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The $γ$-ray strength function and the nuclear level density of $^{167}$Ho have been extracted using the Oslo method from a $^{164}\text{Dy}(α,pγ)^{167}$Ho experiment carried out at the Oslo Cyclotron Laboratory. The level density displays a shape that is compatible with %can be approximated with the constant temperature model in the quasicontinuum, while the strength function shows structures indicating the presence of both a scissors and a pygmy dipole resonance. Using our present results as well as data from a previous $^{163}\text{Dy}(α,pγ)^{166}$Ho experiment, the $^{165}\text{Ho}(n,γ)$ and $^{166}\text{Ho}(n,γ)$ MACS uncertainties have been constrained. The possible influence of the low-lying, long-lived 6~keV isomer $^{166}$Ho in the $s$ process is investigated in the context of a 2~$M_\odot$, [Fe/H]=-0.5 AGB star. We show that the newly obtained $^{165}\text{Ho}(n,γ)$ MACS affects the final $^{165}$Ho abundance, while the $^{166}\text{Ho}(n,γ)$ MACS only impacts the enrichment of $^{166,167}$Er to a limited degree due to the relatively rapid $β$ decay of the thermalized $^{166}$Ho at typical $s$-process temperatures., 11 pages, submitted to Physical Reviews C

Nuclei in the $^{135}$I region have been identified as being a possible bottleneck for the \textit{i} process. Here we present an indirect measurement for the Maxwellian-averaged cross section of $^{126}\text{Sb}(n,\gamma)$. The nuclear level density and the $\gamma$-ray strength function of $^{127}$Sb have been extracted from $^{124}$Sn$(\alpha,p\gamma)^{127}$Sb data using the Oslo method. The level density in the low-excitation-energy region agrees well with known discrete levels, and the higher-excitation-energy region follows an exponential curve compatible with the constant-temperature model. The strength function between $E_\gamma\approx$ 1.5-8.0 MeV presents several features, such as an upbend and a possibly double-peaked pygmy-like structure. None of the theoretical models included in the nuclear reaction code TALYS seem to reproduce the experimental data. The Maxwellian-averaged cross section for the $^{126}$Sb$(n,\gamma)^{127}$Sb reaction has been experimentally constrained by using our level-density and strength-function data as input to TALYS. We observe a good agreement with the JINA REACLIB, TENDL, and BRUSLIB libraries, while the ENDF/B-VIII.0 library predicts a significantly higher rate than our results.

Nuclei in the 135I region have been identified as being a possible bottleneck for the i process. Here we present an indirect measurement for the Maxwellian-averaged cross section of 126Sb(n,γ). The nuclear level density and the γ-ray strength function of 127Sb have been extracted from 124Sn(α,pγ)127Sb data using the Oslo method. The level density in the low-excitation-energy region agrees well with known discrete levels, and the higher-excitation-energy region follows an exponential curve compatible with the constant-temperature model. The strength function between Eγ≈1.5–8.0 MeV presents several features, such as an upbend and a possibly double-peaked pygmy-like structure. None of the theoretical models included in the nuclear reaction code talys seem to reproduce the experimental data. The Maxwellian-averaged cross section for the 126Sb(n,γ)127Sb reaction has been experimentally constrained by using our level-density and strength-function data as input to talys. We observe a good agreement with the jina reaclib, tendl, and bruslib libraries, while the endf/b-viii.0 library predicts a significantly higher rate than our results.

Nuclear level densities (NLDs) and γ-ray strength functions (GSFs) of 120,124Sn have been extracted with the Oslo method from proton-γ coincidences in the (p,p′γ) reaction. The functional forms of the GSFs and NLDs have been further constrained with the Shape method by studying primary γ-transitions to the ground and first excited states. The NLDs demonstrate good agreement with the NLDs of 116,118,122Sn isotopes measured previously. Moreover, the extracted partial NLD of 1− levels in 124Sn is shown to be in fair agreement with those deduced from spectra of relativistic Coulomb excitation in forward-angle inelastic proton scattering. The experimental NLDs have been applied to estimate the magnitude of the Porter-Thomas (PT) fluctuations. Within the PT fluctuations, we conclude that the GSFs for both isotopes can be considered to be independent of initial and final excitation energies, in accordance with the generalized Brink-Axel hypothesis. Particularly large fluctuations observed in the Shape-method GSFs present a considerable contribution to the uncertainty of the method and may be one of the reasons for deviations from the Oslo-method strength at low γ-ray energies and low values of the NLD (below ≈1×103–2×103MeV−1).

