Radiation astronomy/Alpha particles

From Wikiversity
Jump to navigation Jump to search

Cosmic rays[edit]

About 89% of cosmic rays are simple protons or hydrogen nuclei, 10% are helium nuclei or alpha particles, and 1% are the nuclei of heavier elements. Solitary electrons constitute much of the remaining 1%.

"The energy spectra of solar protons and helium nuclei [the two most abundant components in solar cosmic rays] have been measured simultaneously on several occasions using nuclear emulsion detectors flown on balloons [...]."[1]

These "have different velocity spectra, similar, but not exactly identical rigidity spectra, and varying relative abundances."[1]

"The multiply charged nuclei, on the other hand, appear to have the same spectral shape and relative abundances each time measurements are made, at least in the region from 42 to 135 MeV/nucleon. Further, these relative abundances seem to reflect those of the solar atmosphere insofar as comparison can be made."[1]

"Finally, there is positive evidence that very small quantities of deuterons exist, probably in an amount which is about 10-3 or less of the proton abundance."[1]

The "rare components [are] deuterons, tritons, He3 nuclei, electrons, neutrons, and the heavier nuclei."[1]

Alpha decays[edit]

"Natural alpha decay takes place in heavy nuclei [...]. Each alpha decay leads to ΔΛ = 4, ΔZ = 2. Since this tends to move nuclei off the line of beta stability to the neutron-rich side, beta (-minus) decays are found in conjunction with alpha decays. There are thus four series (or chains) of alpha decays into which the natural alpha decays can be fitted; these correspond to Λ = 4n, 4n + 1, 4n + 2 and 4n + 3, where n is an integer.

Thorium series: 232
Neptunium series: 237
Uranium series: 238
Actinium series: 235

"A decay starting with the heaviest nucleus in a series can continue down to the lightest, with a sequence of alpha and beta decays following roughly the line of stability."[2]

"It follows from conservation of energy and momentum that the kinetic energy of the alpha and the residual nucleus has a fixed value. Alpha particles are thus emitted with a sharply peaked spectrum."[2]


Neutrons are produced when alpha particles impinge upon any of several low atomic weight isotopes including isotopes of lithium, beryllium, carbon and oxygen.


  1. 1.0 1.1 1.2 1.3 1.4 S. Biswas & C. E. Fichtel (September 1965). "Composition of Solar Cosmic Rays". Space Science Reviews 4 (5-6): 709-736. doi:10.1007/BF00216274. http://adsabs.harvard.edu/full/1965SSRv....4..709B. Retrieved 2018-5-23. 
  2. 2.0 2.1 2.2 np (6 November 1996). Systematics Alpha decay. uct.ac.za: Physics Department. p. 1. Retrieved 2018-04-01.