Academic Interests
- Nuclear structure
- Gamma-ray spectroscopy
- Level densities
- Radioactive ion beams
- Nuclear shapes
- Collective excitations
- Coulomb excitation
- Lifetime measurements
Emneord:
nuclear physics,
nuclear structure
Publikasjoner
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Pasqualato, G; Ansari, S.; Heines, Johannes Sørby; Modamio, Victor; Görgen, Andreas & Beckmann, Kristine Sønstevold
[Vis alle 52 forfattere av denne artikkelen]
(2023).
Shape evolution in even-mass <sup>98 - 104</sup> Zr isotopes via lifetime measurements using the γγ -coincidence technique.
European Physical Journal A.
ISSN 1434-6001.
59(11).
doi:
10.1140/epja/s10050-023-01172-8.
Vis sammendrag
The Zirconium (Z = 40) isotopic chain has attracted interest for more than four decades. The abrupt lowering of the energy of the first 2+ state and the increase in
the transition strength B(E2; 2+→ 0+) going from 98Zr to 100Zr has been the first example of “quantum phase transition” in nuclear shapes, which has few equivalents in the nuclear chart. Although a multitude of experiments have been
performed to measure nuclear properties related to nuclear shapes and collectivity in the region, none of the measured lifetimes were obtained using the Recoil Distance Doppler Shift method in the γγ-coincidence mode where a gate on the direct feeding transition of the state of interest allows a strict control of systematical errors. This work reports the results of lifetime measurements for the first yrast excited states in 98−104Zr carried out to extract reduced transition
probabilities. The new lifetime values in γγ-coincidence and γ -single mode are compared with the results of former experiments. Recent predictions of the Interacting Boson Model with Configuration Mixing, the Symmetry Conserving Configuration Mixing model based on theHartree–Fock–Bogoliubov approach and the Monte Carlo Shell Model are presented and compared with the experimental data.
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Pogliano, Francesco; Bello Garrote, Frank Leonel; Larsen, Ann-Cecilie; Berg, Hannah Christine; Gjestvang, Dorthea & Görgen, Andreas
[Vis alle 19 forfattere av denne artikkelen]
(2023).
Observation of a candidate for the M1 scissors resonance in odd-odd Ho 166.
Physical Review C.
ISSN 2469-9985.
107(3).
doi:
10.1103/PhysRevC.107.034605.
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The γ -strength function and the nuclear level density for the odd-odd, rare-earth nucleus 166 Ho have been
extracted from 163 Dy(α, pγ ) 166 Ho data using the Oslo method. A structure at ≈3 MeV in the γ -strength function
is interpreted as the M1 scissors resonance. By employing three different methods we find that its strength
depends rather strongly on the modeling of the E 1 strength, while its centroid does not. The 166 Ho scissors
resonance parameters are consistent with previous results on other rare-earth nuclei.
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Gjestvang, Dorthea; Siem, Sunniva; Zeiser, Fabio; Randrup, Jørgen; Vogt, Ramona & Wilson, Jonathan Nicholas
[Vis alle 19 forfattere av denne artikkelen]
(2021).
Excitation energy dependence of prompt fission γ-ray emission from 241Pu*.
Physical Review C.
ISSN 2469-9985.
103(3).
doi:
10.1103/PhysRevC.103.034609.
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Prompt fission γ rays (PFGs) resulting from the 240Pu(d,pf) reaction have been measured as a function of fissioning nucleus excitation energy Ex at the Oslo Cyclotron Laboratory. We study the average total PFG multiplicity per fission, the average total PFG energy released per fission, and the average PFG energy. No significant changes in these characteristics are observed over the range 5.75
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Zeiser, Fabio; Tveten, Gry Merete; Bello Garrote, Frank Leonel; Guttormsen, Magne Sveen; Larsen, Ann-Cecilie & Ingeberg, Vetle Wegner
[Vis alle 8 forfattere av denne artikkelen]
(2021).
The gamma-ray energy response of the Oslo Scintillator Array OSCAR.
Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment.
ISSN 0168-9002.
985.
doi:
10.1016/j.nima.2020.164678.
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Ingeberg, Vetle Wegner; Siem, Sunniva; Wiedeking, Mathis; Sieja, Kamila; Bleuel, D.l. & Brits, C.P.
[Vis alle 29 forfattere av denne artikkelen]
(2020).
First application of the Oslo method in inverse kinematics.
European Physical Journal A.
ISSN 1434-6001.
56.
doi:
10.1140/epja/s10050-020-00070-7.
