A neutron diagnostics technique based on the bubble detectors has been used for measurements during the JET experimental campaigns of 2008 and 2009. The main aim of these measurements was the determination of the neutron field characteristics in high performance discharges which produce neutron yields in the range (3-5) ¥1016 neutrons per pulse. The neutron field parameters at a specific location above a narrow collimating channel in the ceiling of the JET Torus Hall (behind the TOFOR [1] time-of-flight spectrometer) have been measured simultaneously by two independent techniques: super-heated fluid detectors or "bubble detectors" and time-of-flight.