Nuclear explosions: Two main processes: fission and fusion.
Fission is the splitting of atomic nuclei. In nuclear weapons, isotopes of Uranium and Plutonium are split to release explosive power in a rapid chain reaction. Free neutrons bombard nuclei, causing them to split, releasing energy. This process releases more neutrons, which cause more fission. Chain reactions go on until all raw material is used up, in the process creating fission products from original elements. Most of 80 or so fission products are unstable, radioactive isotopes of lighter elements. Fission will occur spontaneously for a critical mass of certain isotopes of Plutonium or Uranium, and bomb design is based on mechanisms which bring together a critical mass of these materials, thus triggering the expolsion.
Fusion: in fusion, a pair of light nuclei fuse together, forming a heavier element. An example is the fusing of the hydrogen isotope deuterium. Fusion is achieved by very high temperatures, and releases large amounts of energy (this is the process that goes on in the sun). For this reason, fusion devices are triggered at high temperatures by fission reactions (for this reason they arte known as thermonuclear devices). Thermonuclear devices cause explosions of great power (hydrogen bombs).
Energy yield: is measured by comparison with the explosive power of TNT, the most powerful expolosive in use during WWII. 1 kiloton = 1,000 tons TNT. The bombs dropped on Japan were approximately 20 kT. Modern nuclear weapons arew measured in megatons: MT Millions of tons. Yield includes explosive and thermal energy only: the actual energy release is higher. Types of energy: fission weapons: 85% air blast, heat and thermal radiation; 15% nuclear radiation.
Detonation: Very high concentration of energy at detonation mean extremely high temperatures several tens of million degrees C. This means that initial energy release is mainly extreme shortwave: X-Rays. This is mainly absorbed in air surrounding burst, and re-emitted as longer wave by superheated air as infra red and visible (Thermal radiation). A Fireball is created, this rises rapidly, soon attaining upward velocities of 100 m/sec. Rising sphere soon becomes unstable, deforming into a torus or donut shape (giving the characteristic mushroom). Lower air drawn in, forming stem, along with debris raised by initial blast. Fireball stabilizes when pressure and temperature equal that of surrounding air, so altitude will depend on atmospheric conditions. <100kt will stabilize in upper troposphere (<15km above the ground); >100-200kt will penetrate stratosphere. Cloud attains max height in about 10 minutes, then spreads laterally. The thermal radiation is very harmful: igniting fires, causing burns, blindness and other eye damage.
Blast also releases Nuclear Radiation, Types of radiation: alpha, beta, gamma, neutrons. Alpha radiation consists of positively charged particles (2 protons plus 2 neutrons = helium nucleus); Beta radiation consists of high speed electrons. Harmful, ionizing radiation; Gamma: high energy shortwave radiation. Can travel great distances and penetrate great thicknesses. Can be felt as tingling sensation at very high intensities. Ionizing, with very harmful effects. Neutrons: neutral particles from atomic nuclei; contribute to nuclear chain reactions.
Radiation from nuclear explosion:
30% initial nuclear radiation, produced in fission processes or within
1 minute or so: mainly gamma ray, but also neutrons, alpha and beta.
70% delayed radiation produced by radioactivity of debris: gamma rays
and beta particles.
Fallout: Debris and water droplets become coated or mixed with fission products. Once initial atmospheric disturbance subsides, these contaminated particles fall to earth: fallout. This is the main source of residual or delayed radiation. Main fission products contributing to radioactive fallout: Iodine-131, Caesium-137, and Strontium-90.
Amount of fallout depends on yield, position of burst (air bursts, ground bursts), nature of surface beneath explosion, and weather conditions. Air bursts produce less fallout than ground bursts.
Large particles descend first: the local or early fallout. Very small
particles descend slowly, over very large areas (worldwide or delayed fallout).
Rain may also scavenge radioactive materials, creating concentrations of
fallout.
Nuclear Radiation enters body by inhalation, ingestion.
Ionizes molecules in cells: stripping electrons from atoms, destroying
cells and impairing their function. Poisons can be created by falfunction;
cell division impaired.
Acute Radiation Sickness. Effects vary with dose. Damage
to intestine: vomiting, diarrhoea; fever; ulceration of gums; loss of hair;
destruction of bone marrow; breakdown of immune system.
>1,000 rems will cause death within hours or days: massive damage to
central nervous system.