The study of prompt fission γ rays (PFGs) is crucial for understanding the energy and angular momentum distribution in fission, and over the last decade there has been an revived interest in this aspect of fission. We present the new experimental setup at the Oslo Cyclotron Laboratory for detecting PFGs resulting from charged particle-induced fission. Additionally, PFGs from the reaction 240Pu(d,pf) were measured in April 2018, and the fission gated proton-γ coincidence spectrum is shown. In order to explore the dependence of the PFG emission on the excitation energy and angular momentum of the compound nucleus, we plan several experiments where charged particle reactions are used to induce fission in various plutonium isotopes. The final results will be compared to predictions made by the Fission Reaction Event Yield Algorithm (FREYA) in an upcoming publication, to benchmark the current modelling of both the PFGs and the fission process.

The nuclear level densities (NLDs) and the γ-ray strength functions (γSFs) of Sm153,155 have been extracted from (d,pγ) coincidences using the Oslo method. The experimental NLD of Sm153 is higher than the NLD of Sm155, in accordance with microscopic calculations. The γSFs of Sm153,155 are in fair agreement with QRPA calculations based on the D1M Gogny interaction. An enhancement is observed in the γSF for both Sm153,155 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 μN2 for Sm153 and Sm155, respectively. The strength of the SR for Sm155 is comparable to those for deformed even-even Sm isotopes from nuclear resonance fluorescence measurements, while that of Sm153 is lower than expected., SCOPUS: ar.j, info:eu-repo/semantics/published

Particle-γ coincidence experiments were performed at the Oslo Cyclotron Laboratory with the Ta181(d,X) and Ta181(He3,X) reactions to measure the nuclear level densities (NLDs) and γ-ray strength functions (γSFs) of Ta180,181,182 using the Oslo method. The back-shifted Fermi-gas, constant temperature plus Fermi gas, and Hartree-Fock-Bogoliubov plus combinatorial models were used for the absolute normalizations of the experimental NLDs at the neutron separation energies. The NLDs and γSFs are used to calculate the corresponding Ta181(n,γ) cross sections and these are compared to results from other techniques. The energy region of the scissors resonance strength is investigated and from the data and comparison to prior work it is concluded that the scissors strength splits into two distinct parts. This splitting may allow for the determination of triaxiality and a γ deformation of 14.9 ±1.8 was determined for Ta181., SCOPUS: ar.j, info:eu-repo/semantics/published

Nuclear level densities (NLDs) and Υ-ray strength functions (ΥSFs) of 91,92Zr have been extracted from particle-Υ coincidences using the Oslo method. The extracted ΥSF data, combined with photonuclear cross sections, cover the whole energy range from EΥ = 1.5 MeV up�to the giant dipole resonance at EΥ17MeV. The wide-range ΥSF data display structures at EΥ = 9.5 MeV, compatible with a superposition of the spin-flip M1 resonance and a pygmy E1 resonance. Furthermore, the SF shows a minimum at 2–3 MeV and an increase at lower Υ-ray energies. The experimentally constrained NLDs and SFs are shown to reproduce known and Maxwellian-averaged cross sections for Zr using the TALYS reaction code, thus serving as a benchmark for this indirect method of estimating cross sections for Zr isotopes., SCOPUS: cp.p, info:eu-repo/semantics/published

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.

The transitional nuclei 134 Ba and 133 Ba are investigated after multinucleon transfer employing the high-resolution Advanced GAmma Tracking Array coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy, and after fusion-evaporation reaction at the FN tandem accelerator of the University of Cologne, Germany. The Jπ = 19 / 2 + state at 1942 keV in 133 Ba is identified as an isomer with a half-life of 66.6 ( 20 ) ns corresponding to a B(E1) value of 7.7 ( 4 ) × 10 − 6 e 2 fm 2 for the Jπ = 19 / 2 + to Jπ = 19 / 2 − transition. The level scheme of 134 Ba above the Jπ = 10 + isomer is extended to approximately 6 MeV. A pronounced backbending is observed at ℏ ω = 0.38 MeV along the positive-parity yrast band. The results are compared to the high-spin systematics of the Z=56 isotopes. Large-scale shell-model calculations employing the GCN50:82, SN100PN, SNV, PQM130, Realistic SM, and EPQQM interactions reproduce the experimental findings and elucidate the structure of the high-spin states. The shell-model calculations employing the GCN50:82 and PQM130 interactions reproduce alignment properties and provide detailed insight into the microscopic origin of this phenomenon in transitional 134 Ba .

