Cosmic ray intensity

This technique is useful only when dating objects that are less than 50,000 years old (roughly 10 times the half-life of carbon-14). Older objects have too little activity to be accurately dated. This technique depends on cosmic-ray intensity being constant or at least predictable in order to keep the 14C/12C known throughout the time interval. Also, the sample must not be contaminated with organic matter having a different 14C/12C ratio. 

One of the most interesting of the geophysics results from radiocarbon dates is the history of the sun. Apparently, it is registered in fluctuations of the cosmic ray intensity. These are fluctuations of rather short duration in terms of the radiocarbon lifetime, perhaps a century or so, and apparently they are caused by variations in the solar wind due to long-term changes in the solar emissions. This idea has been developed in some detail recently by Dr. Lai and his collaborators. It promises to give us a way of watching the history of the sun over tens of thousands of years. This fine structure on the curve of calibration was discovered by Dr. Suess and others. 

The advent of new techniques to collect undisturbed sediment cores, with well preserved sediment - water interface has brought into sharper focus the various deep sea sedimentary processes, their rates and their effects on the preserved records. As mentioned earlier, recent studies have shown that the record contained in sediments is not a direct reflection of the delivery pattern of a substance to the ocean floor as has so far been assumed the record is modified as a result of several complex physical, chemical and biological processes. Therefore, information on the temporal variations in the tracer input to oceans, if sought, has to be deciphered from the sediment-residuum. In the following we consider one specific example of retrieval of information from the sediment pile the application of deep sea sediments to obtain historical records of cosmic ray intensity variations. 

The global average production rate of any nuclide, Q(t), at any time, t, will be primarily dependent on the cosmic ray intensity, I(t). If the intensity varies sinusoidally with a period T(u) = 2n/T), Q(t) will also vary sinusoidally. The standing crop of a nuclide in the sea water column for a production function, Q(t) = Q (1 + a cos tot), a being the amplitude, can be deduced to be 0... 

The amplitude attenuation factor, 1 + (tu/Ai)2 for nuclides satisfying relation [14], for various values of Ax and T are presented in figure 9. It is obvious from figure 9 that the attenuation is minimal when Ai > u>, i.e., when the removal residence time of the nuclide from sea water is less than the period in the variation of cosmic ray intensity. 

Figure 9. Calculated attenuation factors for various values of T (period in the sinusoidal cosmic ray intensity variations) and A (the total rate constant). See section on deep-sea sediments and historical records for discussion.

Short-term changes in the cosmic ray intensity (T 200 yrs.) can be best studied through the analyses of 32Si and 14C in relatively fast accumulating sediments ( > 10 cm/103 yr.). Both these nuclides are introduced in surface waters, from where they are transported to sediments by sinking remains of organisms... 

The purpose of the series was to accumulate scientific data, such as inside, outside and skin temperatures density, distribution and momentum of micro-meteorites, cosmic-ray intensity energy and intensity of corpuscular radiations, X-radiation, die extent of the earth s radiation belt, map the earth s magnetic field, etc Note 1 Perigee is the point in the orbit of a satellite of the earth that is nearest to the earth... 

First of all, what happened to the C atom following its production This could be quickly answered. Within a few minutes, or hours at the most, it would have been oxidized to a carbon dioxide molecule. Some intermediate pathway was possible, but the high probability was that all cosmic-ray produced C would be oxidized relatively rapidly and completely to C02. Since cosmic ray intensities varied by a factor of... 

To a first approximation, the all-particle spectrum of cosmic rays can be described by a power law on more than 11 decades on particle energy, so that the dependence of cosmic ray intensity on particle energy is close to E 2-7 at energy more than about 10 GeV. Closer examination reveals some structure in the galactic cosmic ray spectrum that includes the knee at 4 x 1015 eV, the second knee at about 1018 eV, and the ankle at 1019 eV. The steady-state spectrum is shaped by two principle processes - the acceleration at the sources and the subsequent propagation in the Galaxy. 

The characteristic time of particle acceleration at the shock can be estimated as D/u2h. The distribution of accelerated particles on momentum has a power law form f(p) p-3r/9r-1 where r is the gas compression ratio in the shock. The relation between the distribution function f(p) and the cosmic ray intensity 1(E) which is a function of particle energy reads as /(p)p2 = 1(E). The compression in strong shocks is r = 4 and hence the spectrum of accelerated test particles is f(p) p-4 that is close to the required source spectrum of galactic cosmic rays. This result is valid in the case of a step-like profile of the flow velocity at the shock or, more precisely, when the characteristic thickness of the shock Lsh is relatively small Lsh -C D/u. ... 

The primary cosmic rays propagate through the interstellar medium (ISM) until they either escape into extragalactic space, or are removed by interaction or energy losses in the ISM. Their interstellar equilibrium intensity may be recorded with a detector which is usually carried above the earth s atmosphere on spacecraft or balloon. Secondary cosmic rays are those that are generated as products from interactions of the primaries in the ISM positrons and antiprotons mostly come from interactions of primary protons, while the secondary nuclei such as Li, Be, B, and the elements just below iron, which cannot be produced by primary nucleosynthesis, are the products of spallation reactions of heavier primaries in the ISM. The overall arriving cosmic-ray intensity represents a mix of primary and secondary particles. 

In the meanwhile, significant progress in the phenomenological understanding of the arriving cosmic-ray intensity, and in the identification of the individual components was made. Nevertheless, it took until the late 1970 s before the currently accepted model of cosmic-ray origin was developed. This model reconciles the Baade/Zwicky and Fermi proposals by describing a first-order... 

The observed cosmic ray intensity NP(E) is determined by the competition between escape and spallation. It is important to realize that the numerical values of At and A at 1 GeV/nucleon are of comparable magnitude, for instance Ai 6.5g/cm2 for nitrogen, and 2.3g/cm2 for iron, and, as mentioned, A lg/cm2. While we may take A to be energy independent, A apparently is not. Hence, the measured energy spectrum NP(E) does not necessarily follow the same power law as the source spectrum. 

Hampel W, Schaeffer OA (1979) A1 in iron meteorites and the constancy of cosmic ray intensity in the past. Earth Planet Sci Lett 42 348-358... 

Figure 10.3 shows the effect of high energy cosmic rays hitting the helmets of Apollo 12 astronauts. It is probable that the cosmic ray intensity will put a limit to how long man can endure in outer space it has been calculated that in a journey to the planet Mars about 0.1% of the cerebral cortex will be destroyed. The aimihilation process occurs to such an extent that below an altitude of approximately 25 km above the earth the number of primary cosmic particles has been reduced to quite a small fraction of the original intensity. 

This article is concerned primarily with nuclides that are useful as tracers in oceanography, and therefore shorter-lived nuclides have been excluded from Table 1. Since cosmic ray intensity is appreciably reduced at sea level due to nuclear interactions in the atmosphere isotope production rates (per gram target element per second), in surficial materials, are appreciably smaller than in the atmosphere. Therefore, nuclides, which can be produced in nuclear interactions with the major elements present in the atmosphere, N and O, have their principal source in the atmosphere. The next most abundant element, Ar, in the atmosphere occurs at an abundance of only... 

Be produced by cosmic-ray-induced nuclear reactions is useful for studying atmospheric transport mechanisms. Since the production of Be and other cosmogenic nuclides is directly dependent on the cosmic-ray intensity, a relationship between the production rate of these nuclides and the 11-year solar cycle has been found (Kulan et al. 2006). It is known that the galactic cosmic-ray intensity at the earth s orbit is inversely related to solar activity (Hotzl etal. 1991). 

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