Precise Half-Life Measurement of Neutron-Rich Nucleus ¹⁸N

Stability of nucleus is related to the balance of proton and neutron numbers. I am keen to study more about such quantum many-body system and decided to measure half-life of unstable nuclei. In this work, I have developed the method to precisely determine the half-life of nuclei which beta decays and measured the half-life of the unstable nuclei ¹⁸N.

To perform highly precise measurement of beta ray for half-life, the following points were improved; (1) by using the radio-active (RI) beam, impurities could be rejected, (2) beta ray was measured during beam on and beam off, whose time in one cycle was optimized by computer simulation to obtain the highest accuracy, and (3) to correct the number of uncounted events during busy time of computer, which are drastically changed by the count rates, a unique method of event-by-event dead time correction was developed by using clock signal.

The ¹⁸N nucleus was produced by the direct reaction of ⁹Be(¹⁸O, ¹⁸N)⁹B with ¹⁸O beam energy of 169 MeV and beam intensity of 3 μA. The secondary ¹⁸N beam was separated by RCNP secondary beam line and transported to a gold foil with beam intensity of ~1000 pps and high purity of ~100%.

As a result, we could determine half-life of ¹⁸N to be 611±1 ms with the highest accuracy in the reported values.