At the interface between the upper atmosphere and the radiation belt region there exists a secondary radiation belt consisting mainly of energetic ions that have become neutralized in the ring current and in the main radiation belt and then re‐ionized by collisions in the inner exosphere. The time history of the proton fluxes in the 0.64–35 MeV energy range was traced in the equatorial region beneath the main radiation belts during the 3‐year period from February 21, 1984, to March 26, 1987, using data obtained with the High‐Energy Particle experiment on board the Japanese OHZORA satellite. During most of this period a fairly small proton flux of ∼1.2 cm−2 s−1 sr−1 was detected on geomagnetic field lines in the range 1.05 < L < 1.15. We report a few surprisingly deep and rapid flux decreases (flux reduction by typically 2 orders of magnitude). These flux decreases were also long in duration (lasting up to 3 months). We also registered abrupt flux increases, such that magnitude of the proton flux enhancements could reach 3 orders of magnitude and with an enhancement duration of 1–3 days. Possible reasons for these unexpected phenomena are discussed.
The CMS drift tubes (DT) muon detector, built for withstanding the LHC expected integrated and instantaneous luminosities, will be used also in the High Luminosity LHC (HL-LHC) at a 5 times larger instantaneous luminosity and, consequently, much higher levels of radiation, reaching about 10 times the LHC integrated luminosity. Initial irradiation tests of a spare DT chamber at the CERN gamma irradiation facility (GIF++), at large (∼ O(100)) acceleration factor, showed ageing effects resulting in a degradation of the DT cell performance. However, full CMS simulations have shown almost no impact in the muon reconstruction efficiency over the full barrel acceptance and for the full integrated luminosity. A second spare DT chamber was moved inside the GIF++ bunker in October 2017. The chamber was being irradiated at lower acceleration factors, and only 2 out of the 12 layers of the chamber were switched at working voltage when the radioactive source was active, being the other layers in standby. In this way the other non-aged layers are used as reference and as a precise and unbiased telescope of muon tracks for the efficiency computation of the aged layers of the chamber, when set at working voltage for measurements. An integrated dose equivalent to two times the expected integrated luminosity of the HL-LHC run has been absorbed by this second spare DT chamber and the final impact on the muon reconstruction efficiency is under study. Direct inspection of some extracted aged anode wires presented a melted resistive deposition of materials. Investigation on the outgassing of cell materials and of the gas components used at the GIF++ are underway. Strategies to mitigate the ageing effects are also being developed. From the long irradiation measurements of the second spare DT chamber, the effects of radiation in the performance of the DTs expected during the HL-LHC run will be presented.
An analysis of the north–south asymmetry in the cosmic ray flux was made with data taken in the north and south polar atmosphere from 1963 through 1991. For altitudes corresponding to column densities between 100 and 800 g/cm2 the N–S asymmetry is near zero during the negative phase of the solar magnetic cycle (1963–1969 and 1982–1989) and is positive during the positive one (1972–1979). The maximum amplitude of N–S asymmetry (up to 3%) occurs at an atmospheric depth of X= 500–600 g/cm2 and could be caused by primaries with rigidities of more than 30–50 GV. At higher altitudes, X < 25 g/cm2 during almost all periods an excess of particles in the northern polar hemisphere was observed. This excess is due to the presence of reentrant albedo electrons on closed magnetic field lines.
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