Last Wednesday at 17:20 a balloon was successfully launched from Esrange in Northern Sweden to an altitude of 30.5 km. This balloon was carrying, besides test equipment from SSC, a 14 kg spin-off instrument from PoGOLite called PoGOLino.
Unlike the future planned PoGO and the currently flight-ready PoGOLite instrument, PoGOLino is not built for measuring the polarisation of X-rays emitted by point sources such as the Crab. Rather, it is built to measure the atmospheric radiation which will be the main source of background for the PoGOLite measurements – more specifically it is designed to measure the neutron flux in different energy bands. It does this using LiCAF
scintillators which contain 6Li to capture neutrons, the subsequent decay of the lithium produces a characteristic signal we can measure using a photomultiplier.
The reason we built this experiment is that in the high radiation environment between 30 km and 40 km altitude in which PoGOLite will fly, neutrons are expected to form the main
background. This is due to their ability to move through the PoGOLite anticoincidence shields undetected and scatter in the plastic scintillator array, producing a signal which is
indistinguishable from that expected from a Compton scattering X-ray. Especially at the high latitudes where PoGOLite is going to fly this summer, this neutron background is relatively large.
The exact magnitude is however unknown due to a lack of measurements. On top of that the neutron background is directly correlated to solar activity since the neutrons are secondary particles originating from cosmic rays. A direct measurement of the background now will therefore be very useful for the analysis of the PoGOLite data after its flight this summer. The PoGOLino data will also be used to verify existing software models used to simulate neutron production in the atmosphere.
For the PoGOLite Collaboration, a successful flight seems to indicate that after a cancelled launch in 2010, a balloon leak in 2011 and a summer with weather which made launching impossible in 2012, our luck seems finally to be changing!
Merlin Kole, PhD student – email@example.com