Cosmic ray diffusion

Shaviv, N. (2004). Cosmic ray diffusion in the Milky Way model, measurement and terrestrial effects , in Proc. of ISCRA 13th Course, Eds. M. Shapiro, T. Stanev and J. Wefel, World Scientific Publ., p.l 13. 

The solution of this problem was suggested in [40], [41] where the strong nonlinear processes that accomany the cosmic-ray streaming instability in a precursor of a supernova shock was studied. The level of magnetohydrody-namic turbulence in this region determines the value of cosmic ray diffusion... 

Abstract We map and study the dynamics of the Milky Way s spiral arms in our vicinity, using the birth place of open clusters. Since these objects are located in the galactic plane and are born primarily in the arms, they are an excellent tool for analyzing the dynamics of the spiral structure. Using their birth place, we find evidence for multiple spiral patterns with different speeds. The Carina arm appears now to be a superposition of both. The results are important for proper modeling of cosmic ray diffusion in our galactic vicinity. 

Tritium has also been observed in meteorites and material recovered from sateUites (see also Extraterrestrial materials). The tritium activity in meteorites can be reasonably well explained by the interaction of cosmic-ray particles and meteoritic material. The tritium contents of recovered sateUite materials have not in general agreed with predictions based on cosmic-ray exposure. Eor observations higher than those predicted (Discoverer XVII and sateUites), a theory of exposure to incident tritium flux in solar flares has been proposed. Eor observations lower than predicted (Sputnik 4), the suggested explanation is a diffusive loss of tritium during heating up on reentry. 

The concentration of small ions in the atmosphere is determined by 1) the rate of ion-pair production by the cosmic rays and radioactive decay due to natural radioactive substances, 2) recombination with negative ions, 3) attachment to condensation nuclei, 4) precipitation scavenging, and 5) transport processes including convection, advection, eddy diffusion, sedimentation, and ion migration under the influence of electric fields. A detailed differential equation for the concentration of short-lived Rn-222 daughter ions including these terms as well as those pertaining to the rate of formation of the... 

Curiously, there are some nearby interstellar diffuse clouds displaying anomalously low isotope ratios for 7Li/6Li, with a ratio apparently as small as 2 in one case (Lemoine et at. 1994 Knauth, Federman Lambert 2003), compared to the Solar-System (and more usual interstellar) ratio of 12 the anomaly here is that the low ratio in such clouds is consistent with cosmic-ray spallation whereas that in the Solar-System is not. 

Radioactive or stable isotopes of noble gases are also used to determine vertical turbulent diffusion in natural water bodies. For instance, the decay of tritium (3H)— either produced by cosmic rays in the atmosphere or introduced into the hydrosphere by anthropogenic sources—causes the natural stable isotope ratio of helium, 3He/ 4He, to increase. Only if water contacts the atmosphere can the helium ratio be set back to its atmospheric equilibrium value. Thus the combined measurement of the 3H-concentration and the 3He/4He ratio yields information on the so-called water age, that is, the time since the analyzed water was last exposed to the atmosphere (Aeschbach-Hertig et al., 1996). The vertical distribution of water age in lakes and oceans allows us to quantify vertical mixing. 

Cosmic rays residing in galaxy clusters produce several astrophysical signatures among which there are diffuse synchrotron radio emission, ICS of CMB (and other background) photons which are then moved to higher frequencies... 

Isotopes in interstellar gas With the aid of the Hubble Space Telescope it has been possible for the first time to measure the boron isotopic ratio within diffuse clouds of the Milky Way. The interstellar ultraviolet radiation renders B ionized (B+) in the diffuse clouds therefore its spectrum is similar to that of the element Be, but at shorter wavelengths. The strongest resonance line lies in the ultraviolet, visible to Hubble spectrometers. The smaller mass of the 10B isotope shifts its line by 0.013 A (about 0.001%) toward longer wavelengths. Very detailed analysis of the line pair has shown in several clouds that today s interstellar abundance ratio is UB/ 10B = 3.4 0.7, which is consistent with the solar ratio 4.05. For the first time one can conclude that the solar ratio is not an abnormal one, but is shared by interstellar gas at a value larger than the ratio 2.5 that is produced by cosmic-ray collisions in the interstellar gas. Another source of11B is needed. 

