Bleeker J A, Deerenberg A J
Cosmic Ray Working Group, The Royal Dutch Academy of Sciences, Kamerlingh Onnes Laboratorium, Leiden.
Nature. 1970 Aug 1;227(5257):470-3. doi: 10.1038/227470a0.
An X-ray survey experiment, consisting of four balloon-borne X-ray telescopes, was flown over Texas last year to search for hard X-ray emission (E(x) > 20 keV) from the Galaxy.