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The γ-ray strength function (SF) and nuclear level density (NLD) have been extracted for the first time from inverse kinematic reactions with the Oslo method. This novel technique allows measurements of these properties across a wide range of previously inaccessible nuclei. Proton–γ coincidence events from the d(⁸⁷Kr,p)⁸⁶Kr reaction were measured at iThemba LABS and the γSF and NLD in ⁸⁶Kr was obtained. The low-energy region of the γSF is compared to shell-model calculations, which suggest this region to be dominated by M1 strength. The γSF and NLD are used as input parameters to Hauser–Feshbach calculations to constrain (n,γ) cross sections of nuclei using the TALYS reaction code. These results are compared to ⁸⁶Kr(n,γ) data from direct measurements.
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Krzysiek, Mateusz; Utsunomiya, Hiroaki; Gheorghe, Ioana; Filipescu, Dan Mihai; Renstrøm, Therese & Tveten, Gry Merete
[Vis alle 19 forfattere av denne artikkelen]
(2019).
Photoneutron cross-section measurements for 165HO by the direct neutron-multiplicity sorting at Newsubaru .
Acta Physica Polonica B.
ISSN 0587-4254.
50(3),
s. 487–494.
doi:
10.5506/APhysPolB.50.487.
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Guttormsen, Magne Sveen; Goriely, Stephane; Larsen, Ann-Cecilie; Görgen, Andreas; Hagen, Trine Wiborg & Renstrøm, Therese
[Vis alle 12 forfattere av denne artikkelen]
(2019).
Indirect(n,γ)91,92Zr Cross SectionMeasurements for the s-Process.
I Formicola, Alba; Junker, Matthias; Gialanella, Lucio & Imbriani, Gianluca (Red.),
Nuclei in the Cosmos XV.
Springer.
ISSN 978-3-030-13875-2.
s. 359–362.
doi:
10.1007/978-3-030-13876-9_65.
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Kullmann, Ina Kristine Berentsen; Larsen, Ann-Cecilie; Renstrøm, Therese; Beckmann, Kristine Sønstevold; Bello Garrote, Frank Leonel & Crespo Campo, Lucia
[Vis alle 13 forfattere av denne artikkelen]
(2019).
First experimental constraint on the 191Os(n,γ) reaction rate relevant to s-process nucleosynthesis
.
Physical Review C.
ISSN 2469-9985.
99(6).
doi:
10.1103/PhysRevC.99.065806.
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Vis sammendrag
The nuclear level density and
γ
-decay strength of
192
Os
have been extracted using particle-
γ
coincidence data from the
192
Os
(
α
,
α
′
γ
)
192
Os
reaction by means of the Oslo method. The level density is found to be a rather smooth function of excitation energy, approximately following the constant temperature model. The
γ
-decay strength is compared to photoneutron cross-section data above the neutron separation energy, and to
E
1
and
M
1
strengths for nuclei in this mass region derived from primary transitions following neutron capture. Our results are in good agreement with these previous data and draw a consistent picture of the
γ
-strength function in the range
E
γ
≈
1.5
–
6
MeV
. Using the measured nuclear level density and
γ
-decay strength as input to the nuclear-reaction code talys, we provide the first experimentally constrained Maxwellian-averaged cross section (MACS) for the
191
Os
(
n
,
γ
)
192
Os
reaction relevant to
s
-process nucleosynthesis. The systematic uncertainties introduced by the normalization procedure of the level density and
γ
-strength function were investigated and propagated to the calculated Maxwellian-averaged cross section. The obtained result of the Maxwellian-averaged cross section at
k
B
T
=
30
keV
,
⟨
σ
⟩
n
,
γ
=
1134
±
375
mb
, is in very good agreement with the theoretical estimate provided by the KADoNiS project, giving experimental support to the adopted KADoNiS value. Good agreement is also found with MACS values obtained from other libraries, such as TENDL-2017, ENDF/B-VII.0, and JEFF.
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Crespo Campo, Lucia; Guttormsen, Magne Sveen; Bello Garrote, Frank Leonel; Eriksen, Tomas Kvalheim; Giacoppo, Francesca & Görgen, Andreas
[Vis alle 15 forfattere av denne artikkelen]
(2018).
Test of the generalized Brink-Axel hypothesis in 64,65Ni.
Physical Review C.
ISSN 2469-9985.
98,
s. 054303-1–054303-10.
doi:
10.1103/PhysRevC.98.054303.
