RHIANN CANAVAN, M. Rudigier, PATRICK HENRY REGAN, D. Thisse, M. Lebois, J N Wilson, N. Jovancevic, P.-A. Söderström, SEAN MICHAEL COLLINS, Jaime Benito García, S. Bottoni, MATTHEW HENRY BRUNET, N. Cieplicka-Orynczak, S. Courtin, DANIEL THOMAS DOHERTY, Luis Mario Fraile Prieto, K. Hadynska-Klek, G. Hafner, M. Heine, V. Karayonchev, Ł.W. Iskra, ADAM RUSSELL KENNINGTON, P. Koseoglou, GAVIN JAMES LOTAY, G Lorusso, M Nakhostin, C.R. Nita, S. Oberstedt, ZSOLT PODOLYAK, L Qi, J.-M. Régis, V. Sánchez-Tembleque, R Shearman, María Victoria Vedia Fernández, W. Witt (2020)Half-life measurements in Dy-164,Dy-166 using γ−γ fast-timing spectroscopy with the ν-Ball spectrometer, In: Physical Review. C101(2)
American Physical Society
We report on the measurement of lifetimes of excited states in the near-mid-shell nuclei Dy-164,Dy-166 using the gamma-ray coincidence fast-timing method. The nuclei of interest were populated using reactions between an O-18 beam and a gold-backed isotopically enriched Dy-164 target of thickness 6.3 mg/cm(2) at primary beam energies of 71, 76, and 80 MeV from the IPN-Orsay laboratory, France. Excited states were populated in Dy-164, Dy-166, and W-178,W-179 following Coulomb excitation, inelastic nuclear scattering, two-neutron transfer, and fusion-evaporation reaction channels respectively. Gamma rays from excited states were measured using the nu-Ball high-purity germanium (HPGe)-LaBr3 hybrid gamma-ray spectrometer with the excited state lifetimes extracted using the fast-timing coincidence method using HPGe-gated LaBr3-LaBr3 triple coincident events. The lifetime of the first I-pi = 2(+) excited state in Dy-166 was used to determine the transition quadrupole deformation of this neutron-rich nucleus for the first time. The experimental methodology was validated by showing consistency with previously determined excited state lifetimes in Dy-164. The half-lives of the yrast 2(+) states in Dy-164 and Dy-166 were 2.35(6) and 2.3(2) ns, respectively, corresponding to transition quadrupole moment values of Q(0) = 7.58(9) and 7.5(4) eb, respectively. The lifetime of the yrast 2(+) state in Dy-166 is consistent with a quenching of nuclear quadrupole deformation at beta approximate to 0.35 as the N = 104 mid-shell is approached.
M. Rudigier, P. M. Walker, R.L. Canavan, Zs. Podolyak, P. H. Regan, P.-A. Söderström, M. Lebois, J.N. Wilson, N. Jovancevic, A. Blazhev, J. Benito, S. Bottoni, M. Brunet, N. Cieplicka-Orynczak, S. Courtin, D. T. Doherty, L.M. Fraile, K. Hadynska-Klek, M. Heine, Ł.W. Iskra, J. Jolie, V. Karayonchev, A. R. Kennington, P. Koseoglou, G. Lotay, G. Lorusso, M. Nakhostin, C.R. Nita, S. Oberstedt, L. Qi, J.-M. Régis, V. Sánchez-Tembleque, R. Shearman, W. Witt, V. Vedia, K.O. Zell (2020)Multi-quasiparticle sub-nanosecond isomers in 178W, In: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics801135140
We report on the first measurement of the half-lives of and four-quasiparticle states in the even-even nucleus 178W. The sub-nanosecond half-lives were measured by applying the centroid shift method to data taken with LaBr3(Ce) scintillator detectors of the NuBall array at the ALTO facility in Orsay, France. The half-lives of these states only became experimentally accessible by the combination of several experimental techniques - scintillator fast timing, isomer spectroscopy with a pulsed beam, and the event-by-event calorimetry information provided by the NuBall array. The measured half-lives are and for the and states, respectively. The decay transitions include weakly hindered E1 and E2 branches directly to the ground-state band, bypassing the two-quasiparticle states. This is the first such observation for an E1 transition. The interpretation of the small hindrance hinges on mixing between the ground-state band and the t-band.
K Auranen, D Seweryniak, M Albers, A.D Ayangeakaa, S Bottoni, M.P Carpenter, C.J Chiara, P Copp, H.M David, D.T Doherty, J Harker, C.R Hoffman, R.V.F Janssens, T.L Khoo, S.A Kuvin, T Lauritsen, G Lotay, A.M Rogers, C Scholey, R Talwar, J Sethi, W.B Walters, P.J Woods, S Zhu (2019)Proton decay of 108I and its significance for the termination of the astrophysical rp-process, In: Physics Letters. B792(C)pp. 187-192
Employing the Argonne Fragment Mass Analyzer and the implantation-decay-decay correlation technique, a weak 0.50(21)% proton decay branch was identified in 108I for the first time. The 108I proton-decay width is consistent with a hindered l=2 emission, suggesting a d52 origin. Using the extracted 108I proton-decay Q value of 597(13) keV, and the Qα values of the 108I and 107Te isotopes, a proton-decay Q value of 510(20) keV for 104Sb was deduced. Similarly to the 112,113Cs proton-emitter pair, the Qp(I108) value is lower than that for the less-exotic neighbor 109I, possibly due to enhanced proton-neutron interactions in N≈Z nuclei. In contrast, the present Qp(Sb104) is higher than that of 105Sb, suggesting a weaker interaction energy. For the present Qp(Sb104) value, network calculations with the one-zone X-ray burst model Mazzocchi et al. (2007)  predict no significant branching into the Sn-Sb-Te cycle at 103Sn.
