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High-resolution $(p,t)$ study of low-spin states in $^{240}$Pu: Octupole excitations, $\alpha$ clustering, and other structure features
Nuclear Experiment · Submitted 18 Jul 2018
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim At least two different and distinct structures for $J^{\pi} = 0^+$ states are present in the actinides.
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The abstract, sentence by sentence
A high-resolution $(p,t)$ experiment at $E_{p}$= 24 MeV was performed to populate low-spin states in the actinide nucleus ${}^{240}$Pu. The Q3D magnetic spectrograph of the Maier-Leibnitz Laboratory (MLL) in Munich (Germany) was used to identify the ejected tritons via $dE/E$ particle identification with its focal-plane detection system. Angular distributions were measured at nine different Q3D angles to assign spin and parity to the excited states based on a comparison with coupled-channels DWBA calculations. In total, 209 states have been excited in $^{240}$Pu up to an excitation energy of 3 MeV. Many previously known states have also been observed and their spin-parity assignments were confirmed. However, many of the populated states have been seen for the first time. The low-spin one-octupole phonon excitations, i.e. $K^{\pi} = 0^-,1^-,2^-,3^-$, could be observed and a new candidate for the $K = 3$ projection is proposed. Furthermore, the double-octupole or $\alpha$-cluster structure of the $0^+_2$ state in $^{240}$Pu has been studied in more detail. It is shown that the $0^+_2$ state in $^{230}$Th has a distinctly different structure. In addition, strongly excited $1^-$ states have been observed at 1.5\,MeV and 1.8\,MeV in $^{240}$Pu. The present study suggests that similar states might be observed in $^{230}$Th. At least two different and distinct structures for $J^{\pi} = 0^+$ states are present in the actinides. These are pairing states and states with enhanced octupole correlations. We have shown that it is crucial to consider negative-parity single-particle states being admixed to some $K^{\pi} = 0^+_2$ rotational bands to understand the $\alpha$-decay hindrance factors and enhanced $E1$-decay rates. Based on our analysis, we have identified the double-octupole or $\alpha$-cluster $K^{\pi} = 0^+$ candidates from $^{224}$Ra to $^{240}$Pu.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | A high-resolution $(p,t)$ experiment at $E_{p}$= 24 MeV was performed to populate low-spin states in the actinide nucleus ${}^{240}$Pu. | method 0.51 | 0.96 | 0.02 | asserted 1.00 |
| s1 | The Q3D magnetic spectrograph of the Maier-Leibnitz Laboratory (MLL) in Munich (Germany) was used to identify the ejected tritons via $dE/E$ particle identification with its focal-plane detection system. | method 1.00 | 0.75 | 0.01 | asserted 1.00 |
| s2 | Angular distributions were measured at nine different Q3D angles to assign spin and parity to the excited states based on a comparison with coupled-channels DWBA calculations. | method 1.00 | 0.94 | 0.02 | asserted 1.00 |
| s3 | In total, 209 states have been excited in $^{240}$Pu up to an excitation energy of 3 MeV. | result 1.00 | 0.95 | 0.05 | asserted 1.00 |
| s4 | Many previously known states have also been observed and their spin-parity assignments were confirmed. | result 0.97 | 0.82 | 0.04 | asserted 1.00 |
| s5 | However, many of the populated states have been seen for the first time. | result 0.79 | 0.84 | 0.04 | asserted 1.00 |
| s6 | The low-spin one-octupole phonon excitations, i.e. $K^{\pi} = 0^-,1^-,2^-,3^-$, could be observed and a new candidate for the $K = 3$ projection is proposed. | result 1.00 | 0.94 | 0.15 | hedged possibility 0.84 |
| s7 | Furthermore, the double-octupole or $\alpha$-cluster structure of the $0^+_2$ state in $^{240}$Pu has been studied in more detail. | contribution 0.82 | 0.91 | 0.09 | asserted 0.98 |
| s8 | It is shown that the $0^+_2$ state in $^{230}$Th has a distinctly different structure. | result 0.94 | 0.68 | 0.07 | asserted 1.00 |
| s9 | In addition, strongly excited $1^-$ states have been observed at 1.5\,MeV and 1.8\,MeV in $^{240}$Pu. | result 1.00 | 0.95 | 0.05 | asserted 1.00 |
| s10 | The present study suggests that similar states might be observed in $^{230}$Th. | interpretation 0.56 | 0.33 | 0.06 | hedged possibility 0.81 |
| s11 | At least two different and distinct structures for $J^{\pi} = 0^+$ states are present in the actinides. | result 0.54 | 0.74 | 0.30 | asserted 0.90 |
| s12 | These are pairing states and states with enhanced octupole correlations. | interpretation 0.52 | 0.68 | 0.16 | asserted 1.00 |
| s13 | We have shown that it is crucial to consider negative-parity single-particle states being admixed to some $K^{\pi} = 0^+_2$ rotational bands to understand the $\alpha$-decay hindrance factors and enhanced $E1$-decay rates. | interpretation 0.94 | 0.90 | 0.26 | asserted 1.00 |
| s14 | Based on our analysis, we have identified the double-octupole or $\alpha$-cluster $K^{\pi} = 0^+$ candidates from $^{224}$Ra to $^{240}$Pu. | result 0.88 | 0.93 | 0.25 | asserted 1.00 |
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The paper
Original abstract
A high-resolution $(p,t)$ experiment at $E_{p}$= 24 MeV was performed to populate low-spin states in the actinide nucleus ${}^{240}$Pu. The Q3D magnetic spectrograph of the Maier-Leibnitz Laboratory (MLL) in Munich (Germany) was used to identify the ejected tritons via $dE/E$ particle identification with its focal-plane detection system. Angular distributions were measured at nine different Q3D angles to assign spin and parity to the excited states based on a comparison with coupled-channels DWBA calculations. In total, 209 states have been excited in $^{240}$Pu up to an excitation energy of 3 MeV. Many previously known states have also been observed and their spin-parity assignments were confirmed. However, many of the populated states have been seen for the first time. The low-spin one-octupole phonon excitations, i.e. $K^{\pi} = 0^-,1^-,2^-,3^-$, could be observed and a new candidate for the $K = 3$ projection is proposed. Furthermore, the double-octupole or $\alpha$-cluster structure of the $0^+_2$ state in $^{240}$Pu has been studied in more detail. It is shown that the $0^+_2$ state in $^{230}$Th has a distinctly different structure. In addition, strongly excited $1^-$ states have been observed at 1.5\,MeV and 1.8\,MeV in $^{240}$Pu. The present study suggests that similar states might be observed in $^{230}$Th. At least two different and distinct structures for $J^{\pi} = 0^+$ states are present in the actinides. These are pairing states and states with enhanced octupole correlations. We have shown that it is crucial to consider negative-parity single-particle states being admixed to some $K^{\pi} = 0^+_2$ rotational bands to understand the $\alpha$-decay hindrance factors and enhanced $E1$-decay rates. Based on our analysis, we have identified the double-octupole or $\alpha$-cluster $K^{\pi} = 0^+$ candidates from $^{224}$Ra to $^{240}$Pu.
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