Lifetimes of low-lying excited states in $^{86}_{36}$Kr$_{50}

• Main Authors: Henderson, J, Chester, A, Ball, G. C, Caballero-Folch, R, Domingo, T, Drake, T. E, Evitts, L. J, Hackman, G, Hallam, S, Garnsworthy, A. B, Moukaddam, M, Ruotsalainen, P, Smallcombe, J, Smith, J. K, Starosta, K, Svensson, C. E, Williams, J
• Format: Journal Article
• Language: English
• Published: 12-01-2018
• Subjects: Physics - Nuclear Experiment
• DOI: 10.48550/arxiv.1801.03022

Phys. Rev. C 97, 044311 (2018) The evolution of nuclear magic numbers at extremes of isospin is a topic at
the forefront of contemporary nuclear physics. $N=50$ is a prime example, with
increasing experimental data coming to light on potentially doubly-magic
$^{100}$Sn and $^{78}$Ni at the proton-rich and proton-deficient extremes,
respectively. Experimental discrepancies exist in the data for less exotic
systems. In $^{86}$Kr the $B(E2;2^+_1\rightarrow0^+_1)$ value - a key indicator
of shell evolution - has been experimentally determined by two different
methodologies, with the results deviating by $3\sigma$. Here, we report on a
new high-precision measurement of this value, as well as the first measured
lifetimes and hence transition strengths for the $2^+_2$ and $3^-_{(2)}$ states
in the nucleus. The Doppler-shift attenuation method was implemented using the
TIGRESS gamma-ray spectrometer and TIGRESS integrated plunger (TIP) device.
High-statistics Monte-Carlo simulations were utilized to extract lifetimes in
accordance with state-of-the-art methodologies. Lifetimes of
$\tau(2^+_1)=336\pm4\text{(stat.)}\pm20\text{(sys.)}$ fs,
$\tau(2^+_2)=263\pm9\text{(stat.)}\pm19\text{(sys.)}$ fs and
$\tau(3^-_{(2)})=73\pm6\text{(stat.)}\pm32\text{(sys.)}$ fs were extracted.
This yields a transition strength for the first-excited state of
$B(E2;2^+_1\rightarrow0^+)=259\pm3\text{(stat.)}\pm16\text{(sys.)}$
e$^2$fm$^4$. The measured lifetime disagrees with the previous Doppler-shift
attenuation method measurement by more than $3\sigma$, while agreeing well with
a previous value extracted from Coulomb excitation. The newly extracted
$B(E2;2^+_1\rightarrow0^+_1)$ value indicates a more sudden reduction in
collectivity in the $N=50$ isotones approaching $Z=40$.