K Auranen, D Seweryniak, M Albers, A. D Ayangeakaa, S Bottoni, M. P Carpenter, C. J Chiara, P Copp, H. M David, D. T Doherty, J Harker, C. R Hoffman, R. V. F Janssens, T. L Khoo, S. A Kuvin, T Lauritsen, G Lotay, A. M Rogers, J Sethi, C Scholey, R Talwar, W. B Walters, P. J Woods, S Zhu (2018)Superallowed alpha Decay to Doubly Magic Sn-100, In: Physical Review Letters121(18)
American Physical Society
We report the first observation of the 108Xe → 104Te → 100Sn α-decay chain. The α emitters, 108Xe [Eα ¼ 4.4ð2Þ MeV, T1=2 ¼ 58þ106 −23 μs] and 104Te [Eα ¼ 4.9ð2Þ MeV, T1=2 < 18 ns], decaying into doubly magic 100Sn were produced using a fusion-evaporation reaction 54Feð58Ni; 4nÞ108Xe, and identified with a recoil mass separator and an implantation-decay correlation technique. This is the first time α radioactivity has been observed to a heavy self-conjugate nucleus. A previous benchmark for study of this fundamental decay mode has been the decay of 212Po into doubly magic 208Pb. Enhanced proton-neutron interactions in the N ¼ Z parent nuclei may result in superallowed α decays with reduced α-decay widths significantly greater than that for 212Po. From the decay chain, we deduce that the α-reduced width for 108Xe or 104Te is more than a factor of 5 larger than that for 212Po.
A. R. L Kennington, G Lotay, D. T Doherty, D Seweryniak, C Andreoiu, K Auranen, M. P Carpenter, W. N Catford, C. M Deibel, K Hadyńska-Klęk, S Hallam, D. E. M Hoff, T Huang, R. V. F Janssens, S Jazrawi, J José, F. G Kondev, T Lauritsen, J Li, A. M Rogers, J Saiz, G Savard, S Stolze, G. L Wilson, S Zhu (2020)Search for Nova Presolar Grains: $γ$-Ray Spectroscopy of 34Ar and its Relevance for the Astrophysical 33Cl($p,γ$) Reaction, In: Physical Review Letters124(25)
American Physical Society (APS)
The discovery of presolar grains in primitive meteorites has launched a new era of research in the study of stellar nucleosynthesis. However, the accurate classification of presolar grains as being of specific stellar origins is particularly challenging. Recently, it has been suggested that sulfur isotopic abundances may hold the key to definitively identifying presolar grains with being of nova origins and, in this regard, the astrophysical Cl33 ( p,γ ) Ar34 reaction is expected to play a decisive role. As such, we have performed a detailed γ -ray spectroscopy study of Ar34 . Excitation energies have been measured with high precision and spin-parity assignments for resonant states, located above the proton threshold in Ar34 , have been made for the first time. Uncertainties in the Cl33 ( p,γ ) reaction have been dramatically reduced and the results indicate that a newly identified ℓ=0 resonance at Er=396.9 ( 13 ) keV dominates the entire rate for T=0.25–0.40 GK . Furthermore, nova hydrodynamic simulations based on the present work indicate an ejected S 32/ S 33 abundance ratio distinctive from type-II supernovae and potentially compatible with recent measurements of a presolar grain.
A Kankainen, PJ Woods, H Schatz, T Poxon-Pearson, Daniel Doherty, V Bader, T Baugher, D Bazin, BA Brown, J Browne, A Estrade, A Gade, J José, A Kontos, C Langer, Gavin Lotay, Z Meisel, F Montes, S Noji, F Nunes, G Perdikakis, J Pereira, F Recchia, T Redpath, R Stroberg, M Scott, D Seweryniak, J Stevens, D Weisshaar, R Zegers (2017)Measurement of key resonance states for the 30P(p, γ)31Sreaction rate, and the production of intermediate-mass elements in nova explosions, In: Physics Letters B769pp. 549-553
We report the first experimental constraints on spectroscopic factors and strengths of key resonances in the 30P(p, γ)31Sreaction critical for determining the production of intermediate-mass elements up to Ca in nova ejecta. The 30P(d, n)31Sreaction was studied in inverse kinematics using the GRETINA γ-ray array to measure the angle-integrated cross-sections of states above the proton threshold. In general, negative-parity states are found to be most strongly produced but the absolute values of spectroscopic factors are typically an order of magnitude lower than predicted by the shell-model calculations employing WBP Hamiltonian for the negative-parity states. The results clearly indicate the dominance of a single 3/2−resonance state at 196 keV in the region of nova burning T≈0.10–0.17GK, well within the region of interest for nova nucleosynthesis. Hydrodynamic simulations of nova explosions have been performed to demonstrate the effect on the composition of nova ejecta.
