Isomeric Character of the Lowest Observed 4^{+} State in ^{44}S

Area of Science:

• Nuclear Physics
• Atomic Physics

Background:

• Previous experiments suggested a 4+ state in the N=28 nucleus ^{44}S may have a hindered E2-decay rate.
• This hindered decay is inconsistent with the state belonging to the collective ground state band.

Purpose of the Study:

• To populate the 4+ state in ^{44}S via two-proton knockout.
• To measure the lifetime of this state to determine its decay properties.
• To investigate the nature of the 4+ state, specifically if it is a high-K isomer.

Main Methods:

• Utilized a beam of exotic ^{46}Ar projectiles.
• Employed two-proton knockout reactions to populate the 4+ state in ^{44}S.
• Measured the state's lifetime using the recoil distance method with the GRETINA γ-ray spectrometer.

Main Results:

• The lifetime of the 4+ state was measured to be 76(14)_{stat}(20)_{syst} ps.
• This lifetime implies a hindered E2 transition with B(E2;4^{+}→2_{1}^{+})=0.61(19) single-particle units.
• This hindered transition strength supports the interpretation of the 4+ state as a K=4 isomer.

Conclusions:

• The 4+ state in ^{44}S is confirmed to be a K=4 isomer.
• This represents the first observation of a high-K isomer in such a light nucleus.
• The findings challenge existing nuclear models and provide new benchmarks for understanding nuclear structure and decay mechanisms.