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Beta delayed neutron emission of $N=84$ $^{132}$Cd
Authors:
M. Madurga,
Z. Y. Xu,
1 R. Grzywacz,
A. Andreyev,
G. Benzoni,
M. J. G. Borge,
C. Costache,
I. Cox,
B. Dimitrov,
P. Van Duppen,
L. M. Fraile,
S. Franchoo,
H. Fynbo,
B. Gonsalves,
A. Gottardo,
P. T. Greenless,
C. J. Gross,
L. J. Harkness-Brennan,
M. Hyuse,
D. S. Judson,
S. Kisyov,
K. Kolos,
J. Konki,
J. Kurzewicz,
I. Lazarus
, et al. (29 additional authors not shown)
Abstract:
Using the time-of-flight technique, we measured the beta-delayed neutron emission of $^{132}$Cd. From our large-scale shell model (LSSM) calculation using the N$^3$LO interaction [Z.Y. Xu et al., Phys. Rev. Lett. 131, 022501 (2023)], we suggest the decay is dominated by the transformation of a neutron in the $g_{7/2}$ orbital, deep below the Fermi surface, into a proton in the $g_{9/2}$ orbital. W…
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Using the time-of-flight technique, we measured the beta-delayed neutron emission of $^{132}$Cd. From our large-scale shell model (LSSM) calculation using the N$^3$LO interaction [Z.Y. Xu et al., Phys. Rev. Lett. 131, 022501 (2023)], we suggest the decay is dominated by the transformation of a neutron in the $g_{7/2}$ orbital, deep below the Fermi surface, into a proton in the $g_{9/2}$ orbital. We compare the beta-decay half-lives and neutron branching ratios of nuclei with $Z<50$ and $N\geq82$ obtained with our LSSM with those of leading "global" models. Our calculations match known half-lives and neutron branching ratios well and suggest that current leading models overestimate the yet-to-be-measured half-lives. Our model, backed by the $^{132}$Cd decay data presented here, offers robust predictive power for nuclei of astrophysical interest such as $r$-process waiting points.
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Submitted 5 December, 2024;
originally announced December 2024.
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Revealing the nature of yrast states in neutron-rich polonium isotopes
Authors:
R. Lică,
A. N. Andreyev,
H. Naïdja,
A. Blazhev,
P. Van Duppen,
B. Andel,
A. Algora,
S. Antalic,
J. Benito,
G. Benzoni,
T. Berry,
M. J. G. Borge,
C. Costache,
J. G. Cubiss,
H. De Witte,
L. M. Fraile,
H. O. U. Fynbo,
P. T. Greenlees,
L. J. Harkness-Brennan,
M. Huyse,
A. Illana,
J. Jolie,
D. S. Judson,
J. Konki,
I. Lazarus
, et al. (21 additional authors not shown)
Abstract:
Polonium isotopes having two protons above the shell closure at $Z=82$ show a wide variety of low-lying high-spin isomeric states across the whole chain. The structure of neutron-deficient isotopes up to $^{210}$Po ($N=126$) is well established as they are easily produced through various methods. However, there is not much information available for the neutron-rich counterparts for which only sele…
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Polonium isotopes having two protons above the shell closure at $Z=82$ show a wide variety of low-lying high-spin isomeric states across the whole chain. The structure of neutron-deficient isotopes up to $^{210}$Po ($N=126$) is well established as they are easily produced through various methods. However, there is not much information available for the neutron-rich counterparts for which only selective techniques can be used for their production. We report on the first fast-timing measurements of yrast states up to the 8$^+$ level in $^{214,216,218}$Po isotopes produced in the $β^-$ decay of $^{214,216,218}$Bi at ISOLDE, CERN. In particular, our new half-life value of 607(14) ps for the 8$_1^+$ state in $^{214}$Po is nearly 20 times shorter than the one available in literature and comparable with the newly measured half-lives of 409(16) and 628(25) ps for the corresponding 8$_1^+$ states in $^{216,218}$Po, respectively. The measured $B(E2;8_1^+ \to 6_1^+)$ transition probability values follow an increasing trend relative to isotope mass, reaching a maximum for $^{216}$Po. The increase contradicts the previous claims of isomerism for the $8^+$ yrast states in neutron-rich $^{214}$Po and beyond. Together with the other measured yrast transitions, the $B(E2)$ values provide a crucial test of the different theoretical approaches describing the underlying configurations of the yrast band. The new experimental results are compared to shell-model calculations using the KHPE and H208 effective interactions and their pairing modified versions, showing an increase in configuration mixing when moving towards the heavier isotopes.
