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Dr Gavin Lotay


Senior Lecturer

Academic and research departments

Department of Physics.

My publications

Publications

Wallace JP, Lotay G, Woods PJ, Alharbi A, Banu A, David HM, Davinson T, McCleskey M, Roeder B, Simmons E, Spiridon A, Tribble R, Trache L (2010) Measurement of the ²-p emission of 20Mg and the breakout from the hot CNO cycle, AIP Conference Proceedings 1304 pp. 429-431
In the astrophysically important reaction 19Ne(p,³) 20Na, the rate is dominated by a single key resonance at 450 keV above the proton-emission threshold in 20Na. Throughout the last few decades many experiments have been performed aimed at finding the identity of this state. Despite this, the spin-parity of the key resonant state is still up for debate. The present paper describes a new experiment studying the ²-delayed proton decay of 20Mg aimed at solving this issue. © 2010 American Institute of Physics.
Seweryniak D, Starosta K, Davids CN, Gros S, Hecht AA, Hoteling N, Khoo TL, Lagergren K, Lotay G, Peterson D, Robinson A, Vaman C, Walters WB, Woods PJ, Zhu S (2006) ± decay of Te105, Physical Review C - Nuclear Physics 73 (6)
The ± decay of the neutron-deficient nuclide Te105 was observed. The Cr50(Ni58,3n) reaction was used to produce Te105 nuclei. The Te105 residues were selected with the Argonne Fragment Mass Analyzer and implanted into a double-sided Si strip detector where their subsequent ± decay was detected. An ±-decay Q value of Q±=4900(50) keV and a half life of T1/2=0.70(-0.17+0.25)¼s were measured for Te105 and a reduced ±-decay width of W±=3.3(-1.7+2.1) was deduced. The decay properties of Te105 are compared with those of heavier Te isotopes and theoretical predictions. © 2006 The American Physical Society.
Lotay G, Wallace JP, Woods PJ, Seweryniak D, Carpenter MP, Chiara CJ, Doherty DT, Janssens RVF, Lauritsen T, Rogers AM, Zhu S (2012) Level structure of 30S: Implications for the astrophysical 29P(p,³)30S reaction rate in ONe novae and x-ray bursts, Physical Review C - Nuclear Physics 86 (4)
A ³-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,³)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,³)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,³)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.
Salter PJC, Aliotta M, Davinson T, Al Falou H, Chen A, Davids B, Fulton BR, Galinski N, Howell D, Lotay G, MacHule P, Murphy AS, Ruiz C, Sjue S, Taggart M, Walden P, Woods PJ (2012) Measurement of the Ne18(±,p 0)Na21 reaction cross section in the burning energy region for x-ray bursts, Physical Review Letters 108 (24)
The Ne18(±,p)Na21 reaction provides one of the main HCNO-breakout routes into the rp process in x-ray bursts. The Ne18(±,p 0)Na21 reaction cross section has been determined for the first time in the Gamow energy region for peak temperatures T
Lotay G, Woods PJ, Seweryniak D, Carpenter MP, Janssens RVF, Zhu S (2010) Erratum: ³-ray spectroscopy study of states in Si27 relevant for the Al26m(p,³)Si27 reaction in novae and supernovae (Physical Review C - Nuclear Physics (2009) 80, (055802)), Physical Review C - Nuclear Physics 81 (2)
Soederstroem P-A, Regan PH, Walker PM, Watanabe H, Doornenbal P, Korkulu Z, Lee P, Liu HL, Liu JJ, Lorusso G, Nishimura S, Sumikama T, Phong VH, Wu J, Xu FR, Yagi A, Zhang GX, Alharbi T, Baba H, Browne F, Bruce AM, Carroll R, Chae KY, Dombradi Z, Estrade A, Fukuda N, Griffin C, Ideguchi E, Inabe N, Isobe T, Kanaoka H, Kojouharov I, Kondev FG, Kubo T, Kubono S, Kurz N, Kuti I, Lalkovski S, Lane GJ, Lee CS, Lee EJ, Lotay G, Moon C-B, Nishizuka I, Nita CR, Odahara A, Patel Z, Podolyak Z, Roberts OJ, Sakurai H, Schaffner H, Shand CM, Suzuki H, Takeda H, Terashima S, Vajta Z, Valiente-Dobon JJ, Xu ZY, Yoshida S (2015) Heavy Rotation - Evolution of quadrupole collectivity centred at the neutron-rich doubly mid-shell nucleus Dy-170, NUCLEAR STRUCTURE AND DYNAMICS '15 1681 AMER INST PHYSICS
Lotay G, Woods PJ, Seweryniak D, Carpenter MP, Hoteling N, Janssens RVF, Jenkins DG, Lauritsen T, Lister CJ, Robinson A, Zhu S (2008) First in-beam ³-ray spectroscopy study of Al24 and its implications for the astrophysical Mg23(p,³)Al24 reaction rate in ONe novae, Physical Review C - Nuclear Physics 77 (4)
The first in-beam ³-ray spectroscopy study of Al24 is presented. A complete level structure of Al24 incorporating all states below the proton-emission threshold, has been constructed. The first excited state above the proton threshold has also been identified as a 3+ state at 2345.1 ± 1.4 keV. This state, corresponding to a resonance energy of 473 ± 3 keV, has been suggested to be the dominant resonance contributing to the Mg23(p,³)Al24 stellar reaction rate. The improved precision of the level energy and unambiguous assignment of the state has reduced the uncertainty of the Mg23(p,³)Al24 stellar reaction rate, which constrains the production of A>20 nuclei in ONe novae. © 2008 The American Physical Society.
