24 results on '"L Crespo Campo"'
Search Results
2. Statistical properties of the well deformed Sm153,155 nuclei and the scissors resonance
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Gry Merete Tveten, Peter B. Jones, M. Wiedeking, K. L. Malatji, Sunniva Siem, P. von Neumann-Cosel, Gregory Potel, Andreas Görgen, A. C. Larsen, M. Ozgur, L. Crespo Campo, K. S. Beckmann, L. Pellegri, V. W. Ingeberg, Fabio Zeiser, Therese Renstrøm, B. V. Kheswa, S. Goriely, F. L. Bello Garrote, Magne Guttormsen, and K. O. Ay
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Physics ,010308 nuclear & particles physics ,0103 physical sciences ,Resonance ,Atomic physics ,010306 general physics ,01 natural sciences ,Energy (signal processing) ,Excitation - Abstract
The nuclear level densities (NLDs) and the $\ensuremath{\gamma}$-ray strength functions ($\ensuremath{\gamma}\mathrm{SFs}$) of $^{153,155}\mathrm{Sm}$ have been extracted from ($d,p\ensuremath{\gamma}$) coincidences using the Oslo method. The experimental NLD of $^{153}\mathrm{Sm}$ is higher than the NLD of $^{155}\mathrm{Sm}$, in accordance with microscopic calculations. The $\ensuremath{\gamma}\mathrm{SFs}$ of $^{153,155}\mathrm{Sm}$ are in fair agreement with QRPA calculations based on the D1M Gogny interaction. An enhancement is observed in the $\ensuremath{\gamma}\mathrm{SF}$ for both $^{153,155}\mathrm{Sm}$ nuclei around 3 MeV in excitation energy and is attributed to the $M1$ scissors resonance (SR). Their integrated strengths were found to be in the range 1.3--2.1 and 4.4--6.4 ${\ensuremath{\mu}}_{N}^{2}$ for $^{153}\mathrm{Sm}$ and $^{155}\mathrm{Sm}$, respectively. The strength of the SR for $^{155}\mathrm{Sm}$ is comparable to those for deformed even-even Sm isotopes from nuclear resonance fluorescence measurements, while that of $^{153}\mathrm{Sm}$ is lower than expected.
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- 2021
3. Strong enhancement of level densities in the crossover from spherical to deformed neodymium isotopes
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E. Algin, Fabio Zeiser, F. L. Bello Garrote, Andreas Görgen, V. W. Ingeberg, M. Klintefjord, Trine Wiborg Hagen, Wouter Ryssens, Gry Merete Tveten, Yoram Alhassid, B. V. Kheswa, E. Sahin, L. Crespo Campo, Ann-Cecilie Larsen, V. Modamio, M. Ozgur, Therese Renstrøm, Sunniva Siem, J. E. Midtbø, T. Dahl-Jacobsen, Magne Guttormsen, and K. O. Ay
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Nuclear and High Energy Physics ,Monte Carlo method ,Crossover ,Nuclear Theory ,FOS: Physical sciences ,chemistry.chemical_element ,Collective enhancement ,01 natural sciences ,Neodymium ,Molecular physics ,0103 physical sciences ,Neutron ,Mean-field theory ,Nuclear Experiment (nucl-ex) ,010306 general physics ,Nuclear Experiment ,Physics ,Isotope ,Oslo method ,010308 nuclear & particles physics ,Shell model Monte Carlo ,lcsh:QC1-999 ,chemistry ,Mean field theory ,Nuclear level density ,Saturation (chemistry) ,lcsh:Physics ,Excitation - Abstract
Understanding the evolution of level densities in the crossover from spherical to well-deformed nuclei has been a long-standing problem in nuclear physics. We measure nuclear level densities for a chain of neodymium isotopes $^{142,144-151}$Nd which exhibit such a crossover. These results represent to date the most complete data set of nuclear level densities for an isotopic chain between neutron shell-closure and towards mid-shell. We observe a strong increase of the level densities along the chain with an overall increase by a factor of $\approx 170$ at an excitation energy of 7.5 MeV and saturation around mass 150. Level densities calculated by the shell model Monte Carlo (SMMC) are in excellent agreement with these experimental results. Based on our experimental and theoretical findings, we offer an explanation of the observed mass dependence of the level densities in terms of the intrinsic single-particle level density and the collective enhancement., 7 pages, 4 figures
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- 2021
4. Impact of Restricted Spin-Ranges in the Oslo Method: The Example of (d,p)240Pu
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L. Crespo Campo, D. L. Bleuel, T. K. Eriksen, Gry Merete Tveten, Therese Renstrøm, E. Sahin, Andreas Görgen, M. Wiedeking, Gregory Potel, T. A. Laplace, F. L. Bello Garrote, A. C. Larsen, J. E. Midtbø, Magne Guttormsen, K. Hadynska-Klek, Bethany L. Goldblum, Alexander Voinov, L. A. Bernstein, Sunniva Siem, Tamas Gabor Tornyi, and Fabio Zeiser
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Physics ,Distribution (number theory) ,010308 nuclear & particles physics ,Strength function ,Cyclotron ,01 natural sciences ,law.invention ,Nuclear physics ,Deuterium ,law ,0103 physical sciences ,Nuclear Experiment ,010306 general physics ,Radioactive decay ,Beam (structure) ,Spin-½ - Abstract
In this paper we present the first systematic analysis of the impact of the populated vs. intrinsic spin distribution on the nuclear level density and γ-ray strength function retrieved through the Oslo Method. We illustrate the effect of the spin distribution on the recently performed 239Pu(d,pγ)240Pu experiment using a 12 MeV deuteron beam performed at the Oslo Cyclotron Lab. In the analysis we couple state-of-the-art calculations for the populated spin-distributions with the Monte-Carlo nuclear decay code RAINIER to compare Oslo Method results to the known input. We find that good knowledge of the populated spin distribution is crucial and show that the populated distribution has a significant impact on the extracted nuclear level density and γ-ray strength function for the 239Pu(d,pγ)240Pu case.