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Submitted 15 November, 2024; v1 submitted 4 July, 2024;
originally announced July 2024.
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Simultaneous $γ$-ray and electron spectroscopy of $^{182,184,186}$Hg isotopes
Authors:
M. Stryjczyk,
B. Andel,
J. G. Cubiss,
K. Rezynkina,
T. R. Rodríguez,
J. E. García-Ramos,
A. N. Andreyev,
J. Pakarinen,
P. Van Duppen,
S. Antalic,
T. Berry,
M. J. G. Borge,
C. Clisu,
D. M. Cox,
H. De Witte,
L. M. Fraile,
H. O. U. Fynbo,
L. P. Gaffney,
L. J. Harkness-Brennan,
M. Huyse,
A. Illana,
D. S. Judson,
J. Konki,
J. Kurcewicz,
I. Lazarus
, et al. (26 additional authors not shown)
Abstract:
Background: The mercury isotopes around $N=104$ are a well-known example of nuclei exhibiting shape coexistence. Mixing of configurations can be studied by measuring the monopole strength $ρ^2(E0)$, however, currently the experimental information is scarce and lacks precision, especially for the $I^π\rightarrow I^π$ ($I \neq 0$) transitions. Purpose: The goals of this study were to increase the pr…
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Background: The mercury isotopes around $N=104$ are a well-known example of nuclei exhibiting shape coexistence. Mixing of configurations can be studied by measuring the monopole strength $ρ^2(E0)$, however, currently the experimental information is scarce and lacks precision, especially for the $I^π\rightarrow I^π$ ($I \neq 0$) transitions. Purpose: The goals of this study were to increase the precision of the known branching ratios and internal conversion coefficients, to increase the amount of available information regarding excited states in $^{182,184,186}$Hg and to interpret the results in the framework of shape coexistence using different models. Method: The low-energy structures in $^{182,184,186}$Hg were populated in the $β$ decay of $^{182,184,186}$Tl, produced at ISOLDE and purified by laser ionization and mass separation. The $γ$-ray and internal conversion electron events were detected by five germanium clover detectors and a segmented silicon detector, respectively, and correlated in time to build decay schemes. Results: In total, 193, 178 and 156 transitions, including 144, 140 and 108 observed for the first time in a $β$-decay experiment, were assigned to $^{182,184,186}$Hg, respectively. Internal conversion coefficients were determined for 23 transitions, out of which 12 had an $E0$ component. Extracted branching ratios allowed the sign of the interference term in $^{182}$Hg as well as $ρ^2(E0;0^+_2\rightarrow 0^+_1)$ and $B(E2;0^+_2\rightarrow 2^+_1)$ in $^{184}$Hg to be determined. By means of electron-electron coincidences, the $0^+_3$ state was identified in $^{184}$Hg. The experimental results were qualitatively reproduced by five theoretical approaches, the IBM with configuration mixing with two different parametrizations, the General Bohr Hamiltonian, the BMF model and the SCCM model. However, a quantitative description is lacking.
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Submitted 6 June, 2023; v1 submitted 25 May, 2023;
originally announced May 2023.
