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ISO 20785-1-2012 pdf free download
ISO 20785-1-2012 pdf free download.Dosimetry for exposures to cosmic radiation in civilian aircraft
Part 1:Conceptual basis for measurements
Dosimétrie pour l’exposition au rayonnement cosmique a bord d’un avion civil — Partie 1: Fondement théorique des mesurages.
Note 1 to entry: Installed worldwide at different locations and altitudes on the ground (and occasionally placed on ships or aircraft), cosmic radiation neutron monitors are used for various cosmic radiation studies and to determine solar modulation.
3 General considerations
3.1 General description of the cosmic radiation field in the atmosphere
The primary galactic cosmic radiation (and energetic solar particles) interact with the atomic nuclei of atmospheric constituents, producing a cascade of interactions and secondary reaction products that contribute to cosmic radiation exposures that decrease in intensity with depth in the atmosphere from aviation altitudes to sea leveLllM Galactic cosmic radiation (GCRJ can have energies up to 1020 eV, but lower energy particles are the most frequent. After the GCRs penetrate the magnetic field of the solar system, the peak of their energy distribution is at a few hundred MeV to 1 GeV per nucleon, depending on solar magnetic activity, and the spectrum follows a power [unction of the form E2.7 eV up to 1015 eV; above that energy, the spectrum steepens to E-3 eV. The fluence rate of GCR entering the solar system is fairly constant in time, and these energetic ions approach the Earth isotropically.
The magnetic fields of the Earth and sun alter the relative number of GCR protons and heavier ions reaching the atmosphere. The GCR ion composition for low geomagnetic cut-off and low solar activity is approximately 90% protons, 9% He ions, 1 % heavier nuclei; at a vertical cut-off of 15 GV, the composition is approximately 83 % protons, 15 % He ions, and nearly 2 % heavier ions.lZllUl
The changing components of ambient dose equivalent caused by the various secondary cosmic radiation constituents in the atmosphere as a function of altitude are Illustrated in Figure 1. At sea level, the muon component is the most important contributor to ambient dose equivalent and effective dose; at aviation altitudes, neutrons, electrons, positrons, protons, photons, and muons are the most significant components. At higher altitudes, nuclear ions heavier than protons start to contribute. Figures showing representative normalized energy distributions of fluence rates of all the important particles at low and high cut-offs and altitudes at solar minimum and maximum are shown in Annex A.
The Earth is also exposed to bursts of energetic protons and heavier particles from magnetic disturbances near the surface of the SUfl and from ejection of large amounts of matter (coronal mass ejections — CM Es) with, in some cases, acceleration by the CMEs and associated solar wind shock waves. The particles of these solar particle events, or solar proton events (both abbreviated to SPEs), are much lower in energy than GCR: generally below 100 MeV and only rarely above 10 GeV. SPEs are of short duration, a few hours to a few days, and highly variable in intensity. Only a small fraction of SPEs, on average one per year, produce large numbers of high-energy particles which cause significant dose rates at high altitudes and low geomagnetic cut-offs and can be observed by neutron monitors on the ground. Such events are called ground-level events (GLEs). For aircraft crews, the cumulative dose from GCR Is far greater than the dose from SPEs. Intense SPEs can affect GCR dose rates by disturbing the Earth’s magnetic field in such a way as to change the galactic particle intensity reaching the atmosphere.ISO 20785-1-2012 pdf free download.
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