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- 2020
5. Radiative Width of the Hoyle State from γ-Ray Spectroscopy
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Tamas Gabor Tornyi, Therese Renstrøm, Andreas Görgen, M. Klintefjord, B. Alshahrani, Magne Guttormsen, Gry Merete Tveten, Tibor Kibedi, Andrew Stuchbery, L. Crespo Campo, Hilde-Therese Nyhus, Ann-Cecilie Larsen, Sunniva Siem, S. Maharramova, A. I. Morales, F. L. Bello Garrote, F. Giacoppo, W. Paulsen, E. Sahin, and T. K. Eriksen
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Physics ,Branching fraction ,Astrophysics::High Energy Astrophysical Phenomena ,General Physics and Astronomy ,State (functional analysis) ,01 natural sciences ,13. Climate action ,Nucleosynthesis ,Excited state ,0103 physical sciences ,Quadrupole ,Radiative transfer ,Atomic physics ,010306 general physics ,Spectroscopy ,Energy (signal processing) - Abstract
The cascading 3.21 and 4.44 MeV electric quadrupole transitions have been observed from the Hoyle state at 7.65 MeV excitation energy in $^{12}\mathrm{C}$, excited by the $^{12}\mathrm{C}(p,{p}^{\ensuremath{'}})$ reaction at 10.7 MeV proton energy. From the proton-$\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ triple coincidence data, a value of ${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{rad}}/\mathrm{\ensuremath{\Gamma}}=6.2(6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ was obtained for the radiative branching ratio. Using our results, together with ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\pi}}^{E0}/\mathrm{\ensuremath{\Gamma}}$ from Eriksen et al. [Phys. Rev. C 102, 024320 (2020)] and the currently adopted ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\pi}}(E0)$ values, the radiative width of the Hoyle state is determined as ${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{rad}}=5.1(6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }\mathrm{eV}$. This value is about 34% higher than the currently adopted value and will impact models of stellar evolution and nucleosynthesis.
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- 2019
6. Co69,71 β -decay strength distributions from total absorption spectroscopy
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Matthew Mumpower, C. J. Prokop, Shea Mosby, Mallory Smith, D. L. Bleuel, A. Spyrou, S. J. Quinn, Aaron Couture, F. Naqvi, A. Palmisano, Magne Guttormsen, Sean Liddick, L. Crespo Campo, G. Perdikakis, B. A. Brown, A. C. Larsen, R. Lewis, Benjamin P. Crider, Sunniva Siem, Alexander Dombos, Stephanie Lyons, E. M. Ney, Peter Möller, Jonathan Engel, and Therese Renstrøm
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Physics ,Total absorption spectroscopy ,010308 nuclear & particles physics ,Center (category theory) ,Electron ,01 natural sciences ,7. Clean energy ,Particle identification ,Ion ,Nuclear physics ,Nucleosynthesis ,0103 physical sciences ,Neutron ,010306 general physics ,Random phase approximation - Abstract
Background: The rapid neutron capture process is one of the main nucleosynthesis processes of elements heavier than Fe. Uncertainties in nuclear properties, such as masses, half-lives, and $\ensuremath{\beta}$-delayed neutron probabilities can cause orders of magnitude of variation within astrophysical $r$-process simulations. Presently, theoretical models are used to make global predictions of various nuclear properties for the thousands of nuclei required for these simulations, and measurements are required to benchmark these models, especially far from stability.Purpose: $\ensuremath{\beta}$-decay strength distributions can be used to not only inform astrophysical $r$-process simulations, but also to provide a stringent test for theoretical calculations. The aim of this work is to provide accurate strength distributions for $^{69,71}\mathrm{Co}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$ decay.Method: The technique of total absorption spectroscopy was used to measure the $\ensuremath{\beta}$ decay of $^{69,71}\mathrm{Co}$ for the first time at the National Superconducting Cyclotron Laboratory. The ions were implanted in a double-sided silicon strip detector at the center of the Summing NaI(Tl) detector and identified using standard particle identification methods. The response of the detection system to the $\ensuremath{\beta}$-decay electron and subsequent $\ensuremath{\gamma}$-ray radiation was fit to the observed experimental data using a ${\ensuremath{\chi}}^{2}$-minimization technique.Results: $\ensuremath{\beta}$-feeding intensities and Gamow-Teller strength distributions were extracted from the fits of the experimental data. The $\ensuremath{\beta}$-decay intensities show that there is a large percentage of feeding to levels above 2 MeV, which have not been observed in previous studies. The resultant $\ensuremath{\beta}$-feeding intensities and Gamow-Teller strength distributions were compared to shell model and quasiparticle random phase approximation (QRPA) calculations.Conclusions: Comparing experimentally determined $\ensuremath{\beta}$-decay strength distributions provides a test of models, which are commonly used for global $\ensuremath{\beta}$-decay properties for astrophysical calculations. This work highlights the importance of performing detailed comparisons of models to experimental data, particularly far from stability and as close to the $r$-process path as possible.