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First observation of high-$K$ isomeric states in $^{249}$Md and $^{251}$Md
Authors:
T. Goigoux,
Ch. Theisen,
B. Sulignano,
M. Airiau,
K. Auranen,
H. Badran,
R. Briselet,
T. Calverley,
D. Cox,
F. Déchery,
F. Defranchi Bisso,
A. Drouart,
Z. Favier,
B. Gall,
T. Grahn,
P. T. Greenlees,
K. Hauschild,
A. Herzáň,
R. -D. Herzberg,
U. Jakobsson,
R. Julin,
S. Juutinen,
J. Konki,
M. Leino,
A. Lightfoot
, et al. (23 additional authors not shown)
Abstract:
Decay spectroscopy of the odd-proton nuclei $^{249}$Md and $^{251}$Md has been performed. High-$K$ isomeric states were identified for the first time in these two nuclei through the measurement of their electromagnetic decay. An isomeric state with a half-life of $2.8(5)$ ms and an excitation energy $\geq 910$ keV was found in $^{249}$Md. In $^{251}$Md, an isomeric state with a half-life of…
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Decay spectroscopy of the odd-proton nuclei $^{249}$Md and $^{251}$Md has been performed. High-$K$ isomeric states were identified for the first time in these two nuclei through the measurement of their electromagnetic decay. An isomeric state with a half-life of $2.8(5)$ ms and an excitation energy $\geq 910$ keV was found in $^{249}$Md. In $^{251}$Md, an isomeric state with a half-life of $1.4(3)$ s and an excitation energy $\geq 844$ keV was found. Similarly to the neighbouring $^{255}$Lr, these two isomeric states are interpreted as 3 quasi-particle high-$K$ states and compared to new theoretical calculations. Excited nuclear configurations were calculated within two scenarios: via blocking nuclear states located in proximity to the Fermi surface or/and using the quasiparticle Bardeen-Cooper-Schrieffer method. Relevant states were selected on the basis of the microscopic-macroscopic model with a deformed Woods-Saxon potential. The most probable candidates for the configurations of $K$-isomeric states in Md nuclei are proposed.
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Submitted 24 November, 2021; v1 submitted 1 July, 2021;
originally announced July 2021.
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Multiple chiral bands in $^{137}$Nd
Authors:
C. M. Petrache,
B. F. Lv,
Q. B. Chen,
J. Meng,
A. Astier,
E. Dupont,
K. K. Zheng,
P. T. Greenlees,
H. Badran,
T. Calverley,
D. M. Cox,
T. Grahn,
J. Hilton,
R. Julin,
S. Juutinen,
J. Konki,
J. Pakarinen,
P. Papadakis,
J. Partanen,
P. Rahkila,
P. Ruotsalainen,
M. Sandzelius,
J. Saren,
C. Scholey,
J. Sorri
, et al. (13 additional authors not shown)
Abstract:
Two new bands have been identified in $^{137}$Nd from a high-statistics JUROGAM II gamma-ray spectroscopy experiment. Constrained density functional theory and particle rotor model calculations are used to assign configurations and investigate the band properties, which are well described and understood. It is demonstrated that these two new bands can be interpreted as chiral partners of previousl…
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Two new bands have been identified in $^{137}$Nd from a high-statistics JUROGAM II gamma-ray spectroscopy experiment. Constrained density functional theory and particle rotor model calculations are used to assign configurations and investigate the band properties, which are well described and understood. It is demonstrated that these two new bands can be interpreted as chiral partners of previously known three-quasiparticle positive- and negative-parity bands. The newly observed chiral doublet bands in $^{137}$Nd represent an important support to the existence of multiple chiral bands in nuclei. The present results constitute the missing stone in the series of Nd nuclei showing multiple chiral bands, which becomes the most extended sequence of nuclei presenting multiple chiral bands in the Segré chart.
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Submitted 18 August, 2020;
originally announced August 2020.
