TRINAT apparatus for measurements of correlations from the beta decay of magneto-optically trapped polarized alkali atoms

Measurements of correlations from beta decay of highly polarized atoms from MOT requires a fast transition between trapping and polarization/measurement cycles to reduce an unwanted expansion of decaying atoms. To achieve this, we have developed an apparatus employing AC MOT, which required placing high-current and low-inductance coils of magnetic quadrupole inside the stainless steel vacuum vessel and allowed us to reduce a time gap between trapping and measurement cycles (the quadrupole magnetic field in the trap region has to become less than 50mG) to less than 100$\mu$s. The nuclear detection system consists of an electrostatic spectrometer of recoiling ions and shake-off electrons with MCP based detectors in back-to-back geometry as well as two scintillator based $\beta-$telescopes, normal to the MCP-MCP axis. This system allowed us to successfully measure the beta asymmetry in the $\beta^+$ decay of polarized $^{37}$K atoms with significantly reduced backgrounds. Time-varying magnetic field from the AC MOT and stationary guiding electric field allowed us to probe the energy distribution of the shakeoff electrons in the range 5$-$30eV.