E McCleskey, A Banu, M McCleskey, T Davinson, D. T Doherty, G Lotay, B. T Roeder, A Saastamoinen, A Spiridon, L Trache, J. P Wallace, P. J Woods, R. E Tribble (2016)Simultaneous measurement of β -delayed proton and γ decay of P 27, In: Physical Review. C94(6)
American Physical Society
This is the first study of 27P to measure both the β-delayed proton and β-delayed γ decays. While no new proton groups in the astrophysically interesting energy region of 300–400 keV were observed, a new upper limit on the proton branching of 0.16% was estimated. Several new γ -ray lines were observed, mainly coming from the isobaric analog state in 27Si, which has been assigned a more accurate energy value of 6638(1) keV.
G Lotay, D. T Doherty, D Seweryniak, S Almaraz-Calderon, M. P Carpenter, C. J Chiara, H. M David, C. R Hoffman, R. V. F Janssens, A Kankainen, T Lauritsen, R Wilkinson, P. J Woods, S Zhu (2019)Identification of $\gamma$-decaying resonant states in 26Mg and their importance for the astrophysical s process, In: The European Physical Journal. A, Hadrons and nuclei55109
The 22Ne(α, n) reaction is expected to provide the dominant neutron source for the weak s process in massive stars and intermediate-mass (IM) Asymptotic Giant Branch (AGB) stars. However, the production of neutrons in such environments is hindered by the competing 22Ne(α,γ)26Mg reaction. Here, the 11B(16O,p) fusion-evaporation reaction was used to identify γ-decay transitions from 22Ne + α resonant states in 26Mg. Spin-parity restrictions have been placed on a number of α-unbound excited states in 26 Mg and their role in the 22Ne(α,γ)26Mg reaction has been investigated. In particular, a suspected natural-parity resonance at Ec.m. = 557(3) keV, that lies above the neutron threshold in 26Mg, and is known to exhibit a strong α-cluster character, was observed to γ decay. Furthermore, a known resonance at Ec.m.= 466(4) keV has been definitively assigned 2+ spin and parity. Consequently, uncertainties in the 22Ne(α,γ) stellar reaction rate have been reduced by a factor of ~20 for temperatures ~0.2 GK.
RHIANN CANAVAN, M Rudigier, PATRICK HENRY REGAN, M Lebois, JULIET WILSON, N Jovancevic, P.-A Söderström, D Thisse, J Benito, S Bottoni, MATTHEW HENRY BRUNET, N Cieplicka-Oryńczak, SEAN MICHAEL COLLINS, S Courtin, DANIEL THOMAS DOHERTY, L.M Fraile, K Hadyńska-Klęk, M Heine, Ł.W Iskra, V Karayonchev, ADAM RUSSELL KENNINGTON, P Koseoglou, GAVIN JAMES LOTAY, G Lorusso, M Nakhostin, C.R Niţă, S Oberstedt, Zs Podolyák, L Qi, J.-M Régis, R Shearman, V Vedia, W Witt (2020)Reaction Channel selection techniques and γ - γ fast-timing spectroscopy using the ν-Ball Spectrometer, In: Journal of physics. Conference series1643(1)
The reaction of a pulsed 18O beam on a self-supporting and gold-backed isotopically-enriched 164Dy target of thickness 6.3 mg/cm2 at separate primary beam energies of 71, 76 and 80 MeV was studied at the accelerator at the ALTO facility of the IPN Orsay. The γ rays produced were detected using the newly-constructed ν-Ball spectrometer which comprised of HPGe and LaBr3(Ce) detectors. This conference paper describes the methodology and effectiveness of multiplicity/sum-energy gating, for channel selection between fusion evaporation events and lower multiplicity/energy events from inelastic nuclear scattering and Coulomb excitation of the target, and from two-neutron transfer reactions to 166Dy.
SHAHEEN JAZRAWI, DANIEL THOMAS DOHERTY, J.M Allmond, PATRICK HENRY REGAN, R.V.F Janssens, W Korten, S Zhu, M Zielińska, D Radford, S Ansari, K Auranen, B Bucher, M.P Carpenter, WILTON NEIL CATFORD, K Hadyńska-Klek, JACK HENDERSON, M Hendricks, M Komorowska, F.G Kondev, T Lauritsen, JUERONG LI, GAVIN JAMES LOTAY, P.J Napiorkowski, E Padilla-Rodal, R.C Pardo, B.C Rasco, W Reviol, D.G Sarantites, D Seweryniak, D Santiago-Gonzalez, G Savard, P Singh, S.M Stolze, R Vondrasek, G Wilson, CHUAN-YU WU, J Wu (2020)A High-Resolution Study of the 110Tc → 110Ru → 110Rh → 110Pd Decay Chain with the GRETINA Array, In: Journal of Physics. Conference Series1643(1)
Spectroscopic data, such as precise γ-ray branching and E2/M1 multipole-mixing ratios, provide vital constraints when performing multi-dimensional Coulomb-excitation analyses. Consequently, as part of our new Coulomb-excitation campaign aimed at investigating the role of exotic non-axial (triaxial) deformations in the unstable refractory Ru-Mo isotopes, additional beta-decay data was obtained. These measurements make use of ANL's CARIBU facility, which provides intense beams of radioactive refractory isotopes along with the excellent efficiency and angular resolution of the GRETINA γ-ray tracking array. In this article, we report on the analysis of the A = 110 decay chain, focussing on the identification of previously unreported states in 110Ru following the decay of 110Tc.