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The observation of vibrating pear shapes in radon nuclei: update
Authors:
P. A. Butler,
L. P. Gaffney,
P. Spagnoletti,
J. Konki,
M. Scheck,
J. F. Smith,
K. Abrahams,
M. Bowry,
J. Cederkäll,
T. Chupp,
G. De Angelis,
H. De Witte,
P. E. Garrett,
A. Goldkuhle,
C. Henrich,
A. Illana,
K. Johnston,
D. T. Joss,
J. M. Keatings,
N. A. Kelly,
M. Komorowska,
T. Kröll,
M. Lozano,
B. S. Nara Singh,
D. O'Donnell
, et al. (19 additional authors not shown)
Abstract:
There is a large body of evidence that atomic nuclei can undergo octupole distortion and assume the shape of a pear. This phenomenon is important for measurements of electric-dipole moments of atoms, which would indicate CP violation and hence probe physics beyond the standard model of particle physics. Isotopes of both radon and radium have been identified as candidates for such measurements. Her…
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There is a large body of evidence that atomic nuclei can undergo octupole distortion and assume the shape of a pear. This phenomenon is important for measurements of electric-dipole moments of atoms, which would indicate CP violation and hence probe physics beyond the standard model of particle physics. Isotopes of both radon and radium have been identified as candidates for such measurements. Here, we have observed the low-lying quantum states in $^{224}$Rn and $^{226}$Rn by accelerating beams of these radioactive nuclei. We report here additional states not assigned in our 2019 publication. We show that radon isotopes undergo octupole vibrations but do not possess static pear-shapes in their ground states. We conclude that radon atoms provide less favourable conditions for the enhancement of a measurable atomic electric-dipole moment.
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Submitted 10 June, 2020; v1 submitted 23 March, 2020;
originally announced March 2020.
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In-beam gamma-ray and electron spectroscopy of $^{249,251}$Md
Authors:
R. Briselet,
Ch. Theisen,
B. Sulignano,
M. Airiau,
K. Auranen,
D. M. Cox,
F. Déchery,
A. Drouart,
Z. Favier,
B. Gall,
T. Goigoux,
T. Grahn,
P. T. Greenlees,
K. Hauschild,
A. Herzan,
R. -D. Herzberg,
U. Jakobsson,
R. Julin,
S. Juutinen,
J. Konki,
M. Leino,
A. Lopez-Martens,
A. Mistry,
P. Nieminen,
J. Pakarinen
, et al. (18 additional authors not shown)
Abstract:
The odd-$Z$ $^{251}$Md nucleus was studied using combined $γ$-ray and conversion-electron in-beam spectroscopy. Besides the previously observed rotational band based on the $[521]1/2^-$ configuration, another rotational structure has been identified using $γ$-$γ$ coincidences. The use of electron spectroscopy allowed the rotational bands to be observed over a larger rotational frequency range. Usi…
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The odd-$Z$ $^{251}$Md nucleus was studied using combined $γ$-ray and conversion-electron in-beam spectroscopy. Besides the previously observed rotational band based on the $[521]1/2^-$ configuration, another rotational structure has been identified using $γ$-$γ$ coincidences. The use of electron spectroscopy allowed the rotational bands to be observed over a larger rotational frequency range. Using the transition intensities that depend on the gyromagnetic factor, a $[514]7/2^-$ single-particle configuration has been inferred for this band, i.e., the ground-state band. A physical background that dominates the electron spectrum with an intensity of $\simeq$ 60% was well reproduced by simulating a set of unresolved excited bands. Moreover, a detailed analysis of the intensity profile as a function of the angular momentum provided a method for deriving the orbital gyromagnetic factor, namely $g_K = 0.69^{+0.19}_{-0.16}$ for the ground-state band. The odd-$Z$ $^{249}$Md was studied using $γ$-ray in-beam spectroscopy. Evidence for octupole correlations resulting from the mixing of the $Δl = Δj = 3$ $[521]3/2^-$ and $[633]7/2^+$ Nilsson orbitals were found in both $^{249,251}$Md. A surprising similarity of the $^{251}$Md ground-state band transition energies with those of the excited band of $^{255}$Lr has been discussed in terms of identical bands. Skyrme-Hartree-Fock-Bogoliubov calculations were performed to investigate the origin of the similarities between these bands.
