451 lines
20 KiB
Plaintext
451 lines
20 KiB
Plaintext
A Note on Radiation Damage
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"There is no safe level of radiation exposure. So the question is not: What
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is a safe level? The question is: How great is the risk?"
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Karl Z. Morgan
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There have been three major theories as to how radiation damages living
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tissue, all set by physicians. All are approximations, and based on broad
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assumptions.
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(1) The threshold hypothesis: asserts that there exists a safe level of
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radiation. The idea behind this thinking is that if the does is low, then
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the cell repair rate is of the order of the damage rate. Hence you get
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no resultant damage.
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(2) The linear hypothesis: under this theory, you would expect 1 malignant
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cancer for 1000 person-rems. For example, you would find one cancerous
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patient if you exposed 500 people to 2 rems, or 10000 people to 0.1 rems.
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(3) The supralinear hypothesis: the main result here is that for low doses
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you get more cancers/person-rem than at high doses. Here they not saying you
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get more radiation; instead, you get more damaged surviving cells.
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Some Facts
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There are 4 types of ionising radiation. These are alphas
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(fast moving helium nuclei),
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betas (electrons), gammas (high energy EM radiation), and neutrons (highly
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penetrating).
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How does damage occur? In other words, how does radiation cause cancer?
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A typical cell is around 0.02mm across, a cell nucleus is about 0.001mm.
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When radiation, say a gamma, enters your body, there is a chance it will
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intersect with one of your cells. Inside any cell is a nucleus, which
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contains chromosomes. These are essentially DNA helixes. DNA looks like
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two entwined strings of nucleotides - the amino acids A, T, C, and G. Across
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strands they are paired A-T and C-G. A portion of DNA (a series of these
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acids) is called a gene. Genes exist along chromosomes, and they contain
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the data for proteins.
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If the radiation happens to pass into the cell nucleus (which is a relatively
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large entity compared to the rest of the cell), one of 4 things can happen.
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All exposure subjects cells to risk. In order of decreasing probability:
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(1) radiation goes right thru, no interaction.
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(2) radiation does irrepairable destruction, and cell dies.
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(3) radiation does damage to nucleus. Cell survives in
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this damaged state. After it repetitively divides, it
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grows into a solid tumour after 30 odd years - cancer.
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(4) radiation does repairable damage, and cell returns to
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normal state. (Very low probability).
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Possibility (3) is the one to watch out for. During division, the DNA
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strands stretch out, and it is during this time which your cells are most
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susceptible to damage.
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It is also possible for the radiation to ionise the water in the cell
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cytoplasm, leading to the formation of free radicals, which can travel
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some distance. They can react chemically with the DNA in the nucleus,
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interfering with the chemical bonding along the helix.
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Two types of damaging interaction can occur with the amino acids.
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(a) point mutations
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- deletion
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- substitution
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- inversion
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- addition
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(b) large scale mutations (chromosome aberrations)
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- deletion e.g. retinoblastoma
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- amplification
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- translocation
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It is also possible to have compound breaks along the DNA, which is not
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easy for the cell to repair, unlike single strand or double strand breaks.
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The cell and nuclear membranes are also susceptible to damage. This could
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be due to alterations in permeability/osmosis in the membrane due to the
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radiation-induced imbalance of ionised particles.
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Once a certain threshold is exceeded, you will start saturating the cells.
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This lethal threshold serves to define two categories of radiation.
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Effects
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EFFECT NATURE THRESHOLD? DOSE DEPENDENCE
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Stochastic Non-lethal mutations No Probability of
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(somatic or affecting single cells effect increases
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genetic) with dose
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Deterministic Lethal mutations Yes Severity of
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affecting large number effect increases
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of cells with dose
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Cancer
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Stem cells are ones which are able to undergo mitosis when the human body
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has reached full maturity. Examples are blood cells, and the cells lining
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your intestines. During normal functioning of your body, cell replacement
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balances cell loss.
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In cancer, a stem fails to stop its mitosis. It and its descendants divide
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uncontrolled, forming a tumour. A bit like a binary tree in cell
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multiplicity.
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Oncogenes are genes which interfere with the cell division process. They
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are mutations of proto-oncogenes, whose role are to control cell growth
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and mitosis. It is thought radiation promotes creation of oncogenes.
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There are also cancer-suppressing genes, which inhibit oncogene formation.
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The best known example is the Rb gene, which inhibits retinoblastoma.