M. Rudigier, R.L. Canavan, P.H. Regan, P.-A. Söderström, M. Lebois, J.N. Wilson, N. Jovancevic, S. Bottoni, M. Brunet, N. Cieplicka-Orynczak, S. Courtin, D.T. Doherty, K. Hadynska-Klek, M. Heine, W. Iskra, V. Karayonchev, A. Kennington, P. Koseoglou, G. Lotay, G. Lorusso, M. Nakhostin, C.R. Nita, S. S. Oberstedt, Zs. Podolyak, L. Qi, J.-M. Régis, R. Shearman, P.M. Walker, W. Witt (2019)Isomer spectroscopy and sub-nanosecond half-live determination in 178w using the NuBall array, In: Acta Physica Polonica B50(3)pp. 661-667
The reaction of a pulsed 18O beam on a 164Dy target was studied in the first experiment with the NuBall array at the IPN Orsay, France. Excited state half-lives were measured using the fast timing method with 20 LaBr3(Ce) detectors. The timing characteristics of the fully digital acquisition system is briefly discussed. A value for the previously unknown half-life of the first excited 4+ state in 178W is presented.
L Morrison, K Hadyńska-Klek, Zs Podolyák, D. T Doherty, L. P Gaffney, L Kaya, L Próchniak, J Samorajczyk-Pyśk, J Srebrny, T Berry, A Boukhari, M Brunet, R Canavan, R Catherall, S. J Colosimo, J. G Cubiss, H De Witte, Ch Fransen, E Giannopoulos, T Kröll, H Hess, N Lalović, B Marsh, Y. Martinez Palenzuela, P. J Napiorkowski, G O'Neill, J Pakarinen, J. P Ramos, P Reiter, J. A Rodriguez, D Rosiak, S Rothe, M Rudigier, M Siciliano, J Snäll, P Spagnoletti, S Thiel, N Warr, F Wenander, R Zidarova, ZSOLT PODOLYAK, M Zielińska (2020)Quadrupole deformation of Xe 130 measured in a Coulomb-excitation experiment, In: Physical Review. C102054304
Low-lying states in the isotope Xe130 were populated in a Coulomb-excitation experiment performed at CERN's HIE-ISOLDE facility. The magnitudes and relative signs of seven E2 matrix elements and one M1 matrix element coupling five low-lying states in Xe130 were determined using the semiclassical coupled-channel Coulomb-excitation least-squares search code gosia. The diagonal E2 matrix elements of both the 21+ and 41+ states were extracted for the first time. The reduced transition strengths are in line with those obtained from previous measurements. Experimental results were compared with the general Bohr Hamiltonian with the microscopic input from mean-field theory utilizing universal nuclear energy density functional (UNEDF0), shell-model calculations using the GCN50:82 and SN100PN interactions, and simple phenomenological models (Davydov-Filippov and γ-soft). The extracted shape parameters indicate triaxial-prolate deformation in the ground-state band. In general, good agreement between theoretical predictions and experimental values was found, while neither phenomenological model was found to provide an adequate description of Xe130.
S. Ota, G. Christian, G. Lotay, W.N Catford, E.A Bennett, S. Dede, Daniel Doherty, Sam Hallam, J. Hooker, C. Hunt, H. Jayatissa, A. Matta, Mohamad Moukaddam, G.V Rogachev, A. Saastamoinen, Jeffrey Tostevin, S. Upadhyayula, Ryan Wilkinson Decay properties of 22Ne + resonances and their impact on s-process nucleosynthesis, In: Physics Letters B802135256
The astrophysical s-process is one of the two main processes forming elements heavier than iron. A key outstanding uncertainty surrounding s-process nucleosynthesis is the neutron flux generated by the 22Ne(; n)25Mg reaction during the He-core and C-shell burning phases of massive stars. This reaction, as well as the competing 22Ne(;)26Mg reaction, is not well constrained in the important temperature regime from 0:2–0:4 GK, owing to uncertainties in the nuclear properties of resonances lying within the Gamow window. To address these uncertainties, we have performed a new measurement of the 22Ne(6Li; d)26Mg reaction in inverse kinematics, detecting the outgoing deuterons and 25;26Mg recoils in coincidence. We have established a new n= decay branching ratio of 1:14(26) for the key Ex = 11:32 MeV resonance in 26Mg, which results in a new (; n) strength for this resonance of 42(11) eV when combined with the well-established (; ) strength of this resonance. We have also determined new upper limits on the partial widths of neutron-unbound resonances at Ex = 11:112; 11:163, 11:169, and 11:171 MeV. Monte-Carlo calculations of the stellar 22Ne(; n)25Mg and 22Ne(; )26Mg rates, which incorporate these results, indicate that both rates are substantially lower than previously thought in the temperature range from 0:2–0:4 GK.
