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This beautiful valley of Jezreel/Megiddo will never see an end-time battle
Last site edit: March 27 2017
In defence of the sidelined God Jehovah, Creator of the Universe and Father of Humanity
Carbon-Dating and other love matches
Radiometric techniques were developed after the discovery of radioactivity in 1896. The regular rates of decay for unstable, radioactive elements were found to constitute virtual “clocks” within the earth's rocks.
Radioactive elements such as uranium (U) and thorium (Th) decay naturally to form different elements or isotopes of the same element. (Isotopes are atoms of any elements that differ in mass from that element, but possess the same general chemical and optical properties.) This decay is accompanied by the emission of radiation or particles (alpha, beta, or gamma rays) from the nucleus, by nuclear capture, or by ejection of orbital electrons (see ATOM AND ATOMIC THEORY). A number of isotopes decay to a stable product, a so-called daughter isotope, in a single step (for example, carbon-14), whereas other series involve many steps before a stable isotope is formed. Multistep radioactive decay series include, for example, the uranium-235, uranium-238, and thorium-232 families. If a daughter isotope is stable, it accumulates until the parent isotope has completely decayed. If a daughter isotope is also radioactive, however, equilibrium is reached when the daughter decays as fast as it is formed.
Radioactive decay may take different routes. Thus, if the isotope decays by alpha emission, it loses the two protons and two neutrons that make up an alpha particle; the atomic number (number of protons) is reduced by two and the atomic mass (number of nuclear particles, or nucleons) by four. In beta decay, or electron loss, a radioactive nucleus can gain or lose one unit of electric charge without changing the number of nucleons. More radioactive substances are beta-ray emitters than alpha-ray emitters. A third important mode of decay involves electron capture; the nucleus of an atom absorbs an electron, which unites with a proton of the nucleus to form a neutron. Thus, the atomic number is reduced by one, but the mass of the nucleus remains unchanged. The fourth mode of decay, gamma radiation, consists of the emission of waves of electromagnetic energy.
Scientists describe the radioactivity of an element in terms of half-life, the time the element takes to lose 50 percent of its activity by decay. This covers an extraordinary range of time, from billions of years to a few microseconds. At the end of the period constituting one half-life, half of the original quantity of radioactive element has decayed; after another half-life, half of what was left is halved again, leaving one-fourth of the original quantity, and so on. Every radioactive element has its own half-life; for example, that of carbon-14 is 5730 years and that of uranium-238 is 4.5 billion years.
Radiometric dating techniques are based on radio-decay series with constant rates of isotope decay. Once a quantity of a radioactive element becomes part of a growing mineral crystal, that quantity will begin to decay at a steady rate, with a definite percentage of daughter products in each time interval. These “clocks in rocks” are the geologists' timekeepers.
Radiocarbon dating techniques, first developed by the American chemist Willard F. Libby and his associates at the University of Chicago in 1947, are frequently useful in deciphering time-related problems in archaeology, anthropology, oceanography, pedology, climatology, and recent geology. Through metabolic activity, the level of carbon-14 in a living organism remains in constant balance with the level in the atmosphere or some other portion of the earth's dynamic reservoir, such as the ocean. Upon the organism's death, carbon-14 begins to disintegrate at a known rate, and no further replacement of carbon from atmospheric carbon dioxide can take place. The rapid disintegration of carbon-14 generally limits the dating period to approximately 50,000 years, although the method is sometimes extended to 70,000 years. Uncertainty in measurement increases with the age of the sample.
Although the method is suited to a variety of organic materials, accuracy depends on the half-life to be used, variations in levels of atmospheric carbon-14, and contamination. (The half-life of radiocarbon was redefined from 5570 ± 30 years to 5730 ± 40 years in 1962, so some dates determined earlier required adjustment; and due to radioactivity more recently introduced into the atmosphere, radiocarbon dates are calculated from AD 1950.) The radiocarbon time scale contains other uncertainties, as well, and errors as great as 2000 to 5000 years may occur. Postdepositional contamination, which is the most serious problem, may be caused by percolating groundwater, incorporation of older or younger carbon, and contamination in the field or laboratory.
The decay of radioactive potassium isotopes to argon is widely used for dating rocks. (The decay of potassium-40 to calcium-40 that also takes place is not useful.) Geologists are able to date entire rock samples in this way, because potassium-40 is abundant in micas, feldspars, and hornblendes. Leakage of argon is a problem if the rock has been exposed to temperatures above 125° C (257° F), because the age of the rock will then reflect the last episode of heating rather than the time of original rock formation.
Used to date ancient igneous and metamorphic terrestrial rocks as well as lunar samples, this method is based on disintegration by beta decay of rubidium-87 to strontium-87. The method is frequently used to check potassium-argon dates, because the strontium daughter element is not diffused by mild heating, as is argon.
Methods Involving Thorium-230
Thorium ratio methods are used to date older oceanic sediments beyond the range of radiocarbon techniques. Uranium in seawater eventually decays to the thorium isotope, thorium-230 (also called ionium), which is precipitated into ocean-floor sediments. Because it has been undergoing decay longer, scientists can detect a decrease in quantity in higher levels, and a time scale can be developed in this way.
Thorium-230, part of the uranium-238 decay series, has a half-life of 80,000 years. Protactinium-231, derived from uranium-235, has a half-life of 34,300 years. Both parent elements are precipitated in the same proportions but at different rates. The ratio of the two changes regularly with time, showing greater differences in the quantity of undecayed parent isotopes in older sediments.