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Submitted 7 July, 2020; v1 submitted 28 January, 2020;
originally announced January 2020.
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Evolution of Octupole Deformation in Radium Nuclei from Coulomb Excitation of Radioactive $^{222}$Ra and $^{228}$Ra Beams
Authors:
P. A. Butler,
L. P. Gaffney,
P. Spagnoletti,
K. Abrahams,
M. Bowry,
J. Cederkäll,
G. De Angelis,
H. De Witte,
P. E. Garrett,
A. Goldkuhle,
C. Henrich,
A. Illana,
K. Johnston,
D. T. Joss,
J. M. Keatings,
N. A. Kelly,
M. Komorowska,
J. Konki,
T. Kröll,
M. Lozano,
B. S. Nara Singh,
D. O'Donnell,
J. Ojala,
R. D. Page,
L. G. Pedersen
, et al. (18 additional authors not shown)
Abstract:
There is sparse direct experimental evidence that atomic nuclei can exhibit stable pear shapes arising from strong octupole correlations. In order to investigate the nature of octupole collectivity in radium isotopes, electric octupole ($E3$) matrix elements have been determined for transitions in $^{222,228}$Ra nuclei using the method of sub-barrier, multi-step Coulomb excitation. Beams of the ra…
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There is sparse direct experimental evidence that atomic nuclei can exhibit stable pear shapes arising from strong octupole correlations. In order to investigate the nature of octupole collectivity in radium isotopes, electric octupole ($E3$) matrix elements have been determined for transitions in $^{222,228}$Ra nuclei using the method of sub-barrier, multi-step Coulomb excitation. Beams of the radioactive radium isotopes were provided by the HIE-ISOLDE facility at CERN. The observed pattern of $E$3 matrix elements for different nuclear transitions is explained by describing $^{222}$Ra as pear-shaped with stable octupole deformation, while $^{228}$Ra behaves like an octupole vibrator.
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Submitted 27 January, 2020;
originally announced January 2020.
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First Exploration of Neutron Shell Structure Below Lead and Beyond $\boldsymbol{N=126}$
Authors:
T. L. Tang,
B. P. Kay,
C. R. Hoffman,
J. P. Schiffer,
D. K. Sharp,
L. P. Gaffney,
S. J. Freeman,
M. R. Mumpower,
A. Arokiaraj,
E. F. Baader,
P. A. Butler,
W. N. Catford,
G. de Angelis,
F. Flavigny,
M. D. Gott,
E. T. Gregor,
J. Konki,
M. Labiche,
I. H. Lazurus,
P. T. MacGregor,
I. Martel,
R. D. Page,
Zs. Podolyák,
O. Poleshchuk,
R. Raabe
, et al. (4 additional authors not shown)
Abstract:
The nuclei below lead but with more than 126 neutrons are crucial to an understanding of the astrophysical $r$-process in producing nuclei heavier than $A\sim190$. Despite their importance, the structure and properties of these nuclei remain experimentally untested as they are difficult to produce in nuclear reactions with stable beams. In a first exploration of the shell structure of this region,…
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The nuclei below lead but with more than 126 neutrons are crucial to an understanding of the astrophysical $r$-process in producing nuclei heavier than $A\sim190$. Despite their importance, the structure and properties of these nuclei remain experimentally untested as they are difficult to produce in nuclear reactions with stable beams. In a first exploration of the shell structure of this region, neutron excitations in $^{207}$Hg have been probed using the neutron-adding ($d$,$p$) reaction in inverse kinematics. The radioactive beam of $^{206}$Hg was delivered to the new ISOLDE Solenoidal Spectrometer at an energy above the Coulomb barrier. The spectroscopy of $^{207}$Hg marks a first step in improving our understanding of the relevant structural properties of nuclei involved in a key part of the path of the $r$-process.
