Propagation of inclined solar neutrons: scattering, energy decrease,
attenuation and refraction effect
Lev I. Dorman
Israel Cosmic Ray Center, affiliated to Tel Aviv University;
Technion and IZMIRAN; Current address: P.O.Box 2217, Qazrin 12900, ISRAEL
Irina V. Dorman
Institute of History of Science and Technology, Russian Academy
of Science, Staropansky 1/5, Moscow 103012, RUSSIA
Jose F. Valdes-Galicia
Institute of Geofisica of UNAM, Mexico D.F., 04510, MEXICO
We develop our simulation and analytical calculation results of solar
neutron propagation in the atmosphere for different initial zenith
angles taking into account not only scattering and attenuation but also
neutron energy decrease (what leads to increase both of cross-section and
scattering angles, what is especially important for small energy solar
neutrons). We test the usually used suggestion that solar neutron
propagation through the atmosphere of depth H for some initial zenith
angle Z of the Sun will be the same as for vertical direction, but for
the depth H/cosZ. Our calculations of multi-scattering of neutrons on
small angles with attenuation and energy change for different initial
zenith angles shows that this suggestion is not correct. Taking into
account the neutron energy change shows that with decreasing of solar
neutron energy the assymmetry in solar neutron propagation and
refraction effect became stronger. We show that during the propagation
through the earth's atmosphere the effective zenith angle of solar
neutron flux sufficiently decrease. These decreases are especially
great for the big initial zenith angles what gives expected solar
neutron fluxes many times bigger than in the frame of previous theory
of solar neutron propagation. We show also that the optimum direction
of solar neutron telescope must be not the direction on the Sun (as for
optical telescope), but between the Sun and vertical.