Study of Hafnium α Emitters: New Isotopes 159Hf, 160Hf, and 161Hf

With the use of α spectroscopy and the helium gas-jet technique the α decay of the previously unknown isotopes, ¹⁵⁹Hf, ¹⁶⁰Hf, and ¹⁶¹Hf, was observed. These hafnium nuclides were produced by bombarding targets of ¹⁴⁴Sm and ¹⁴⁷Sm with ²⁰Ne ions accelerated in the Oak Ridge isochronous cyclotron. The decay characteristics and mass assignments (made on the basis of yield curve measurements, cross bombardments, and parent-daughter relationships) of the three new α emitters are as follows: (1) ¹⁵⁹Hf, E_α=5.09+/-0.01 MeV, T₁₂=5.6+/-0.5 sec; (2) ¹⁶⁰Hf, E_α=4.77+/-0.02 MeV, T₁₂~12 sec; and (3) ¹⁶¹Hf, E_α=4.60+/-0.01 MeV, T₁₂=17+/-2 sec. The latter two isotopes with neutron numbers of 88 and 89 are of some interest with respect to α-decay systematics in the 82-neutron region. The only 88-neutron α emitters known up to now are naturally occurring ¹⁵²Gd and long-lived ¹⁵⁴Dy, while ¹⁶¹Hf is the first 89-neutron nuclide to exhibit α decay.