Long term effects
Iodine collects in Thyroid gland (located in the throat: controls growth
in children). Strontium is similar chemically to Calcium, so collects in
bones. Caesium behaves similarly to potassium, so readily enters and becomes
incorporated in tissues. Thus radioisotopes of these elements accumulate
in particular parts of the body, and can cause cancers. Strontium 90 causes
cancers of the bone marrow (leukemia), while Iodine 131 causes thyroid
cancers in children. Exposure to radiation also increases infertility;
miscarriages; stillbirths; genetic mutations, which are passed on from
generation to generation; and cataracts.
Immediate death toll of 120,000, which had risen to 210,000 by 1980s. Huge human suffering from radiation effects, plus long term cancers, genetic defects. Dramatic increase in leukemias.
Weapons Testing. During atmospheric bomb tests, many military and civilian personnel were exposed to high levels of radiation.
Military personnel: during atmospheric testing, military personnel
were required to work in test zones, setting up areas, monitoring effects,
and as guinea pigs.
Example: November 1957-September 1958, Britain exploded 6 nuclear weapons,
including 4 hydrogen bombs, at Christmas Island in central Pacific. Safety
measures very lax. Troops were lined up on beaches to witness explosions
on each occasion (some men several times). They were given no protective
clothing, told to cover their ears when the flash appeared. Apart from
terrifying experience of the sights and sounds of the blasts, many suffered
from acute radiation sickness and radiation burns, and long term effects.
Long term effects came to light in early 1980s: when many test veterans
suffered sterility, cancers, cataracts, abnormalities in children. British
Nuclear Tests Veterans Association set up to press compensation claims.
Within two years of BNTVA formation, c. 90 members had died, many with
cancers. They, and similar groups set up elsewhere, are still awaiting
proper recognition of their case by their governments. This experience
is not unusual: troops involved in practice assaults on test sites immediately
after tests in Nevada. US, Canadian, Australian and British troops were
involved in different tests around the world. Nothing is known of USSR
and Chinese experience.
Civilian Populations
Example: Marshall Islands
66 tests were conducted in this area of the Pacific, most of which
only resulted in small radiation doses for inhabitants of islands. One
event was traumatic: the largest ever hydrogen bomb test on the 1st March
1954: a15 MT blast on Bikini Atoll. Change from predicted wind direction
resulted in substantial contamination of 7,000 square miles. Area extended
350 miles downwind, 20 miles upwind, and 60 miles across. Marshall Islands
were contaminated by fallout. Fallout arrived first on Rongelap, 100 miles
from Bikini, then passed over inhabited islands of Rongerik and Utirik.
The inhabited islands were evacuated two days after the blast, but until
then, Islanders were exposed to fallout, receiving external doses and internal
doses from eating contaminated food or drank water from open containers.
Some fallout was white and powdery, and lay 4cm thick in places: children
allowed to play in it, believing it was snow (which they had heard about
but never seen). Total gamma dose estimated as 175 REM on Rongelap (cf.
5-12 acceptable annual dose for nuclear workers).
Rongelap Islanders: Short term: acute radiation sickness - vomiting,
diarrhoea, skin burns, eye damage, respiratory diseases, 90% of childern
suffered hair loss. Long-term effects - significant increase in miscarriages
and stillbirths. High rate of thyroid abnormalities among children (radioactive
iodine accumulates in the thyroid gland): 1 case in 1963, 18 cases in 1966,
28 cases by 1974, three of which were malignant tumours. 1 case of leukemia.
Bikini Island was resettled in 1971, evacuated again in 1978 by Greenpeace,
and declared uninhabitable for another 50 years, due to radioactive isotopes
in foods.
Civilian populations were also affected in Nevada and Australia. At the Maralinga test site in Australia, local Aboriginal populations were not warned of tests, and some families remained in test areas, receiving high doses of radiation.
Worldwide Civilian casualties? Global effects of atmospheric testing
may never be known: impossible to separate cancers etc, due to radiation
from those due to other causes. Opinions vary widely. Wales: cancer incidence
in 1980s, suggested link with fallout scavenged by rain during 1960s.
