Revalidation of the isobaric multiplet mass equation for the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>A</mml:mi><mml:mo>=</mml:mo><mml:mn>20</mml:mn></mml:mrow></mml:math>quintet

Glassman, Brent; Pérez–Loureiro, D.; Wrede, C.; Allen, J.; Bardayan, D. W.; Bennett, Michael B.; Brown, B. A.; Chipps, K. A.; Febbraro, M.; Fry, C.; Hall, M. R.; Hall, O.; Liddick, S. N.; O’Malley, P. D.; Ong, Wei Jia; Pain, S. D.; Schwartz, Sanford; Shidling, P. D.; Sims, Howard E.; Thompson, P.; Zhang, H.

doi:10.1103/physrevc.92.042501

Cited by 17 publications

(80 citation statements)

References 38 publications

(71 reference statements)

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“…The ab initio predictions based on MBPT [22] show a stronger isospin dependence of the IMME than is experimentally observed [23]. The energy of the lowest T = 2, J π = 0 + state in 20 Na measured from superallowed β + decay of 20 Mg however successfully describes the T = 2, mass 20 multiplet by a quadratic IMME [26]. Excited states of the mirror nuclei 20 Mg and 20 O can provide further insight into the isospin dependence of the nuclear interaction and the nature of the N = 8 shell closure at the proton drip-line.…”

mentioning

confidence: 67%

Observation of excited states in Mg20 sheds light on nuclear forces and shell evolution

Randhawa¹,

Kanungo²,

Holl³

et al. 2019

Phys. Rev. C

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The exotic Borromean nucleus 20 Mg with N = 8, located at the proton drip-line provides a unique testing ground for nuclear forces and the evolution of shell structure in the neutron-deficient region. We report on the first observation of proton unbound resonances together with bound states in 20 Mg from the 20 Mg(d,d ) reaction performed at TRIUMF. Phenomenological shell-model calculations offer a reasonable description. However, our experimental results present a challenge for current first-principles nuclear structure approaches and point to the need for improved chiral forces and ab initio calculations. Furthermore, the differential cross section of the first excited state is compared with distorted-wave Born approximation calculations to deduce a neutron quadrupole deformation parameter of βn=0.46±0.21. This provides the first indication of a possible weakening of the N = 8 shell closure at the proton drip-line. PACS numbers: 24.50+g, 25.45.De, 25.60.-t, 25.70.EfThe evolution of shell structure over the nuclear landscape is a manifestation of strong interactions in the complex nuclear many-body system. Properties of nuclei at the neutron and proton drip-lines provide new arenas to investigate the effects of large proton-neutron asymmetry and understand the persistence of mirror symmetry. Shell structure evolution in neutron-rich and proton-rich nuclei [1][2][3][4][5][6][7][8][9][10][11][12] are leading to new insights into nuclear forces, including the role of three-body forces [13,14]. The region around the N = 8 shell closure draws particular interest, since this shell gap disappears at the neutron drip-line and leads to the formation of a twoneutron halo in the Borromean nucleus 11 Li. The small two-neutron separation energy (S 2n = 360 keV) of 11 Li results in the excited states of 11 Li being unbound. Less is known about the structure of nuclei at the proton drip- * Present address: KVI-CART, University of Groningen, 9747 AA Groningen, The Netherlands line. The N = 8 isotone at the proton drip-line, 20 Mg, is also a Borromean system whose two-proton separation energy is S 2p = 2.337(27) MeV [15]. There is no experimental information on resonances above the proton threshold in 20 Mg. In this work we present the first observation of a resonance in 20 Mg through deuteron inelastic scattering. This measurement provides new insight into shell evolution as well as tests of ab initio predictions. The resonance(s) in 20 Mg could also contribute to a potential breakout path from the hot CNO cycle via two-proton capture on the waiting point nucleus 18 Ne in Type-I x-ray bursts [16].Microscopic cluster model [17] predictions for the 2 + state agree with the experiment [18,19]. A 4 + state is predicted at 3 MeV, this state is predicted around 3.8 MeV, using a beyond the mean field approach [20]. Predictions based on an angular momentum projected generator coordinate framework [21], find the 2 + 1 and the 4 + 1 states to be higher in energy around, 3.5 MeV and 7.8 MeV, respectively. Ab initio calculations in a manyb...

