Cosmic ray sources

Table 4.4 shows the yields for the masked and unmasked photomultiplier for both the Ru (3 source and for cosmic ray muons, as well as the HAPD result with the (3 source cosmic ray test of the HAPD is underway. As expected, the HAPD result with the [3 source correlates well with the result using the masked photomultiplier. 

Everyone receives small radiation doses every day Figure 8.3-5 illustrates some of the doses received from background and other types of radiation. Note that the scale is logarithmic , and that background and cosmic-ray doses vary over an order of magnitude just with location and elevation. In addition to these natural sources, most people receive some medical and dental doses each year. 

Though measurements of solar output have been taken only for the past eighteen years, longer trend patterns can be derived from indirect data sources, such as ice cores and tree rings. Cosmic rays, which fluctuate with the sun s activity, also strike constituents of the atmosphere, creating radioactive versions of certain elements. Beiyllium, in particular, is ionized to "Be by cosmic rays. The "Be then gets incorporated into trees as they grow, and is trapped in bubbles in ice masses, as is carbon dioxide. 

Most CO and CO2 in the atmosphere contain the mass 12 isotope of carbon. However, due to the reaction of cosmic ray neutrons with nitrogen in the upper atmosphere, C is produced. Nuclear bomb explosions also produce C. The C is oxidized, first to CO and then to C02 by OH- radicals. As a result, all CO2 in the atmosphere contains some 0, currently a fraction of ca. 10 of all CO2. Since C is radioactive (j -emitter, 0.156 MeV, half-life of 5770 years), all atmospheric CO2 is slightly radioactive. Again, since atmospheric CO2 is the carbon source for photos5mthesis, aU biomass contains C and its level of radioactivity can be used to date the age of the biological material. 

For radiocarbon, the standard ratio s is provided by the preindustrial atmosphere, for which 8 = 0. Cosmic rays interacting with atmospheric nitrogen were the main source of preindustrial radiocarbon. In the steady state, this source drsource is just large enough to generate an atmospheric delta value equal to zero. The source appears in equation 9 for atmospheric radiocarbon. Its value, specified in subroutine SPECS, I adjust to yield a steady-state atmospheric delta value of 0. The source balances the decay of radiocarbon in the atmosphere and in all of the oceanic reservoirs. Because radiocarbon has an overall source and sink—unlike the phosphorus, total carbon, 13C, and alkalinity in this simulation—the steady-state values of radiocarbon do not depend on the initial values. 

Nuclides (i.e., 14C and 3H) formed by continuing natural nuclear transformations driven by cosmic rays, natural sources of neutrons, or energetic particles that are formed in the upper atmosphere by cosmic rays... 

Exposure to natural sources of radiation is unavoidable. Externally, individuals receive cosmic rays, terrestrial X-rays, and gamma radiation. Internally, naturally occurring radionuclides of Pb, Po, Bi, Ra, Rn, K, C, H, U, and Th contribute to the natural radiation dose from inhalation and ingestion. Potassium-40 is the most abundant radionuclide in foods and in all tissues. The mean effective human dose equivalent from natural radiations is 2.4 milliSieverts (mSv). This value includes the lung dose from radon daughter products and is about 20% higher than a 1982 estimate that did not take lung dose into account (Table 32.4). 

Fig. 9.2. Schematic view of the life history of a cosmic ray from acceleration in the source through propagation in the Galaxy to observation above the Earth s atmosphere. Adapted from Rolfs and Rodney (1988).

Hubert Reeves once summed up the similarity of cosmic-ray source and Solar-System abundances in the form of a graffito seen at times in Paris CRS = SS ... 

The light elements present in cosmic rays are partly thermalized, i.e. brought down to low velocities by ionization losses, and thus make a minor contribution to their abundance in the ISM (perhaps about 20 per cent). The main source is usually thought to come from reactions of cosmic-ray protons and a-particles with stationary nuclei of He, C, N and O in the ISM. 

In this textbook many exciting topics in astrophysics and cosmology are covered, from abundance measurements in astronomical sources, to light element production by cosmic rays and the effects of galactic processes on the evolution of the elements. Simple derivations for key results are provided, together with problems and helpful solution hints, enabling the student to develop an understanding of results from numerical models and real observations. 

The exposure to ionizing radiation from natural sources is continuous and unavoidable. For most individuals, this exposure exceeds that from all human-made sources combined (UNSCEAR 2000a). The two main contributors to natural radiation exposures are high-energy cosmic ray particles incident on the earth s atmosphere and radioactive nuclides that originate in the earth s crust and are present everywhere in the environment, including the human body itself. 

In order to reconstruct relative abundances of these nuclei at source, we must first expurgate all the fragmentation debris. This is done with the help of a model to be described shortly. The Galaxy is not totally closed as regards cosmic ray movements. Three dangers await any particle launched at high speed in the Galaxy ... 

SNII events alone explain the observed solar abundance distribution between oxygen and chromium. This can be taken as a major theoretical achievement. Complementary sources of hydrogen, helium, lithium, beryllium, boron, carbon and nitrogen are required, and these have been identified. They are the Big Bang, cosmic rays and intermediate-mass stars. Around iron and a little beyond, we must invoke a contribution from type la supernovas (Pig. 8.5). These must be included to reproduce the evolution of iron abundances, a fact which suggests... 

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