ELECTRON DETECTOR

This flight was part of a program developed at the Department of Physics, Imperial College of Science and Technology in London, with support from the Cosmic Rays and Space Physics Group to measure low-energy primary cosmic ray electrons in the 25-600 MeV range. The experiments involved balloon flights carrying detectors launched from two locations: Kiruna Geophysical Observatory in Northern Sweden and RAF Cardington in England, between 1964 and 1966.

In the scheme at left we can see the so-called "A" detector aimed to investigate the existence and characteristics of primary cosmic ray electrons at the top of the atmosphere

The A detector consisted of a three-element Cerenkov telescope combined with a lead absorber and scintillation detector arrangement. The Cerenkov telescope had a threshold of β = 0.67. The device utilized a Perspex material with dimensions of 102mm in diameter and 12.7mm in thickness. One of the Perspex Cerenkov elements (the middle one) had its upper surface blackened, which allowed it to reject more than 80% of upward-moving particles through its directional properties. After passing through the Cerenkov telescope, particles encountered ten radiation lengths of lead absorber. Following the lead absorber, there was a plastic scintillator detector (NE 102A) measuring 229mm in diameter and 3.2mm in thickness. This scintillator component served a dual purpose - it functioned both as a detector and as a guard against particle scattering in the lead. The detector registered electron events when it received a telescope coincidence pulse without an accompanying pulse from the scintillator. The entire system had a geometrical factor of 10.8 ± 0.6 cm² sr.

The detector's efficiency varied with electron energy, and at energies below 50 MeV, the probability of detecting an electron with the telescope became less than unity. The plastic scintillators extended beyond the solid angle defined by the Cerenkov telescope, specifically designed to minimize the effect of proton-nucleon scattering in the absorber material. The extension of this guard was carefully calculated to cover a possible scattering angle of 20-25 degrees outside the most oblique direction defined by the telescope, as extending beyond this limit would not have been advantageous since the majority of particles emerging from the lead at larger angles were electrons.

Balloon launched on: 4/26/1966
Launch site: Cardington, Bedfordshire, England  
Balloon manufacturer/size/composition: Zero Pressure Balloon  
End of flight (L for landing time, W for last contact, otherwise termination time): 4/26/1966
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 11 h

• Primary cosmic ray electrons below 600 MeV Planetary and Space Science, Volume 15, Issue 11, Pag. 1787 (1967)