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Previously published particle-γ coincidence data on the 64Ni(p,p′γ)64Ni and 64Ni(d,pγ)65Ni reactions were further analyzed to study the statistical properties of γ decay in 64,65Ni. To do so, the γ decay to the quasicontinuum region and discrete low-lying states was investigated at γ-ray energies of 2.0–9.6 and 1.6–6.1 MeV in 64 Ni and 65 Ni, respectively. In particular, the dependence of the γ -strength function with initial and final excitation energy was studied to test the validity of the generalized Brink-Axel hypothesis. Finally, the role of fluctuations in transition strengths was estimated as a function of γ-ray and excitation energy. The γ -strength function is consistent with the hypothesis of the independence of initial excitation energy, in accordance with the generalized Brink-Axel hypothesis. The results show that the γ decay to low-lying levels displays large fluctuations for low initial excitation energies.
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Renstrøm, Therese; Utsunomiya, H.; Nyhus, Hilde-Therese; Larsen, Ann-Cecilie; Guttormsen, Magne Sveen & Tveten, Gry Merete
[Vis alle 16 forfattere av denne artikkelen]
(2018).
Verification of detailed balance for γ absorption and emission in Dy isotopes.
Physical Review C.
ISSN 2469-9985.
98(5),
s. 1–14.
doi:
10.1103/PhysRevC.98.054310.
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The photoneutron cross sections of 162,163Dy have been measured for the first time in an energy region from the neutron threshold (Sn) up to ≈13MeV. The (γ,n) reaction was induced with quasimonochromatic laser Compton-scattered γ rays, produced at the NewSUBARU laboratory. The corresponding γ -ray strength functions (γ SF) have been calculated from the photoneutron cross sections. The data are compared to reanalyzed γSFs of 160–164Dy, which are measured below Sn. The excellent agreement with the photoneutron data at Sn confirms the principle of detailed balance. Thus, a complete γ SF is established covering in total the energy regionof1 Eγ 13MeV.Thesemid-shellwell-deformeddysprosiumisotopesallshowscissorsresonances with very similar structures. We find that our data predict the same integrated scissors strength as (γ,γ′) data when integrated over the same energy range, which shows that the scissors mode very likely is consistent with the generalized Brink hypothesis. Finally, using the γSFs as input in the reaction code TALYS, we have deduced radiative neutron-capture cross sections and compared them to direct measurements. We find a very good agreement within the uncertainties, which gives further support to the experimentally determined γ SFs.
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Utsunomiya, Hiroaki; Renstrøm, Therese; Tveten, Gry Merete; Goriely, Stéphane; Katayama, Seitaro & Ari-Izumi, Takashi
[Vis alle 22 forfattere av denne artikkelen]
(2018).
Photoneutron cross sections for Ni isotopes: Toward understanding (n, γ ) cross sections relevant to weak s-process nucleosynthesis.
Physical Review C.
ISSN 2469-9985.
98(5),
s. 1–9.
doi:
10.1103/PhysRevC.98.054619.
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Vis sammendrag
Photoneutron cross sections were measured for 58Ni, 60Ni, 61Ni, and 64Ni at energies between the one-neutron and two-neutron thresholds using quasimonochromatic γ -ray beams produced in laser Compton scattering at the NewSUBARU synchrotron radiation facility. These photoneutron data are used to extract the γ -ray strength function above the neutron threshold, complementing the information obtained by the Oslo method below the threshold. We discuss radiative neutron-capture cross sections and the Maxwellian-averaged cross sections for Ni isotopes including 63Ni, a branching point nucleus along the weak s-process path. The cross sections are calculated with the experimentally constrained γ-ray strength functions from the Hartree-Fock-Bogolyubov plus quasiparticle–random-phase approximation based on the Gogny D1M interaction for both E1 and M1 components and supplemented with the M1 upbend.
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Tveten, Gry Merete; Spyrou, Artemis; Schwengner, Ronald; Naqvi, Farheen; Larsen, Ann-Cecilie & Renstrøm, Therese
[Vis alle 22 forfattere av denne artikkelen]
(2017).
The Statistical Properties Of 92Mo And Implications For The p-process.
Proceedings of Science (PoS).
ISSN 1824-8039.
INPC2016.
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Vis sammendrag
A particularly challenging part of the question of how elements heavier than iron are created in extreme, astrophysical environments is the creation of the so-called p-nuclei, which are believed to be mainly produced in the O-Ne layer of type II supernovae or type Ia supernovae. The lack of needed nuclear data presents an obstacle in nailing down the precise site and astrophysical conditions for the production of these isotopes. Astrophysical model calculations are able to reproduce abundance patterns of most p-isotopes reasonably well, with some pivotal exceptions. In particular, p-isotopes of mass 92 ≤ A ≤ 98 are underproduced in calculations compared to the actual abundance of these isotopes. The p-isotope 92Mo represents one of the most severe cases of underproduction. State-of-the-art p-process calculations systematically underestimate the observed solar abundance of this isotope.