V Margerin, G Lotay, PJ Woods, M Aliotta, G Christian, B Davids, T Davinson, DT Doherty, J Fallis, D Howell, OS Kirsebom, DJ Mountford, A Rojas, C Ruiz, JA Tostevin (2015)Inverse Kinematic Study of the Al26g(d,p)Al27 Reaction and Implications for Destruction of Al26 in Wolf-Rayet and Asymptotic Giant Branch Stars, In: Physical Review Letters115062701
American Physical Society
In Wolf-Rayet and asymptotic giant branch (AGB) stars, the Al26g(p,γ)Si27 reaction is expected to govern the destruction of the cosmic γ-ray emitting nucleus Al26. The rate of this reaction, however, is highly uncertain due to the unknown properties of key resonances in the temperature regime of hydrogen burning. We present a high-resolution inverse kinematic study of the Al26g(d,p)Al27 reaction as a method for constraining the strengths of key astrophysical resonances in the Al26g(p,γ)Si27 reaction. In particular, the results indicate that the resonance at Er=127 keV in Si27 determines the entire Al26g(p,γ)Si27 reaction rate over almost the complete temperature range of Wolf-Rayet stars and AGB stars.
A Kankainen, PJ Woods, F Nunes, C Langer, H Schatz, V Bader, T Baugher, D Bazin, BA Brown, J Browne, DT Doherty, A Estrade, A Gade, A Kontos, G Lotay, Z Meisel, F Montes, S Noji, G Perdikakis, J Pereira, F Recchia, T Redpath, R Stroberg, M Scott, D Seweryniak, J Stevens, D Weisshaar, K Wimmer, R Zegers (2016)Angle-integrated measurements of the Al-26(d, n)Si-27 reaction cross section: a probe of spectroscopic factors and astrophysical resonance strengths, In: EUROPEAN PHYSICAL JOURNAL A52(1)ARTN 6
Daniel Doherty, JM Allmond, RVF Janssens, W Korten, S Zhu, M Zielinska, DC Radford, AD Ayangeakaa, B Bucher, JC Batchelder, CW Beausang, C Campbell, MP Carpenter, D Cline, HL Crawford, HM David, JP Delaroche, C Dickerson, P Fallon, A Galindo-Uribarri, FG Kondev, JL Harker, AB Hayes, M Hendricks, P Humby, M Girod, CJ Gross, M Klintefjord, K Kolos, GJ Lane, T Lauritsen, J Libert, AO Macchiavelli, PJ Napiorkowski, E Padilla-Rodal, RC Pardo, W Reviol, DG Sarantites, G Savard, D Seweryniak, J Srebrny, R Varner, R Vondrasek, A Wiens, E Wilson, JL Wood, CY Wu (2017)Triaxiality near the 110Ru ground state from Coulomb excitation, In: Physics Letters B766pp. 334-338
A multi-step Coulomb excitation measurement with the GRETINA and CHICO2 detector arrays was carried out with a 430-MeV beam of the neutron-rich 110Ru (t1/2=12s) isotope produced at the CARIBU facility. This represents the first successful measurement following the post-acceleration of an unstable isotope of a refractory element. The reduced transition probabilities obtained for levels near the ground state provide strong evidence for a triaxial shape; a conclusion confirmed by comparisons with the results of beyond-mean-field and triaxial rotor model calculations.
DT Doherty, G Lotay, PJ Woods, D Seweryniak, MP Carpenter, CJ Chiara, HM David, RV Janssens, L Trache, S Zhu (2012)Key resonances in the 30P(p,γ)31S gateway reaction for the production of heavy elements in ONe novae., In: Phys Rev Lett108(26)pp. 262502-?
Material emitted as ejecta from ONe novae outbursts is observed to be rich in elements as heavy as Ca. The bottleneck for the synthesis of elements beyond sulphur is the (30)P(p,γ)(31)S reaction. Its reaction rate is, however, not well determined due to uncertainties in the properties of key resonances in the burning regime. In the present study, gamma-ray transitions are reported for the first time from all key states in (31)S relevant for the (30)P(p,γ)(31)S reaction. The spins and parity of these resonances have been deduced, and energies have been measured with the highest precision to date. The uncertainty in the estimated (30)P(p,γ)(31)S reaction rate has been drastically reduced. The rate using this new information is typically higher than previous estimates based on earlier experimental data, implying a higher flux of material processed to high-Z elements in novae, but it is in good agreement with predictions using the Hauser-Feshbach approach at higher burning temperatures.
