15th March 2007 - 12:29 PM
QUOTE (Palpatane+Mar 15 2007, 02:27 AM)
Mushroom clouds are not unique to nuclear explosions. They can occur with any explosion that generates a large cloud of super heated gas.
A conventional explosion made from thousands of tons of TNT a while back produced the same mushroom cloud.
15th March 2007 - 12:32 PM
turin. A rocket with no protection against fast neutrons would be no good in space if there was a storm on the sun.
16th March 2007 - 01:29 AM
I am not aware of any neutron radiation from the Sun. Perhaps you are thinking of neutrino radiation, which is certainly NOT dangerous? Do you have a source that refers to this neutron radiation, or can you at least explain the mechanism for the free neutron production? And something else to keep in mind: our atmosphere would also not provide good shielding from neutrons that are energetic enough to reach us from the Sun. (The half-life of neutrons is approximately 1 AU, so nonenergetic neutrons would die before they got here, and energetic neutrons have a reduced cross-section.)
16th March 2007 - 02:55 PM
turin. I assume you do not have a search engine with your internet? A simple search produced over a million sites. Here's one :http://exploration.nasa.gov/programs/station/BBND.html
Which tells us :
Bonner Ball Neutron Detector (BBND)
Neutron radiation can deeply penetrate the body and damage blood forming organs. Neutron radiation is estimated to be 20 percent of the total radiation on ISS. This study characterized the neutron radiation environment to develop safety measures to protect future ISS crews.
which talks of dangers on future manned missions to Mars. NASA will be glad to hear that such radiation cannot exist past the Earth's orbit.
16th March 2007 - 04:04 PM
Thank you for those two (albeit redundant) NASA pages. However, those examples mention a completely different kind of neutron radiation from what would be produced in a nuclear explosion, namely thermal neutron radiation. Indeed, I would expect a space-ship to be a good protection against thermal neutrons, for the same reason that nuclear reactors use some moderating substance to thermalize their neutrons to increase the collision rate with the fissionable material. The faster neutrons that initially result from the fission would typically fly right out of the reactor and greatly degrade the efficiency of the reactor without a moderator (not to mention pose a danger to the personell working near the reactor). It is the fast neutrons that I would expect from a nuclear explosion, not thermal neutrons. It is hard to tell from those NASA pages, but it looks like they are detecting secondary neutrons that are produced from other forms of radiation that are energetic enough to obliterate nuclei, like gamma rays. I don't think that NASA is suggesting solar production of primary neutrons, although one of those NASA pages did mention storms on the Sun. Hmm.
16th March 2007 - 05:59 PM
The existence of a region of trapped radiation surrounding the earth was first proposed by Carl Stömer and others at the turn of the century but its presence was not confirmed until the advent of artificial satellites in the late 1950s. Ironically, as soon as James Van Allen and his colleagues at the University of Iowa “discovered” the inner radiation belt in the spring of 1958, the US military started trying to modify it with high altitude atomic explosions. These attempts to modify the earth’s radiation belts stemmed from a classified proposal submitted to the US Air Force in October 1957 by Nicholas Christofilos, a Lawrence Radiation Laboratory scientist.
The basic idea put forward by Christofilos was that an atomic bomb exploded in the earth’s upper atmosphere would produce a slowly decaying region of high-energy electrons from the trapping of the fission product beta-decay particles in the earth’s geomagnetic field. Christofilos noted that the lifetimes of the trapped electrons would be proportional to the air density at the so called mirror points in the trapped electron’s trajectories. He estimated that electrons injected by an explosion a few hundred miles above the earth would form a radiation belt lasting several days that could be detected by rocket-borne instruments or ground-based auroral observations.
By the end of April 1958 it was decided to detonate three 1.7 kiloton W-25 nuclear warheads at high altitudes above the South Atlantic to test these predictions. Thus, shrouded in great secrecy, Operation Argus came into being. The full resources of the US military were dedicated to these tests which were conducted by Task Force 88, a naval organization consisting of nine ships and approximately 4500 men; the tests also included the launching of 19 sounding rockets and two earth orbiting satellites, Explorer IV and Explorer V.
The detonations were carried out in Aug - Sept 1958 as follows:
Argus I: Aug 27, altitude 160 km
Argus II: Aug 30, altitude 293 km
Argus III: Sept 6, altitude 750 km
After each detonation aurora were observed in the vicinity of the burst and at the so-called “conjugate mirror points” above the Azores Islands in the North Atlantic. The fission product residues from the Argus explosions rose rapidly into the extreme reaches of the earth’s upper atmosphere so that most of the beta-decay electrons were released at much greater altitudes than the injection altitudes. Geiger counters on the Explorer IV satellite recorded the creation of a well-defined radiation belt, a few hundred km deep at an altitude of about 6000 km. This new radiation belt decayed slowly over a period of several weeks.
The very existence of Operation Argus was not reported to the world’s press until about 6 months after its completion and technical details were only made available to scientists in August 1959 in a collection of articles published in Volume 64 of the Journal of Geophysical Research (JGR).
