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Chapter 2. Flare Region Diagnostic from Nuclear and Neutron Capture Gamma Lines in Energy Spectraстатья
- Авторы: Arkhangelskaja I.V., Troitskaya E.V., Gan W.Q.
- Сборник: Horizons in World Physics
- Серия: Horizons in World Physics
- Том: 274
- Глава в коллективной монографии
- Год издания: 2012
- Место издания: Nova Science Publishers Inc Imprint: Nova Press, New York
- Первая страница: 39
- Последняя страница: 78
- Аннотация: ABSTRACT Accelerated energetic particles in solar flares produce nuclear -lines in the processes of interaction with ambient solar atmosphere. Gamma-ray emissions from solar flares give information about the nature of the accelerated particles and physical conditions in the area, in which the flare occurs, and in the surrounding medium. Nuclear lines properties represent the abundance of elements, density and temperature of the ambient solar atmosphere and the parameters of the accelerated ions. In this chapter we study the processes of the neutron capture and nuclear gamma lines formation during solar flares as well as the methods and the results of estimations of the abundance of the elements, parameters of surrounding media and other solar characteristics. Several types of gamma-lines presented in the energy spectra of solar flares: narrow nuclear de-excitation lines with fractional FWHM around 2% which generated via de-excitation processes of excited nuclei produced in the interactions of flare-accelerated protons and -particles with the ambient nuclei heavier than He (as the recoil velocity of a heavier nucleus is relatively low) and broad gamma-lines with fractional FWHM around 20% caused due to de-excitation processes of excited nuclei produced in the interactions of accelerated particles and heavier ions with ambient H and He (as the recoil velocity of a nucleus is relatively high). Also flare spectra contain lines caused by neutron capture on hydrogen and helium-3 and relatively narrow gamma-lines via the de-excitation processes of excited nuclei produced in heavy-heavy interactions (for example, 1.634 MeV 20Ne, 1.369 MeV 24Mg and 0.937 MeV 18F). Thus the time integrated spectra up to 10 MeV could be fitted with a model of multi-components, including the bremsstrahlung, the annihilation line, neutron–hydrogen capture line, several narrow nuclear lines as well as the broad lines. Based on the fitted data, we discuss the spectral index of accelerated ions, the abundance of ambient medium and so on. For example, it was shown that during some events the abundance of Ne/O tends to be of 0.15 rather than 0.25, and that accelerated α/p tends to be within the range of 0.01–0.1 but not bigger than 0.1. We present the results of the analysis of some solar flares characteristics and surrounding medium (solar plasma) by means of 2.223 MeV line time profile of gamma-emission from neutron captures by hydrogen nuclei. This analysis is based on the comparison between the observations and profiles computed taking into account a number of parameters describing the generation and transport of the flare neutrons in the atmospheric layers of various densities. The composed code makes allowance for the main processes of neutron interactions and deceleration in the solar atmosphere, character of neutron source, losses of neutrons and density model of the solar atmosphere. Comparing of the simulated temporal profiles of 2.223 MeV gamma-line with observed ones allowed us to reveal the density enhancements in the sub-flare regions of some extreme flares. Using the same analysis the values of spectral indices of charged particles were estimated and their evolution with the time during gamma-emission of the flares was obtained. The hardening of charged particles spectrum which was found, using our methods, is discussed. Just as in this chapter we consider the flux ratio between two lines from excited states of 12C (f15.11/f4.44) and our results of preliminary calculation of intensity ratio between two neutron capture lines at 3He and 1H (f20.58/f2.223). In particular, we consider the opportunity to obtain n(3He)/n(1H) ratio during solar flares and using high energy gamma-emission studying based on the satellite data. The possible interpretation of the spectral features observed during some very intensive events is discussed.
- Добавил в систему: Троицкая Евгения Викторовна