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by Boris Kuzhevsky, Cand. Sc. (Phys. & Math.), senior researcher, Institute of Nuclear Physics, Lomonosov Moscow State University
A NEUTRON CORONA AROUND THE SUN?
For several months our research team had been getting ready to obtain experimental proof on a neutron corona of the sun. Both the theoretical and the empirical data of astronomical observations showed continuous nuclear reactions to be occurring in the luminary's atmosphere.* So the sun should be surrounded by a corona of neutrons with mean energy of hundreds of thousands of electron-volts (eV). Yet detecting that corona in near space, from circumterrestrial orbit, seemed a Utopia.
Neutrons are unstable particles. Each of them has a rather short lifetime, about 15 minutes, and so singly it can hardly make it to our planet. Their flux will be so small as to escape detection with conventional instruments-one needs super-sensitive gadgets with very great light-gathering power. But our Institute of Nuclear Physics has done this job: a team under Dr. Mikhail Panasyuk has developed such instruments on the basis of gas-discharge helium counters that have performed well in cosmic experiments.
And thus equipped with this gear we-Oleg Nechayev, Viktor Shiltsyn of our staff, the author of this article and Igor Kuzhevsky, a schoolboy volunteer-set out for Tixi where we were to have a kit of instruments lifted in a balloon during a total solar eclipse.
But why this day and this method? You see, we can register neutrons on the surface of the earth from outer space only if their energy amounts to hundreds of millions of eV and more. Otherwise these particles will never pierce the atmosphere of our planet. Colliding with the nuclei of oxygen and nitrogen atoms, they attenuate and develop
* See: L. Miroshnichenko, "Solar Cosmic Rays: Puzzles and Discoveries", Science in Russia, No. 4, l995.-Ed.
into thermal particles, whereupon they live on for yet another 0.1s to be absorbed by nitrogen atoms. At best, neutrons can be detected as high as 25 to 30 km above sea level. That's where air balloons come in handy.
As to the moment of a total solar eclipse, we chose it proceeding from the "day-night" effect. Indeed, if we carry out measurements before the solar disc is covered by the moon, and then during the eclipse and after, we can expect an effect similar to an optical one: in some period of time (30 min. or (hereabouts) after the luminary has been eclipsed by the moon, the rate of neutron counts per second (cps) should go down and then up again.
So, we seemed to have considered every trifle-the right time and the right place too, for the district of the Tixi bay happened to be just within an area of total solar eclipse. Yet man proposes...
Inspite of the foul weather and the gale-force wind, we did not take a rain check on our work to get the airship ready for the start. Hydrogen kept filling its huge gondola. Violent gusts of wind were tearing it this way and that. Our people thought of anchoring it to the platform. And here we heard a clap-and the gondola started sinking to the ground. The balloon burst! This dashed our plans of finding out then and there if there was a neutron corona around the sun or not.
GRAVITATION, TIDES AND NEUTRON BURSTS
Meanwhile another research team under Dr. Nikolai Volodichev, also from our department, was taking neutron counts on the ground thousands of miles to the south, in the Pamirs, 4,200 meters above sea level. He and his men kept vigil during the solar eclipse period too. All of a sudden their instruments registered a neutron flux burst.
Things returned back to normal only a few hours after. The very duration of this effect was another surprise. Since the astronomical moment of the solar eclipse had come well before our Pamirs team switched on their instruments, the length and amplitude of the burst must have been far greater actually. That immense flux of registered neutrons could not be a stray visitor from the distant parts of the universe. Using cadmium plates in their experiment, our researchers found the neutron flux to be coming from the terrestrial surface! The picture obtained as follows.
The tidal wave within the earth shell (a phenomenon caused by the gravitational impact of celestial bodies) was activated during the solar eclipse to send forth an increasing flow of natural radioactive gases (radium emanations in the form of radon isotopes). Their decay gives rise to alpha particles with an energy of 5 to 9 nun eV. This energy is strong enough to knock out neutrons from the nuclei of elements contained in the air and soil.
As is often the case, a solution of this or that problem spawns ever more new questions. At any rate, such neutron flux bursts were not an accidental phenomenon. Strange that physicists had never suspected that before.