The main destruction mechanism of this isotope in the standard description of the p-process is through the 92Mo(γ, p)91Nb reaction. Measurements on the nuclear level density and average gamma strength function of 92Mo have been carried out at the Oslo Cyclotron Laboratory. TALYS cross section and reaction rate calculations where the experimental results are used as input will be presented. The data provide stringent constraints on the 91Nb(p, γ)92Mo (and consequently the inverse) reaction rate. The reaction rate extracted in this work was used in reaction network calculations for the scenario of a p-process taking place in a type II supernova explosion as the shock front passes through the O-Ne layer of a 25 solar mass star.
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Kheswa, Bonginkosi Vincent; Wiedeking, Mathis; Brown, Joshua A.; Larsen, Ann-Cecilie; Goriely, Stéphane & Guttormsen, Magne Sveen
[Vis alle 24 forfattere av denne artikkelen]
(2017).
137,138,139La(n,γ) cross sections constrained with statistical decay properties of 138,139,140La nuclei.
Physical Review C.
ISSN 2469-9985.
95(4).
doi:
10.1103/PhysRevC.95.045805.
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Larsen, Ann-Cecilie; Spyrou, Artemisia; Liddick, Sean N.; Guttormsen, Magne Sveen; Ingeberg, Vetle Wegner & Siem, Sunniva
[Vis alle 25 forfattere av denne artikkelen]
(2016).
Novel techniques for constraining neutron-capture rates relevant to heavy-element nucleosynthesis.
Proceedings of Science (PoS).
ISSN 1824-8039.
2016-September:360,
s. 1–9.
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Tveten, Gry Merete; Spyrou, Artemis; Schwengner, Ronald; Naqvi, Farheen; Larsen, Ann-Cecilie & Renstrøm, Therese
[Vis alle 22 forfattere av denne artikkelen]
(2016).
The statistical properties of 92Mo and implications for the p-process.
Proceedings of Science (PoS).
ISSN 1824-8039.
2016-September:163.
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Bleuel, Darren L.; Bernstein, Lee A.; Brand, Christopher A; Cassata, William S; Daub, Brian H & Dauffy, Lucile S
[Vis alle 16 forfattere av denne artikkelen]
(2016).
Method for detection of nuclear-plasma interactions in a 134Xe-doped exploding pusher at the national ignition facility.
Plasma and Fusion Research.
ISSN 1880-6821.
11(2).
doi:
10.1585/pfr.11.3401075.
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Paulsen, Wanja; Li, Kevin Ching Wei; Siem, Sunniva; Ingeberg, Vetle Wegner; Larsen, Ann-Cecilie & Eriksen, Tomas Kvalheim
[Vis alle 20 forfattere av denne artikkelen]
(2023).
Remeasuring the gamma-decay branching ratio of the Hoyle state.
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Grigalavicius, Mantas; Mastrangelopoulou, Maria; Berg, K.; Arous, Delmon; Ménard, M. & Raabe-Henriksen, T.
[Vis alle 12 forfattere av denne artikkelen]
(2021).
Publisher Correction: Proton-dynamic therapy following photosensitiser activation by accelerated protons demonstrated through fluorescence and singlet oxygen production (Nature Communications, (2019), 10, 1, (3986), 10.1038/s41467-019-12042-7).
Nature Communications.
ISSN 2041-1723.
12(1).
doi:
10.1038/s41467-021-27175-x.
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Paulsen, Wanja; Görgen, Andreas; Siem, Sunniva & Li, Kevin Ching Wei
(2021).
Studies of shape coexistence in 140Sm.
Vis sammendrag
The shape of atomic nuclei can vary vastly, several shapes can even coexist within the same nucleus in certain regions of the nuclear chart. Shape coexistence is believed to be present at higher excitation energies in the N=78 isotones 140Sm and 142Gd [1], where the nucleus of interest is 140Sm in this case. 140Sm has previously been studied in a coulomb excitation experiment performed by M. Klintefjord et. al. [2] at REX-ISOLDE where results showed considerable gamma-softness and the resulting level scheme follows the theoretical prediction of a triaxial nucleus [3], but further investigation is needed to conclude. A new coulomb experiment on 140Sm has been performed using HIE-ISOLDE, yielding data of incredible quality which has also let us vastly improve the level scheme of this nucleus. Preliminary results from this dataset will be presented as well as a deeper look into gamma-softness as well as the possibility of 140Sm having shape coexistence.
