User:Marshallsumter/Radiation astronomy2/Spallations

Observations of cosmic ray spallation had already been made in the 1930s, but the first observations from a particle accelerator occurred in 1947, and the term "spallation" was coined by Glenn T. Seaborg that same year.

Def. a "nuclear reaction in which a nucleus fragments into many nucleons" or "fragmentation due to stress or impact" is called spallation.

Cosmic rays

Main article: Radiation/Cosmic rays

The flux of cosmic-ray particles is a function of their energy. Credit: Sven Lafebre, after Swordy.

Cosmic rays cause spallation when a ray particle (e.g. a proton) impacts with matter, including other cosmic rays. The result of the collision is the expulsion of large numbers of nucleons (protons and neutrons) from the object hit.

At right is an image indicating the range of cosmic-ray energies. The flux for the lowest energies (yellow zone) is mainly attributed to solar cosmic rays, intermediate energies (blue) to galactic cosmic rays, and highest energies (purple) to extragalactic cosmic rays.

"High sunspot activity increases the weak magnetic field that exists between the planets, and at such times there is a greater deflection of cosmic rays and hence ¹⁴C decreases."

"Cosmic rays originate from the Sun as well as from galactic sources."

"Cosmic-ray variations are associated with changes in the strength of the Earth's magnetic field. A weak field allows more cosmic radiation to reach the upper atmosphere, and the production of carbon-14 is consequently enhanced--causing raw radiocarbon ages to be underestimates of calendar ages. The short-term wiggles mentioned above are associated with sunspot activity."

"Direct observations of cosmic rays within the heliosphere over several decades have revealed a great deal of information about the acceleration and propagation of cosmic radiation through the interstellar space and the heliosphere. We now know that the cosmic radiation incident at the top of the earth’s atmosphere comes to us through several “filters”:

1. Galactic magnetic fields,
2. Interstellar magnetic fields,
3. Solar magnetic plasma within the heliosphere, regulated by solar activity, and finally,
4. the Terrestrial geomagnetic field."

"Additionally, cosmic ray particles are frequently accelerated by the sun, and sometimes in a nearby supernova to make an appreciable difference in the total cosmic ray flux at the earth!"

"Since fairly extensive cosmic-ray data on primary and secondary cosmic rays are available for more than the past five decades, covering five solar cycles, it is fairly easy to make reliable calculations of the magnitude of variations in cosmogenic production rates in terrestrial solids due to solar modulation of galactic cosmic-ray flux. This exercise is based on a study of relative changes in the primary cosmic-ray flux at the top of the atmosphere, and flux of low energy neutrons as measured by neutron monitors. Solar modulation of galactic cosmic-ray flux is conveniently described in terms of a modulation potential, ∅, which is a phase-lagged function of solar activity (see Castagnoli and Lal 1980; Lal 1988b, 2000 and references therein). Continuous data are available for several neutron monitors at sea-level and mountain altitudes located at different latitudes, and these data have been analyzed in terms of transfer functions relating changes in the secondary nucleon fluxes in the atmosphere to those in the primary cosmic-ray spectra (cf. Webber and Lockwood 1988; Nagashima et al. 1989). For a recent discussion on changes in cosmic-ray fluxes as measured on spacecrafts and in neutron monitor counting rates, the reader is referred to Lal (2000). The manner in which the primary and secondary cosmic-ray flux changes occur with the march of solar activity is described in detail by Lal and Peters (1967), who also estimate the changes in the isotope production rates as a function of altitude and latitude during 1956 (a period of solar minimum) and 1958 (a period of unusually high solar activity). Using this approach, and using the neutron monitor data available to date, one can improve on the earlier estimates of solar temporal variations in cosmogenic nuclide production rates at sea level and at mountain altitudes. We must mention here that several direct experiments are also being made at present by exposing targets to cosmic radiation at different altitudes and latitudes (cf. Lal 2000)."

