Lifetime of first excited state in 139La and the role of core-excitation on L-forbidden M1 transition Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, 519082, Zhuhai, China.
Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, 519082, Zhuhai, China.
Key Laboratory of Nuclear Data, China Institute of Atomic Energy, 102413, Beijing, China.
Key Laboratory of Nuclear Data, China Institute of Atomic Energy, 102413, Beijing, China.
Spallation Neutron Source Science Center, 523803, Dongguan, China.
Spallation Neutron Source Science Center, 523803, Dongguan, China.
Spallation Neutron Source Science Center, 523803, Dongguan, China.
Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, 519082, Zhuhai, China.
Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, 519082, Zhuhai, China.
Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, 519082, Zhuhai, China.
Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, 519082, Zhuhai, China.
Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, 519082, Zhuhai, China.
Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, 519082, Zhuhai, China.
Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, 519082, Zhuhai, China.
Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, 519082, Zhuhai, China.
Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, 519082, Zhuhai, China.
Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, 519082, Zhuhai, China.
Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, 519082, Zhuhai, China.
School of Physics, Beihang University, 100191, Beijing, China.
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2025 (English) In: Nuclear Science and Techniques, ISSN 1001-8042, Vol. 36, no 10, article id 179Article in journal (Refereed) Published
Abstract [en]
This study determined the lifetime of the first excited state (5/21+) in 139La via β–γ time-difference measurement using a LaBr3 + plastic scintillator array. This state is populated following the decay of 139Ba produced in the 138Ba(n,γ) reaction. Compared with previous experiments using only stilbene/plastic crystals, this experiment separates the background contribution in the γ-ray spectrum owing to the high energy resolution of LaBr3. The L-forbidden M1 transition strength, B(M1, 5/21+→7/21+), in 139La was measured and compared with detailed large-scale shell model calculations, with a special focus on the core-excitation effect. The results showed the importance of both proton and neutron core-excitations in explaining the M1 transition strength. Meanwhile, the effective g-factor for the tensor term of the M1 operator was smaller than the previously reported value in this region or around 208Pb.
Place, publisher, year, edition, pages Springer Nature , 2025. Vol. 36, no 10, article id 179
Keywords [en]
Effective g-factor, Fast-timing measurement, L-forbidden M1 transition, LaBr3
National Category
Subatomic Physics
Identifiers URN: urn:nbn:se:kth:diva-369049 DOI: 10.1007/s41365-025-01756-7 ISI: 001530752500003 Scopus ID: 2-s2.0-105010894196 OAI: oai:DiVA.org:kth-369049 DiVA, id: diva2:1997527
Note QC 20250912
2025-09-122025-09-122025-09-12 Bibliographically approved