E Simmons, L Trache, A Banu, M McCleskey, B Roeder, A Spiridon, RE Tribble, T Davinson, PJ Woods, GJ Lotay, J Wallace, D Doherty, A Saastamoinen (2013)The beta-delayed proton and gamma decay of 27P for nuclear astrophysics, In: Journal of Physics: Conference Series420(1)
The creation site of 26Al is still under debate. It is thought to be produced in hydrogen burning and in explosive helium burning in novae and supernovae, and possibly also in the H-burning in outer shells of red giant stars. Also, the reactions for its creation or destruction are not completely known. When 26Al is created in novae, the reaction chain is: 24Mg(p,γ)25AI(β+v)25 Mg(p,γ)26Al, but this chain can be by-passed by another chain, 25Al(p, γ)26Si(p, γ)27P and it can also be destroyed directly. The reaction 26m Al (p, γ) 27 Si* is another avenue to bypass the production of 26Al and it is dominated by resonant capture. We find and study these resonances by an indirect method, through the beta-decay of 27P. A clean and abundant source of 27P was produced for the first time and separated with MARS. A new implantation-decay station which allows increased efficiency for low energy protons and for high-energy gamma-rays was used. We measured gamma-rays and beta-delayed protons emitted from states above the proton threshold in the daughter nucleus 27Si to identify and characterize the resonances. The lifetime of 27P was also measured with accuracy under 2%.
J. N. Wilson, M. Lebois, L. Qi, P. Amador-Celdran, D. Bleuel, J. A. Briz, R. Carroll, Wilton Catford, H. De Witte, D. T. Doherty, R. Eloirdi, G. Georgiev, A. Gottardo, A. Goasduff, K. Hadyńska-Klęk, K. Hauschild, H. Hess, V. Ingeberg, T. Konstantinopoulos, J. Ljungvall, A. Lopez-Martens, G. Lorusso, R. Lozeva, R. Lutter, P. Marini, I. Matea, T. Materna, L. Mathieu, A. Oberstedt, S. Oberstedt, S. Panebianco, Zsolt Podolyak, A. Porta, Patrick Regan, P. Reiter, K. Rezynkina, S. J. Rose, E. Sahin, M. Seidlitz, O. Serot, Robert Shearman, B. Siebeck, S. Siem, A. G. Smith, G. M. Tveten, D. Verney, N. Warr, F. Zeiser, M. Zielinska (2017)Anomalies in the Charge Yields of Fission Fragments from the U(n,f)238 Reaction, In: Physical Review Letters118(22)pp. 222501-1
American Physical Society
Fast-neutron-induced fission of 238U at an energy just above the fission threshold is studied with a novel technique which involves the coupling of a high-efficiency γ-ray spectrometer (MINIBALL) to an inverse-kinematics neutron source (LICORNE) to extract charge yields of fission fragments via γ−γ coincidence spectroscopy. Experimental data and fission models are compared and found to be in reasonable agreement for many nuclei; however, significant discrepancies of up to 600% are observed, particularly for isotopes of Sn and Mo. This indicates that these models significantly overestimate the standard 1 fission mode and suggests that spherical shell effects in the nascent fission fragments are less important for low-energy fast-neutron-induced fission than for thermal neutron-induced fission. This has consequences for understanding and modeling the fission process, for experimental nuclear structure studies of the most neutron-rich nuclei, for future energy applications (e.g., Generation IV reactors which use fast-neutron spectra), and for the reactor antineutrino anomaly.
JN Wilson, M Lebois, L Qi, P Amador-Celdran, D Bleuel, JA Briz, R Carroll, Wilton Catford, H De Witte, D Doherty, R Eloirdi, G Georgiev, A Gottardo, A Goasduff, K Hadynska-Klek, K Hauschild, M Hess, V Ingeberg, T Konstantinopoulos, J Ljungvall, A Lopez-Martens, G Lorusso, R Lozeva, R Lutter, P Marini, I Matea, T Materna, L Mathieu, A Oberstedt, S Oberstedt, S Panebianco, Zsolt Podolyak, D Porta, Patrick Regan, P Reiter, K Rezynkina, SJ Rose, E Sahin, M Seidlitz, Robert Shearman, B Siebeck, S Siem, AG Smith, GM Tveten, D Verney, N Warr, F Zeiser, M Zielinska (2017)PRODUCTION AND STUDY OF NEUTRON-RICH NUCLEI USING THE LICORNE DIRECTIONAL NEUTRON SOURCE, In: Acta Physica Polonica B48(3)pp. 395-401
Państwowe Wydawn. Naukowe
We have recently successfully demonstrated a new technique for production and study of many of the most exotic neutron-rich nuclei at moderate spins. LICORNE, a newly developed directional inverse-kinematic fast neutron source at the IPN Orsay, was coupled to the MINIBALL high resolution -ray spectrometer to study nuclei the furthest from stability using the 238U(n; f) reaction. This reaction and 232Th(n; f) are the most neutron-rich fission production mechanisms achievable and can be used to simultaneously populate hundreds of neutron-rich nuclei up to spins of 16 ~. High selectivity in the experiment was achieved via triple -ray coincidences and the use of a 400 ns period pulsed neutron beam, a technique which is unavailable to other population mechanisms such as 235U(nth; f) and 252Cf(SF). The pulsing allows time correlations to be exploited to separate delayed rays from isomeric states in the hundreds of nuclei produced, which are then used to cleanly select a particular nucleus and its exotic binary partners. In the recent experiment, several physics cases are simultaneously addressed such as shape coexistence, the evolution of shell closures far from stability, and the spectroscopy of nuclei in the r-process path near N = 82. Preliminary physics results on anomalies in the 238U(n; f) fission yields and the structure of the 138Te and 100Sr nuclei will soon be published. A future project, -ball, to couple LICORNE with a hybrid escape-suppressed spectrometer to refine further the technique and achieve a large increase in the observational limit is discussed.
