Page 68 - ILL Annual Report 2019

NUCLEAR AND PARTICLE PHYSICS
Costel Petrache. Italian CNRS/IN2P3, University Paris-Sud, Orsay, France
‘I am a professor at the University Paris-Sud and my research activity is performed at the Centre de Sciences Nucléaires et Sciences de la Matière, CNRS/IN2P3, Orsay, France.
My field of interest is nuclear spectroscopy. I study medium-heavy nuclei using fusion-evaporation and (nth, g) reactions, with a particular focus on collective excitations such as chiral and wobbling bands in triaxial nuclei and intruder bands in mid-shell Sn nuclei.’
Shape coexistence in Sn isotopes: evidence for collective structures in 116Sn based on 2 particle–2 hole proton configuration
FIssion Product Prompt gamma–ray Spectrometer FIPPS
The fast timing technique was used to measure the lifetime of the second excited 4+ state in 116Sn, providing the first evidence obtained in (nth,g) experiments for a band based on an intruder configuration and shape coexistence in the semi-magic
116Sn nucleus. The FIssion Product Prompt gamma-ray Spectrometer (FIPPS) array, equipped with 16 LaBr3 fast scintillators, was used for to detect the gamma rays emitted following 115Sn (nth,g) reactions.
AUTHORS
C.M. Petrache (Centre de Sciences Nucléaires et Sciences de la Matière, France) J.-M. Régis (Köln University, Germany)
C. Andreoiu (Simon Fraser University, Canada)
C. Michelagnoli (ILL)
ARTICLE FROM
Phys. Rev. C 99 (2019)—doi: 10.1103/PhysRevC.99.024303
REFERENCES
[1] J.-M. Régis, M. Dannhoff and J. Jolie, Nucl. Instrum. Methods Phys. Res. A 897 (2018) 38
[2] J.L. Pore et al., Eur. Phys. J. A 53 (2017) 27
[3] D.S. Cross et al., Eur. Phys. J. A 53 (2017) 216
Sn isotopes play a pivotal role in the development of our understanding of nuclear structure, particularly because
they are some of the best examples of seniority structures in nuclei. Indeed, the near constancy of the 2+1 energies from N = 52 (102Sn) to N = 80 (130Sn) is remarkable (figure 1). Another well-documented phenomenon in Sn isotopes is shape coexistence. The lifetimes of the 0+2,3 and 4+2 states assigned to intruder bands built on 2 particle–2 hole proton configurations are poorly known or only have lower/higher limits determined, preventing clear conclusions being drawn on the collectivity of the bands and their band-heads. The band-head of the intruder band of the neutron mid-shell nucleus 116Sn was recently assigned the 0+3 state, which is more strongly populated from the 2+2 state of the intruder band than is the 0+2 state.
The present study was concerned with measuring the lifetimes
of the low-spin, highly excited, normal and intruder states, in
+
particular of the 4 2 state of the intruder band. We determined
•
····· . ···
0 . 4 2 p s· · . . . ·
o·s ......................
the lifetime of the 4+ 2 529 keV state of 116Sn using the FIPPS 2
array in conjunction with LaBr3 ancillary detectors (figure 2). Moreover, we demonstrated the utility of (nth,g) reactions for probing low-spin, highly-excited states and measuring their lifetimes, which are often in the range of 1–200 ps.
o·.
----
>0.2ps >0.4ps0.64ps
Sn isotopes
4; ---- ___······ .... 29ps>0.55ps0.32ps·····
02 ---·=···"""·····························?.2,7ps>4ps..········
2+2 ---- ·····- 2
?J : ::
114
.........
120 122
- ___..........- - - -······ <::::' 160ps
2·, ____
110 112 ANNUAL REPORT 2019
---'""----······················
116
Mass Number (A)
1118
Excitation Energy (MeV)
0
Figure 1
Systematics of the Sn isotopes showing the half-lives or the half-life limits of the 0+2 (red), 0+3 (blue) and 4+2 (green) states.
0
••••••••••
.4 :; -_ 7
;a
44ps