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confidence: 67%

Observation of excited states in Mg20 sheds light on nuclear forces and shell evolution

Randhawa¹,

Kanungo²,

Holl³

et al. 2019

Phys. Rev. C

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“…The present experiment is one in a series of recent β-delayed γ decay experiments to investigate the sd shell using fast neutron-deficient beams at the National Superconducting Cyclotron Laboratory [16,[38][39][40][41]. In particular, the β-delayed γ decay of 31 Cl was measured using an experimental procedure that was already described in [38].…”

Section: Methodsmentioning

confidence: 99%

“…[10] reported, in addition to the findings on 21 Mg, a new 20 Mg mass and a resulting IMME breakdown requiring a cubic term of 2.8(11) keV for the A = 20, T = 2 quintent. In this case, a recent experimental measurement of 20 Mg beta decay [16] used the superallowed 0 + → 0 + transition to the T = 2 20 Na IAS and the state's subsequent gamma decay to deduce an excitation energy for the IAS. This result was 28 times more precise than the previous measurement and, together with the ground state mass excess of 20 Na, was shown to revalidate the IMME for the A = 20, T = 2 quintet.…”

Section: Introductionmentioning

confidence: 99%

“…Although this J π = 1/2 + 31 S state is expected to be nearly 1 MeV above the proton threshold, the proton emission is isospin forbidden and, therefore, it should have a substantial gamma-decay branch unlike the other low-spin levels in the region [16]. Precise observation of a high energy γ-ray transition from a low-spin state in this region would be a signature of the second T = 3/2 state, allowing for a precise determination of its energy.…”

Section: Introductionmentioning

confidence: 99%

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Isobaric multiplet mass equation in theA=31,T=3/2quartets

Bennett¹,

Wrede²,

Brown³

et al. 2016

Phys. Rev. C

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Background: The observed mass excesses of analog nuclear states with the same mass number A and isospin T can be used to test the isobaric multiplet mass equation (IMME), which has, in most cases, been validated to a high degree of precision. A recent measurement (Kankainen et al., Phys. Rev. C 93 041304(R) (2016)) of the ground-state mass of 31 Cl led to a substantial breakdown of the IMME for the lowest A = 31, T = 3/2 quartet. The second-lowest A = 31, T = 3/2 quartet is not complete, due to uncertainties associated with the identity of the 31 S member state.Purpose: To populate the two lowest T = 3/2 states in 31 S and use the data to investigate the influence of isospin mixing on tests of the IMME in the two lowest A = 31, T = 3/2 quartets.Methods: Using a fast 31 Cl beam implanted into a plastic scintillator and a high-purity Ge γ-ray detection array, γ rays from the 31 Cl(βγ) 31 S sequence were measured. Shell-model calculations using USDB and the recently-developed USDE interactions were performed for comparison.Results: Isospin mixing between the 31 S isobaric analog state (IAS) at 6279.0(6) keV and a nearby state at 6390.2(7) keV was observed. The second T = 3/2 state in 31 S was observed at Ex = 7050.0(8) keV. Calculations using both USDB and USDE predict a triplet of isospin-mixed states, including the lowest T = 3/2 state in 31 P, mirroring the observed mixing in 31 S, and two isospin-mixed triplets including the second-lowest T = 3/2 states in both 31 S and 31 P.Conclusions: Isospin mixing in 31 S does not by itself explain the IMME breakdown in the lowest quartet, but it likely points to similar isospin mixing in the mirror nucleus 31 P, which would result in a perturbation of the 31 P IAS energy. USDB and USDE calculations both predict candidate 31 P states responsible for the mixing in the energy region slightly above Ex = 6400 keV. The second quartet has been completed thanks to the identification of the second 31 S T = 3/2 state, and the IMME is validated in this quartet.

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“…[15]. This is a crucial aspect, as other similar experimental investigations in the past have been prone to misinterpretations on account of inaccurately known IAS excitation energies [11,[28][29][30][31][32]. To resolve the above issue, we remeasured the energy of the second J π ; T = 1/2 − ; 3/2 state in 9 B using the 9 Be( 3 He, t) reaction.…”

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confidence: 99%

SecondT=3/2state inB9and the isobaric multiplet mass equation

et al. 2018

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Recent high-precision mass measurements and shell model calculations [Phys. Rev. Lett. 108, 212501 (2012)] have challenged a longstanding explanation for the requirement of a cubic isobaric multiplet mass equation for the lowest A = 9 isospin quartet. The conclusions relied upon the choice of the excitation energy for the second T = 3/2 state in 9 B, which had two conflicting measurements prior to this work. We remeasured the energy of the state using the 9 Be( 3 He, t) reaction and significantly disagree with the most recent measurement. Our result supports the contention that continuum coupling in the most proton-rich member of the quartet is not the predominant reason for the large cubic term required for A = 9 nuclei.

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Revalidation of the isobaric multiplet mass equation for theA=20quintet

Cited by 17 publications

References 38 publications

Observation of excited states in Mg20 sheds light on nuclear forces and shell evolution

Observation of excited states in Mg20 sheds light on nuclear forces and shell evolution

Isobaric multiplet mass equation in theA=31,T=3/2quartets

SecondT=3/2state inB9and the isobaric multiplet mass equation

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