DT Doherty, PJ Woods, G Lotay, D Seweryniak, MP Carpenter, CJ Chiara, HM David, RVF Janssens, L Trache, S Zhu (2014)Level structure of S 31: From low excitation energies to the region of interest for hydrogen burning in novae through the P 30 (p, γ) S 31 reaction, In: Physical Review C - Nuclear Physics89(4)
Comprehensive measurements of the excitation energy and spin-parity assignments for states in S31 are presented, from the first excited state, up to energies relevant for the P30(p,γ)S31 reaction in ONe novae. This reaction rate strongly influences heavy element abundances in novae ejecta. States in S31 are paired with their P31 analogues using γ rays detected with the Gammasphere detector array following the Si28(He4, n) fusion-evaporation reaction. The evolution of mirror energy differences is explored and the results are compared with new shell-model calculations. The excellent agreement observed in this work between experimental data and shell-model calculations provides confidence in using computed estimates in situations where experimental data are unavailable. © 2014 American Physical Society.
G Lotay, JP Wallace, PJ Woods, D Seweryniak, MP Carpenter, CJ Chiara, DT Doherty, RVF Janssens, T Lauritsen, AM Rogers, S Zhu (2012)Erratum: Level structure of 30S: Implications for the astrophysical 29P(p,γ)30S reaction rate in ONe novae and x-ray bursts(Physical Review C (2012) 86 (042801)), In: Physical Review C - Nuclear Physics86(4) G Lotay, JP Wallace, PJ Woods, D Seweryniak, MP Carpenter, CJ Chiara, DT Doherty, RVF Janssens, T Lauritsen, AM Rogers, S Zhu (2012)Level structure of 30S: Implications for the astrophysical 29P(p,γ)30S reaction rate in ONe novae and x-ray bursts, In: Physical Review C - Nuclear Physics86(4)
A γ-ray spectroscopy study of 30S is presented. Excitation energies have been determined with improved precision over previous studies and firm spin-parity assignments have been made for key 29P+p resonant states. An evaluation of the 29P(p,γ)30S reaction for T=0.08-2.5 GK shows that the 3 + and 2 + resonant states located at E r=289(3) and 410(3) keV, respectively, dominate the 29P(p,γ)30S reaction rate in ONe novae, while the 410-keV resonance is expected to govern the rate in x-ray burster environments. These new, precise resonance energy measurements and firm spin-parity assignments have significantly reduced uncertainties in the 29P(p,γ)30S reaction in ONe novae and x-ray bursts. In particular, the reaction rate is now specified precisely enough for calculations of isotopic abundances in ONe novae ejecta. © 2012 American Physical Society.
W. Korten, A. Atac, D. Beaumel, P. Bednarczyk, M.A Bentley, G. Benzoni, A. Boston, A. Bracco, J. Cederkall, B. Cederwall, M. Ciemala, E. Clement, F .C. L. Crespi, D. Curien, G. de Angelis, F. Didierjean, D.T Doherty, Zs. Dombradi, G. Duchene, J. Dudek, B. Fernandez-Dominguez, B. Fornal, A. Gadea, L. P. Gaffney, J. Gerl, K. Gladnishki, A. Goasduff, M. Gorska, P.T Greenlees, H. Hess, D.G Jenkins, P. R. John, A. Jungclaus, M. Kmiecik, A. Korichi, M. Labiche, S. Leoni, J. Ljungvall, A. Lopez-Martens, A. Maj, D. Mengoni, B. Million, A. Nannini, D. Napoli, P.J Nolan, J. Nyberg, A. Obertelli, J. Pakarinen, N. Pietralla, Zsolt Podolyak, B. Quintana, R. Raabe, G. Rainovski, F. Recchia, P. Reiter, D. Rudolph, J. Simpson, Ch. Theisen, D. Tonev, A. Tumino, J.J Valiente-Dobon, O. Wieland, K. Wimmer, M. Zielinska (2020)Physics opportunities with the Advanced Gamma Tracking Array - AGATA, In: European Physical Journal A56(137)
New physics opportunities are opening up by the Advanced Gamma Tracking Array, AGATA,as it evolves to the full 4 instrument. AGATA is a high-resolution -ray spectrometer, solely built from highly segmented high-purity Ge detectors, capable of measuring rays from a few tens of keV to beyond 10 MeV, with unprecedented effciency, excellent position resolution for individual -ray interactions, and very high count-rate capability. As a travelling detector AGATA will be employed at all major current and near-future European research facilities delivering stable and radioactive ion beams.
