Freelance Traveller

by Robert O'Connor

Nuclear transformations and some electronic rearrangements can yield highly energetic particles and photons. Colloquially these are called 'radiation'.

The damaging effects produced by radiation arise from molecular disruption (direct effect) and energy transfer leading to the production of charged species called free radicals (indirect effect) which can bind to other molecules, impairing their function.

There are dose-dependent (nonstochastic) effects which are an inevitable consequence of a given dose (e.g. skin burns). Stochastic effects are those whose probability of occurrence is related to dose, e.g., leukaemia or thyroid cancer.

Dosage is the amount of energy absorbed per unit mass. It is measured in rads (radiation absorbed dose) (1 rad = 0.01J/kg) or grays (Gy) (1 Gy = 1J/kg).

Biological effect is related to the amount of energy and the way in which it is transferred along the trajectory of the particle or photon.

Dose equivalent = absorbed dose * quality factor

The units of dose equivalent are the rem (one rad of radiation with a quality factor of one) and the sievert (Sv - one gray of radiation with a quality factor of one).

Alpha particles

Alpha particles have 2 protons and two neutrons. They are therefore quite large (large damage potential) and have poor penetrative ability.

 

Beta particles

Beta particles are electrons or positrons. The slower they are the more damage they can cause (more chance to form free radicals or gamma rays in tissue).

 

Neutrons

Neutrons are uncharged and therefore have good penetrative ability. Their damage potential is high because of this and their size.

 

Electron Volts (eV)

The electron volt is an energy unit. An electron which moves across a potential difference of one volt has a kinetic energy of one electron volt. It is equal to 1.6 X 10^(-19)J.

Radiation Sources

We are continually bathed in low-level radiation. The discovery of nuclear energy and electronics adds several new sources to the mix.

Natural Sources

There are two sources in this category, cosmic rays and terrestrial radiation (originating from radioactive material in the planet and in our bodies).

Cosmic Radiation

The origin of cosmic radiation is still not yet understood. There is a background throughout known space of high energy protons (~87%), alpha particles (~11%) and other nuclei and electrons. Energy levels range between 10^8 and 10^20 eV, with the majority between 10^8 and 10^11eV.

Baseline 2.7 rem per year (unprotected) - range 27 mrem to 7.3 rems per year. (mrem = millirem or 1/1000 rem)

Radiation belts, particularly around gas giants, can have levels up to a *thousand times* greater than this.

Standard atmospheres absorb most of the incident cosmic radiation. Secondary particles are generated (neutrons, photons and pions). The radiation flux varies with altitude and latitude. At 'sea level' (1 atmosphere pressure), 27 mrem per year. This doubles with every 1600m increment in altitude.

Near the magnetic poles of a world, the exposure rate varies with the strength of the local field.

 

Terrestrial radiation

Of the elements found on or in a given world, about a fifth are radioactive. Heavy core worlds usually have larger concentrations of radioactives than are the average. Gamma rays account for nearly all terrestrial radiation. The range varies from 15 to 200mrem per year, depending on local conditions.

 

Internal Radioactivity

Internal radioactivity arises from potassium 40 (which comprises 0.0118% of body potassium - some 0.0157g in a 70kg human), and ingested environmental nuclides such as carbon 14 and radon 222. The typical exposure is 28mrem per year.

Occupational exposures should not exceed 400mrem per year.

For character generation, assume base exposure 100mrem per year (200 if heavy core world, 50 if icy body) and 400mrem per year of service in any spacefaring or nuclear energy related field. Exposure cannot be 'rolled back' by conventional means (but see below).

Weapons

Roughly 15% of the energy of a detonating nuclear weapon is high energy radiation. 'Enhanced radiation weapons' or neutron bombs are designed to increase this fraction to nearly 50%. This refers to detonations within an atmosphere ; in space, 90% of the explosion's energy is dissipated in this manner. Particle and meson beams also produce significant radiation effects at their points of impact. Almost all of a meson beam's energy is converted to gamma radiation when the mesons decay.