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- 2019
7. Restricted spin-range correction in the Oslo method: The example of nuclear level density and γ -ray strength function from Pu239(d,pγ)Pu240
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L. A. Bernstein, T. K. Eriksen, E. Sahin, Fabio Zeiser, J. N. Wilson, J. E. Midtbø, Gregory Potel, Gry Merete Tveten, Tamas Gabor Tornyi, T. A. Laplace, V. W. Ingeberg, A. C. Larsen, Bethany L. Goldblum, Alexander Voinov, L. Crespo Campo, F. L. Bello Garrote, M. Wiedeking, Sunniva Siem, Magne Guttormsen, K. Hadynska-Klek, D. L. Bleuel, and Andreas Görgen
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Physics ,education.field_of_study ,Range (particle radiation) ,010308 nuclear & particles physics ,Strength function ,Population ,Cyclotron ,01 natural sciences ,law.invention ,Deuterium ,law ,0103 physical sciences ,Spin transfer ,Atomic physics ,Nuclear Experiment ,010306 general physics ,education ,Spin (physics) ,Radioactive decay - Abstract
The Oslo method has been applied to particle-$\ensuremath{\gamma}$ coincidences following the $^{239}\mathrm{Pu}(d,p)$ reaction to obtain the nuclear level density (NLD) and $\ensuremath{\gamma}$-ray strength function ($\ensuremath{\gamma}\mathrm{SF}$) of $^{240}\mathrm{Pu}$. The experiment was conducted with a 12 MeV deuteron beam at the Oslo Cyclotron Laboratory. The low spin transfer of this reaction leads to a spin-parity mismatch between populated and intrinsic levels. This is a challenge for the Oslo method as it can have a significant impact on the extracted NLD and $\ensuremath{\gamma}\mathrm{SF}$. We have developed an iterative approach to ensure consistent results even for cases with a large spin-parity mismatch, in which we couple Green's function transfer calculations of the spin-parity dependent population cross-section to the nuclear decay code rainier. The resulting $\ensuremath{\gamma}\mathrm{SF}$ shows a pronounced enhancement between 2--4 MeV that is consistent with the location of the low-energy orbital $M1$ scissors mode.
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- 2019
8. First experimental constraint on the Os191(n,γ) reaction rate relevant to s -process nucleosynthesis
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I. K. B. Kullmann, K. S. Beckmann, Fabio Zeiser, E. Sahin, Magne Guttormsen, Gry Merete Tveten, L. Crespo Campo, Sunniva Siem, A. C. Larsen, Therese Renstrøm, Andreas Görgen, F. L. Bello Garrote, and J. E. Midtbø
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Reaction rate ,Physics ,010308 nuclear & particles physics ,Nucleosynthesis ,0103 physical sciences ,Neutron ,Atomic physics ,010306 general physics ,s-process ,7. Clean energy ,01 natural sciences ,Energy (signal processing) - Abstract
The nuclear level density and $\ensuremath{\gamma}$-decay strength of $^{192}\mathrm{Os}$ have been extracted using particle-$\ensuremath{\gamma}$ coincidence data from the $^{192}\mathrm{Os}(\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{\gamma})^{192}\mathrm{Os}$ 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 $\ensuremath{\gamma}$-decay strength is compared to photoneutron cross-section data above the neutron separation energy, and to $E1$ and $M1$ 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 $\ensuremath{\gamma}$-strength function in the range ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}1.5--6\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$. Using the measured nuclear level density and $\ensuremath{\gamma}$-decay strength as input to the nuclear-reaction code talys, we provide the first experimentally constrained Maxwellian-averaged cross section (MACS) for the $^{191}\mathrm{Os}(n,\ensuremath{\gamma})^{192}\mathrm{Os}$ reaction relevant to $s$-process nucleosynthesis. The systematic uncertainties introduced by the normalization procedure of the level density and $\ensuremath{\gamma}$-strength function were investigated and propagated to the calculated Maxwellian-averaged cross section. The obtained result of the Maxwellian-averaged cross section at ${k}_{B}T=30\phantom{\rule{0.28em}{0ex}}\mathrm{keV}$, ${\ensuremath{\langle}\ensuremath{\sigma}\ensuremath{\rangle}}_{n,\ensuremath{\gamma}}=1134\ifmmode\pm\else\textpm\fi{}375\phantom{\rule{0.28em}{0ex}}\mathrm{mb}$, 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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- 2019
9. Experimental constraints on the Zn73(n,γ)Zn74 reaction rate
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Sunniva Siem, Benjamin P. Crider, Therese Renstrøm, Sean Liddick, Alexander Dombos, A. Spyrou, G. Perdikakis, L. Crespo Campo, C. J. Prokop, S. J. Quinn, F. Naqvi, Shea Mosby, Aaron Couture, R. Lewis, A. C. Larsen, D. L. Bleuel, and Magne Guttormsen
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Physics ,Total absorption spectroscopy ,010308 nuclear & particles physics ,Astrophysics::High Energy Astrophysical Phenomena ,Strength function ,01 natural sciences ,Reaction rate ,Superconducting cyclotron ,0103 physical sciences ,Neutron ,Production (computer science) ,Atomic physics ,Nuclear Experiment ,010306 general physics - Abstract
Background: The recent observation of a neutron-star merger finally confirmed one astrophysical location of the rapid neutron-capture process (r-process). Evidence of the production of $Al140$ nuclei was seen, but there is still little detailed information about how those lighter elements are produced in such an environment. Many of the questions surrounding the $A\ensuremath{\approx}80$ nuclei are likely to be answered only when the nuclear physics involved in the production of r-process nuclei is well understood. Neutron-capture reactions are an important component of the r-process, and neutron-capture cross sections of r-process nuclei, which are very neutron rich, have large uncertainties.Purpose: Indirectly determine the neutron-capture cross section and reaction rate of $^{73}\mathrm{Zn}(n,\ensuremath{\gamma})^{74}\mathrm{Zn}$.Methods: The nuclear level density (NLD) and $\ensuremath{\gamma}$-ray strength function ($\ensuremath{\gamma}\mathrm{SF}$) of $^{74}\mathrm{Zn}$ were determined following a total absorption spectroscopy (TAS) experiment focused on the $\ensuremath{\beta}$ decay of $^{74}\mathrm{Cu}$ into $^{74}\mathrm{Zn}$ performed at the National Superconducting Cyclotron Laboratory. The NLD and $\ensuremath{\gamma}\mathrm{SF}$ were used as inputs in a Hauser-Feshbach statistical model to calculate the neutron-capture cross section and reaction rate.Results: The NLD and $\ensuremath{\gamma}\mathrm{SF}$ of $^{74}\mathrm{Zn}$ were experimentally constrained for the first time using $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$ rays measured with TAS and the $\ensuremath{\beta}$-Oslo method. The NLD and $\ensuremath{\gamma}\mathrm{SF}$ were then used to constrain the neutron-capture cross section and reaction rate for the $^{73}\mathrm{Zn}(n,\ensuremath{\gamma})^{74}\mathrm{Zn}$ reaction.Conclusions: The uncertainty in the neutron-capture cross section and reaction rate of $^{73}\mathrm{Zn}(n,\ensuremath{\gamma})^{74}\mathrm{Zn}$ calculated in TALYS was reduced to under a factor of 2 from a factor of 5 in the cross section and a factor of 11 in the reaction rate using the experimentally obtained NLD and $\ensuremath{\gamma}\mathrm{SF}$.