The use of neutron sensors is a key requirement across many technology areas, including medical particle accelerators, nuclear power technologies, personnel dosimetry, national defence, and a wide range of scientiﬁc experiments. With a zero electric charge, neutrons present particular challenges for their eﬀective detection. In the present study I report the ﬁrst demonstration of a solid-state, direct conversion sensor for thermal neutrons based on a polymer/inorganic nanocomposite. Sensors were fabricated from ultra-thick ﬁlms of poly(triarylamine) (PTAA) semiconducting polymer, with thicknesses up to 100 micrometres. Boron nanoparticles were dispersed throughout the PTAA ﬁlm to provide the neutron stopping power arising from the high thermal neutron cross-section of the isotope Boron-10. To maximise the quantum eﬃciency of the sensor to thermal neutrons, a high volume fraction of homogeneously dispersed boron nanoparticles was achieved in the thick PTAA film using an optimised processing method. Thick active layers were realised using a high molecular weight of the PTAA (Mw=350 kg/mol), so that molecular entanglements provide a high cohesive strength. A non-ionic surfactant was used to stabilise the boron dispersion in solvent and hence suppress the formation of agglomerates and associated electrical pathways. Boron nanoparticle loadings of up to 17 vol.% were achieved, with thermal neutron quantum eﬃciency estimates up to 6 % resulting. The sensors’ neutron responses were characterised under a high ﬂux thermal neutron exposure, showing a linear correlation between the response current and the thermal neutron ﬂux. The sensitivity reached up to 194 pC at maximum thermal neutron flux. Polymer-based boron nanocomposite sensors oﬀer a new neutron detection technology that uses low-cost, scalable solution processing, and provides an alternative to traditional neutron sensors that use rare isotopes, such as Helium-3.
Current fusion devices, such as the Joint European Torus (JET) operated by the UKAEA, operate using batch process fuel cycles with tritium (3H) flow rates in the order of 10s of grams per day. Future planned fusion devices, such as ITER and DEMO, would operate with continuous fuel cycles and tritium flow rates in the order of 1 to 2 kg per hour. Existing tritium measurement and accountancy instruments employ ionisation chambers which whilst barely sufficient for the needs of JET would not meet the requirements of ITER or DEMO, both of which would also likely be nuclear licensed sites. The inaccuracy of ionisation chambers stems from the variability of unknown gas species within the detector volume and/or errors in assessing the pressure and temperature of the gas stream containing the tritium, all of which effect the final reading. Some work has been done, and devices built and operated, that measure the tritium content of a volume by measurement of x-rays generated by the beta decay of the tritium. These devices have been employed in either the measurement of bulk materials or on gas streams of very pure and concentrated tritium. The systems to date measure the total counts generated (across the full energy range) which is heavily influenced by the broad spectrum bremsstrahlung x-ray signal. In this work the possibility of using the energy spectrum of x-rays generated by the tritium beta decay to better understand the sample containing the tritium, and potentially correct for any signal loss or modification of the energy dependence of the x-ray spectrum detected. Such a device would be based on the characteristic x-rays of materials impacted by the tritium beta decay rather than the gross count rate (including bremsstrahlung). A Monte Carlo code called PENELOPE is used to compare simulated results with experimental data for a series of configurations. Whilst the initial experimental tests are performed, a failure in the safety systems of the JET Active Gas Handling System (AGHS) prohibited the running of higher activity gaseous source tests. Nevertheless, the simulated and experimental data collected informs a series of more comprehensive PENELOPE simulations that indicate that if the tritium beta spectrum is modified by attenuating gases as described by literature, then an energy sensitive detector based on x-ray emission induced by beta decay could compensate and correct for errors induced in a detector by gas compositions and other factors. Such a detector would be greatly beneficial to the operation of large-scale fusion devices such as ITER and DEMO.
My research has been focused on time-dependent aspects of nuclear physics both at the mean-field and at the beyond-mean-field level. At the mean field level, the objective of my PhD has been to understand how the introduction of the tensor part of the Skyrme interaction affects heavy ion collisions and giant magnetic resonances, in a self consistent and symmetry unrestricted manner. The introduction of the tensor force redistributes the strength of the giant magnetic resonances within the same energy range. Within the study of heavy ion collisions of 16O+16O the introduction of the tensor decreased the amount of dissipation in the system. At the beyond mean field level, the objective of my PhD was to implement a time dependent density matrix (TDDM) theory, self consistently, without symmetry restrictions using the full Skyrme force. TDDM allows an order by order truncation of the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy, which relates the evolution of many body densities. If two-body correlations are assumed to dominate the dynamics of the system, the resulting equations incorporate one-particle-one-hole and two-particle-two-hole correlations. A variety of different nuclei below A=40 were chosen to study the formation of correlations for different nuclear ground states. Two body correlations were found to have a noticeable effect on the ground state properties of these nuclei. For example on average 4 - 5 % of the total energy is due to correlations. When time dependent calculations were performed with these correlated nuclei, computational limitations led to problems with conservation laws.