Particle- γ coincidence experiments were performed at the Oslo Cyclotron Laboratory with the 181 Ta ( d , X ) and 181 Ta ( 3 He , X ) reactions to measure the nuclear level densities (NLDs) and γ -ray strength functions ( γ SFs ) of 180 , 181 , 182 Ta using the Oslo method. The back-shifted Fermi-gas, constant temperature plus Fermi gas, and Hartree-Fock-Bogoliubov plus combinatorial models were used for the absolute normalizations of the experimental NLDs at the neutron separation energies. The NLDs and γ SFs are used to calculate the corresponding 181 Ta ( n , γ ) cross sections and these are compared to results from other techniques. The energy region of the scissors resonance strength is investigated and from the data and comparison to prior work it is concluded that the scissors strength splits into two distinct parts. This splitting may allow for the determination of triaxiality and a γ deformation of 14 . 9 ∘ ± 1 . 8 ∘ was determined for 181 Ta .

Transition probabilities of intermediate-spin yrast and non-yrast excitations in 80,82Se were investigated in a recoil distance Doppler-shift (RDDS) experiment performed at the Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro. The Cologne Plunger device for deep inelastic scattering was used for the RDDS technique and was combined with the AGATA Demonstrator array for the γ -ray detection and coupled to the PRISMA magnetic spectrometer for an event-by-event particle identification. In 80Se, the level lifetimes of the yrast (6+ 1 ) and (8+ 1 ) states and of a non-yrast band feeding the yrast 4+ 1 state are determined. A spin and parity assignment of the head of this sideband is discussed based on the experimental results and supported by large-scale shell-model calculations. In 82Se, the level lifetimes of the yrast 6+ 1 state and the yrare 4+ 2 state and lifetime limits of the yrast (10+ 1 ) state and of the 5− 1 state are determined. Although the experimental results contain large uncertainties, they are interpreted with care in terms of large-scale shell-model calculations using the effective interactions JUN45 and jj44b. The excited states’ wave functions are investigated and discussed with respect to the role of the neutron g9/2 orbital.

A Coulomb-excitation experiment to study electromagnetic properties of 42Ca was performed using a 170-MeV calcium beam from the TANDEM XPU facility at INFN Laboratori Nazionali di Legnaro. γ rays from excited states in 42Ca were measured with the AGATA spectrometer. The magnitudes and relative signs of ten E2 matrix elements coupling six low-lying states in 42Ca, including the diagonal E2 matrix elements of 2+ 1 and 2+ 2 states, were determined using the least-squares code GOSIA. The obtained set of reduced E2 matrix elements was analyzed using the quadrupole sum rule method and yielded overall quadrupole deformation for 0+ 1,2 and 2+ 1,2 states, as well as triaxiality for 0+ 1,2 states, establishing the coexistence of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in 42Ca. The experimental results were compared with the state-of-the-art large-scale shell-model and beyond-mean-field calculations, which reproduce well the general picture of shape coexistence in 42Ca.

Photoneutron cross sections were measured for Ni58,Ni60,Ni61, and Ni64 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 Ni63, 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., SCOPUS: ar.j, info:eu-repo/semantics/published

The lifetimes of the first excited 2þ, 4þ, and 6þ states in 98Zr were measured with the recoil-distance Doppler shift method in an experiment performed at GANIL. Excited states in 98Zr were populated using the fission reaction between a 6.2 MeV=u 238U beam and a 9 Be target. The γ rays were detected with the EXOGAM array in correlation with the fission fragments identified by mass and atomic number in the VAMOS++ spectrometer. Our result shows a very small BðE2; 2þ 1 → 0þ 1 Þ value in 98Zr, thereby confirming the very sudden onset of collectivity at N ¼ 60. The experimental results are compared to large-scale Monte Carlo shell model and beyond-mean-field calculations. The present results indicate the coexistence of two additional deformed shapes in this nucleus along with the spherical ground state.

