One of the extras I put into the little PIC sensor board is a set of three pins connected to the ADC of the PIC. That way, you can use the same board with the same command set equipped with an ultrasonic sensor or an analog distance measuring sensor.
What kind of shielding are you planning to use to minimize false positives in your neutrino sensor? ☺
Are you also planning to detect ionizing radiation? Gas leaks? Carbon monoxide? Pollen/particulate count? (With temperature, humidity, and barometric pressure, the robot might be half way to being a mobile weather station--lacking wind speed and direction and precipitation measurement [perhaps also illumination determination--cloudy, partly cloudy, sunny].)
Why not take a leaf out of the radar technology and have a spinning ultrasonic dector turret on the robot. This could be turned by a stepper motor, so you would know where it was pointing relevant to the robots fixed chassis.
It might also look very cool like Robby from the Forbidden Planet ?