Lotay G, Woods PJ, Seweryniak D, Carpenter MP, David HM, Janssens RVF, Zhu S (2011) Erratum: Identification of analog states in the T=1/2 A=27 mirror system from low excitation energies to the region of hydrogen burning in the 26Alg ,m(p,³)27Si reactions (Physical Review C (2011) 84 (035802)), Physical Review C - Nuclear Physics 84 (3)
Lotay G, Wallace JP, Woods PJ, Seweryniak D, Carpenter MP, Chiara CJ, Doherty DT, Janssens RVF, Lauritsen T, Rogers AM, Zhu S (2012) Erratum: Level structure of 30S: Implications for the astrophysical 29P(p,³)30S reaction rate in ONe novae and x-ray bursts(Physical Review C (2012) 86 (042801)), Physical Review C - Nuclear Physics 86 (4)
Kankainen A, Woods PJ, Nunes F, Langer C, Schatz H, Bader V, Baugher T, Bazin D, Brown BA, Browne J, Doherty DT, Estrade A, Gade A, Kontos A, Lotay G, Meisel Z, Montes F, Noji S, Perdikakis G, Pereira J, Recchia F, Redpath T, Stroberg R, Scott M, Seweryniak D, Stevens J, Weisshaar D, Wimmer K, Zegers R (2016) Angle-integrated measurements of the Al-26(d, n)Si-27 reaction cross section: a probe of spectroscopic factors and astrophysical resonance strengths, EUROPEAN PHYSICAL JOURNAL A 52 (1) ARTN 6 SPRINGER
Simmons E, Trache L, Banu A, McCleskey M, Roeder B, Spiridon A, Tribble RE, Davinson T, Woods PJ, Lotay GJ, Wallace J, Doherty D, Saastamoinen A (2013) The beta-delayed proton and gamma decay of 27P for nuclear astrophysics, Journal of Physics: Conference Series 420 (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,³)25AI(²+v)25 Mg(p,³)26Al, but this chain can be by-passed by another chain, 25Al(p, ³)26Si(p, ³)27P and it can also be destroyed directly. The reaction 26m Al (p, ³) 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%.
Wallace JP, Woods PJ, Lotay G, Alharbi A, Banu A, David HM, Davinson T, McCleskey M, Roeder BT, Simmons E, Spiridon A, Trache L, Tribble RE (2012) ²-Delayed proton-decay study of 20Mg and its implications for the Ne19(p,³)Na20 breakout reaction in X-ray bursts, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 712 (1-2) pp. 59-62
Under astrophysical conditions of high temperature and density, such as for example found in X-ray bursts, breakout can occur from the hot CNO cycles into the rapid proton capture process. A key breakout route is via the sequence O15(±,³)Ne19(p,³)Na20. The Ne19(p,³)Na20 reaction rate is expected to be dominated by a single resonance at 457(3) keV. The identity of the resonance has been under discussion for a long time, with J À=1 + and 3 + assignments suggested. In this study of the ²-delayed proton decay of 20Mg we report a new, significantly more stringent, upper limit on the ²-decay branch to this state of 0.02% with a confidence level of 90%. This makes a 1 + assignment highly unlikely and favours a 3 + assignment for which no branch is expected to be observed. The 3 + state is predicted to have a significantly higher resonance strength, and to produce a proportionately higher Ne19(p,³)Na20 reaction rate in X-ray burst conditions. © 2012 Elsevier B.V.