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- 2019
10. Benchmarking the extraction of statistical neutron capture cross sections on short-lived nuclei for applications using the β-Oslo method
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Therese Renstrøm, S. J. Quinn, V. W. Ingeberg, F. Naqvi, Fabio Zeiser, B. V. Kheswa, E. Sahin, R. Lewis, Magne Guttormsen, S. J. Rose, L. Crespo Campo, D. L. Bleuel, Trine Wiborg Hagen, S. Mosby, C. J. Prokop, Ann-Cecilie Larsen, Sean Liddick, F. L. Bello Garrote, J. E. Midtbø, K. Hadynska-Klek, Andreas Görgen, M. Wiedeking, A. Spyrou, Aaron Couture, B. P. Crider, Alexander Dombos, F. Giacoppo, Gry Merete Tveten, Sunniva Siem, and G. Perdikakis
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Nuclear physics ,Physics ,Neutron capture ,010308 nuclear & particles physics ,0103 physical sciences ,Extraction (chemistry) ,Nuclear Theory ,Benchmarking ,010306 general physics ,Nuclear Experiment ,7. Clean energy ,01 natural sciences - Abstract
Numerous scientific fields including astrophysics, nuclear power, and nuclear forensics require a knowledge of basic nuclear properties for large numbers of short-lived, radioactive isotopes far removed from stable nuclei. Neutron-capture cross sections are one such piece of nuclear data where direct measurements are not possible and theoretical predictions can vary by orders of magnitude. A recently developed indirect technique for inferring neutron capture rates, the β -Oslo method, has been introduced but not compared against a known, directly measured neutron capture cross section. To provide this benchmark, two indirect methods based on β decay and charged-particle reactions were used to extract the nuclear level density and γ -ray strength function of 51 Ti . The nuclear level density and γ -ray strength function from the two data sets were found to be equivalent and were used to extract the neutron capture cross section of 50 Ti which agrees with previous direct measurements at high neutron energies. The results demonstrate the validity of the β -Oslo method for extracting neutron capture cross sections of short-lived nuclei and provide a sufficiently small uncertainty to be used in various applications.
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- 2019
11. Test of the generalized Brink-Axel hypothesis in Ni64,65
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M. Klintefjord, Andreas Görgen, Gry Merete Tveten, A. C. Larsen, F. L. Bello Garrote, A. Springer, Magne Guttormsen, K. Hadynska-Klek, F. Giacoppo, Sunniva Siem, E. Sahin, T. K. Eriksen, T. G. Tornyi, Therese Renstrøm, and L. Crespo Campo
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Physics ,010308 nuclear & particles physics ,Research council ,0103 physical sciences ,010306 general physics ,01 natural sciences ,Management ,Test (assessment) - Abstract
We are also grateful for the financial support received from the Research Council of Norway (NFR). S.S. and G.M.T. acknowledge funding under NFR project Grants No. 210007 and No. 262952/F20. A.C.L. acknowledges financial support from the ERC-STG2014 under Grant No. 637686.
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- 2018
12. Lifetime measurements in Nd138
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Tamas Gabor Tornyi, C. R. Nita, T. Marchlewski, C. Mihai, Therese Renstrøm, Ioana Gheorghe, N. Florea, D. M. Filipescu, Michel Girod, Andreas Görgen, L. Crespo Campo, R. Lica, T. Abraham, D. Ghita, Anna Stolarz, N. Marginean, S. Toma, J. P. Delaroche, T. Glodariu, E. Sahin, J. Srebrny, A. Tucholski, R. Mărginean, Sunniva Siem, A. Olacel, F. Nowacki, S. Pascu, F. L. Bello Garrote, L. Stroe, M. Klintefjord, A. Negret, K. Hadyńska-Klȩk, J. Libert, and I. O. Mitu
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Physics ,Deformation (mechanics) ,Isotope ,010308 nuclear & particles physics ,Nuclear Theory ,Shell (structure) ,01 natural sciences ,symbols.namesake ,Atomic orbital ,13. Climate action ,Excited state ,0103 physical sciences ,symbols ,Neutron ,Atomic physics ,Nuclear Experiment ,010306 general physics ,Doppler effect ,Mixing (physics) - Abstract
Lifetimes of several short-lived excited states in Nd138 were measured with the ROSPHERE array at IFIN-HH, Bucharest, using the recoil-distance Doppler shift technique following the Sb123(F19,4n) reaction. The resulting electromagnetic transition probabilities are compared to large-scale shell model calculations and to constrained Hartree-Fock-Bogoliubov calculations with the Gogny D1S interaction, configuration mixing, and a five-dimensional collective Hamiltonian formalism. The onset of collectivity in Nd isotopes below the N=82 shell closure and the deformation induced by the alignment of protons and neutron holes in the h11/2 orbitals are discussed.
