Towards the pair spectroscopy of the Hoyle state in<sup>12</sup>C

Kibédi, T.; Stuchbery, A.E.; Dracoulis, George; Robertson, Kalman A.

doi:10.1051/epjconf/20123506001

Cited by 10 publications

(13 citation statements)

References 23 publications

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“…Nevertheless there are now a number of experimental setups becoming available worldwide that are bringing new concepts and modern equipment to face these challenges. [5], [6], [7], [8], [9], [10] With renewed interest and renewed capabilities, it is expected that the number of experimentally measured E0 transition strengths will dramatically increase over the next several years.…”

Section: Introductionmentioning

confidence: 99%

Microscopic method for E0 transition matrix elements

et al. 2017

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We present a microscopic model for electric monopole (E0) transition matrix elements by combining a configuration interaction model for orbital occupations with an energy-density functional model for the single-particle potential and radial wavefunctions. The configuration interaction model is used to constrain the orbital occupations for the diagonal and off-diagonal matrix elements. These are used in an energy-density functional calculation to obtain a self-consistent transition density. This density contains the valence contribution, as well as the polarization of the protons by the valence protons and neutrons. We show connections between E0 matrix elements and isomer and isotope shifts of the charge radius. The spin-orbit correction to the charge density is important in some cases. This model accounts for a large part of the data over a wide region of the nuclear chart. It also accounts for the shape of the observed electron scattering form factors. The results depend on the Skyrme parameters used for energy-density functional and might be used to provide new constraints for them.

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Section: Introductionmentioning

confidence: 99%

Microscopic method for E0 transition matrix elements

et al. 2017

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“…The double differential probabilities were calculated within the Born approximation with Coulomb correction [8,[10][11][12], which is valid for carbon to better than 1% [7]. Current experimental results show a clear 7.654-MeV E0 pair transition, as well as signs of the 20 times suppressed 3.215-MeV E2 transition.…”

Section: Resultsmentioning

confidence: 99%

“…A new approach [7] for deducing the radiative width has been proposed at the Australian National University (ANU), and is expected to lower the uncertainty to ∼5%. It proceeds by combining the E2/E0 pair-emission ratio from the Hoyle state, with the well-known pair-conversion coefficient α π [8], and the E0 pair width…”

Section: Stellar Synthesis Of Carbonmentioning

confidence: 99%

The 3\(\alpha \) Process Studied Through Pair Conversion Transitions from the Hoyle State in ¹²C

Kibédi¹,

Reed²,

Stuchbery³

et al. 2017

Proceedings of the 14th International Symposium on Nuclei in the Cosmos (NIC2016)

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The E0 and E2 pair transitions from the Hoyle state have been measured, with the aim of deducing the radiative width and 3α reaction rate by a new approach. The 3α process is the only way carbon is synthesised in stars and is a bottleneck in stellar nucleosynthesis. The new method, which requires the ratio of the pair transitions, is expected to reduce the uncertainty from 10% to 5%. We recently observed the E2 pair transition for the first time, confirming the feasibility of the method. However, more statistics are needed to obtain a precise value for the radiative width.KEYWORDS: 3α process, Hoyle state, pair conversion Stellar synthesis of carbonThe exceedingly short half-life of 8 Be (T 1/2 = 6.7 · 10 −17 s) inhibits the stellar p−p chain, and fusion of three α particles becomes the only gateway to carbon synthesis in stars. This opens in helium burning red giants where the α concentration is sufficient, and occurs via two steps [1]: First, two α particles fuse and form 8 Be. Then, before it decays, the 8 Be is fused with a third α particle, forming 12 C in the excited 7.654-MeV 0 + Hoyle state. This is because the 8 Be ground state energy is close to that of two α particles, and the Hoyle state is close to the 8 Be + α energy. The proximity of the Hoyle state to the 3α threshold enhances the 3α process by a factor of 10-100 millions [2]. However, the process is still very unlikely as the excited carbon nucleus α-decays ∼99.96% of the time. Stable carbon is only formed if the excited carbon nucleus decays electromagnetically, and the process thus depends directly on the electromagnetic decay properties of the Hoyle state. The radiative decay occurs either by a 7.654-MeV E0 transition to the 0 + ground state, or by a 3.215-MeV E2 transition to the first excited 2 + state. Both transitions synthesise carbon. In order of intensity, transitions occur by E2 γ decay, and then by E0 and E2 pair conversion, respectively. Conversion electrons are negligible. The 3α process is a bottleneck in stellar nucleosynthesis, and precise knowledge of the reaction rate is imperative for proper stellar modelling [3].

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“…The 14UD Heavy Ion accelerator at the Australian National University was used to bombard an isotropically enriched 62 Ni target inside the Super-e electron spectrometer [12,13] with a proton beam. A target and tuning aperture are available on a common actuator.…”

Section: Methodsmentioning

confidence: 99%

Electric Monopole Transition Strengths in⁶²Ni

et al. 2016

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Abstract. Excited states in 62 Ni were populated with a (p, p') reaction using the 14UD Pelletron accelerator at the Australian National University. Electric monopole transition strengths, ρ 2 (E0), were measured through simultaneous detection of the internal conversion electrons and γ rays emitted from the de-excitation of populated states, using the Super-e spectrometer coupled with a germanium detector. The strength of the 0 + 2 to 0 + 1 transition has been measured to be 77 +23 −34 × 10 −3 and agrees with previously reported values. Upper limits have been placed on the 0 + 3 to 0 + 1 and 0 + 3 to 0 + 2 transitions. The measured ρ 2 (E0) value of the 2 + 2 to 2 + 1 transition in 62 Ni has been measured for the first time and found to be one of the largest ρ 2 (E0) values measured to date in nuclei heavier than Ca. The low-lying states of 62 Ni have previously been classified as one-and two-phonon vibrational states based on level energies. The measured electric quadrupole transition strengths are consistent with this interpretation. However as electric monopole transitions are forbidden between states which differ by one phonon number, the simple harmonic quadrupole vibrational picture is not sufficient to explain the large ρ 2 (E0) value for the 2 + 2 to 2 + 1 transition.

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Towards the pair spectroscopy of the Hoyle state in¹²C

Cited by 10 publications

References 23 publications

Microscopic method for E0 transition matrix elements

Microscopic method for E0 transition matrix elements

The 3\(\alpha \) Process Studied Through Pair Conversion Transitions from the Hoyle State in ¹²C

Electric Monopole Transition Strengths in⁶²Ni

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Towards the pair spectroscopy of the Hoyle state in12C

Cited by 10 publications

References 23 publications

Microscopic method for E0 transition matrix elements

Microscopic method for E0 transition matrix elements

The 3\(\alpha \) Process Studied Through Pair Conversion Transitions from the Hoyle State in 12C

Electric Monopole Transition Strengths in62Ni

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Towards the pair spectroscopy of the Hoyle state in¹²C

The 3\(\alpha \) Process Studied Through Pair Conversion Transitions from the Hoyle State in ¹²C

Electric Monopole Transition Strengths in⁶²Ni