Seweryniak D, Carpenter MP, Gros S, Hecht AA, Hoteling N, Janssens RVF, Khoo TL, Lauritsen T, Lister CJ, Lotay G, Peterson D, Robinson AP, Walters WB, Wang X, Woods PJ, Zhu S (2009) New results near 100Sn: Observation of single-neutron states in 101Sn, Acta Physica Polonica B 40 (3) pp. 621-627
A search for in-beam ³-ray transitions in 101Sn, which contains only one neutron outside the 100Sn core, using a novel approach was carried out at the Argonne Tandem-Linac System. 101Sn nuclei were produced using the 46Ti(58Ni, 3n) 101Sn fusion-evaporation reaction. Beta-delayed protons with energies and decay times consistent with previous 101Sn decay studies were observed at the focal plane of the Fragment Mass Analyzer. In-beam ³ rays were detected in the Gammasphere Ge-detector array and were correlated with the 101Sn ²-delayed protons using the Recoil-Decay Tagging method. As a result, a ³-ray transition between the single-neutron vg7/2 and vd5/2 states situated at the Fermi surface was identified. The measured vg7/2-vd5/2 energy splitting was compared with predictions corresponding to various mean-field potentials and was used to calculate multi-neutron configurations in light Sn isotopes. Similar approach can be used to study core excitations in 101Sn and other exotic nuclei near 100Sn.
Seweryniak D, Carpenter MP, Gros S, Hecht AA, Hoteling N, Janssens RVF, Khoo TL, Lauritsen T, Lister CJ, Lotay G, Peterson D, Robinson AP, Walters WB, Wang X, Woods PJ, Zhu S (2007) Single-neutron states in Sn101, Physical Review Letters 99 (2)
The first data on the relative single-particle energies outside the doubly magic Sn100 nucleus were obtained. A prompt 171.7(6)keV ³-ray transition was correlated with protons emitted following the ² decay of Sn101 and is interpreted as the transition between the single-neutron g7/2 and d5/2 orbitals in Sn101. This observation provides a stringent test of current nuclear structure models. The measured ½g7/2-½d5/2 energy splitting is compared with values calculated using mean-field nuclear potentials and is used to calculate low-energy excited states in light Sn isotopes in the framework of the shell model. The correlation technique used in this work offers possibilities for future, more extensive spectroscopy near Sn100. © 2007 The American Physical Society.
Zhong Q, Aumann T, Bishop S, Blaum K, Boretzky K, Bosch F, Bräuning H, Brandau C, Davinson T, Dillmann I, Ershova O, Geissel H, Gyürky G, Heil M, Käppeler F, Keli? A, Kozhuharov C, Langer C, Le Bleis T, Litvinov YA, Lotay G, Marganiec J, Petridis N, Plag R, Popp U, Reifarth R, Riese B, Rigollet C, Scheidenberger C, Simon H, Stöhlker T, Szücs T, Weber G, Weick H, Winters DFA, Winters N, Woods J (2010) 96Ru(p,³)97Rh measurement at the GSI storage ring, Journal of Physics: Conference Series 202
A pioneering experiment was recently performed at the Experimental Storage Ring (ESR) at GSI. Fully stripped ions of 96Ru were injected into the storage ring and slowed down to a few MeV per nucleon. The 97Rh ions from the 96Ru(p,³) reaction at a newly developed hydrogen jet target were detected with Double Sided Silicon Strip Detectors (DSSSD) mounted inside a pocket. The experiment and the status of the analysis at a beam energy of 11 MeV per nucleon will be presented. © 2010 IOP Publishing Ltd.
