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Gregorich, K. E.

Publications and source records attributed to Gregorich, K. E..

Toward the Discovery of New Elements: Production of Livermorium (𝑍 = 116) with 50 Ti

The 244 Pu ⁢(50 Ti ,𝑥⁢𝑛)⁢ 294−𝑥 Lv reaction was investigated at Lawrence Berkeley National Laboratory’s 88-Inch Cyclotron. The experiment was aimed at the production of a superheavy element with 𝑍 ≥114 by irradiating an actinide target with a beam heavier than 48 Ca. Produced Lv ions were separated from the unwanted beam and nuclear reaction products using the Berkeley Gas-filled Separator and implanted into a newly commissioned focal-plane detector system. Two decay chains were observed and assigned to the decay of 290 Lv . The production cross section was measured to be 𝜎 prod = 0.44($^{+0.58}_{−0.28}$) pb at a center-of-target center-of-mass energy of 220(3) MeV. Furthermore, this represents the first published measurement of the production of a superheavy element near the “island of stability,” with a beam of 50 Ti and is an essential precursor in the pursuit of searching for new elements beyond 𝑍 =118.

36 MATERIALS SCIENCE↗

Half-life of Ge 71 and the gallium anomaly

Recent discussions about the origin of the so-called gallium anomaly have motivated a remeasurement of the half-life of 71 Ge. Here, we have conducted three separate measurements using dedicated planar Ge detectors—one with 55 Fe as a standard, one with 57 Co as a standard, and one standalone 71 Ge measurement. Our results yield a half-life of 11.468±0.008 days, which is consistent with, but significantly more precise than, the currently accepted value. With this experiment, the potential explanation of the gallium anomaly being due to an unexpectedly long 71 Ge half-life has been ruled out, leaving the anomaly's origin as an open question.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Search for elements 119 and 120

In this work, a search for production of the superheavy elements with atomic numbers 119 and 120 was performed in the 50 Ti + 249 Bk and 50 Ti + 249 Cf fusion-evaporation reactions, respectively, at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. Over four months of irradiation, the 249 Bk target partially decayed into 249 Cf, which allowed for a simultaneous search for both elements. Neither was detected at cross-section sensitivity levels of 65 and 200 fb for the 50 Ti + 249 Bk and 50 Ti + 249 Cf reactions, respectively, at a midtarget beam energy of E lab = 281.5 MeV. The nonobservation of elements 119 and 120 is discussed within the concept of fusion-evaporation reactions including various theoretical predictions on the fission-barrier heights of superheavy nuclei in the region of the island of stability.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