Final answer:
A device that detects radiation between 3 MHz and 30 MHz is operating within the radio waves region of the electromagnetic spectrum.
Step-by-step explanation:
The electromagnetic spectrum is a range of all types of electromagnetic radiation, consisting of different regions based on their wavelength and frequency, such as gamma rays, x-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves. A device that detects radiation between 3 MHz and 30 MHz operates within the radio waves region of the spectrum. This range corresponds to the lower frequency end of the spectrum, and it is given that radio waves have frequencies starting from 105 Hz (or 100 kHz) to 108 Hz (or 100 MHz) and include frequencies within the range detected by the device (3 MHz to 30 MHz).