Assié M, de Oliveira Santos F, Davinson T, de Grancey F, Achouri L, Alcántara-Núñez J, Al Kalanee T, Angélique JC, Borcea C, Borcea R, Caceres L, Celikovic I, Chudoba V, Pang DY, Ducoin C, Fallot M, Kamalou O, Kiener J, Lam Y, Lefebvre-Schuhl A, Lotay G, Mrazek J, Perrot L, Sánchez-Benítez AM, Rotaru F, Saint-Laurent MG, Sobolev Y, Smirnova N, Stanoiu M, Stefan I, Subotic K, Ujic P, Wolski R, Woods PJ (2012) Spectroscopy of 18Na: Bridging the two-proton radioactivity of 19Mg, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 712 (3) pp. 198-202
The unbound nucleus 18Na, the intermediate nucleus in the two-proton radioactivity of 19Mg, was studied by the measurement of the resonant elastic scattering reaction H( 17Ne,p) 17Ne performed at 4 A.MeV using a radioactive beam from the SPIRAL Facility. Spectroscopic properties of the low-lying states were obtained in an R-matrix analysis of the excitation function. © 2012 Elsevier B.V.
Margerin V, Lotay G, Woods PJ, Aliotta M, Christian G, Davids B, Davinson T, Doherty DT, Fallis J, Howell D, Kirsebom OS, Mountford DJ, Rojas A, Ruiz C, Tostevin JA (2015) Inverse Kinematic Study of the Al-26g(d,p)Al-27 Reaction and Implications for Destruction of Al-26 in Wolf-Rayet and Asymptotic Giant Branch Stars, PHYSICAL REVIEW LETTERS 115 (6) ARTN 062701 AMER PHYSICAL SOC
Mei B, Aumann T, Bishop S, Blaum K, Boretzky K, Bosch F, Brandau C, Bräuning H, Davinson T, Dillmann I, Dimopoulou C, Ershova O, Fülöp Z, Geissel H, Glorius J, Gyürky G, Heil M, Käppeler F, Kelic-Heil A, Kozhuharov C, Langer C, Le Bleis T, Litvinov Y, Lotay G, Marganiec J, Münzenberg G, Nolden F, Petridis N, Plag R, Popp U, Rastrepina G, Reifarth R, Riese B, Rigollet C, Scheidenberger C, Simon H, Sonnabend K, Steck M, Stöhlker T, Szücs T, Sümmerer K, Weber G, Weick H, Winters D, Winters N, Woods P, Zhong Q (2015) First measurement of the Ru 96 (p,³) Rh 97 cross section for the p process with a storage ring, Physical Review C - Nuclear Physics 92 (3)
© 2015 authors. Published by the American Physical Society.This work presents a direct measurement of the Ru96(p,³)Rh97 cross section via a novel technique using a storage ring, which opens opportunities for reaction measurements on unstable nuclei. A proof-of-principle experiment was performed at the storage ring ESR at GSI in Darmstadt, where circulating Ru96 ions interacted repeatedly with a hydrogen target. The Ru96(p,³)Rh97 cross section between 9 and 11 MeV has been determined using two independent normalization methods. As key ingredients in Hauser-Feshbach calculations, the ³-ray strength function as well as the level density model can be pinned down with the measured (p,³) cross section. Furthermore, the proton optical potential can be optimized after the uncertainties from the ³-ray strength function and the level density have been removed. As a result, a constrained Ru96(p,³)Rh97 reaction rate over a wide temperature range is recommended for p-process network calculations.
Ruotsalainen P, Jenkins DG, Bentley MA, Wadsworth R, Scholey C, Auranen K, Davies PJ, Grahn T, Greenlees PT, Henderson J, HerzáH A, Jakobsson U, Joshi P, Julin R, Juutinen S, Konki J, Leino M, Lotay G, Nichols AJ, Obertelli A, Pakarinen J, Partanen J, Peura P, Rahkila P, Sandzelius M, Sarén J, Sorri J, Stolze S, Uusitalo J (2013) Spectroscopy of proton-rich 66Se up to JÀ=6+: Isospin-breaking effect in the A=66 isobaric triplet, Physical Review C - Nuclear Physics 88 (4)
Candidates for three excited states in the 66Se have been identified using the recoil-² tagging method together with a veto detector for charged-particle evaporation channels. These results allow a comparison of mirror and triplet energy differences between analog states across the A=66 triplet as a function of angular momentum. The extracted triplet energy differences follow the negative trend observed in the f7/2 shell. Shell-model calculations indicate that the strength of the Coulomb isotensor part alone is not sufficient to account for this trend in the case of the A=66 triplet. © 2013 American Physical Society.