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Submitted 3 January, 2020;
originally announced January 2020.
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Chirality of $^{135}$Nd reexamined: Evidence for multiple chiral doublet bands
Authors:
B. F. Lv,
C. M. Petrache,
Q. B. Chen,
J. Meng,
A. Astier,
E. Dupont,
P. Greenlees,
H. Badran,
T. Calverley,
D. M. Cox,
T. Grahn,
J. Hilton,
R. Julin,
S. Juutinen,
J. Konki,
J. Pakarinen,
P. Papadakis,
J. Partanen,
P. Rahkila,
P. Ruotsalainen,
M. Sandzelius,
J. Saren,
C. Scholey,
J. Sorri,
S. Stolze
, et al. (13 additional authors not shown)
Abstract:
One new pair of positive-parity chiral doublet bands have been identified in the odd-$A$ nucleus $^{135}$Nd which together with the previously reported negative-parity chiral doublet bands constitute a third case of multiple chiral doublet (M$χ$D) bands in the $A\approx130$ mass region. The properties of the M$χ$D bands are well reproduced by constrained covariant density functional theory and par…
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One new pair of positive-parity chiral doublet bands have been identified in the odd-$A$ nucleus $^{135}$Nd which together with the previously reported negative-parity chiral doublet bands constitute a third case of multiple chiral doublet (M$χ$D) bands in the $A\approx130$ mass region. The properties of the M$χ$D bands are well reproduced by constrained covariant density functional theory and particle rotor model calculations. The newly observed M$χ$D bands in $^{135}$Nd represents an important milestone in supporting the existence of M$χ$D in nuclei.
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Submitted 30 July, 2019;
originally announced July 2019.
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Spectroscopy of 46Ar by the (t,p) two-neutron transfer reaction
Authors:
K. Nowak,
K. Wimmer,
S. Hellgartner,
D. Mücher,
V. Bildstein,
J. Diriken,
J. Elseviers,
L. P. Gaffney,
R. Gernhäuser,
J. Iwanicki,
J. G. Johansen,
M. Huyse,
J. Konki,
T. Kröll R. Krücken,
R. Lutter,
R. Orlandi,
J. Pakarinen,
R. Raabe,
P. Reiter,
T. Roger,
G. Schrieder,
M. Seidlitz,
O. Sorlin,
P. Van Duppen,
N. Warr
, et al. (2 additional authors not shown)
Abstract:
States in the $N=28$ nucleus $^{46}$Ar have been studied by a two-neutron transfer reaction at REX-ISOLDE (CERN). A beam of radioactive $^{44}$ at an energy of 2.16~AMeV and a tritium loaded titanium target were used to populate $^{46}$ by the t($^{44}$,p) two-neutron transfer reaction. Protons emitted from the target were identified in the T-REX silicon detector array. The excitation energies of…
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States in the $N=28$ nucleus $^{46}$Ar have been studied by a two-neutron transfer reaction at REX-ISOLDE (CERN). A beam of radioactive $^{44}$ at an energy of 2.16~AMeV and a tritium loaded titanium target were used to populate $^{46}$ by the t($^{44}$,p) two-neutron transfer reaction. Protons emitted from the target were identified in the T-REX silicon detector array. The excitation energies of states in $^{46}$ have been reconstructed from the measured angles and energies of recoil protons. Angular distributions for three final states were measured and based on the shape of the differential cross section an excited state at 3695~keV has been identified as $J^π= 0^+$. The angular differential cross section for the population of different states are compared to calculations using a reaction model employing both sequential and direct transfer of two neutrons. Results are compared to shell model calculations using state-of-the-art effective interactions.
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Submitted 13 April, 2016;
originally announced April 2016.