The ionium-thorium age method, applied to deep-sea sediments formed during the last 300,000 years, is based on the assumption that the initial ionium content of accumulating sediments has remained constant for the total section under study and is not derived from uranium decay; the age of the sample depends on this ionium excess, which decreases with time. In the ionium-deficiency method, the age of fossil shell or coral from 10,000 to 250,000 years old is based on the growth of ionium toward equilibrium with uranium-238 and uranium-224, which entered the carbonate shortly after its formation or burial. Similar disequilibrium relationships can be used to assess ages of carbonates in soils; this method is a complement to carbon-14 methodology.
Methods Involving Lead
Lead-alpha age is estimated by spectrographically determining the total lead content and alpha-particle activity (uranium-thorium content) of zircon, monazite, or xenotime concentrates. The lead-alpha, or Larsen, method is applied to rocks younger than Precambrian. In the uranium-lead method, age in years is calculated for geologic material based on the known radioactive decay rate of uranium-238 to lead-206 and of uranium-235 to lead-207. Coupled with decay rates for thorium-232 to lead-208, three independent ages may be obtained for the same sample. The determined lead-206 and lead-207 ratios can be converted into a so-called lead-lead age. The method is most applicable to materials Precambrian in age. Additionally, a uranium-uranium age, derived from the ratio of uranium-235 to uranium-238, can be calculated as a by-product of uranium-thorium-lead dating.
The fission-track method, also known as spontaneous fission-track dating, involves the paths, or tracks, of radiation damage made by nuclear particles in a mineral or glass by the spontaneous fission of uranium-238 impurities. Age in years is calculated by determining the ratio of spontaneous fission-track density to that of induced fission tracks. The method works best for micas, tektites, and meteorites. It has been used to help date the period from about 40,000 to 1 million years ago, an interval not covered by carbon-14 or potassium-argon methods. Rocks subjected to high temperatures or exposed to cosmic-ray bombardment at the earth's surface, however, may yield erroneous ages.
New techniques date various rock deposits by determining the concentrations of rhenium and osmium isotopes in them.
"Dating Methods," Microsoft (R) Encarta. Copyright (c) 1994 Microsoft Corporation. Copyright (c) 1994 Funk & Wagnall's Corporation.
From Wikipedia, the free encyclopedia
Carbon (pronounced /kαrbən/) is a chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. There are three naturally occurring isotopes, with carbo, coal, and, in some Romance and Slavic languages, the word carbon can refer both to the element and to coal.
There are several allotropes of carbon of which the best known are graphite, diamond, and amorphous carbon. The physical properties of carbon vary widely with the allotropic form. For example, diamond is highly transparent, while graphite is opaque and black. Diamond is among the hardest materials known, while graphite is soft enough to form a streak on paper. Diamond has a very low electrical conductivity, while graphite is a very good conductor. Under normal conditions, diamond has the highest thermal conductivity of all known materials. All the allotropic forms are solids under normal conditions but graphite is the most thermodynamically stable.
All forms of carbon are highly stable, requiring high temperature to react even with oxygen. The most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and other transition metal carbonyl complexes. The largest sources of inorganic carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil and methane clathrates. Carbon forms more compounds than any other element, with almost ten million pure organic compounds described to date, which in turn are a tiny fraction of such compounds that are theoretically possible under standard conditions.
Carbon is the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is present in all known lifeforms, and in the human body carbon is the second most abundant element by mass (about 18.5%) after oxygen. This abundance, together with the unique diversity of organic compounds and their unusual polymer-forming ability at the temperatures commonly encountered on Earth, make this element the chemical basis of all known life.
Awake 86 9/22 21-6 The Radiocarbon Clock
It Dates Once-Living Remains. Or Does It?
(The Uranium-Lead Clock; The Potassium-Argon Clock;
The Rubidium-Strontium Clock; discussed in previous article)
ALL the foregoing clocks run so slowly that they are of little or no use in studying archaeological problems. Something much faster is needed to match the time scale of human history. This need has been met by the radiocarbon clock.
Carbon 14, a radioactive isotope of ordinary carbon 12, was first found in atom-smashing experiments in a cyclotron. Then it was found also in the earth's atmosphere. It emits weak beta rays, which can be counted by a suitable instrument. Carbon 14 has a half-life of only 5,700 years, which is suitable for dating things associated with man's early history.
The other radioactive elements we have discussed have lives that are long compared to the earth's age, so they have existed since earth's creation down to the present day. But radiocarbon has such a short life, relative to the earth's age, that it can still be here only if it has been continually produced in some way. That way is the bombardment of the atmosphere by cosmic rays, which convert nitrogen atoms into radioactive carbon.
This carbon, in the form of carbon dioxide, is used by plants in the process of photosynthesis and is converted into all kinds of organic compounds in living cells. Animals and, yes, we humans, eat the plant tissues, so everything that lives comes to contain radiocarbon in the same proportion as it is found in the air. As long as anything lives, the radiocarbon in it, which decays, is replenished by fresh intake. But when a tree or an animal dies, the supply of fresh radiocarbon is cut off, and the radiocarbon level in it begins to drop. If a piece of wood charcoal or an animal bone is preserved for 5,700 years, it will contain only half as much radiocarbon as it had when alive. So, in principle, if we measure the proportion of carbon 14 remaining in something that once was alive, we can tell how long it has been dead.
The radiocarbon method can be applied to a wide variety of things of organic origin. Many thousands of samples have been dated by it. Their fascinating diversity is suggested by just a few examples:
Wood from the funerary ship found in the tomb of Pharaoh Seostris III was dated at 1670 B.C.E.
Heartwood from a giant redwood in California, which had 2,905 annual rings when it was cut down in 1874, was dated at 760 B.C.E.
Linen wrappings from the Dead Sea Scrolls, dated to the first or second century B.C.E. by the style of handwriting, were measured by the radiocarbon content to be 1,900 years old.