At this time “Argus” was billed as nothing more than an ingenious scientific experiment of value to geophysicists but only of passing interest to the general public. However, the paper contributed to the JGR by Nicholas Christofilos hinted at other, more sinister, aspects of Operation Argus. Thus, in his discussion of the physics behind the Argus experiment, Christofilos used the example of a 1 Megaton nuclear detonation, (as opposed to the 1.7 kiloton explosion that was actually used), to calculate the electron density and flux in the artificially created radiation belt. He arrived at a value for the flux of 1.5 x 10^9 electrons/cm2 sec and then, somewhat off-topic, he considered the associated radiation level inside a space vehicle. This he estimates to be more than 100 rad/hour. Christofilos concluded his paper with the following note of alarm:
“100 r/hr is a good fraction of the lethal dose. Consequently, it is obvious that any explosion of such magnitude can create a radiation hazard in outer space, and any space experiments involving A-bomb explosions must be carefully designed to avoid creation of hazardous radiation. Fortunately a much smaller yield, namely in the kiloton range, is sufficient to yield detectable quantities without creating any radiation hazard at all.”
These words were probably the first on record to reveal the potential for military applications of Argus-type experiments in space. However, back in 1958, the military’s real interest in man-made radiation belts above the earth was not simply to create radiation hazards to humans in space, since there was nobody up there (at that time), but more to interfere with radar tracking, communications and the electronics of satellites and ballistic missiles.
16th March 2007 - 06:08 PM
As a response to the Soviet 58 Megaton test in October, 1961, Kennedy approved a new round of American weapons testing, codenamed Operation Dominic, which began in April 1962. Dominic was to include 36 tests, some of which were to be high altitude explosions carried out in the Central Pacific.
On June 20th 1962, in a test dubbed Starfish, a 1665 lb W-49 plutonium-based warhead was launched from Johnston Island in the nose-cone of a Thor rocket. Only 59 seconds into its trajectory the engine failed and the range safety officer destroyed the vehicle 10 km above Sand Island, scattering debris far and wide. Undeterred, the Americans tried again on July 9, this time with complete success. Being a second try, the US military called the test Starfish Prime although many discussions of this test still refer to it simply as Starfish. By whatever name authors choose to designate this 1.45 megaton explosion, (and we shall also call it Starfish for simplicity), it remains the subject of great controversy. The auroral effects of the blast were visible on Hawaii, more than a thousand kilometers from Johnston Island. At the same time, on the island of Oahu, a giant electromagnetic pulse surged through power lines, knocking out streetlights and tripping circuit breakers.
The effects of the Starfish test on the Van Allen radiation belts proved to be quite spectacular, more than living up to the 1957 predictions of Nick Christofilos for the effects of a high altitude 1 Megaton burst.
The Starfish test involved the explosion of a 1.45 megaton (Mt) thermonuclear device. As discussed by Wilmot Hess, (See: Space Physics, Wiley & Sons, 1964), the fusion component of a high altitude nuclear explosion contributes very little to the long-term natural radiation environment. On the contrary, it is electrons from the beta-decay of fission fragments that leads to the enhancement of the existing radiation field, or even to the creation of new, semi-permanent, radiation belts.
Starfish lead to the instantaneous release of about 150 moles of fission products, at a point some 400 kilometers above the Central Pacific.
How many electrons did Starfish release, and where did these electrons go?
Answer: 150 moles of fission product contains 150 x 6.02 x 10^23 = 10^26 atoms. Newly formed fission products consist of highly ionized atoms with unstable, neutron rich, nuclei. Over a period of a few days these radionuclides follow complex beta-decay chains to stable or long-lived isotopes such as Cs-137 and Sr-90. The average decay chain length is 6.08 so approximately six beta particles are emitted per fission product atom. Thus we estimate that 6 x 10^26 electrons were released by the Starfish test. This is identical to the number reported by W. L. Brown et. al. in 1963, (See: Bell System Technical Journal Vol 42, page 1525).
Fission product beta particle emissions have average energies ~ 1 MeV and are called relativistic electrons because their velocities are close to the speed of light, or 3 x 10^10 centimeters per second. Charged particles released at high altitudes do not follow linear trajectories but spiral around the geomagnetic lines of force. Now since the earth’s field strength increases at lower altitudes where the lines of magnetic force converge, a charged particle moving in such a field executes a tighter and tighter downward spiral until the direction of its motion is reversed at a “magnetic mirror” point. Thereafter the charged particle spirals back along a great arc to the so-called conjugate mirror point in the opposite hemisphere. In this way both natural and artificial radiation belts are maintained. For electrons this process works very effectively between latitudes 75° N and 75° S at altitudes from about 1000 to 10,000 km.
Measurements by a number of artificial satellites showed that the Starfish electrons formed a radiation belt centered at an altitude of about 1300 km, although electron fluxes well above the natural Van Allen pre-Starfish levels were detected out to about 4000 km.
18th March 2007 - 04:07 PM
turin. Redundant pages? Does this mean that the sun no longer radiates any neutrons?
Solar flares occur much of the time on the sun. A prime source of fast neutrons. Who cares about nuclear reactors?