Measurement of radiation in the lower Van Allen belt

The experimental information about the radiation belt is summarized. Calculations of the radiation belt spectra and fluxes based on the neutron decay source are compared with the experiments. The purpose is to find out in what ways the neutron decay source explains the observed features of the radiation belt and where other sources may be needed. The conclusion reached is that the inner zone of the radiation belt is quite likely supplied by neutron decay alone and also the e2 region of the outer zone may well be due to neutrons alone but that there may be as well as the neutron source another source of particles that supplies electrons of less than 100 kev to the e3 region of the outer zone.

Section: The 1xteutron Flux In Spacementioning

confidence: 88%

The radiation belt produced by neutrons leaking out of the atmosphere of the Earth

Hess¹

1960

“…13). A measurement, employing shielded Geiger tubes, at ~ 1100 km along lines of force extending to ~ 1.3 --1.6R [Holly and Johnson, 1960;Holly, 1960] found an electron energy spectrum similar to the higher altitude spectrum (Walt) above ~ 200 kev (Fig. 13).…”

Section: Comparison •Riti-i Observationsmentioning

confidence: 92%

Geomagnetically trapped electrons from cosmic ray albedo neutrons

Lenchek¹,

Singer²,

Wentworth³

1961

118

112

The ability of the cosmic‐ray neutron albedo mechanism to account for geomagnetically trapped electrons is investigated quantitatively. Injection as a function of energy, pitch angle, and altitude is computed from a reasonable neutron albedo model. Loss mechanisms (slowing down and pitch‐angle diffusion) based on Coulomb interactions with the residual atmosphere are considered to act both independently and simultaneously. It is found that slowing down is generally dominant. The resulting electron belt has the following features: (a) an intensity whose energy spectrum shows a peak at ∼200 kev; (b) an angular distribution that is approximately ‘isotropic’ up to the loss cone; and (c) an omnidirectional, integral intensity in the geomagnetic equatorial plane that is approximately constant vs. altitude. The absolute intensities depend directly on the atmospheric model used in the calculation; namely, rv−2.7, where atmospheric density is taken as ρ0r−v. These results agree only poorly with spectrometer observations which show an energy spectrum with a peak at a much lower energy. However, the quantitative agreement as to intensity is good at energies ≳400 kev. It is concluded that only a small fraction of the trapped electrons can be accounted for in terms of neutron albedo, essentially all trapped electrons >400 kev. An ‘auroral’ component of low‐energy electrons is also present. The energy of this low‐energy component probably derives from local acceleration, and ultimately from the sun. The effect of the Capetown magnetic anomaly is investigated and shown to produce a ‘slot’ of only 2 per cent in the equatorial plane in the vicinity of 2.7 earth radii.

“…The Van Allen radiation is a belt of energetic particles trapped in the earth's magnetic field. This belt has been shown to consist of two components: (1) a hard proton component (the proton belt) centered at about 104 km from the earth's magnetic axis [Freden and White, 1959; Fan, Meyer, and Simpson, 1960; McIlwain, Resuits from Explorer IV, presented at NASA seminar on Van Allen radiation, March 26-27, 1959, unpublished]; and (2) an electron component which extends through the region occupied by the proton belt [Holly and Johnson, 1960]. The work of Vernov, Chudakov, Vakulov, and Logachev [1959] and Walt, Chase, Cladis, Imho•, and K•echt [1960] has shown that the penetrating component of the outer belt is composed of electrons.…”

Section: Introductionmentioning

confidence: 99%

Effect of hydromagnetic waves on the lifetime of Van Allen radiation protons

Dragt¹

1961

The effect of hydromagnetic waves upon the motion of charged particles trapped in the geomagnetic field is studied. Applicatio.n is made to the proton component of the Van Allen radiation belt. It is shown, in agreement with the suggestion of Welch and Whitaker, that hydromagnetic waves of low frequency and amplitude are able to account for the rapid decrease in proton flux that delimits the outer edge of the inner zone of the Van Allen radiation belt. Both the location of the boundary of the inner zone and the ratio between the proton fluxes in the inner and outer zones are obtained. It is found that, near 2 earth radii from the earth's center, the maximum energy of the trapped protons decreases with geocentric distance as r -•. ß