A piece of wood found on Mt. Ararat, and considered by some to be possibly from Noah's ark, proved to date only from 700 C.E.-old wood, indeed, but not nearly old enough to predate the Flood.
Woven rope sandals dug out of volcanic pumice in an Oregon cave showed an age of 9,000 years.
Flesh from a baby mammoth, frozen in Siberian muck for thousands of years, was found to be 40,000 years old.
How reliable are these dates?
Errors in the Radiocarbon Clock
The radiocarbon clock looked very simple and straightforward when it was first demonstrated, but it is now known to be prone to many kinds of error. After some 20 years' use of the method, a conference on radiocarbon chronology and other related methods of dating was held in Uppsala, Sweden, in 1969. The discussions there between chemists who practice the method and archaeologists and geologists who use the results brought to light a dozen flaws that might invalidate the dates. In the 17 years since then, little has been accomplished to remedy these shortcomings.
One nagging problem has always been to ensure that the sample tested has not been contaminated, either with modern (live) carbon or with ancient (dead) carbon. A bit of wood, for example, from the heart of an old tree might contain live sap. Or if that has been extracted with an organic solvent (made from dead petroleum), a trace of the solvent might be left in the portion analyzed. Old buried charcoal might be penetrated by rootlets from living plants. Or it might be contaminated with much older bitumen, difficult to remove. Live shellfish have been found with carbonate from minerals long buried or from seawater upwelling from the deep ocean where it had been for thousands of years. Such things can make a specimen appear either older or younger than it really is.
The most serious fault in radiocarbon-dating theory is in the assumption that the level of carbon 14 in the atmosphere has always been the same as it is now. That level depends, in the first instance, on the rate at which it is produced by cosmic rays. Cosmic rays vary greatly in intensity at times, being largely affected by changes in the earth's magnetic field. Magnetic storms on the sun sometimes increase the cosmic rays a thousandfold for a few hours. The earth's magnetic field has been both stronger and weaker in past millenniums. And since the explosion of nuclear bombs, the worldwide level of carbon 14 has increased substantially.
On the other hand, the proportion is affected by the quantity of stable carbon in the air. Great volcanic eruptions add measurably to the stable carbon-dioxide reservoir, thus diluting the radiocarbon. In the past century, man's burning of fossil fuels, especially coal and oil, at an unprecedented rate has permanently increased the quantity of atmospheric carbon dioxide. (More details on these and other uncertainties in the carbon-14 clock were given in the April 8, 1972, issue of Awake!)
Dendrochronology-Dating by the Growth Rings of Trees
Faced with all these fundamental weaknesses, the radiocarbon people have turned to standardizing their dates with the help of wood samples dated by counting tree rings, notably those of bristlecone pines, which live hundreds and even thousands of years in the southwestern United States. This field of study is called dendrochronology.
So the radiocarbon clock is no longer regarded as yielding an absolute chronology but one which measures only relative dates. To get the true date, the radiocarbon date has to be corrected by the tree-ring chronology. Accordingly, the result of a measurement of radiocarbon is referred to as a "radiocarbon date." By referring this to a calibration curve based on tree rings, the absolute date is inferred.
This is sound for as far back as the bristlecone ring count is reliable. The problem now comes up that the oldest living tree whose age is known goes back only to 800 C.E. In order to extend the scale, scientists try to match overlapping patterns of thin and thick rings in pieces of dead wood found lying nearby. By patching together 17 remnants of fallen trees, they claim to go back over 7,000 years.
But the tree-ring standard does not stand alone either. Sometimes they are not sure just where to put one of the dead pieces, so what do they do? They ask for a radiocarbon measurement on it and use that as a guide in fitting it in. It reminds one of two lame men with only one crutch between them, who take turns using it, one leaning for a while on his partner, then helping to hold him up.
One must wonder at the miraculous preservation of loose bits of wood lying so long in the open. It would seem they might have been washed away by heavy rainfall or picked up by passersby for firewood or some other use. What has prevented rot or insect attack? It is credible that a living tree might withstand the ravages of time and weather, an occasional one surviving for a thousand years or more. But dead wood? For six thousand years? It strains credibility. Yet this is what the older radiocarbon dates are based on.
Nevertheless, the radiocarbon experts and the dendrochronologists have managed to put aside such doubts and smooth over the gaps and inconsistencies, and both feel satisfied with their compromise. But how about their customers, the archaeologists? They are not always happy with the dates they get back on the samples they send in. One expressed himself this way at the Uppsala conference:
"If a carbon-14 date supports our theories, we put it in the main text. If it does not entirely contradict them, we put it in a footnote. And if it is completely 'out of date,' we just drop it."
Some of them still feel that way. One wrote recently concerning a radiocarbon date that was supposed to mark the earliest domestication of animals:
"Archeologists [are coming] to have second thoughts about the immediate usefulness of radiocarbon age determinations simply because they come out of 'scientific' laboratories. The more that confusion mounts in regard to which method, which laboratory, which half-life value, and which calibration is most reliable, the less we archeologists will feel slavishly bound to accept any 'date' offered to us without question."
The radiochemist who had supplied the date retorted: "We prefer to deal with facts based on sound measurements-not with fashionable nor emotional archeology."
If scientists disagree so sharply about the validity of these dates reaching back into man's antiquity, is it not understandable that laymen might be skeptical about news reports based on scientific "authority," such as those quoted at the head of this series of articles?
