Response of SIMPLE SDDs to monochromatic neutron irradiations

We report measurements of the response of large-volume superheated droplet detectors for the SIMPLE project to filtered monochromatic neutron beams of energies 54 and 149 keV. The results continue to indicate a significantly higher than anticipated response at low temperatures, but provide good support for the theoretical device calibration in temperature. A significant moderation of the incident beams by the aqueous gel of the detector and the temperature-stabilizing water bath is observed, such that the detector response is primarily governed by the superheating factor of the detector refrigerant. Translated into background neutron sensitivity of WIMP searches, these features indicate that a good choice of operating conditions is 9°C and 2 atm, with the temperature implying a mass sensitivity >5 GeV given that sufficient background reduction below this temperature can be achieved.