Now look: the tidal gravitational wave is ever present. It always tours our planet and causes ocean tides twice within every twenty-four hours. Sure, its amplitude in the earth's crust stands no comparison with the ocean tides which can be even dozens of meters long, depending on coastal relief features. According to laser measurements from outer space, the amplitude of the gravitational tidal wave varies with different continents, but its averaged value is 0.5 m. This amplitude intensifies in full and new moon periods, and so it does during solar and lunar eclipses. Consequently, the effect of a sharp increase in neutron fluxes could be observed during full and new moons rather often, though not always.
But why "not always"? The point is that the value of a neutron burst determines not only the astronomical moment of a new or a full moon. Certain geophysical factors are also implicated-such as the concentration of natural radioactive gases, the concrete conditions of their release abroad (these are related to the elastic and viscous properties of the earth's crust in a given locality), the state of the soil and atmosphere (say, their moisture level)... Mind you, the Pamirs region where Nikolai Volodichev was conducting his studies is a seismic area rich in radon springs. Subsequently other field expeditions dispatched thither confirmed the validity of a physical scenario for the origin of neutron bursts sent by the earth shell and found these events to be correlated with the lunar phases.
Our kit of instruments that we could not use at Tixi found a good application elsewhere, namely on the Kola Peninsula where it was launched in an air balloon in October of the same year, 1990. The experiment carried out there as well as two other experiments- at Dolgoprudny northwest of Moscow in July 1991 and at Rylsk (Kursk Region) in February 1992-furnished additional evidence that the earth's crust is a permanent and important source of neutrons. The design of our apparatuses became the prototype of a large setup built on the Vorobyevy gory (hills) in Moscow (it is still in service) for studying the nature of sundry variations occurring in a neutron flux just above the terrestrial surface. Among other things, neutron bursts are taking place not only in the seismically active areas of our planet either.
So that's that: a flux of neutrons coming from our planet attests to the deformation of its crust under the action of gravitational tides. However, other causes are responsible for changes there too. Among these are natural phenomena like earthquakes, intensification of eruptive activity, landslides, mud-and-rock torrents. There are likewise technogenic factors at work, such as man-made lakes, dams, tunnels, oil- and gas pipelines, and so forth.
Now it's pertinent to ask: can we identify a particular variation responsible for this or that deformation? I think we can. In terms of accuracy our method is in no way inferior to other ones used in gravimetry; and, on the other hand, it offers such advantages as simplicity and informative-ness.
And yet the many attempts made by scientists of various countries to find out if there is any connection between natural disasters like earth tremors and deformations caused by the tidal wave have not been successful because in some districts such events might be occurring during new or full moons, while in others-not.
LUNAR PHASES AND RECURRENCE OF EARTHQUAKES
To prove or disprove this interdependence, Dr. Alexander Podorolsky of our staff has made a statistical study of the global catalog of earthquakes of magnitude >=4.0 and >=5.0 in a period between 1964 and 1992. He studied both large and small series of quakes singly, one by one. Here's what Dr. Podorol-sky found: large series (with the number of shocks >=30 per day) of magnitude >=4.0, with the epicenters at >=40N or >10S, began as a rule not later than 3 days after the onset of new or full moon phases. The same conclusion stood for tremors of M >=5.0, even though the number of shocks in a series might be under 30.
We may thus say: neutron bursts correlate with the gravitational tidal wave, and the same is true of series of earthquakes with a different number of shocks depending on the magnitude value. And were neutrons registered in districts subsequently hit by earthquakes, it might then become possible to identify the peculiarities of the temporal or amplitude-related distribution of a neutron burst. That would be important for developing an earthquake prediction method.
Comparing the correlation analysis data on the lunar phases both with neutron bursts and with series of seismic events, we shall see that while the neutron bursts are observed the same day as new and full moons, and sometimes even concur with them, the seismic events may come even as late as three days thereafter. Neutron bursts occur at least a few hours before tremors, a reprieve enabling us to make a short-term forecast.