Direct Counting of Carbon 14
A recent development in radiocarbon dating is a method for counting not just the beta rays from the atoms that decay but all the carbon-14 atoms in a small sample. This is particularly useful in dating very old specimens in which only a tiny fraction of the carbon 14 is left. Out of a million carbon-14 atoms, only one, on the average, will decay every three days. This makes it quite tedious, when measuring old samples, to accumulate enough counts to distinguish the radioactivity from the cosmic-ray background.
But if we can count all the carbon-14 atoms now, without waiting for them to decay, we can gain a millionfold in sensitivity. This is accomplished by bending a beam of positively charged carbon atoms in a magnetic field to separate the carbon 14 from the carbon 12. The lighter carbon 12 is forced into a tighter circle, and the heavier carbon 14 is admitted through a slit into a counter.
This method, although more complicated and more expensive than the beta-ray-counting method, has the advantage that the amount of material needed for a test is a thousand times less. It opens up the possibility of dating rare ancient manuscripts and other artifacts from which a sample of several grams that would be destroyed in testing just cannot be had. Now such articles can be dated with just milligrams of sample.
One suggested application of this would be to date the Shroud of Turin, which some believe Jesus' body was wrapped in for burial. If radiocarbon dating was to show that the cloth is not that old, it would confirm the suspicions of doubters that the shroud is a hoax. Until now, the archbishop of Turin has refused to donate a sample for dating because it would take too large a piece. But with the new method, one square centimeter would be enough to determine whether the material dates from the time of Christ or only from the Middle Ages.
In any event, attempts to extend the time range have little significance as long as the greater problems remain unsolved. The older the sample is, the more difficult it is to ensure the complete absence of slight traces of younger carbon. And the farther we try to go beyond the few thousand years for which we have a reliable calibration, the less we know about the atmospheric level of carbon 14 in those ancient times.
Several other methods have been studied for dating events in the past. Some of these are related indirectly to radioactivity, such as the measurement of fission tracks and radioactive halos. Some involve other processes, such as the deposition of varves (layers of sediment) by streams flowing from a glacier and the hydration of obsidian artifacts.
The racemization of amino acids is another dating method used. But what does "racemization" mean?
Amino acids belong to the group of carbon compounds that have four different groups of atoms attached to a central carbon atom. The tetrahedral arrangement of the groups makes the molecule asymmetrical as a whole. Such molecules exist in two forms. Although chemically identical, one is physically the mirror image of the other. A simple illustration of this is a pair of gloves. They have the same size and shape, but one fits only your right hand, the other only your left.
A solution of one form of such a compound twists a beam of polarized light to the left; the other kind rotates it to the right. When a chemist synthesizes an amino acid from simpler compounds, he gets equal amounts of both forms. Each form cancels out the effect of the other on polarized light. This is called a racemic mixture, when both left-handed and right-handed amino acids are equally present in the mixture.
When amino-acid compounds are formed in living plants or animals, they come in only one form, usually the left-handed, or l- (for levo-) form. If such a compound is heated, the thermal agitation of the molecules turns some of them inside out, changing the left-handed form to the right-handed (the dextro form). This change is called racemization. Continued long enough, it produces equal amounts of the l- and d-forms. It is of special interest because it relates to living things, as does radiocarbon dating.
At lower temperatures, racemization goes at a slower pace. How much slower depends on the energy it takes to invert the molecule. It follows a well-known chemical law, known as the Arrhenius equation. If the amino acid is cooled more and more, the reaction goes slower and slower until, at ordinary temperatures, we cannot see it changing at all. But we can still use the equation to calculate how fast it is changing. It turns out that it would take tens of thousands of years for a typical amino acid to approach the racemized state, when both left-handed and right-handed forms of the amino acids are present in equal quantities.
The idea for dating by this method is this: If a bone, for example, is buried and left undisturbed, the aspartic acid (a crystallized amino acid) in the bone is slowly racemized. We dig up the bone a long time later, extract and purify the remaining aspartic acid, and compare its degree of polarization with that of pure l-aspartic acid. Thus we can estimate how long ago the bone was part of a living creature.
The decay curve is similar to that of a radioactive element. Each amino acid has its own characteristic rate of decay, just as uranium decays slower than potassium. However, note this important difference: Radioactive rates are unaffected by temperature, whereas racemization, being a chemical reaction, is markedly dependent on temperature.
Some of the most highly publicized applications of the racemization method have been to human skeletal remains found along the coast of California. One, called the Del Mar man, was dated by this method at 48,000 years. Another, the skeleton of a female found in an excavation near Sunnyvale, appeared to be even older, a startling 70,000 years! These ages created quite a stir not only in the public press but especially among paleontologists, because no one had believed that man was in North America that long ago. Speculation arose that man could have wandered across the Bering Strait from Asia as much as a hundred thousand years ago. But how certain were the dates turned out by this novel method?
To answer this, tests were made by a radioactive method involving intermediate decay products between uranium and lead that have half-lives suitable for this range. This gave ages of 11,000 years for the Del Mar skeleton and only 8,000 or 9,000 for the Sunnyvale. Something was wrong.
The big uncertainty in racemization ages is the unknown thermal history of the specimen. As mentioned above, the rate of racemization is extremely sensitive to temperature. If the temperature goes up by 25 degrees Fahrenheit (14° C), the reaction goes ten times as fast. How could anyone know what temperatures the bones could have been exposed to so many years in the past? How many summers might they have lain bare under a hot California sun? Or might they even have been in a campfire or a forest fire? Besides the temperature, other factors have been found to affect the rate greatly, such as the pH (degree of acidity). One report says: "Amino acids in sediments show an initial rate of racemization almost an order of magnitude (tenfold) faster than the rate observed for free amino acids at a comparable pH and temperature."
Even that is not the end of the story. One of the Sunnyvale bones was tested for radiocarbon, both by the counting of beta particles from decaying atoms and by the newer atom-counting method. These gave roughly concordant values. The average was only 4,400 years!
