  We present an apparatus for detection of cyclotron radiation that allows a
frequency-based beta energy determination in the 5 keV to 5 MeV range,
characteristic of nuclear beta decays. The cyclotron frequency of the radiating
beta particles in a magnetic field is used to determine the beta energy
precisely. Our work establishes the foundation to apply the cyclotron radiation
emission spectroscopy (CRES) technique, developed by the Project 8
collaboration, far beyond the 18-keV tritium endpoint region. We report initial
measurements of beta^-s from 6He and beta^+s from 19Ne decays to demonstrate
the broadband response of our detection system and assess potential systematic
uncertainties for beta spectroscopy over the full (MeV) energy range. This work
is an important benchmark for the practical application of the CRES technique
to a variety of nuclei, in particular, opening its reach to searches for
evidence of new physics beyond the TeV scale via precision beta-decay
measurements.