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After all of this, let me add a fourth idea on radiation damage:
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(4) probability of hereditary genetic damage or cancer is a function of:
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type of radiation (a,b,g,n) x energy of radiation x dose rate
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Here you have 4 discrete degrees of freedom, and 2 continuous degrees: rate &
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energy. Assume that there is a cut-off energy for a unit of a particular type
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of radiation, E_max, such that if E > E_max a cell will die, and E < E_max
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the cell will survive (either in damaged or undamaged state). We are worried
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about the E < E_max cases. If E > E_max then you get radiation poisoning and
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you will definitely die if you get a large enough dose.
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The probability of nucleus intersection is a function of radiation type. (The
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size of radiation varies considerably.)
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The probability of a nucleus being hit twice or more is very low, unless
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the number of incident radiation approaches the sample size. In which case
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you get radiation poisoning and die anyway.
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You get a 6D phase space of statistical mechanics. Supplement this with an
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action in path integral form. Plotted, you'd have a 6D graph, unlike your
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normal 3D graphs. It's worse than the 4D spacetime of general relativity.
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No wonder the physicicans only plot projections! You can trace out a person's
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history in this phase space, and then give them a final probability of
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cancer/hereditary damage.
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============================================================================
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Plutonium's Risk to Human Health Depend On Its Form
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In a nuclear explosium, plutonium-239 fissions and releases a huge amount of
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energy and radiation. But plutonium itself is a highly toxic element that requires
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a great deal of care in handling.
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Experts agree that the silvery, unstable metal plutonium-239, with a half-life of
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24,000 years, is hazardous and sould be isolated from the biosphere. However, the
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risks posed to workers and communities by stored plutonium depend on the route of
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exposure as well as the particle size, isotope, and chemical form.
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Weapons-grade plutonium outside the body presents little risk unless exposures are
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frequent and extensive. It emits primarily alpha particles, which cannot penetrate
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skin, clothing, or even paper. Nearly all the energy from plutonium is deposited
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on the outer, nonliving layer of the skin, where it causes no damage. The neutrons
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and the relatively weak gamma photons it emits can penetrate the body, but large
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amounts of weapons-grade plutonium would be needed to yield substantial doses.
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Workers wearing only lead aprons can handle steel drums containing solid plutonium
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metal with no immediate untoward effects. However, as weapons-grade plutonium
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ages, it becomes more dangerous because some of the contaminating plutonium-241 is
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converted via beta decay to americium-241, which emits far stronger gamma
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radiation.
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On the other hand, plutonium inside the body is highly toxi. Solid plutonium metal
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is neither easily dispersed nor easily inhaled or absorbed into the body. But if
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plutonium metal is exposed to air to any degree, it slowly oxidizes to plutonium
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oxide (PuO2), which is a powdery, much more dispersable substance. Depending on
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the particle size, plutonium-239 oxide may lodge deep in the alveoli of the lung
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where it has a biological half-life of 500 days, and alpha particles from the
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opxide can cause cancer. Also, fractions of the inhaled plutonium oxide can slowly
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dissolve, enter the bloodstream, and end up primarily in bone or liver.
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Plutonium oxide is weakly soluble in water. If it is ingested in food or water,
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only a small fraction (4 parts per 10,000) is absorbed into the gastrointestinal
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tract. However, it may take just a few millionths of a gram to cause cancer over
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time. In animals, small doses induce cancer, especially in lung and bone.
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In published studies of plutonium's effects on humans, most subjects were exposed
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to multiple sources of radiation. Some researchers say the available health data
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on plutonium workers have not yet been used to do careful epidemiological studies,
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because researchers have been denied access to much of the data on workers and
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military personnel exposed to plutonium. In the studies done so far, plutonium
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workers do not show major excesses of any type of cancer.
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Becuase of the relative lack of human data, the risks of chronic exposure to
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plutonium are uncertain. Exposure standards in the U.S. are based partly on
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studies of survivors of Hiroshima and Nagasaki and partly on animal experiments. A
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1991 White House Office of Science & Technology Policy studye says that
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"sufficient human data are not available to provide accurate risk assessment of
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exposure."
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============================================================================
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Nuclear Blast Effects
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The first thing bomb victims experience is the intense flux of photons from
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the blast, which releases 70-80% of the bomb's energy. See the Hiroshima-
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Nagasaki file for first hand accounts. The effects go up to third degree
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thermal burns, and are not a pretty sight. Initial deaths are due to this
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effect.