Secondary cosmic rays

Def. cosmic rays that are created when primary cosmic rays interact with interstellar matter are called secondary cosmic rays.

Carbon and oxygen nuclei collide with interstellar matter to form lithium, beryllium and boron in a process termed cosmic ray spallation. Spallation is also responsible for the abundances of scandium, titanium, vanadium, and manganese ions in cosmic rays produced by collisions of iron and nickel nuclei with interstellar matter.

Ultra-heavy element nuclei

Main article: Radiation astronomy/Subatomics

File:Absolute flux of cosmic–ray elements at 1 TeV-nucleus versus nuclear charge.png

Absolute flux Φ⁰_Z of cosmic–ray elements at E₀ = 1 TeV/nucleus is plotted versus nuclear charge. Credit: Jörg R. Hörandel.{{fairuse}}

"The iron group and the ultra–heavy elements are more pronounced in cosmic rays as compared to the solar system. Especially the r–process elements beyond xenon (Z=54) are enhanced, partly due to spallation products of the platinum and lead nuclei (Z=78, 82). For the latter direct measurements at low energies around 1 GeV/n yield about a factor two more abundance as compared to the solar system and a factor of four for the actinides thorium and uranium (Z=90, 92) [66]. This has been attributed to the hypothesis that cosmic rays are accelerated out of supernova ejecta–enriched matter [67]."

Nitrogen nuclei

Main article: Radiation astronomy/Subatomics

"For cosmic rays the low abundance ”valleys” in the solar system composition around Z=4, 21, 46, and 70 are not present. This is usually believed to be the result of spallation of heavier nuclei during their propagation through the galaxy. Hydrogen, helium, and the CNO–group are suppressed in cosmic rays. This has been explained by the high first ionization potential of these atoms [63] or by the high volatility of these elements which do not condense on interstellar grains [64]. Which property is the right descriptor of cosmic–ray abundances has proved elusive, however, the volatility seems to become the more accepted solution [65]."

Carbon nuclei

Main article: Radiation astronomy/Subatomics

These "are nevertheless present in the cosmic radiation as spallation products of the abundant nuclei of carbon and oxygen (Li,Be,B) and of iron (Sc,Ti,V,Cr,Mn)."

Fast neutrons

Main article: Radiation/Neutrons

"THE first suggestion that appreciable ¹⁴
C might be produced in situ in polar ice was made by Fireman and Norris¹, who studied ¹⁴
C in CO₂ extracted from both accumulation and ablation samples. In some ablation samples they observed ¹⁴
C activities between four and six times higher than those expected due to trapped atmospheric CO₂."

"The ¹⁴C is produced mainly by nuclear spallations of oxygen in ice. The observed concentration of ¹⁴C in ablation ice samples is 1–3 x 10³ atom per g ice, three orders of magnitude higher than expected from the amount of trapped atmospheric CO₂ in this ice."

"Spallation of atmospheric oxygen nuclei might contribute up to 20% to production of ¹⁴
C produced in the atmosphere (Lal and Peters 1967)."

"The fraction of cosmogenic ¹⁴
C produced below the atmosphere at the earth’s surface is estimated to be less than 0.1% of the total (Lal 1988a, 1992b)."

Hypotheses

Main article: Hypotheses

1. The use of satellites should provide ten times the information as sounding rockets or balloons.

See also

• Gamma-ray astronomy
• Neutron astronomy
• Optical astronomy
• Radiation satellites/Quiz
• Submillimeter astronomy
• X-ray astronomy

External links

• International Astronomical Union
• NASA/IPAC Extragalactic Database - NED
• NASA's National Space Science Data Center
• Office of Scientific & Technical Information
• The SAO/NASA Astrophysics Data System
• Scirus for scientific information only advanced search
• SDSS Quick Look tool: SkyServer
• SIMBAD Astronomical Database
• Spacecraft Query at NASA
• Universal coordinate converter

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