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- 2018
13. Enhanced low-energy γ-decay strength of Ni70 and its robustness within the shell model
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Sunniva Siem, J. E. Midtbø, A. C. Larsen, A. Spyrou, F. Naqvi, G. Perdikakis, L. Crespo Campo, Alexander Dombos, Shea Mosby, Therese Renstrøm, R. Lewis, Aaron Couture, Sergei Kamerdzhiev, Benjamin P. Crider, S. Karampagia, Sean Liddick, Magne Guttormsen, D. L. Bleuel, O. Achakovskiy, S. J. Quinn, C. J. Prokop, and B. A. Brown
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Physics ,010308 nuclear & particles physics ,Astrophysics::High Energy Astrophysical Phenomena ,Nuclear Theory ,SHELL model ,Space (mathematics) ,01 natural sciences ,Low energy ,Nucleosynthesis ,0103 physical sciences ,Quasiparticle ,Radiative transfer ,Atomic physics ,Nuclear Experiment ,010306 general physics ,Nuclear theory - Abstract
Neutron-capture reactions on very neutron-rich nuclei are essential for heavy-element nucleosynthesis through the rapid neutron-capture process, now shown to take place in neutron-star merger events. For these exotic nuclei, radiative neutron capture is extremely sensitive to their $\ensuremath{\gamma}$-emission probability at very low $\ensuremath{\gamma}$ energies. In this work, we present measurements of the $\ensuremath{\gamma}\text{-decay}$ strength of $^{70}\mathrm{Ni}$ over the wide range $1.3\ensuremath{\le}{E}_{\ensuremath{\gamma}}\ensuremath{\le}8$ MeV. A significant enhancement is found in the $\ensuremath{\gamma}\text{-decay}$ strength for transitions with ${E}_{\ensuremath{\gamma}}l3$ MeV. At present, this is the most neutron-rich nucleus displaying this feature, proving that this phenomenon is not restricted to stable nuclei. We have performed $E1$-strength calculations within the quasiparticle time-blocking approximation, which describe our data above ${E}_{\ensuremath{\gamma}}\ensuremath{\simeq}5$ MeV very well. Moreover, large-scale shell-model calculations indicate an $M1$ nature of the low-energy $\ensuremath{\gamma}$ strength. This turns out to be remarkably robust with respect to the choice of interaction, truncation, and model space, and we predict its presence in the whole isotopic chain, in particular the neutron-rich $^{72,74,76}\mathrm{Ni}$.
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- 2018
14. Gamma-widths, lifetimes and fluctuations in the nuclear quasi-continuum
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V. W. Ingeberg, L. E. Kirsch, L. Crespo Campo, Ann-Cecilie Larsen, Gry Merete Tveten, Fabio Zeiser, Therese Renstrøm, J. E. Midtbø, Sunniva Siem, Andreas Görgen, and Magne Guttormsen
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Physics ,Continuum (measurement) ,010308 nuclear & particles physics ,Strength function ,Astrophysics::High Energy Astrophysical Phenomena ,QC1-999 ,Binding energy ,Nuclear Theory ,Nuclear structure ,FOS: Physical sciences ,01 natural sciences ,Reaction rate ,Neutron star ,13. Climate action ,Excited state ,0103 physical sciences ,Neutron ,Atomic physics ,Nuclear Experiment (nucl-ex) ,010306 general physics ,Nuclear Experiment - Abstract
Statistical $\gamma$-decay from highly excited states is determined by the nuclear level density (NLD) and the $\gamma$-ray strength function ($\gamma$SF). These average quantities have been measured for several nuclei using the Oslo method. For the first time, we exploit the NLD and $\gamma$SF to evaluate the $\gamma$-width in the energy region below the neutron binding energy, often called the quasi-continuum region. The lifetimes of states in the quasi-continuum are important benchmarks for a theoretical description of nuclear structure and dynamics at high temperature. The lifetimes may also have impact on reaction rates for the rapid neutron-capture process, now demonstrated to take place in neutron star mergers., Comment: CGS16, Shanghai 2017, Proceedings, 5 pages, 3 figures
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- 2018
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15. Investigating the γ decay of Ni65 from particle- γ coincidence data
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Therese Renstrøm, E. Sahin, A. C. Larsen, Magne Guttormsen, L. Crespo Campo, Andreas Görgen, M. Klintefjord, F. L. Bello Garrote, T. G. Tornyi, Gry Merete Tveten, F. Giacoppo, Sunniva Siem, and T. K. Eriksen
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Physics ,010308 nuclear & particles physics ,Astrophysics::High Energy Astrophysical Phenomena ,0103 physical sciences ,Nuclear structure ,Particle ,Atomic physics ,010306 general physics ,01 natural sciences ,Coincidence ,Excitation ,Spectral line - Abstract
The $\ensuremath{\gamma}$ decay of $^{65}\mathrm{Ni}$ has been studied from particle-$\ensuremath{\gamma}$ coincidence data on the $^{64}\mathrm{Ni}(d,p\ensuremath{\gamma})^{65}\mathrm{Ni}$ reaction. $\ensuremath{\gamma}$-ray spectra at excitation energies below ${E}_{x}\ensuremath{\approx}2\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$ have been studied and compared with previous measurements. Coincidences corresponding to ${E}_{x}\ensuremath{\approx}4.4--6.1\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$ have been used to constrain the shape of the nuclear level density and $\ensuremath{\gamma}$-strength function of $^{65}\mathrm{Ni}$ by means of the Oslo method. The experimental $\ensuremath{\gamma}$-strength function presents an enhancement at $\ensuremath{\gamma}$ energies below ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}3\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$. In addition, a resonance-like structure centered at ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}4.6\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$ is seen together with accumulated strength at ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}2.6--3.6\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$. The obtained results contribute to the systematic study of $\ensuremath{\gamma}$ decay in the Ni isotopes, which is of great interest for the understanding of both single-particle and collective nuclear structure phenomena.