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Then next phenomenon is the supersonic blast front. You see it before you
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hear it. The pressure front has the effect of blowing away anything in its
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path. Heavy steel girders were found bent at 90 degree angles after the
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Japanese bombings.
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After the front comes the overpressure phase. It would feel like being under
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water a few hundred metres. At a few thousand metres under the sea, pressurised
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hulls implode. The pressure gradually dies off, and there is a negative
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overpressure phase, with a reversed blast wind. This reversal is due to
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air rushing back to fill the void left by the explosion.
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The air gradually returns to room pressure. At this stage, fires caused by
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electrical destruction and ignited debris, turn the place into a firestorm.
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Just like Dresden in WWII. It is estimated over fifty thousand died in the
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first few days of the Hiroshima bombing.
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Then come the middle term effects such as keloid formation and retinal
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blastoma.
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Genetic or hereditary damage can show up up to forty years after initial
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irradiation.
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The following diagram is of blast zone radii, courtesy of Outlaw Labs.
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Note that damage from blast pressure falls off as a function of 1/r^3.
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============================================================================
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- Breakdown of the Atomic Bomb's Blast Zones -
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----------------------------------------------
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.
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. .
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. . .
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. .
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[5] [4] [5]
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.
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. . . .
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. . . .
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. [3] _ [3] .
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. . [2] . .
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. _._ .
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. .~ ~. .
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. . [4] . .[2]. [1] .[2]. . [4] . .
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. . . .
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. ~-.-~ .
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. . [2] . .
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. [3] - [3] .
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. . . .
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. ~ ~ .
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~
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[5] . [4] . [5]
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.
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. .
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. .
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.
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============================================================================
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- Diagram Outline -
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---------------------
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[1] Vaporization Point
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------------------
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Everything is vaporized by the atomic blast. 98% fatalities.
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Overpress=25 psi. Wind velocity=320 mph.
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[2] Total Destruction
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-----------------
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All structures above ground are destroyed. 90% fatalities.
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Overpress=17 psi. Wind velocity=290 mph.
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[3] Severe Blast Damage
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-------------------
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Factories and other large-scale building collapse. Severe damage
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to highway bridges. Rivers sometimes flow countercurrent.
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65% fatalities, 30% injured.
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Overpress=9 psi. Wind velocity=260 mph.
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[4] Severe Heat Damage
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------------------
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Everything flammable burns. People in the area suffocate due to
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the fact that most available oxygen is consumed by the fires.
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50% fatalities, 45% injured.
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Overpress=6 psi. Wind velocity=140 mph.
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[5] Severe Fire & Wind Damage
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-------------------------
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Residency structures are severely damaged. People are blown
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around. 2nd and 3rd-degree burns suffered by most survivors.
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15% dead. 50% injured.
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Overpress=3 psi. Wind velocity=98 mph.
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----------------------------------------------------------------------------
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- Blast Zone Radii -
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----------------------
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[3 different bomb types]
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____________________________________________________________________________
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______________________ ______________________ ______________________
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| -[10 KILOTONS]- | | -[1 MEGATON]- | | -[20 MEGATONS]- |
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|----------------------| |----------------------| |----------------------|
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| Airburst - 1,980 ft | | Airburst - 8,000 ft | | Airburst - 17,500 ft |
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|______________________| |______________________| |______________________|
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| [1] 0.5 miles | | [1] 2.5 miles | | [1] 8.75 miles |
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| [2] 1 mile | | [2] 3.75 miles | | [2] 14 miles |
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| [3] 1.75 miles | | [3] 6.5 miles | | [3] 27 miles |
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| [4] 2.5 miles | | [4] 7.75 miles | | [4] 31 miles |
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| [5] 3 miles | | [5] 10 miles | | [5] 35 miles |
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|______________________| |______________________| |______________________|
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____________________________________________________________________________
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============================================================================
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Atmospheric Effects of Blasts
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The Mushroom Cloud
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The heat from fusion and fission instantaneously raises the surrounding air
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to 10 million degrees C. This superheated air plasma gives off so much light
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that it looks brighter than the sun, and is visible hundreds of kms away.
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The resultant fireball quickly expands. It is made up of hot air, and hence
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rises, at a rate of a few hundred metres per second. After a minute or so,
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the fireball has risen to a few kilometres, and has cooled off to the extent
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that it no longer radiates.
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The surrounding cooler air exerts some drag on this rising air, which slows
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down the outer edges of the cloud. The unimpeded inner portion rises a bit
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more quicker than the outer edges. A vacuum effect occurs when the outer
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portion occupies the vacuum left by the higher inner portion. The result is
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a smoke ring.