A model-independent technique was used to determine the γ -ray strength function ( γ SF ) of 56 Fe down to γ -ray energies less than 1 MeV for the first time with GRETINA using the (p,p′ ) reaction at 16 MeV. No difference was observed in the energy dependence of the γ SF built on 2+ and 4+ final states, supporting the Brink hypothesis. In addition, angular distribution and polarization measurements were performed. The angular distributions are consistent with dipole radiation. The polarization results show a small bias towards magnetic character in the region of the enhancement.

The nuclear level densities and $\gamma$-ray strength functions of $^{138,139,140}$La were measured using the $^{139}$La($^{3}$He, $\alpha$), $^{139}$La($^{3}$He, $^{3}$He$^\prime$) and $^{139}$La(d, p) reactions. The particle-$\gamma$ coincidences were recorded with the silicon particle telescope (SiRi) and NaI(Tl) (CACTUS) arrays. In the context of these experimental results, the low-energy enhancement in the A$\sim$140 region is discussed. The $^{137,138,139}$La($n, \gamma)$ cross sections were calculated at $s$- and $p$-process temperatures using the experimentally measured nuclear level densities and $\gamma$-ray strength functions. Good agreement is found between $^{139}$La($n, \gamma)$ calculated cross sections and previous measurements.

Nuclear level densities (NLDs) and γ-ray strength functions (γSFs) have been extracted from particle-γ coincidences of the 92Zr(p,p′γ)92Zr and 92Zr(p,dγ)91Zr reactions using the Oslo method. The new 91,92ZrγSF data, combined with photonuclear cross sections, cover the whole energy range from Eγ≈1.5MeV up to the giant dipole resonance at Eγ≈17 MeV. The wide-range γSF data display structures at Eγ≈9.5 MeV, compatible with a superposition of the spin-flip M1 resonance and a pygmy E1 resonance. Furthermore, the γSF shows a minimum at Eγ≈2–3MeV and an increase at lower γ-ray energies. The experimentally constrained NLDs and γSFs are shown to reproduce known (n,γ) and Maxwellian-averaged cross sections for 91,92Zr using the talys reaction code, thus serving as a benchmark for this indirect method of estimating (n,γ) cross sections for Zr isotopes. This research was originally published in Physical Review C - Nuclear Physics. © American Physical Society

The nuclear level densities and γ-ray strength functions of 138,139,140La were measured using the 139La(3He,α), 139La(3He,'3He), and 139La(d,p) reactions. The particle-γ coincidences were recorded with the silicon particle telescope (SiRi) and NaI(Tl) (CACTUS) arrays. In the context of these experimental results, the low-energy enhancement in the A∼140 region is discussed. The 137,138,139La(n,γ) cross sections were calculated at s- and p-process temperatures using the experimentally measured nuclear level densities and γ-ray strength functions. Good agreement is found between 139La(n,γ) calculated cross sections and previous measurements. This research was first published in Physical Review C - Nuclear Physics. © American Physical Society.

Background: In order to determine the relative biological effectiveness (RBE) of protons with high accuracy, radiobiological experiments with detailed knowledge of the linear energy transfer (LET) are needed. Cell survival data from high LET protons are sparse and experiments with low energy protons to achieve high LET values are therefore required. The aim of this study was to quantify LET distributions from a low energy proton beam by using Monte Carlo (MC) simulations, and to further compare to a proton beam representing a typical minimum energy available at clinical facilities. Materials and methods: A Markus ionization chamber and Gafchromic films were employed in dose measurements in the proton beam at Oslo Cyclotron Laboratory. Dose profiles were also calculated using the FLUKA MC code, with the MC beam parameters optimized based on comparisons with the measurements. LET spectra and dose-averaged LET (LETd) were then estimated in FLUKA, and compared with LET calculated from an 80 MeV proton beam. Results: The initial proton energy was determined to be 15.5 MeV, with a Gaussian energy distribution of 0.2% full width at half maximum (FWHM) and a Gaussian lateral spread of 2 mm FWHM. The LETd increased with depth, from approximately 5 keV/μm in the entrance to approximately 40 keV/μm in the distal dose fall-off. The LETd values were considerably higher and the LET spectra were much narrower than the corresponding spectra from the 80 MeV beam. Conclusions: MC simulations accurately modeled the dose distribution from the proton beam and could be used to estimate the LET at any position in the setup. The setup can be used to study the RBE for protons at high LETd, which is not achievable in clinical proton therapy facilities.