Regan PH, Shearman R, Judge SM, Lorusso G, Main P, Bell S, Collins SM, Ivanov P, Jerome SM, Keightley JD, Larijani C, Lotay G, Pearce AK (2015) Development of NANA: A Fast-Scintillator, Coincidence Gamma-ray Array for Radioactive Source Characterisation and Absolute Activity Measurements at the UK National Physical Laboratory, APPLICATIONS OF NOVEL SCINTILLATORS FOR RESEARCH AND INDUSTRY (ANSRI 2015) 620 IOP PUBLISHING LTD
Doherty DT, Woods PJ, Lotay G, Seweryniak D, Carpenter MP, Chiara CJ, David HM, Janssens RVF, Trache L, Zhu S (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, ³) S 31 reaction, Physical Review C - Nuclear Physics 89 (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,³)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 ³ 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.
Salter PJC, Aliotta M, Davinson T, Al Falou H, Chen A, Davids B, Fulton BR, Galinski N, Howell D, Lotay G, MacHule P, Murphy ASJ, Ruiz C, Sjue S, Taggart M, Walden P, Woods PJ (2012) Erratum: Measurement of the Ne18(±,p 0)Na21 reaction cross section in the burning energy region for X-ray bursts (Physical Review Letters (2012) 108 (242701)), Physical Review Letters 109 (6)
Lotay G, Woods PJ, Seweryniak D, Carpenter MP, David HM, Janssens RVF, Zhu S (2011) Identification of analog states in the T=1/2 A=27 mirror system from low excitation energies to the region of hydrogen burning in the 26Alg ,m(p,³)27Si reactions, Physical Review C - Nuclear Physics 84 (3)
The reactions 26Alg(p,³)27Si and 26Alm(p,³)27Si are important for influencing the galactic abundance of the cosmic ³-ray emitter 26Alg and for the excess abundance of 26Mg found in presolar grains, respectively. Precise excitation energies and spin assignments of states from the ground state to the region of astrophysical interest in 27Si, including the identification and pairing of key astrophysical resonances with analog states in the mirror nucleus 27Al, are reported using ³ rays observed in the 12C + 16O fusion reaction. The detailed evolution of Coulomb energy differences between the states in 27Si and 27Al is explored, including the region above the astrophysical reaction thresholds. © 2011 American Physical Society.
Assié M, De Oliveira Santos F, De Grancey F, Achouri L, Alcantara-Nunez J, AngÉlique JC, Borcea C, Caceres L, Celikovic I, Chudoba V, Pang DY, Davinson T, Ducoin C, Fallot M, Kiener J, Lefebvre-Schuhl A, Lotay GL, Mrazek J, Perrot L, Sanchez-Benitez AM, Rotaru F, Saint-Laurent MG, Sobolev Y, Stanoiu M, Stanoiu R, Stefan I, Subotic K, Woods PJ, Ujic P, Wolski R (2011) Spectroscopy of the unbound nucleus 18Na, International Journal of Modern Physics E 20 (4) pp. 971-975
The unbound nucleus 18Na, the intermediate nucleus in the two-proton radioactivity of 19Mg, is studied through the resonant elastic scattering 17Ne(p,17Ne)p. The spectroscopic information obtained in this experiment is discussed and put in perspective with previous measurements and the structure of the mirror nucleus 18N. © 2011 World Scientific Publishing Company.
Lotay G, Christian G, Ruiz C, Akers C, Burke DS, Catford WN, Chen AA, Connolly D, Davids B, Fallis J, Hager U, Hutcheon DA, Mahl A, Rojas A, Sun X (2016) Direct Measurement of the Astrophysical K-38(p,gamma)Ca-39 Reaction and Its Influence on the Production of Nuclides toward the End Point of Nova Nucleosynthesis, PHYSICAL REVIEW LETTERS 116 (13) ARTN 132701 AMER PHYSICAL SOC
Trache L, Banu A, Hardy JC, Iacob VE, McCleskey M, Roeder BT, Simmons E, Spiridon A, Tribble RE, Saastamoinen A, Jokinen A, Äysto J, Davinson T, Lotay G, Woods PJ, Pollacco E (2012) Decay spectroscopy for nuclear astrophysics: ²- and ²-delayed proton decay, Journal of Physics: Conference Series 337 (1)
In several radiative proton capture reactions important in novae and XRBs, the resonant parts play the capital role. We use decay spectroscopy techniques to find these resonances and study their properties. We have developed techniques to measure beta- and beta-delayed proton decay of sd-shell, proton-rich nuclei produced and separated with the MARS recoil spectrometer of Texas A&M University. The short-lived radioactive species are produced in-flight, separated, then slowed down (from about 40 MeV/u) and implanted in the middle of very thin Si detectors. This allows us to measure protons with energies as low as 200 keV from nuclei with lifetimes of 100 ms or less. At the same time we measure gamma-rays up to 8 MeV with high resolution HPGe detectors. We have studied the decay of 23Al, 27P, 31Cl, all important for understanding explosive H-burning in novae. The technique has shown a remarkable selectivity to beta-delayed charged-particle emission and works even at radioactive beam rates of a few pps. The states populated are resonances for the radiative proton capture reactions 22Na(p,³) 23Mg (crucial for the depletion of 22Na in novae), 26mAl(p,³) 27Si and 30P(p,³) 31S (bottleneck in novae and XRB burning), respectively. Lastly, results with a new detector that allowed us to measure down to about 80 keV proton energy are announced.