[1] W. Starzecki et al., Phys. Lett. B 200, 419 (1988).
[2] M. Klintefjord et al. Phys. Rev. C 93, 054303 (2016)
[3] F. Iachello, Phys. Rev. Lett. 85, 3580 (2000)
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Paulsen, Wanja; Siem, Sunniva & Görgen, Andreas
(2020).
Assessment of the radiative width of the Hoyle state.
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Ingeberg, Vetle Wegner; Siem, Sunniva; Wiedeking, M.; Abrahams, Kenzo John; Arnswald, K. & Bello Garrote, Frank Leonel
[Vis alle 36 forfattere av denne artikkelen]
(2019).
Inverse-Oslo Method – a tool for expanding our understanding of the r-process.
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Edin, Nina Frederike J; Rykkelid, Anne Marit; Görgen, Andreas; Baker, Agnes; Siem, Sunniva & Ytre-Hauge, Kristian
[Vis alle 7 forfattere av denne artikkelen]
(2019).
Very high yield of double strand breaks found at the distal end of the proton Bragg peak.
Radiotherapy and Oncology.
ISSN 0167-8140.
133,
s. 594–594.
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Rykkelid, Anne Marit; Tormodsrud, Vera; Siem, Sunniva; Görgen, Andreas; Ytre-Hauge, Kristian & Malinen, Eirik
[Vis alle 7 forfattere av denne artikkelen]
(2019).
Very high RBE values found at the distal end of the proton Bragg peak.
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Rykkelid, Anne Marit; Siem, Sunniva; Ytre-Hauge, Kristian; Malinen, Eirik & Edin, Nina Frederike J
(2018).
Very high relative biological effectiveness found at the distal end of the proton Bragg peak.
Radiotherapy and Oncology.
ISSN 0167-8140.
127,
s. 1259–1259.
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Guttormsen, Magne Sveen; Larsen, Ann-Cecilie; Midtbø, Jørgen E.; Crespo Campo, Lucia; Görgen, Andreas & Ingeberg, Vetle Wegner
[Vis alle 11 forfattere av denne artikkelen]
(2017).
Gamma-widths, lifetimes and fluctuations in the nuclear quasi-continuum.
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Rykkelid, Anne Marit; Siem, Sunniva; Görgen, Andreas; Ytre-Hauge, Kristian; Brondz, Efim & Sandvik, Joe Alexander
[Vis alle 9 forfattere av denne artikkelen]
(2017).
A high-resolution proton irradiator for in vitro studies of relative biological effectiveness.
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Tveten, Gry Merete; Spyrou, Artemis; Schwengner, Ronald; Naqvi, Farheen; Larsen, Ann-Cecilie & Eriksen, Tomas Kvalheim
[Vis alle 22 forfattere av denne artikkelen]
(2016).
The Statistical Properties Of 92Mo And Implications For The p-process.
Vis sammendrag
A particularly challenging part of the question of how elements heavier than iron are created in extreme, astrophysical environments is the creation of the so-called p-nuclei, which are believed to be mainly produced in the O-Ne layer of type II supernovae or type Ia supernovae. The lack of needed nuclear data presents an obstacle in nailing down the precise site and astrophysical conditions for the production of these isotopes. Astrophysical model calculations are able to reproduce abundance patterns of most p-isotopes reasonably well, with some pivotal exceptions. In particular, p-isotopes of mass 92 ≤ A ≤ 98 are underproduced in calculations compared to the actual abundance of these isotopes. The p-isotope 92Mo represents one of the most severe cases of underproduction. State-of-the-art p-process calculations systematically underestimate the observed solar abundance of this isotope.
The main destruction mechanism of this isotope in the standard description of the p-process is through the 92Mo(γ, p)91Nb reaction. Measurements on the nuclear level density and average gamma strength function of 92Mo have been carried out at the Oslo Cyclotron Laboratory. TALYS cross section and reaction rate calculations where the experimental results are used as input will be presented. The data provide stringent constraints on the 91Nb(p, γ)92Mo (and consequently the inverse) reaction rate. The reaction rate extracted in this work was used in reaction network calculations for the scenario of a p-process taking place in a type II supernova explosion as the shock front passes through the O-Ne layer of a 25 solar mass star.
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Hasanbegovic, Amir; Siem, Sunniva; Søråsen, Oddvar & Aunet, Snorre
(2017).
Exploring the SEU Dependence on Supply Voltage scaling in 90 nm and 65 nm CMOS Flip-flops.
Universitetet i Oslo.
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Publisert
4. nov. 2010 12:35
- Sist endret
21. jan. 2015 23:08