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 233 U ( d , p f ) reaction for excitation energies between 4.8 and 10 MeV, and for the 239 Pu ( d , p f ) 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.

The γ decay of 65 Ni has been studied from particle- γ coincidence data on the 64 Ni ( d , p γ ) 65 Ni reaction. γ -ray spectra at excitation energies below Ex≈ 2 MeV have been studied and compared with previous measurements. Coincidences corresponding to Ex≈ 4.4 – 6.1 MeV have been used to constrain the shape of the nuclear level density and γ -strength function of 65 Ni by means of the Oslo method. The experimental γ -strength function presents an enhancement at γ energies below Eγ ≈ 3 MeV . In addition, a resonance-like structure centered at Eγ ≈ 4.6 MeV is seen together with accumulated strength at Eγ ≈ 2.6 – 3.6 MeV . The obtained results contribute to the systematic study of γ decay in the Ni isotopes, which is of great interest for the understanding of both single-particle and collective nuclear structure phenomena.

The average electromagnetic dipole response of levels in the quasicontinuum of 197,198Au has been measured using (3He,3He ) and (d,p) reactions. The extracted γ -ray strength functions have been normalized according to three model assumptions for the nuclear spin distribution. An enhancement in the energy region Eγ = 3.0–6.5 MeV is observed for both isotopes. The E1 component of such excess of strength is studied in detail for 198Au and is interpreted as the pygmy dipole resonance with an energy centroid of 5.9(1) MeV and exhausts about 1% of the total integrated strength. The pygmy dipole resonance is shown to have a significant impact on the calculated 197Au(n,γ ) 198Au cross section.

An enhanced probability for low-energy γ-emission (upbend, Eγ γ ≈ 2-3 MeV). These phenomena, if present in neutron-rich nuclei, have the potential to increase radiative neutron-capture rates relevant for the r-process. The experimental and theoretical status of the upbend is discussed, and preliminary calculations of (n,γ) reaction rates for neutronrich, mid-mass nuclei including the scissors mode are shown.

Background: The chain of Sm isotopes exhibits a wide range of nuclear shapes and collective behavior. While the onset of deformation for N > 82 has been well studied both experimentally and theoretically, fundamental data is lacking for some Sm isotopes with N < 82. Purpose: Electromagnetic transition rates represent a sensitive test of theoretical nuclear structure models. Lifetime measurements are furthermore complementary to Coulomb excitation experiments, and the two methods together can give access to spectroscopic quadrupole moments. Method: The lifetime of the 2+ 1 state in 140Sm was measured with the recoil-distance Doppler shift technique using the reaction 124Te( 20Ne, 4n) 140Sm at 82 MeV. Theoretical calculations were performed based on a mapped collective Hamiltonian in five quadrupole coordinates (5DCH) and the Gogny D1S interaction. Results: The lifetime of the 2+ 1 state in 140Sm was found to be 9.1(6) ps, corresponding to aB(E2; 2+ 1 → 0+ 1 ) value of 51(4) Weisskopf units. The theoretical calculations are in very good agreement with the experimental result. Conclusions: The B(E2; 2+ 1 → 0+ 1 ) value for 140Sm fits smoothly into the systematic trend for the chain of Sm isotopes. The new beyond-mean field calculations are able to correctly describe the onset of collectivity in the Sm isotopes below the N = 82 shell closure for the first time.

An unexpected enhancement in the $\gamma$-ray strength function, as compared to the low energy tail of the Giant Dipole Resonance (GDR), has been observed for Sc, Ti, V, Fe and Mo isotopes for $E_\gamma4$ MeV, which is interpreted as a PDR centered at $E_{\gamma}\approx8$ MeV. An enhanced $\gamma$-ray strength at low energies is also observed for $^{105}$Pd, which is the lightest isotope measured in this work. Further, the results correspond and agree very well with the observations from the Cd isotopes, and support the suggested transitional region for the onset of low-energy enhancement with decreasing mass number. The neutron number dependency of the PDR strength is also evident.