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- 2017
16. Energy dependence of the promptγ-ray emission from the(d,p)-induced fission ofU*234andPu*240
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Therese Renstrøm, S. J. Rose, Magne Guttormsen, J. N. Wilson, JA Brown, A Hafreager, K Hadyńska, Fabio Zeiser, E. Sahin, L. Crespo Campo, Stephan Oberstedt, D. L. Bleuel, T. A. Laplace, Tamas Gabor Tornyi, Andreas Görgen, Sunniva Siem, C. Schmitt, F. Giacoppo, Trine Wiborg Hagen, Gry Merete Tveten, A. C. Larsen, M. Wiedeking, Andreas Oberstedt, L. A. Bernstein, and M. Klintefjord
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Physics ,Work (thermodynamics) ,010308 nuclear & particles physics ,Fission ,7. Clean energy ,01 natural sciences ,Neutron temperature ,Spectral line ,Excited state ,0103 physical sciences ,Total energy ,Atomic physics ,010306 general physics ,Excitation ,Energy (signal processing) - Abstract
Author(s): Rose, SJ; Zeiser, F; Wilson, JN; Oberstedt, A; Oberstedt, S; Siem, S; Tveten, GM; Bernstein, LA; Bleuel, DL; Brown, JA; Crespo Campo, L; Giacoppo, F; Gorgen, A; Guttormsen, M; Hadynska, K; Hafreager, A; Hagen, TW; Klintefjord, M; Laplace, TA; Larsen, AC; Renstrom, T; Sahin, E; Schmitt, C; Tornyi, TG; Wiedeking, M | Abstract: Prompt-fission γ rays are responsible for approximately 5% of the total energy released in fission, and therefore important to understand when modeling nuclear reactors. In this work we present prompt γ-ray emission characteristics in fission as a function of the nuclear excitation energy of the fissioning system. Emitted γ-ray spectra were measured, and γ-ray multiplicities and average and total γ energies per fission were determined for the U(d,pf)233 reaction for excitation energies between 4.8 and 10 MeV, and for the Pu(d,pf)239 reaction between 4.5 and 9 MeV. The spectral characteristics show no significant change as a function of excitation energy above the fission barrier, despite the fact that an extra ∼5 MeV of energy is potentially available in the excited fragments for γ decay. The measured results are compared with model calculations made for prompt γ-ray emission with the fission model code gef. Further comparison with previously obtained results from thermal neutron induced fission is made to characterize possible differences arising from using the surrogate (d,p) reaction.
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- 2017
17. Low-energy enhancement and fluctuations of γ-ray strength functions in 56,57Fe: test of the Brink–Axel hypothesis
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S. J. Rose, Trine Wiborg Hagen, Gry Merete Tveten, L. Crespo Campo, V. W. Ingeberg, Tamas Gabor Tornyi, T. K. Eriksen, B. Million, I. E. Ruud, F. Camera, Hilde-Therese Nyhus, Andreas Görgen, Alexander Voinov, Therese Renstrøm, S. Leoni, Magne Guttormsen, J. E. Midtbø, A. Bracco, Sunniva Siem, N. Blasi, M. Wiedeking, A. C. Larsen, Fabio Zeiser, and B. V. Kheswa
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Physics ,Nuclear and High Energy Physics ,010308 nuclear & particles physics ,Strength function ,Astrophysics::High Energy Astrophysical Phenomena ,Resolution (electron density) ,Gamma ray ,Function (mathematics) ,01 natural sciences ,Dipole ,Low energy ,0103 physical sciences ,Atomic physics ,010306 general physics ,Nuclear Experiment ,Excitation ,Energy (signal processing) - Abstract
Nuclear level densities and $\gamma$-ray strength functions of $^{56,57}$Fe have been extracted from proton-$\gamma$ coincidences. A low-energy enhancement in the $\gamma$-ray strength functions up to a factor of 30 over common theoretical E1 models is confirmed. Angular distributions of the low-energy enhancement in $^{57}$Fe indicate its dipole nature, in agreement with findings for $^{56}$Fe. The high statistics and the excellent energy resolution of the large-volume LaBr$_{3}$(Ce) detectors allowed for a thorough analysis of $\gamma$ strength as function of excitation energy. Taking into account the presence of strong Porter-Thomas fluctuations, there is no indication of any significant excitation-energy dependence in the $\gamma$-ray strength function, in support of the generalized Brink-Axel hypothesis., Comment: 24 pages, 17 figures, accepted for publication in J. Phys. G: Nucl. Phys; Special Issue
- Published
- 2017
18. Neutron-capture rates for explosive nucleosynthesis: the case of 68 Ni( n , γ ) 69 Ni
- Author
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G. Perdikakis, Rebecca Lewis, D. L. Bleuel, Sunniva Siem, F. Naqvi, C. J. Prokop, Therese Renstrøm, S. J. Quinn, L. Crespo Campo, Ann-Cecilie Larsen, Magne Guttormsen, Aaron Couture, Alexander Dombos, A. Spyrou, Sean Liddick, Matthew Mumpower, Benjamin P. Crider, Shea Mosby, and Rebecca Surman
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Nuclear reaction ,Physics ,Nuclear and High Energy Physics ,010308 nuclear & particles physics ,01 natural sciences ,7. Clean energy ,Nuclear physics ,Reaction rate ,Neutron capture ,Nucleosynthesis ,Excited state ,0103 physical sciences ,Nuclear astrophysics ,r-process ,Atomic physics ,010306 general physics ,Radioactive decay - Abstract
Neutron-capture reactions play an important role in heavy element nucleosynthesis, since they are the driving force for the two processes that create the vast majority of the heavy elements. When a neutron capture occurs on a short-lived nucleus, it is extremely challenging to study the reaction directly and therefore the use of indirect techniques is essential. The present work reports on such an indirect measurement that provides strong constraints on the 68Ni(n, γ)69Ni reaction rate. This is done by populating the compound nucleus 69Ni via the β decay of 69Co and measuring the γ-ray deexcitation of excited states in 69Ni. The β-Oslo method was used to extract the γ-ray strength function and the nuclear level density. In addition the half-life of 69Co was extracted and found to be in agreement with previous literature values. Before the present results, the 68Ni(n, γ)69Ni reaction was unconstrained and the purely theoretical reaction rate was highly uncertain. The new uncertainty on the reaction rate based on the present experiment (variation between upper and lower limit) is approximately a factor of 3. The commonly used reaction libraries JINA-REACLIB and BRUSLIB are in relatively good agreement with the experimental rate. The impact of the new rate on weak r-process calculations is discussed. This research was first published in Journal of Physics G: Nuclear and Particle Physics. © IOP Publishing.