Multiply by 3 for neutron weapon OR Multiply by 6 for detonation in space

Multiply by 3 for neutron weapon OR Multiply by 6 for detonation in space

The half life for fallout is two hours.

The half life for induced radiation is one year.

Fallout activity is about half the radiation load of aconventional nuke, 1/10 that of a neutron bomb.

Tables have been listed in FF&S(1 and 2?), Striker and JTAS 23 for blast radii with yield.

The values above assume that you're standing right next to the source, unshielded.

• High level : highly enriched fuel or weapons grade material.
• Medium level : reactor grade fuel, 'tailings' from reprocessing plant, activated materials from within reactor vessel (e.g., old shielding, coolant).
• Low level : reactor or mine worker's protective clothing. Ores.

Protection

Distance and shielding are the primary protection methods after exposure minimisation. Radiation intensity falls with the square of distance from the source. (1/4 at 2m, 1/9 at 3m, etc..)

Shielding

Efficacy depends on material and its thickness. The table below shows the thickness of material required to reduce the intensity of gamma radiation by 50%. Alpha particles travel 5-7cm in air, betas 2-8m. Fast neutrons (energy > 500keV ) may have more penetration than gamma rays.

Composites or plastics containing elements with good neutron capture or absorption properties e.g., boron, cadmium, silver, indium, graphite, beryllium, and hydrogen will have better values than plain composite laminate.

Alloys containing depleted uranium and similar heavy atoms will be at a penalty due to induced radiation (e.g., neutrons may cause fission).

Crystaliron, superdense materials and electropolymorphic plastics may have an extra advantage in protecting from cosmic radiation, due to the presence of the stabilising current, or its magnetic properties (crystaliron hulls are effectively a single magnetic domain). A protective belt of charged particles may form around the ship.

Radiation Effects

Whole body exposures are the most problematic. Doses which would be lethal if applied to the entire body are routinely used in radiotherapy.

Radiation most readily damages dividing cells. Those tissues which turn over rapidly are the most radiosensitive e.g., bone marrow, gonads, gut lining, cornea of the eye, and skin.

Haemopoietic syndrome

100 to 1000 rems.
The bone marrow is suppressed or destroyed. There are few or no functional white blood cells to fight infection.

 

Gastrointestinal syndrome

1000 to 5000 rems.
The cells lining the gut are suppressed or destroyed. Diarrhoea results from inability to absorb and exaggerated secretion of fluid. Infection is common as gut bacteria enter the body.

 

Central nervous system syndrome

5000+ rems.
An acute inflammatory reaction takes place in the blood vessels of the brain, as well as the brain itself. The brain suffocates as oxygen can't diffuse across the inflamed vessel walls.

Treatment

Effective treatment of high levels of radiation exposure are not available until TL 13.

Make consciousness check (Difficult, End).

Establish venous access, volume resuscitate (Minor+).

To treat high-level radiation exposure

(Difficulty), Medical, Edu, uncertain

Lab investigations can be ordered as per trauma articles

Chelation therapy is used for ingested or inhaled material (exposure to fallout, usually).

Recovery rates as per trauma articles.

Some effects of radiation exposure may be delayed.

Cataract

The lens of the eye becomes cloudy and/or opaque.  Check the following task 3 months after exposure:

 

To avoid developing cataracts

(exposure severity), End
Failure leads to the development of cataracts.
Treatment is required as blindness will ensue within 2D months.

Malignancy

Cancerous tumors develop and spread. Check the following task at each aging point after exposure

To avoid developing a malignancy

(exposure severity), End.
Failure leads to the detection of a malignancy.
Roll 2D to determine system

Sterility

The reproductive system is affected such that viable offspring cannot be created. May be temporary or permanent.

Rolling back radiation damage

Cloned or regenerated parts, or reanimation will reduce total exposure. For simplicity, replacement parts reduce exposure by 10% per part.

Reanimation returns total exposure to the level before the lethal dose. Cataract and malignancy checks are one level of difficulty easier.

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