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The inner material gradually expands out into a mushroom cloud, due to
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convection. If the explosion is on the ground, dirt and radioactive debris
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get sucked up the stem, which sits below the fireball.
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Collisions and ionisation of the cloud particles result in lightning bolts
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flickering to the ground.
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Initially, the cloud is orange-red due to nitrous oxide formation (cf car
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smog). This reaction happens whenever air is heated.
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When the cloud cools to air temperature, the water vapour starts to
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condense. The cloud turns from red to white.
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In the final stages, the cloud can get about 100km across and 40km high,
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for a megaton class explosion.
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============================================================================
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Electromagnetic Pulse (EMP)
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A nuclear explosion gives off radiation at all wavelengths of light. Some
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is in the radio/radar portion of the spectrum - the EMP effect. The EMP
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effect increases the higher you go into the atmosphere. High altitude
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explosions can knock out electronics by inducing a current surge in
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closed circuit metallic objects - computers, power lines, phone lines,
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TVs, radios, etc. The damage range can be over 1000km.
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============================================================================
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Here are some good references on radiation damage. See also the main
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References file.
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AUTHOR: Sumner, David, D. Phil
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TITLE: Radiation risks : an evaluation / David Sumner, Tom Wheldon, Walter
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Watson. -- 3rd ed.
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ISBN/ISSN: 187078104X
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IMPRINT: Glasgow [Scotland], Tarragon Press, 1991
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PHYS DESC: 236 p., ill., map, 21 cm.
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ADD AUTH1: Wheldon, Tom
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ADD AUTH2: Watson, Walter
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NOTE 1: Includes index Bibliography: p. 227-229
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SUBJECT 1: Radiation--Physiological effect
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SUBJECT 2: Cells--Effect of radiation on
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[Good introductory work.]
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CALL NO: Me f 616.989707 LOW
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TITLE: Low-level radiation effects: a fact book: prepared by Subcommittee
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on Risks of Low-Level Ionizing Radiation: A. Bertrand Brill ... [et
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al.]
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ISBN/ISSN: 0932004148
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IMPRINT: New York, NY: Society of Nuclear Medicine: c1982-
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PHYS DESC: 1 v. (loose-leaf): ill: 30 cm.
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ADD AUTH1: Brill, A. Bertrand
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ADD AUTH2: Society of Nuclear Medicine. Subcommittee on Risks of Low-Level
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Ionizing Radiation
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NOTE 1: To be kept up to date by inserts
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SUBJECT 1: Ionizing radiation--Physiological effect
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SUBJECT 2: Ionizing radiation--Toxicology
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SUBJECT 3: Radiation injuries
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SUBJECT 4: Low-level radiation--Physiological effect
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CALL NO: Me 574.1915 BIOL
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TITLE: Biological effects of low-level radiation : proceedings of an
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international symposium on the effects of low-level radiation with
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special regard to stochastic and non-stochastic effects / jointly
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organized by the International Atomic Energy Agency and the World
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Health Organisation, and held in Venice, Italy, 11-15 April 1983
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ISBN/ISSN: 9200101836
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IMPRINT: Vienna, International Atomic Energy Agency, 1983
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PHYS DESC: 682 p., ill, 24 cm. (Proceedings series)
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ADD AUTH1: International Atomic Energy Agency
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ADD AUTH2: World Health Organization
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SERIES 1: Proceedings series (International Atomic Energy Agency)
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NOTE 1: English and French
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SUBJECT 1: Radiation--Toxicology--Congresses
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SUBJECT 2: Radiation--Physiological effect--Congresses
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CALL NO: DS 574.1915 KIEF
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AUTHOR: Kiefer, J (Jurgen) , 1936- [Biologische Strahlenwirkung. English]
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TITLE: Biological radiation effects / Jurgen Kiefer
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ISBN/ISSN: 3540510893
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IMPRINT: Berlin, New York, Springer-Verlag, c1990
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PHYS DESC: xvii, 444 p., ill, 24 cm.
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NOTE 1: Rev. translation of: Biologishce Strahlenwirkung Includes
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bibliographical references (p. [415]-435) and indexes
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SUBJECT 1: Radiobiology
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SUBJECT 2: Radiation--Physiological effect
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SUBJECT 4: Radiation protection
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To learn more about air explosions, see the Reference by Kinney and Graham,
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"Explosive Shocks in Air".
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The Red Phoenix, 1994.
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