Physicists at the Heavy Ion Research Facility in China have observed the lightest uranium isotope to date, uranium-214 (214U), and precisely measured the α-decay properties of two previously known isotopes, 216U and 218U.
Uranium is a chemical element with the symbol U and atomic number 92.
Discovered in 1789 by the German chemist Martin Heinrich Klaproth, it is a silvery white, weakly radioactive metal in the actinide series of the periodic table.
Naturally occurring uranium consists of 99.3% 238U, 0.7% 235U, and a very small amount of 234U.
All these isotopes are radioactive, emitting α-particles, and have half-lives between 159,200 years and 4.47 billion years.
The new uranium isotope, 214U, was observed in a series of experiments at the Spectrometer for Heavy Atoms and Nuclear Structure (SHANS) at the Heavy Ion Research Facility in Lanzhou, China.
To produce nuclei of 214U, the physicists fired a beam of argon-36 (36Ar) at a tungsten-182 (182W) target.
“For 214U, the fusion-evaporation reaction of 182W(36Ar, 4n)214U with a beam energy of 184 MeV and a typical beam intensity of 500 pnA was used,” they explained.
“The 182W targets were prepared by sputtering the material onto carbon foils and then covered by carbon layer.”
The researchers identified 214U by searching for the position-time correlated α-decay chains with the help of known α-decay properties of its descendants.
“The measured decay properties of daughter products match well with the known data for 210Th, 206Ra, 202Rn, and 198Po,” they said.
“Based on these measurements, the mean α-particle energy and half-life of 214U were determined to be 8,533 keV and 0.52 ms, respectively.”
The authors also fired beams of argon and calcium at tungsten targets to obtain precise decay properties of two other light uranium isotopes, 216U and 218U.
“More precise α-decay properties of even-even nuclei 216U and 218U were measured in reactions of 40Ar, 40Ca with 180W, 182W, and 184W targets,” they said.
The findings were published in the journal Physical Review Letters.
Z.Y. Zhang et al. 2021. New α-Emitting Isotope 214U and Abnormal Enhancement of α-Particle Clustering in Lightest Uranium Isotopes. Phys. Rev. Lett 126 (15): 152502; doi: 10.1103/PhysRevLett.126.152502