Nanosecond-Scale Proton Emission from Strongly Oblate-Deformed ^{149}Lu

Area of Science:

• Nuclear Physics
• Experimental Nuclear Physics
• Radioactive Decay Studies

Background:

• Proton emission is a rare radioactive decay mode involving the emission of a proton from an atomic nucleus.
• Identifying new proton emitters aids in understanding nuclear structure, particularly for proton-rich nuclei.
• Ground-state proton decay provides direct information about the nuclear wave function and decay energetics.

Purpose of the Study:

• To synthesize and identify a new proton-emitting isotope, Lutetium-149 (¹⁴⁹Lu).
• To measure the decay properties, including the Q value and half-life, of the newly identified isotope.
• To investigate the nuclear structure of ¹⁴⁹Lu, including its deformation and the nature of the proton-emitting state.

Main Methods:

• Fusion-evaporation reaction: ^{96}Ru(^{58}Ni,p4n)^{149}Lu.
• Utilizing the MARA vacuum-mode recoil separator for isotope identification.
• Measuring decay properties such as Q value and half-life.

Main Results:

• Successful identification of the new proton-emitting isotope ¹⁴⁹Lu.
• Measured decay Q value of 1920(20) keV, the highest observed for ground-state proton decay.
• Shortest directly measured half-life for a ground-state proton emitter: 450_{-100}^{+170} ns.
• Decay rate suggests l_{p}=5 emission, indicating a dominant πh_{11/2} component in the wave function.
• ¹⁴⁹Lu identified as the most oblate deformed proton emitter to date based on calculations.

Conclusions:

• The discovery of ¹⁴⁹Lu expands the landscape of known proton emitters.
• The measured properties provide crucial data for refining nuclear models.
• ¹⁴⁹Lu serves as a unique case study for understanding proton emission in highly deformed, proton-rich nuclei.