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- 2017
- Full Text
- View/download PDF
19. Statistical γ -decay properties of Ni64 and deduced ( n,γ ) cross section of the s -process branch-point nucleus Ni63
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L. Crespo Campo, F. L. Bello Garrote, T. K. Eriksen, E. Sahin, Andreas Görgen, Sunniva Siem, Therese Renstrøm, Tamas Gabor Tornyi, A. Springer, Magne Guttormsen, K. Hadynska-Klek, Gry Merete Tveten, M. Klintefjord, and A. C. Larsen
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Physics ,010308 nuclear & particles physics ,Astrophysics::High Energy Astrophysical Phenomena ,01 natural sciences ,Nuclear physics ,Cross section (physics) ,medicine.anatomical_structure ,0103 physical sciences ,medicine ,Atomic physics ,Nuclear Experiment ,010306 general physics ,s-process ,Nucleus ,Energy (signal processing) ,Excitation - Abstract
Particle-$\ensuremath{\gamma}$ coincidence data have been analyzed to obtain the nuclear level density and the $\ensuremath{\gamma}$-strength function of $^{64}\mathrm{Ni}$ by means of the Oslo method. The level density found in this work is in very good agreement with known energy levels at low excitation energies as well as with data deduced from particle-evaporation measurements at excitation energies above ${E}_{x}\ensuremath{\approx}5.5$ MeV. The experimental $\ensuremath{\gamma}$-strength function presents an enhancement at $\ensuremath{\gamma}$ energies below ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}3$ MeV and possibly a resonancelike structure centered at ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}9.2$ MeV. The obtained nuclear level density and $\ensuremath{\gamma}$-strength function have been used to estimate the $(n,\ensuremath{\gamma})$ cross section for the $s$-process branch-point nucleus $^{63}\mathrm{Ni}$, of particular interest for astrophysical calculations of elemental abundances.
- Published
- 2016
20. Strong Neutron-γCompetition above the Neutron Threshold in the Decay ofCo70
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Benjamin P. Crider, S. Valenta, Alexander Dombos, G. Perdikakis, Magne Guttormsen, F. Naqvi, A. Spyrou, B. A. Brown, A. C. Larsen, Aaron Couture, D. L. Bleuel, S. J. Quinn, R. Lewis, C. J. Prokop, L. Crespo Campo, Peter Möller, Sunniva Siem, Sean Liddick, Therese Renstrøm, Matthew Mumpower, and Shea Mosby
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Physics ,Total absorption spectroscopy ,010308 nuclear & particles physics ,Neutron emission ,Nuclear Theory ,Nuclear structure ,General Physics and Astronomy ,01 natural sciences ,7. Clean energy ,Nuclear physics ,Nucleosynthesis ,0103 physical sciences ,Neutron cross section ,Quasiparticle ,Neutron ,010306 general physics ,Random phase approximation - Abstract
The $\ensuremath{\beta}$-decay intensity of $^{70}\mathrm{Co}$ was measured for the first time using the technique of total absorption spectroscopy. The large $\ensuremath{\beta}$-decay $Q$ value [12.3(3) MeV] offers a rare opportunity to study $\ensuremath{\beta}$-decay properties in a broad energy range. Two surprising features were observed in the experimental results, namely, the large fragmentation of the $\ensuremath{\beta}$ intensity at high energies, as well as the strong competition between $\ensuremath{\gamma}$ rays and neutrons, up to more than 2 MeV above the neutron-separation energy. The data are compared to two theoretical calculations: the shell model and the quasiparticle random phase approximation (QRPA). Both models seem to be missing a significant strength at high excitation energies. Possible interpretations of this discrepancy are discussed. The shell model is used for a detailed nuclear structure interpretation and helps to explain the observed $\ensuremath{\gamma}$-neutron competition. The comparison to the QRPA calculations is done as a means to test a model that provides global $\ensuremath{\beta}$-decay properties for astrophysical calculations. Our work demonstrates the importance of performing detailed comparisons to experimental results, beyond the simple half-life comparisons. A realistic and robust description of the $\ensuremath{\beta}$-decay intensity is crucial for our understanding of nuclear structure as well as of $r$-process nucleosynthesis.
