Final answer:
The amount of radio frequency required to tip the nuclei is tied to the NMR phenomenon and is dependent on the external magnetic field, type of nucleus, and surrounding chemical environment, notably used in MRI for imaging nuclei density.
Step-by-step explanation:
The amount of radio frequency required to tip the nuclei is related to the external magnetic field strength, the type of nucleus and the chemical environment surrounding the nucleus. This is due to the nuclear magnetic resonance (NMR) phenomenon, where nuclei behave like resonators, absorbing and reemitting radio frequency signals that match their resonant frequencies. This resonant frequency varies depending on the nucleus type, its environment, and the magnetic field strength.
In medical imaging, especially magnetic resonance imaging (MRI), this principle is crucial as it allows for the production of detailed images by varying the external magnetic field over a region to map the resonant frequencies of protons (usually hydrogen nuclei) and thus the density of nuclei within the body. The frequency of the radio waves typically used in MRI ranges around 100 MHz but will differ based on the magnetic field strength and the specific nuclei being imaged.