C. Tanford and R. N. Pease, J. Cham, Phys.y 16, 861 (1947), have developed a model in which propagation occurs by diffusion of radicals. Since wall initiation of chains is not possible in most flames, it seems quite reasonable to expect that initiation by diffusion of chain carriers may be a necessary condition for propagation. It is difficult, however, to see this as a limiting or controlling condition even in fast flames, particularly for branching chain reactions in which, because of the rapid multiplication of centers, even cosmic rays can act as initiations once ignition temperatures have been reached. 

So far, unsuccessful searches for Hj in BN, GL 2591, LkH 101, NGC 2024/IRS, W33IR, NGC 2264 and AFGL 2591 have been reported. Black et alP observed spectral lines of CO simultaneously with their search for Hj. The abundance of CO thus obtained together with the upper limit of the Hj column density set a limit on the rate of the cosmic ray ionization C through eqn. (7). van Dishoeck and Black have proposed on chemical grounds that the abundance of Hj may be equally high in diffuse interstellar clouds. ... 

This classification has been discussed extensively within the context of a one-dimensional advection-diffusion model, along with simple solutions to the relevant equations (Craig, 1969). It should be noted, however, that specific tracers may fall into different categories depending on the nature of the specific application. For example, radiocarbon is a transient tracer in the surface waters of the ocean because its natural inventory (due to cosmic ray production) has been affected... 

In this picture, the amount of secondary nuclei is a measure of the characteristic time for propagation of cosmic rays before they escape from the galaxy into inter-galactic space. A simplified version of the diffusion equation that relates the observed abundances and spectra to initial values is... 

The thickness of the disk of the galaxy is of order 300 pc = 1000 light years, which is much shorter than the characteristic propagation time of 10 million years. The explanation is that the charged particles are trapped in the turbulent magnetized plasma of the interstellar medium and only diffuse slowly away from the disk, which is assumed to be where the sources are located. Measurements of the ratio of unstable to stable secondary nuclei (especially 10Be/9 lie) are used to determine resc independently of the product np resc and hence to constrain further the models of cosmic-ray propagation. 

The implication of Eq. 17 is that for E1 70 MeV the diffuse gamma-ray spectrum should have the same power law behavior as the proton spectrum, a ss 2.7. What is observed, however, is that the spectrum of gamma-rays from the inner galaxy is harder than this, having a power-law behavior of approximately E 2A (Hunter et al., 1997). This is currently not fully understood. One possibility is that the cosmic-ray spectrum producing the gamma rays is harder than observed locally near Earth (Hunter et al., 1997). 

The relative abundance of chemical elements in cosmic ray sources is in general similar to the solar and to the local galactic abundance but show some significant deviations. The elements that appear underabundant by a factor of about 5 are those elements that are difficult to ionize. The critical ionization potential is approximately 10 eV that corresponds to ionization at an equilibrium temperature 104 K (characteristic e.g. of the solar photosphere). The correlation of abundance with the first ionization potential is also known for solar energetic particles. Thus, it is possible that the outer layers of relatively cool stars serve as injectors of the seed particles required for the subsequent acceleration [17]. For most elements the volatility is correlated with the first ionization potential, so that volatility is also considered as a possible selection factor for the cosmic ray population. Then predominant acceleration and breakup of grains that is natural for the diffusive shock acceleration could explain the situation [18]. 

It is worth noting that the knee observed in the cosmic ray spectrum at 4 x 1015 eV may arise not in the sources but in the process of cosmic ray propagation in the Galaxy, e.g. as a result of interplay between ordinary and Hall diffusion in galactic magnetic fields [54], [Roulet 2004], Of course, this explanation requires the existence of a power-law source spectrum which extends without essential breaks up to about 1018 eV or even further. 

Ptuskin, V.S., and V.N. Zirakashvili. (2003). Limits on diffusive shock acceleration in supernova remnants in the presence of cosmic-ray streaming instability and wave dissipation44, A A 403, 1. 

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