Margerin V, Murphy ASJ, Davinson T, Dressler R, Fallis J, Kankainen A, Laird AM, Lotay G, Mountford DJ, Murphy CD, Seiffert C, Schumann D, Stowasser T, Stora T, Wang CHT, Woods PJ (2014) Study of the Ti44(±,p)V47 reaction and implications for core collapse supernovae, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 731 pp. 358-391
The underlying physics triggering core collapse supernovae is not fully understood but observations of material ejected during such events helps to solve this puzzle. In particular, several satellite based ³-ray observations of the isotope 44Ti have been reported recently. Conveniently, the amount of this isotope in stellar ejecta is thought to depend critically on the explosion mechanism. The most influential reaction to the amount of 44Ti in supernovae is Ti44(±,p)V47. Here we report on a direct study of this reaction conducted at the REX-ISOLDE facility, CERN. The experiment was performed with a 44Ti beam at Elab = 2.16MeV/u, corresponding to an energy distribution, for reacting ±-particles, centred on Ecm = 4.15 with a 1Ã width of 0.23 MeV. This is, for the first time, well within the Gamow window for core collapse supernovae. The material from which the 44Ti beam was extracted originates from highly irradiated components of the SINQ spallation neutron source of the Paul Scherrer Institute. No yield above background was observed, enabling an upper limit for the rate of this reaction to be determined. This result is below expectation, suggesting that the Ti44(±,p)V47 reaction proceeds more slowly than previously thought. Implications for astrophysical events, and remnant age, are discussed. © 2014 The Authors.
Lotay G, Woods PJ, Seweryniak D, Carpenter MP, Janssens RVF, Zhu S (2009) Identification of key astrophysical resonances relevant for the Al26g(p,³)Si27 reaction in Wolf-Rayet stars, AGB stars, and classical novae, Physical Review Letters 102 (16)
A ³-ray spectroscopy study of Al26g+p resonant states in Si27 is presented. Excitation energies were measured with improved precision and first spin-parity assignments made for excited states in Si27 above the proton threshold. The results indicate the presence of low-lying resonances with lp=0 and lp=2 captures that could strongly influence the Al26g(p,³)Si27 reaction rate at low stellar temperatures, found in low-mass asymptotic giant branch (AGB), intermediate-mass AGB, super AGB, and Wolf-Rayet stars. © 2009 The American Physical Society.
Lotay G, Woods PJ, Seweryniak D, Carpenter MP, Janssens RVF, Zhu S (2009) ³-ray spectroscopy study of states in Si27 relevant for the Al26m(p,³)Si27 reaction in novae and supernovae, Physical Review C - Nuclear Physics 80 (5)
The heavy-ion, fusion-evaporation reaction C12(O16,n) was used to identify ³-decay transitions from excited states in Si27 above the proton threshold. The precise level energy measurements, JÀ assignments, and lifetime measurements of astrophysically important Al26m+p resonances have allowed an evaluation of the Al26m(p,³)Si27 reaction rate. An lp=0 resonance has been newly identified at a center-of-mass energy in the Al26m+p system of 146.3(3) keV and is expected to dominate the rate for low stellar temperatures. In addition, an lp=1 resonance has been identified at 378.3(30) keV and is likely to dominate the rate at high astrophysical temperatures, such as those found in oxygen-neon novae and core-collapse supernovae. © 2009 The American Physical Society.
