A search is made for the $\beta$ decay of a long-lived ${\mathrm{H}}^4$, produced by 250-MeV bremsstrahlung in lithium of natural isotopic abundance. No evidence for such a long-lived isotope is found. This corresponds to the following upper limits for the production cross section: ${\sigma }_p<6.7\mathrm{}\times {10}^{-4\mathrm{}}$ μb, assuming that the half-life of ${\mathrm{H}}^4$ is 3 min, and ${\sigma }_p<2.3\mathrm{}\times {10}^{-4\mathrm{}}$ μb, assuming the half-life is 1000 min. The $\beta$ detector is also sensitive to gamma rays, but no evidence for delayed gamma rays is found.

• Received 23 August 1963

DOI:https://doi.org/10.1103/PhysRev.133.B17