What can we believe? Obviously some of the answers are terribly wrong. Should we put more confidence in the radiocarbon date, since there is longer experience in using it? But even with it, different samples from the same bone varied from 3,600 to 4,800 years. Perhaps we should just admit, in the words of the scientist quoted previously, "Maybe all of them are wrong."
[Box on page 22]
Just this year Science News, under the title "New Dates for 'Early' Tools," reported:
"Four bone artifacts thought to provide evidence for human occupation of North America approximately 30,000 years ago are, at most, only about 3,000 years old, report archaeologist D. Earl Nelson of Simon Fraser University in British Columbia and his colleagues in the May 9 SCIENCE. . . .
"The difference in age estimates between the two types of carbon samples from the same bone is, to say the least, significant. For example, a 'flesher' used to remove flesh from animal skins was first given a radiocarbon age of 27,000 years old. That age has now been revised to about 1,350 years old."-May 10, 1986.
The Shroud of Turin—Authentic?
Perhaps the most famous feature of Turin is the shroud that some believe is the winding-sheet in which Christ’s body was wrapped. A travel guidebook explains: “The most famous—and most dubious—holy relic of them all is kept in Turin’s duomo [cathedral].” It is permanently exhibited in one of the duomo’s chapels, locked in an airtight, bulletproof glass case filled with an inert gas. The book goes on to say: “In 1988, however, the myth of the shroud was exploded: a carbon-dating test showed that it dates back no farther than the 12th century.”
From Insight on the Scriptures (an encyclopaedic JW publication) Volume-1 page. 610 Deluge
Effect on the Earth. With the Deluge great changes came, for example, the life span of humans dropped very rapidly. Some have suggested that prior to the Flood the waters above the expanse shielded out some of the harmful radiation and that, with the waters gone, cosmic radiation genetically harmful to man increased. However, the Bible is silent on the matter. Incidentally, any change in radiation would have altered the rate of formation of radioactive carbon-14 to such an extent as to invalidate all radiocarbon dates prior to the Flood.
'the Bible is silent on the matter' comment is not very helpful, even misleading here. True, the Scriptures certainly do not discuss cosmic radiation and their effects. It does however link the implosion of the watercanopy sphere in 2370 B.C.E with the significant reduction of human life span/expectancy from close to 1000 years to around 100 or less. This denotes a clear change in the physical environment of man's habitat. One
Health threat from cosmic rays
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The health threat from cosmic rays is the danger posed by cosmic rays generated by the Sun and other stars to astronauts on interplanetary missions. Cosmic rays consists of high energy protons and other nuclei. They are one of the most important barriers standing in the way of plans for interplanetary travel by crewed spacecraft.
The deep-space radiation environment
The radiation environment of deep space is very different from that on the earth's surface or in low earth orbit, due to the much larger flux of high-energy galactic cosmic rays (GCRs), along with radiation from solar proton events and the radiation belts.
Life on the earth's surface is protected from galactic cosmic rays by a number of factors:
1. The earth's atmosphere is opaque to primary cosmic rays with energies below about 1 GeV, so only secondary radiation can reach the surface. The secondary radiation is also attentuated by absorption in the atmosphere, as well as by radioactive decay in flight of some particles, such as muons.
2. Shielding by the bulk of the planet itself cuts the flux by a factor of two.
3. Except for the very highest energy galactic cosmic rays, the radius of gyration in the earth's magnetic field is small enough to ensure that they are deflected away from Earth ("geomagnetic shielding");
4. The sun's magnetic field has a similar effect, tending to exclude galactic cosmic rays from the plane of the ecliptic in the inner solar system.
As a result the energy input of GCRs to the atmosphere is negligible — about 10−9 of solar radiation - roughly the same as starlight.
Of the above four factors, all but the first one apply to low earth orbit craft, such as the International Space Station (although the ISS crew gets most of its dose while passing through the Van Allen Belt). Therefore, the only astronauts who have ever been exposed to a significant radiation flux from galactic cosmic rays are those in the Apollo program. Since the durations of the Apollo missions were days rather than years, the doses involved were small compared to what would occur, for example, on a crewed mission to Mars.
Like other ionizing radiation, high-energy cosmic rays can damage DNA, increasing the risk of cancer, cataracts, neurological disorders, and non-cancer mortality risks.
The Apollo astronauts reported seeing flashes in their eyeballs, which may have been galactic cosmic rays, and there is some speculation that they may have experienced a higher incidence of cancer. However, the duration of the longest Apollo flights was less than two weeks, limiting the maximum exposure. There were only 24 such astronauts, making statistical analysis of the effects nearly impossible.
The health threat depends on the flux, energy spectrum, and nuclear composition of the rays. The flux and energy spectrum depend on a variety of factors: short-term solar weather, long-term trends (such as an apparent increase since the 1950s), and position in the sun's magnetic field. These factors are incompletely understood. The Mars Radiation Environment Experiment (MARIE) was launched in 2001 in order to collect more data. Estimates are that humans unshielded in interplanetary space would receive annually roughly 400 to 900 mSv (compared to 2.4 mSv on Earth) and that a Mars mission (12 months in flight and 18 months on Mars) might expose shielded astronauts to ~500 to 1000 mSv. These doses approach the 1 to 4 Sv career limits advised by the National Council on Radiation Protection and Measurements for Low Earth orbit activities.
The quantitative biological effects of cosmic rays are poorly known, and are the subject of ongoing research. Several experiments, both in space and on Earth, are being carried out to evaluate the exact degree of danger. Experiments at Brookhaven National Laboratory's Booster accelerator revealed that the biological damage due to a given exposure is actually about half what was previously estimated: specifically, it turns out that low energy protons cause more damage than high energy ones. This is explained by the fact that slower particles have more time to interact with molecules in the body.