In collaboration with their colleagues in the Republic of Kazakhstan (Institute of Seismology, Al-Farabi University), Russian scientists (Institute of Nuclear Physics, Moscow State University) have carried out an experiment in a seismically active region in the Tien Shan mountains near Almaty. The aim of this experiment was to register-simultaneously-a flux of neutrons emitted from the surface of the earth, and the shocks in its interior. A kit of neutron-registering instruments was placed at Medeo where, 40 m deep underground, there is the seismic station of Kazakhstan. Used as a detector was a lithium-glass scintillation counter otherwise widely employed in geophysical investigations of the mineral composition of the earth shell. Unlike the detectors we used in Moscow and in the Pamirs, the one at Medeo had a low neutron registration efficiency. Therefore only hourly neutron counts could be statistically reliable.
Observations carried out nonstop from March 1996 to May 1998 showed an average of 12.5 neutron pulses per hour. At odd moments this indicator was up 2 to 3.5 fold (such fluxes we called anomalous bursts).
In the same period of time, seismic instruments registered different class earthquakes with their epicenters 120 to 900 km away from the Medeo seismic station. Trying to find a dependence between the value of anomalous neutron bursts and an earthquake class*, we obtained a curious picture. First, in 72.5 percent of the cases anomalous bursts were observed 24 hours before quakes of class 9 and higher. Second, there was an increasing nonlinear functional dependence between earthquakes of class 11 and higher, and an anomalous burst value. And third, the minimum time interval between the observed anomalous neutron burst and the moment of the quake was 1h.
Clearly, neutron fluxes emanating from the earth shell are an excellent indicator of dynamic processes within it. This factor may be of good use in studying the fundamental problems of geo- and space physics alike.
COSMOGONY AND NEUTRON FLUXES
It has been proved that tidal waves involve every celestial body implicated in gravitational interaction. So this phenomenon applies to the moon just as well. Yet the period of its revolutions around its axis and that around the earth coincide. Consequently, the tidal gravitational wave on the moon should be actually static. But since the orbit of our celestial neighbor is elliptical, the amplitude of its gravitational wave will "heave" with a period equal to the time of its movement from the apogee to the perigee. This process causes deformation of the lunar crust. And it should emit neutron fluxes if there are radioactive elements inside.
However, the present cosmogonic theory proceeds from the assumption that primary matter was a homogeneous mass at the time when our planetary system came into being. And so the moon should have radioactive elements with a long half-life period, e.g. uranium and thorium, which gave birth to families of radioactive isotopes, the suppliers of energized alpha particles. In that case the subsequent scenario of events should fit in with the pattern we have described relative to the earth. Today we know of a phenomenon of moonquakes with a two-week periodicity under the possible
* Earthquake class-log10 value of the energy (in joules) released in the epicenter.- Auth.
effect of a tidal wave generated by the earth. Yet to make assurance double sure, we should register neutron bursts from the lunar surface with the aid of an artificial satellite put in orbit around our "nightly luminary"...
Besides, Mercury and Io, Jupiter's satellite, are also putative sources of neutron bursts.
Mercury, being a planet closest to the sun, feels the strongest impact of the solar mass. But here, as it is in the case of the moon, changes in the deformation of Mercury's surface must be determined by the value of its orbit eccentricity* rather than by its diurnal rotation. As to Jupiter's satellite, Io , it has a powerful volcano causing strong stresses in the crust and giving rise to neutron bursts from its surface.
Since celestial bodies may differ in their composition, the neutron generation mechanism should not be identical either. Therefore monitoring neutron fluxes from outer space holds good promise as an effective method of experimental cosmogony.
NEUTRON FLUXES AND ECOLOGY
Because the variability of neutron fluxes emanating from the surface of the earth is related to dynamic processes within its crust, it is important to keep tabs on these fluxes when attacking basic and applied problems, e.g. in forecasting natural and technogenic cataclysms. Such things as artificial lakes, tunnels, oil and gas pipelines, strip mining, commercial projects in the Arctic-all that has a tangible effect on changes in the statistical and dynamic stresses in the upper stratum of the earth shell and, as a result, affects processes implicated in the accumulation and release of radioactive gases; this, in turn, impacts the dynamics of neutron fluxes issuing from terrestrial surface. That is why neutron flux variations are an essential factor for ecological feasibility studies with respect to many human projects.
* Eccentricity-the ratio of the focal length of ellipse semi-axes that characterizes the oblate-ness of an orbit. - Ed.
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