Search for 4n IN π− double charge exchange reactions with heavy nuclei

The quest for light multineutron systems

“…For the sake of completeness, let us mention two special, non-conventional uses of the negative-pion probe. Earlier, in 1979, Chultem et al had proposed an original use of a π − beam in a two-step process [31]. They hoped to produce a bound tetraneutron in the 208 Pb(π − , π + ) 4 n reaction, by DCX on an α cluster inside lead, and then measure the tetraneutron absorption by another lead nucleus, leading to 212 Pb.…”

“…As the first step, they irradiated uranium with 700 MeV protons, and exposed a lead sample behind an aluminum screen, again supposed to stop any charged particle. For the second step, they used the one that was described in the previous section for Chultem [31], the search for the 208 Pb( A n, xn) 212 Pb reaction through the α particles from its decay into 212 Bi and 212 Po. No trace of "polyneutrons" was found, shedding doubt on Détraz's results.…”

The extremes of neutron richness

“…Four years later, Miller et al repeated the experiment with better statistics and resolution [36], and confirmed the results. In parallel, Chultem et al proposed an original use of a π − beam in a two-step process [37]. If a bound tetraneutron had been produced in the 208 Pb(π − , π + ) 4 n reaction, by DCX on an α cluster inside lead, they might measure the tetraneutron absorption by another lead nucleus transforming it into 212 Pb, a probe similar to Turkevich's [22].…”