about any cover they would deposit very little energy in their target. In addition, muons are unstable, so you would need to create them on the spot which would be inefficient and reduce the oomph of the beam for a given energy drain from the power cell.
Antiparticle beams are an example of something that doesn't work well. Antiparticles are difficult to create and store, make for a logistics problem if they need to be supplied, will eventually drift out of confinement and annihilate, and once you are boosting particles to relativistic energies anyway they cause very little additional damage and much of that is radiation rather than local heating along the beam path.
Meson beams are another example of something that doesn't work well. Mesons don't give any real advantage over relativistic plasma beams; the electrons and protons needed for plasma beams are just hanging around waiting to be used while mesons need to be created on the spot at the cost of a significant inefficiency in wasted energy; and mesons are unstable, such that only pions or kaons can be expected to have a significant range and even that is only about 1 to 10 meters for pions (although you can get a few more orders of magnitude in range by going to extreme relativistic speeds). Other exotic particles have similar drawbacks and even shorter ranges (except for those which do not interact with matter at all, which have other obvious drawbacks - they cause no damage to your target).

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