“…The situation is the same for PPLM. From this, dibenzo-21-crown-7 (DB21C7) [ 42 , 43 ] was adopted as a transporter instead of DB18C6, membrane transport of Cs + was studied since the isotope 135 Cs, which is formed in nuclear reactors, has a long half-life of 2.3 × 10 6 years, 137 Cs 30.17 years, 134 Cs 2 years, and so forth [ 44 , 45 ].…”