A new beta-ray detector using the Thick Gas Electron Multiplier (THGEM) technology is presented. Traditional proportional counters have been considered the standard for many decades for radiation contamination monitoring. However, it has always been challenging to detect low energy beta-emitters such as 3H and 14C. In order to extend the low energy cut-off of these beta particles, it is important to keep the electron multiplication gain as high as possible. To accomplish this goal, we have developed a new gaseous beta-ray detector using THGEMs. Founded on previous THGEM avalanche simulations [1] and predecessor detectors, a novel prototype THGEM beta-ray detector was designed and fabricated. Its signal performance, effective gain and gain stability were comprehensively studied for single and double-THGEM configurations using an alpha source. The first time THGEM detector response to beta-rays was observed for various operating conditions and compared with Monte Carlo N-Particle Transport 6 (MCNP6) Monte Carlo simulations. / Thesis / Master of Science (MSc)