Radiation basically has either short or long term effects, depending mainly on the dose and the dose rate. The short term effect of high doses is radiation sickness. Longer term effects of lower but sustained doses include cancer.

Radiation sickness

High doses of gamma or neutron radiation of the type experienced by survivors relatively close (i.e. within ten or twenty kilometres) of high yield, low blast weapons will typically lead to radiation sickness. If the dose is high enough, radiation sickness will be fatal within weeks or even days. Really massive doses of radiation can result in radiation sickness which is fatal in only hours, but such high doses are more typical of nuclear power station accident victims or those venturing into the vicinity of the blast within a few days. Anyone receiving such a dose from a from the actual explosion is more likely to die from the thermal effects or the blast.

Cancer and other longer term effects

Cancer is more likely to result from lower doses of gamma or neutron radiation, or from extended or internal contact (i.e. ingestion or inhalation) with alpha or beta emitters present in fallout. Other effects of such contact include longer-term organ damage, teratogenic effects (i.e. birth defect) etc.

Protecting against radiation sickness

Shielding against penetrating radiation resulting from an actual nuclear explosion requires thick layers of lead and/or concrete, or any other dense material. The only realistic protective measure in such cases is a bunker of some sort. If you are caught out in the open in the event of a nuclear explosion and you are close enough to be inconvenienced by the blast wave, by the time it arrives you have in all probability already received a fatal dose of either gamma or neutron radiation, probably both. No reasonably portable item of equipment can protect you from this.

Protecting against long term effects

Most battlefield protective equipment and training focuses on allowing soldiers to operate for limited periods in areas heavily contaminated with fallout. Fallout is dust, particles too small to see and small enough to breathe in, made radioactive by irradiation from the initial blast and by contamination with fission products (even fusion bombs cover the battlefield in fission products, because fusion bombs use fission to generate the enormous heat and pressure required to initiate fusion). Since this dust is mainly radiating alpha and beta radiation, i.e. non-penetrating radiation, the main point of protective measures is to prevent the inhalation or ingestion of any of the fallout. For that reason, the same equipment used to protect the soldier from chemical and biological threats is appropriate, and actually relatively effective for short periods if the equipment is in good order and the operator is properly trained.

Specifically the soldier is equipped with a respirator to prevent inhalation of contaminants, a special suit to prevent skin contact, other special clothing (overboots, gloves etc.) to prevent contamination of standard battledress, and with drugs to counter the symptoms of radiation sickness if required.

It should be noted however that these drugs do counter only the symptoms - nausea, vomiting, bleeding from gums, loss of hair and teeth etc. They allow a fatally irradiated soldier to continue to be operationally effective for longer. They do not and cannot cure radiation sickness. A soldier who survives the initial exposure to a high dose rate of radiation is going to die, sooner rather than later and in an unpleasant way.

Another by-product of a nuclear blast is radon gas, which is radioactive and has a half-life of only a few days. This may be respirable in significant concentrations even kilometres away from the blast. No respirator filter will remove this element - the only defence against it is to rely entirely on bottled air. Radon can therefore very easily be inhaled despite any practicable protective measures. If an atom of radon in the lung decays, it transforms into an atom of Polonium 218 (a solid), which has a half life of only three minutes. This then decays to lead by emitting an alpha particle, the most damaging form of radiation, right there in contact with the lung tissue. The lead, of course, will remain in the lung. Radon gas is naturally emitted by granite deposits, which is why people who live in Cornwall and Devon, UK, experience much higher doses of radiation than people in other areas of the UK, even those near nuclear facilities.

It is worth mentioning here one of the most chilling neologisms coined in the 1980s. "Biorobot" was a word used to describe those humans who went into the vicinity of reactor number four at Chernobyl in the few hours after the accident. They included engineers, rescue workers and helicopter pilots. They went in to do things like dump large quantities of graphite powder on the burning reactor to moderate¹ ongoing nuclear reactions. They were not issued protective equipment, because no protective equipment would been of any use to them. They knew that within minutes of approaching close enough to do any good, they would have received a dose of radiation which would kill them horribly within hours. No machine could have done the work they did, which certainly mitigated the effects of the accident to an extent we cannot know. They all died, as they knew they would, before the news of the accident was even officially announced in the west.