Material shielding may be partially effective against galactic cosmic rays in certain energy ranges, but may actually make the problem worse for some of the higher energy rays, because more shielding causes an increased amount of secondary radiation. The aluminum walls of the ISS, for example, are believed to have a net beneficial effect. In interplanetary space, however, it is believed that aluminum shielding would have a negative net effect.
Several strategies are being studied for ameliorating the effects of this radiation hazard for planned human interplanetary spaceflight:
None of these strategies currently provides a method of protection that would be known to be sufficient, while using known engineering principles and conforming to likely limitations on the mass of the payload. The required amount of material shielding would be too heavy to be lifted into space. Electromagnetic shielding has a number of problems: (1) the fields act in opposite directions on positively and negatively charged particles, so shielding that excludes positively charged galactic cosmic rays will tend to attract negative ions; (2) a very large power supply would be required in order to run the electrostatic and magnetostatic generators, and superconducting materials might have to be used for magnetic coils; (3) the possible field patterns might tend to dump charged particles into one area of the spacecraft. Part of the uncertainty is that the effect of human exposure to galactic cosmic rays is poorly known in quantitative terms. NASA has a Space Radiation Shielding Program to study the problem.
Another line of research is the development of drugs that mimic and/or enhance the body's natural capacity to repair damage caused by radiation. Some of the drugs that are being considered are retinoids, which are vitamins with antioxidant properties, and molecules that retard cell division, giving the body time to fix damage before harmful mutations can be duplicated.
Timing of missions
Due to the potential negative effects of astronaut exposure to cosmic rays, solar activity may play a role in future space travel via the Forbush decrease effect. Coronal mass ejections (CMEs) can temporarily lower the local cosmic ray levels, and radiation from CMEs is easier to shield against than cosmic rays.
From British Airways:
Types of radiation
The different types of radiation are most easily classified according to the effects they have on matter.
There are two broad categories:
Ionising radiation - such as, cosmic rays, x-rays and radiation from radioactive
Non-ionising radiation - such as, ultra violet light, radio waves and microwaves.
The amount of cosmic radiation which reaches the earth from the sun and outer space
varies and depends on the latitude and height above sea level. Man, animals and plants,
have all evolved in an environment with a background of natural radiation and with
few exceptions, it is not a significant risk to health.
What is cosmic radiation?
Cosmic radiation comes from two sources.
1. The largest component is high energy proton radiation from outer space.
2. There are also lower energy protons originating from the sun although these are much less significant except when given off in bursts during solar flares.
The lower energy particles of solar radiation do not contribute significantly to levels of cosmic radiation except at times of increased activity from the sun and solar flares. The amount of cosmic radiation entering the atmosphere follows an 11 year cycle with the intensity of radiation being lowest when solar activity is at its highest. The next solar maximum is due in ? at which time cosmic radiation levels will be at a minimum.
Cosmic radiation is effectively absorbed by the atmosphere and is also affected by the earth's magnetic field. The effect on the body will depend on the latitude and altitude at which the individual is flying and also the length of time in the air.
When ionising radiation passes through the body, energy is transmitted to the tissues which affects the atoms within the individual cells. This may result in:
(i) Development of cancer. A cell may be altered as a result of being irradiated and subsequently become cancerous. The likelihood of this happening will depend on the dose received. For an accumulated dose of 5 mSv per year over a career span of 20 years (more than the anticipated annual exposure for long haul crew) the likelihood of developing cancer due to the radiation will be 0.4%. This though needs to be put in perspective as we know from national mortality data that approximately 23% of the population will die from some type of cancer and so the additional exposure will increase the risk from 23% to 23.4%. Compared with all other risks encountered during the working life, this is very low.
(ii) Genetic risk. A child conceived after exposure of the mother or father to ionising radiation is at risk of inheriting radiation induced genetic defects. These may take the form of anatomical or functional abnormalities apparent at birth or later in life. The risk following an accumulated dose of 5 mSv per year over a career span of 20 years will be 1 in 1,000. Again this needs to be considered against a background incidence in the general population of approximately 1 in 50 for genetic abnormalities. (iii) Risk to the health of the foetus. With regard to pregnancy, although the risks to the unborn child from cosmic radiation are minimal when compared with other risks during pregnancy, radiation exposure should be kept to a level 'as low as reasonably achievable'. Individual passengers will therefore need to make their own assessment of risk taking into account the likely exposure.
Effects on crew
British Airways works closely with the UK Government, Civil Aviation Authority and the National Radiological Protection Board and has monitored cosmic radiation on board its aircraft for more than 20 years. Monitoring instruments were permanently installed on Concorde and regular measurements are also made on long range Boeing 747-400 aircraft. In addition, British Airways has undertaken epidemiological studies examining the incidence of disease and life expectancy of flight crew over the last 40 years.
It has been found that pilots and flight engineers have an increased life expectancy of between 3 and 5 years compared to the general population*. Death rates from heart disease and all cancers combined are considerably less in flight crew then for the population of England and Wales as a whole and, although rare, death from melanoma (which is associated with exposure to sunlight) was the only cause of cancer in excess. Cancer such as leukaemia, which may be linked to radiation exposure, was lower than for the general population.
Further larger studies are continuing to which British Airways is contributing and as a result, more information will be available in due course.
Cosmic Radiation and Air Travel
Several hundred thousand cockpit and cabin crew worldwide are occupationally exposed to
cosmic radiation, and the number of frequent flyers is steadily increasing. Our understanding of
the health effects of cosmic radiation has been advanced through recent scientific studies
focusing on aircrew. This fact sheet provides summary information on the health aspects of
cosmic radiation as they relate to air travel.
