The energy spectrum of the HB11 beam at HFR, Petten, has previously been measured by proton and alpha recoil in hydrogen and helium gas proportional counters at power levels of a few kW. There is some doubt whether the spectrum remains the same at the much higher power of 45 MW required for therapeutic fluxes. In order to test this point, a scintillation detector has been developed at the Paul Scherrer Institute, Villingen, Switzerland. While the device is again based on the proton recoil reaction, a combination of mm-sized plastic scintillators and fast electronics will allow it to operate at both a few kW and 45 MW, permitting direct comparison of energy spectra at these very different power levels. Results of preliminary tests at LFR, Petten, are presented.