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- 2016
21. Completing the nuclear reaction puzzle of the nucleosynthesis of Mo 92
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L. A. Bernstein, S. J. Rose, Trine Wiborg Hagen, F. L. Bello Garrote, A. Spyrou, T. K. Eriksen, Gry Merete Tveten, Magne Guttormsen, K. Hadynska-Klek, F. Giacoppo, Ronald Schwengner, Bradley S. Meyer, D. L. Bleuel, M. Klintefjord, F. Naqvi, Andreas Görgen, Hilde-Therese Nyhus, Therese Renstrøm, E. Sahin, T. G. Tornyi, L. Crespo Campo, Ann-Cecilie Larsen, and Sunniva Siem
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Nuclear reaction ,Strength function ,FOS: Physical sciences ,strength function ,nucl-ex ,01 natural sciences ,Nuclear physics ,Reaction rate ,reaction rate ,Nucleosynthesis ,0103 physical sciences ,Nuclear Experiment (nucl-ex) ,010306 general physics ,Nuclear Experiment ,Physics ,Isotope ,010308 nuclear & particles physics ,P-nuclei ,nucleosynthesis ,Nuclear data ,p-process ,Supernova ,solar abundance ,13. Climate action ,Anomaly (physics) - Abstract
One of the greatest questions for modern physics to address is how elements heavier than iron are created in extreme, astrophysical environments. A particularly challenging part of that question is the creation of the so-called p-nuclei, which are believed to be mainly produced in some types of supernovae. The lack of needed nuclear data presents an obstacle in nailing down the precise site and astrophysical conditions. In this work, we present for the first time measurements on the nuclear level density and average strength function of $^{92}$Mo. State-of-the-art p-process calculations systematically underestimate the observed solar abundance of this isotope. Our data provide stringent constraints on the $^{91}$Nb$(p,{\gamma})^{92}$Mo reaction rate, which is the last unmeasured reaction in the nucleosynthesis puzzle of $^{92}$Mo. Based on our results, we conclude that the $^{92}$Mo abundance anomaly is not due to the nuclear physics input to astrophysical model calculations., Comment: Submitted to PRC
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- 2016
22. Statistical properties ofPu243, andPu242(n,γ)cross section calculation
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M. Wiedeking, Gry Merete Tveten, J. N. Wilson, Magne Guttormsen, F. L. Bello Garotte, L. Crespo Campo, S. J. Rose, Ann-Cecilie Larsen, Sunniva Siem, D. L. Bleuel, K. Hadyńska-Klȩk, Therese Renstrøm, T. A. Laplace, Andreas Görgen, Fabio Zeiser, Tamas Gabor Tornyi, F. Giacoppo, Roger Henderson, E. Sahin, T. K. Eriksen, Walid Younes, J. A. Brown, Bethany L. Goldblum, L. A. Bernstein, M. Lebois, Alexander Voinov, and M. Klintefjord
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Physics ,Isotope ,010308 nuclear & particles physics ,7. Clean energy ,01 natural sciences ,Omega ,Resonance (particle physics) ,Neutron temperature ,Cross section (physics) ,Pairing ,Excited state ,0103 physical sciences ,Atomic physics ,Nuclear Experiment ,010306 general physics ,Excitation - Abstract
The level density and gamma-ray strength function (gammaSF) of 243Pu have been measured in the quasi-continuum using the Oslo method. Excited states in 243Pu were populated using the 242Pu(d,p) reaction. The level density closely follows the constant-temperature level density formula for excitation energies above the pairing gap. The gammaSF displays a double-humped resonance at low energy as also seen in previous investigations of actinide isotopes. The structure is interpreted as the scissors resonance and has a centroid of omega_{SR}=2.42(5)MeV and a total strength of B_{SR}=10.1(15)mu_N^2, which is in excellent agreement with sum-rule estimates. The measured level density and gammaSF were used to calculate the 242Pu(n,gamma) cross section in a neutron energy range for which there were previously no measured data.
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- 2016
23. Experimental Neutron Capture Rate Constraint Far from Stability
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L. Crespo Campo, Ann-Cecilie Larsen, A. Spyrou, Matthew Mumpower, Georgios Perdikakis, Shea Mosby, Benjamin P. Crider, Stylianos Nikas, F. Naqvi, D. L. Bleuel, S. J. Quinn, Sean Liddick, Therese Renstrøm, B. Rubio, C. J. Prokop, Rebecca Lewis, Alexander Dombos, Rebecca Surman, Aaron Couture, Sunniva Siem, and Magne Guttormsen
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Nuclear reaction ,Physics ,010308 nuclear & particles physics ,Stable isotope ratio ,Astrophysics::High Energy Astrophysical Phenomena ,Nuclear Theory ,General Physics and Astronomy ,7. Clean energy ,01 natural sciences ,Stability (probability) ,Nuclear physics ,Neutron capture ,Orders of magnitude (time) ,13. Climate action ,Valley of stability ,Nucleosynthesis ,0103 physical sciences ,Neutron ,Nuclear Experiment ,010306 general physics - Abstract
Nuclear reactions where an exotic nucleus captures a neutron are critical for a wide variety of applications, from energy production and national security, to astrophysical processes, and nucleosynthesis. Neutron capture rates are well constrained near stable isotopes where experimental data are available; however, moving far from the valley of stability, uncertainties grow by orders of magnitude. This is due to the complete lack of experimental constraints, as the direct measurement of a neutron-capture reaction on a short-lived nucleus is extremely challenging. Here, we report on the first experimental extraction of a neutron capture reaction rate on ^{69}Ni, a nucleus that is five neutrons away from the last stable isotope of Ni. The implications of this measurement on nucleosynthesis around mass 70 are discussed, and the impact of similar future measurements on the understanding of the origin of the heavy elements in the cosmos is presented.
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- 2016
- Full Text
- View/download PDF
24. Nuclear level densities and gamma-ray strength functions of145,149,151Nd isotopes
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V. W. Ingeberg, F. L. Bello Garrote, Magne Guttormsen, A. C. Larsen, K. O. Ay, Therese Renstrøm, Fabio Zeiser, Andreas Görgen, M. Ozgur, E. Sahin, E. Algin, Trine Wiborg Hagen, M. Klintefjord, B. V. Kheswa, Gry Merete Tveten, V. Modamio, J. E. Midtbø, L. Crespo Campo, S. J. Rose, and Sunniva Siem
- Subjects
Nuclear reaction ,History ,Isotope ,010308 nuclear & particles physics ,Stable isotope ratio ,Chemistry ,Astrophysics::High Energy Astrophysical Phenomena ,Hadron ,Binding energy ,Gamma ray ,01 natural sciences ,Computer Science Applications ,Education ,Nuclear physics ,0103 physical sciences ,Neutron ,Atomic physics ,Nuclear Experiment ,010306 general physics ,Nucleon - Abstract
The nuclear level densities and gamma-ray strength functions are the key elements for Hauser-Feshbach statistical model calculations to predict reaction cross sections which have many applications including astrophysics. The nuclear level densities and y-ray strength functions have been determined for 145,149,151Nd isotopes below the neutron separation energies using the Oslo method with the 144,148,150Nd(d,p) reactions. The results from the first measurements as well as planned experiments at OCL will be presented.
- Published
- 2016
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