What is Cosmic Radiation?
Cosmic radiation (CR) is a form of ionizing radiation. Radiation particles constantly travel
through the universe and reach the Earth's atmosphere. Cosmic Radiation mainly consists of
primary particles (e.g., protons, electrons, and heavier ions) and secondary particles (e.g.
neutrons) formed when these particles reach the Earth's atmosphere. At sea level CR
contributes about 13% to the natural background radiation.
Cosmic radiation is different from other forms of ionizing radiation. For example, nuclear
industry workers or medical personnel are mostly exposed to gamma-radiation and X-rays. In
contrast, neutrons contribute up to 50% of the effective radiation dose 1 that aircrew and air
travelers receive from CR. The biological effects of these neutrons and CR in general are not
fully understood at this time, which is one reason why health studies of aircrew are being
The level of CR in the Earth’s atmosphere depends primarily on four factors, listed here in order
of their importance in contributing to radiation levels:
1. Altitude The Earth's atmospheric layer provides significant shielding from cosmic
radiation. At higher altitudes, this shielding effect decreases, leading to higher levels of
cosmic radiation. The radiation exposure at conventional aircraft flight altitudes of 30.000
- 40.000 feet (9 - 12 km) is about 100 times higher than on the ground.
2. Geographic Latitude The Earth’s magnetic field deflects many CR particles that would
otherwise reach ground level. This shielding is most effective at the equator and
decreases at higher latitudes, essentially disappearing at the poles. As a result, there is
approximately a doubling of CR exposure from the equator to the magnetic poles.
1 The effective dose is a measure used to estimate the risk resulting from exposure to ionizing radiation. It takes into account the different radiation sensitivity of tissues and the different relative biological effect of different types of ionizing radiation
3. Normal Solar Activity The sun's activity varies in a predictable way with a cycle of approximately 11 years. Higher solar activity leads to lower cosmic radiation levels and vice versa..
4. Solar Proton Events (SPEs) (also sometimes called “solar particle events”, or “solar events”) Occasionally large explosive ejections of charged particles occur on the sun. They can lead to sudden increases in radiation levels in the atmosphere and on Earth, the solar proton events. SPEs are not predictable, and levels of radiation caused by an SPE are not uniform over the Earth. Large SPEs in which significant levels of CR reach Earth are rare events.
Aircrew and frequent flyer exposure
Radiation dose is measured in milliSieverts (mSv). Aircrew flying 600-800 hours per year are exposed to 2 to 5 milliSievert (mSv) of radiation each year in addition to the usual radiation of 2-3 mSv through man-made (mostly medical) and natural radiation sources.
Aircrew are now recognized in many countries as occupationally exposed to radiation, and radiation protection limits for aircrew are similar to those established for nuclear workers.
Frequent flyers generally do not reach the number of hours flown by aircrew. Thus, unless they fly as much or more than typical aircrew, their radiation exposure and associated possible health risks are likely to be lower than that of aircrew.
Short-haul flights are often flown at lower altitudes than long-haul flights, so that generally, shorthaul flights incur less radiation exposure than long-haul flights. The other factors which influence CR exposure levels vary with each flight. Also, methods of measuring CR are still being developed and compared by scientists. An estimate of the radiation dose for a specific flight can be obtained from the following and other websites:
Cancer is the principal health effect that has been associated with low-dose radiation. As cosmic
radiation is a very low-level source of radiation, the associated risk of developing cancer is also
likely to be very low and difficult to establish with the scientific tools at hand.
There is little evidence so far that occupational exposure to cosmic radiation increases cancer
risk, and only limited evidence that increasing amounts of CR exposure may cause a
corresponding increase in certain cancers. Several aircrew studies have shown an increased
risk of melanoma and non-melanoma skin cancer. Solar ultraviolet radiation such as obtained
through sun tanning is an established risk factor for these cancers, but further information is
needed to determine if CR exposure also influences the risk.
Breast cancer among female aircrew, measured as new illness or related death, was also found to be increased in several studies. Causes other than radiation, such as those from a woman’s reproductive history, do not seem to fully explain this increase.
Occasionally studies have found risk increases for other cancers but these may have been chance findings not confirmed in the other studies. More evidence will be available as additional studies of aircrew are conducted, and as aircrew who have already been studied are followed-up further.
There are no studies yet that directly answer questions on the effects of cosmic radiation on pregnancy and the health of offspring. However, based on current knowledge, the limited radiation doses obtained during occasional air travel during pregnancy confer very small risks to the offspring. If pregnant aircrew members continue to fly regularly during pregnancy, they may, however, reach recommended dose limits (see below).
In addition, studies are currently being conducted which examine other health effects or markers of health effects, including cataracts, chromosomal (genetic) damage, and measures of reproductive health.
These studies will expand what is known about the health risks of cosmic
radiation in the near future.
Guidelines on radiation dose limits
In 1990, the International Committee on Radiological Protection (ICRP) recommended that jet
aircrew should be considered occupationally exposed to ionizing radiation.
Guidelines concerning dose limits for occupational exposure have been established by
international agencies involved in radiation protection. Occupational exposure of any worker
should not exceed an effective dose of 20 mSv per year averaged over five consecutive years or
an effective dose of 50 mSv in any single year. In case of pregnancy, the equivalent dose for the
fetus may not exceed 1 mSv during the declared term of the pregnancy. Many airlines follow a
policy of transferring pregnant flight staff to ground duties once the pregnancy has been
declared, based on overall considerations of potential negative effects of flying on pregnancy.