Immediate Soviet response was to send local firefighters to extinguish fires around reactor complex. Bravery of these workers prevented spread of fires to Reactor 3, limiting extent of disaster. 31 lost lives shortly afterward, 200 others developed acute radiation sickness. On 27th April, helicopters began dropping 5000 tons of dolomite, clay, sand, boron and lead onto ruined reactor, while liquid nitrogen was injected below the reactor as a coolant. Eventually sealed the reactor core, and reduced release of radioactivity to low levels by 10th May. Clean-up operations massive, involving some 800,000 personnel (the liquidators). Sealing of reactor the Sarcophagus: main priority was speedy containment, so structure was not designed for long-term.
Wider Soviet response was slow. First indication of accident outside USSR was at Polish reactor, where routine measurements showed analously high radiation levels. However, instruments assumed to be faulty, and results ignored. Measurements at Swedish nuclear plant on 28th April picked up radiation, and interpreted as result of reactor accident in USSR. This was denied at first, then confirmed by satellite images.
At first, Soviet authorities thought fallout would be confined to a 5 km radius, and people living within10 km of reactor (including city of Pripiat) were not evacuated until 36 hours after accident. Exclusion zone extended to 30 km a week later, resulting in the evacuation of 200,000 people. Huge radiation levels in surrounding area, plus fallout carried over much of western Europe by winds. Fallout levels were highest where rainfall occurred, when dust was washed out of the atmosphere. In Britain, fallout was highest in the north and west. Chernobyl deposited more Caesium-137 onto parts of Europe than was deposited by all atmospheric tests.
Health Effects: Plant workers and firefighters suffered acute radiation sickness. Three died on night of accident, and over 200 hospitalised. In the highest exposure group (6-16 Gy), the first reaction was usually vomiting, occurring within 15-30 minutes of exposure. These patients were desperately ill; fever and intoxication as well as diarrhoea and vomiting, were prominent features. Mucous membranes were severely affected, becoming swollen, dry and ulcerated, making breathing and swallowing extremely painful and difficult. Extensive burns both thermal and due to beta radiation often complicated the illness. Within the first two weeks white blood cells and platelets fell dramatically, indicating a very high dose which had compromised the production of blood cells in the bone marrow, making it virtually impossible for the patients to fight infection or to retain the natural clotting activity of the blood. Almost all the patients with such high doses died (20 of 21), in spite of the intensive specialised medical treatment provided. Total fatalities in immediate aftermath of accident: 31.
Long-term effects: Dramatic increase in the incidence of thyroid cancers (due to radioiodine), especially in children, in the worst affected areas of the former USSR. For the eight years prior to 1986, only five cases of childhood thyroid cancer were seen in Minsk, which is the main Belarussian centre for thyroid cancer diagnosis and treatment on children. From 1986 to 1989, 2 to 6 cases of thyroid cancer in children were seen annually in Minsk. In 1990, the number jumped to 29, to 55 in 1991, then to 67 in 1992. By the end of 1994 the total had reached over 300 in Belarus. Nearly 50 per cent of the early (1992) thyroid cancers appeared in children who were aged between one and four years at the time of the accident. Longer term effects on other sectors of population still uncertain. The Liquidators are an especially high risk group, having been exposed to moderate to high levels of radiation.
Beyond the Soviet Union
Throughout affected areas of Europe, livestock and foodstuffs were
destroyed to minimise risk of human contamination. E.G. In the United Kingdom,
restrictions were placed on the movement and slaughter of 4.25 million
sheep in areas in southwest Scotland, northeast England, north Wales and
northern Ireland. Reindeer in northern Scandinavia: 80% of reindeer culled
were deemed unfit for consumption, effectively destroying resource base
of Lapps.
Longer term effects: cancers etc: will not be known for many years. Official estimates claim that cancer deaths will be far fewer than that caused by other factors (e.g. 2,000 in Europe cf. 35,000,000 in next 40 years). Even if estimates are correct, does this make it alright?
Internet Resources:
Atmospheric bomb tests: after decades of official silence, large
amounts of information are now becoming available on the shameful history
of nuclear testing during the Cold War. An excellent source is the Final
Report of the Advisory Committee on Human Radiation Experiments. This
is a book-sized document, well worth dipping into. Chapter 10 deals with
military personnel at test sites, and shows how the military deliberately
exposed servicemen to radiation while denying the risks. Chapter 12, Section
3 deals with the Marshall Islanders, and their continuing problems.
For an official, detailed assessment of the Chernobyl disaster,
see Chernobyl:
10 Years on, a 1995 report by the
OECD Nuclear Energy Agency
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