Development of α-ToF detector for correlation measurement of atomic masses and decay properties

The atomic mass is a unique quantity for each nucleus. Precise mass measurement allows us to identify the atomic number as well as the mass number. Recently, we measured the masses of fusion evaporation products provided from GARIS-II + MRTOF system. Next plan is the measurement the masses of superheavy nuclei (SHN) to identify the nuclides, the expected event rate is less than one event per day due to small cross section.

We should accurately distinguish a true event from large background events such as molecular ions. For this purpose, we have developed an α-ToF detector, the time correlation between a time-of-flight signal and α decay signals can discriminate background events. The α-ToF detector is made of a commercial MagneToF detector and a Si PIN diode. When a heavy ion is hit on the MagneToF, secondary electron(SE) are emitted from the Impact plate of MagneToF and the electron are isochronously transported by a magnetic field an amplified by a multiplier to provide a timing signal of the ion. We replaced the impact plate with an SE emission material coated Si PIN diode. We tested the detector by using a 241Am alpha source, from the result of the test, we confirmed that the correlation between the timing signal and the decay energy can be measured using the α-ToF.