For the general public, exposure limits concerning cosmic radiation as well as other natural
radiation sources have not been set. The dose limit of 1 mSv per year established for artificial
exposures can, however, serve as orientation. Some frequent flyers may, under certain
conditions, reach or exceed this value. However, there is currently no intent or mechanism to
monitor the exposure of frequent flyers.
WHO recommendations concerning cosmic radiation
National governments are advised:
• to protect flying personnel by law from excessive radiation exposure.
Airline management is advised:
• to assess and track aircrew radiation doses;
• to provide aircrew with a record of their personal cumulative radiation dose;
• to consider radiation exposure and to reduce occupational radiation exposure where
feasible in creating flight
• to inform personnel about the effects of cosmic radiation;
• to the extent possible, warn personnel about potential major solar proton events,
and advise those who have
traveled in an area of increased radiation during an SPE.
Aircrew are advised:
• to keep themselves informed about health effects of cosmic radiation;
• to record their personal cumulative radiation doses on a regular and permanent
basis (if not done by the
respective airline or governmental bodies);
• to consider radiation exposure when selecting flight schedules;
• to limit flight travels during pregnancy.
Frequent flyers are advised:
• to keep themselves informed about health effects of cosmic radiation;
• to limit flight travels during pregnancy.
If the flying time of a frequent flyer is similar to that of aircrew, they are advised:
• to record their personal cumulative radiation doses on a regular and permanent basis;
• to consider radiation exposure when selecting flight schedules.
Cosmic radiation - WHO activities
WHO recognizes that there is a widespread interest in clear and trustworthy information on potential health risks associated with cosmic radiation. Through the Radiation and Environmental Health programme, WHO provides authoritative and evidence-based information on health and environmental issues of ionizing - including cosmic - radiation. WHO co-sponsors guidelines and safety standards for the protection against ionizing radiation and is providing guidance to member states regarding radiation protection for specific groups and the public at large.
WHO thanks all involved experts for their contribution in drafting this information sheet.
World Health Organization
Radiation and Environmental Health
20 Avenue Appia
1211-Geneva 27, Switzerland
My Note: There is no long-term test environment currently available to measure the effects of cosmic radiation on longevity. The Bible remains therefore the only source to link shielding to a longer lifespan
Sensor System to Gauge Effects of Cosmic Rays on Lunar Explorers
Boston University Professor Harlan Spence recently joined five other space scientists
at Goddard Space Center in Greenbelt, Maryland to discuss their participation in
NASA’s Lunar Reconnaissance Orbiter (LRO) program.
Spence learned in late December that his proposal for CRaTER, an instrument that will measure and characterize the potential biological effects of cosmic radiation on humans, was one of six selected by the space agency for the LRO mission scheduled for fall 2008.
A professor in Boston University’s Center for Space Physics and a professor in and chairman of the university’s Department of Astronomy, Spence is expected to receive a contract for approximately $9.5 million for CRaTER. He and the other principal investigators will each head institution-based research teams that will build instruments to gather data on the lunar environment, a vital first step in NASA’s preparation for what President Bush has announced will be a series of human and robotic missions to the moon.
CRaTER, which stands for Cosmic Ray Telescope for the Effects of Radiation, will measure the high-energy charged particles (ions and electrons, not “rays” at all) that travel throughout the cosmos at nearly light speed. Consisting of a novel cosmic ray sensor system coupled with proven analog and digital electronics, CRaTER will relay its data back to Earth through the LRO spacecraft’s communication system.
The sensor system will be the scientific heart of the instrument. Designed as a stack of detectors housed in a structure of aluminum and special material known as tissue-equivalent plastic, the sensor system will allow CRaTER scientists to measure and characterize the potential biological effects of radiation that occur in deep space. The aim: gather the data needed to develop equipment and materials that will ensure human safety in the lunar environment.
“In 1971, I stood with my family in the throngs that watched Apollo 15 thunder into space from Cape Canaveral,” Spence recalls. “It was a defining moment for me, hooking me on a career in astronomy and space science. With CRaTER, I get to relive that excitement as a space scientist — and get to experience my own voyage, of sorts, to the moon!”
Scientists on Spence’s team include Larry Kepko, senior research associate in BU’s Center for Space Physics; J. Bernard Blake, director of the Space Sciences Department at the California-based research group, The Aerospace Corporation; Joseph Mazur, research scientist and laboratory manager at Aerospace; Justin Kasper, a research scientist in MIT’s Center for Space Research; and Lawrence Townsend, a professor of nuclear engineering at The University of Tennessee in Knoxville. Team collaborators include Michael Golightly of the Air Force Research Laboratory in Bedford, Massachusetts and Terrence Onsager of the National Oceanic and Atmospheric Administration’s Space Environment Center in Boulder, Colorado.
The LRO mission is part of NASA’s Robotic Lunar Exploration Program. In 2008, the orbiter will carry the instruments built by the teams into space where they will begin gathering the information that will inform the planning and execution of future lunar missions. The five other NASA-selected teams are from Goddard Space Flight Center in Greenbelt, Maryland; Northwestern University in Evanston, Illinois; Institute for Space Research and Federal Space Agency in Moscow; University of California in Los Angeles; and Southwest Research Institute in Boulder, Colorado.
Faculty research in BU’s Department of Astronomy is coordinated through its Institute for Astrophysical Research and its Center for Space Physics. Research areas include observational and theoretical studies in galactic and extragalactic astrophysics, magnetospheric and ionospheric physics, planetary and cometary atmospheres, space weather, space plasma physics, star formation and galactic structure, star and star clusters, active galaxies and quasars, high-energy and particle astrophysics, galaxy formation, and cosmology.
Source: Boston University
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