Seweryniak D, Lotay G, Woods PJ, Carpenter MP, Chiara CJ, David HM, Davinson T, Hoffman C, Janssens RVF, Khoo TL, Lauritsen T, Lister CJ, Liu Z, McCutchan EA, Rogers AM, Walters WB, Zhu S (2011) Nuclear structure studies along the proton dripline at ATLAS, AIP Conference Proceedings 1409 pp. 49-54
Nuclei far from the line of stability are a focal point of contemporary nuclear physics. Nuclear structure studies along the proton dripline remain an important component of the scientific program at the ATLAS facility. The Gammasphere gamma-ray array and the Fragment Mass Analyzer offer the unprecedented sensitivity and selectivity required to study nuclei at and beyond the proton dripline. Recent results in proton decay studies, in-beam ³-ray spectroscopy around 100Sn and studies of proton resonances in light nuclei involved in the astrophysical hydrogen burning are presented. Future prospects in the context of planned and on-going upgrades of ATLAS and experimental apparatus are also briefly discussed. © 2011 American Institute of Physics.
Doherty DT, Lotay G, Woods PJ, Seweryniak D, Carpenter MP, Chiara CJ, David HM, Janssens RVF, Trache L, Zhu S (2012) Key resonances in the P30(p,³)S31 gateway reaction for the production of heavy elements in ONe novae, Physical Review Letters 108 (26)
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 P30(p,³)S31 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 S31 relevant for the P30(p,³)S31 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 P30(p,³)S31 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. © 2012 American Physical Society.
Henderson J, Ruotsalainen P, Jenkins DG, Scholey C, Auranen K, Davies PJ, Grahn T, Greenlees PT, Henry TW, HerzáH A, Jakobsson U, Joshi P, Julin R, Juutinen S, Konki J, Leino M, Lotay G, Nichols AJ, Obertelli A, Pakarinen J, Partanen J, Peura P, Rahkila P, Sandzelius M, Sarén J, Sorri J, Stolze S, Uusitalo J, Wadsworth R (2013) Enhancing the sensitivity of recoil-beta tagging, Journal of Instrumentation 8 (4)
Tagging with ²-particles at the focal plane of a recoil separator has been shown to be an effective technique for the study of exotic proton-rich nuclei. This article describes three new pieces of apparatus used to greatly improve the sensitivity of the recoil-beta tagging technique. These include a highly-pixelated double-sided silicon strip detector, a plastic phoswich detector for discriminating high-energy ²-particles, and a charged-particle veto box. The performance of these new detectors is described and characterised, and the resulting improvements are discussed.© 2013 IOP Publishing Ltd and Sissa Medialab srl.
Jenkins DG, Meadowcroft A, Pattabiraman NS, Seweryniak D, Lister CJ, Carpenter MP, Janssens RVF, Rehm KE, Lauritsen T, Zhu S, Woods PJ, Davinson T, Lotay GJ, José J (2009) Indirect nuclear physics techniques for studying nova nucleosynthesis, AIP Conference Proceedings 1098 pp. 82-87
Classical novae are a site of explosive nucleosynthesis where hydrogen rich material from a companion giant star accretes onto the surface of a white warf. Critical to our understanding of nova explosions are proton-capture reaction rates involved in the nucleosynthesis. While, ideally, all of the relevant (p,³) reactions would be measured directly, in practice, such measurements are very challenging and are only possible in a few cases. This provides considerable scope for indirect measurements including transfer reactions, mass measurements, beta-decay and gamma- ray spectroscopy. The latter technique, until recently largely neglected as an input in nuclear astrophysics analyses, has clear advantages in locating resonances with high energy precision and assisting in determining the spin and parity of resonances. Such information is very valuable in a complementary approach to indirect determinations of key reaction rates. © 2009 American Institute of Physics.
Kankainen A, Woods P, Schatz H, Poxon-Pearson T, Doherty D, Bader V, Baugher T, Bazin D, Brown B, Browne J, Estrade A, Gade A, José J, Kontos A, Langer C, Lotay G, Meisel Z, Montes F, Noji S, Nunes F, Perdikakis G, Pereira J, Recchia F, Redpath T, Stroberg R, Scott M, Seweryniak D, Stevens J, Weisshaar D, Zegers R (2017) Measurement of key resonance states for the 30P(p, ³)31Sreaction rate, and the production of intermediate-mass elements in nova explosions, Physics Letters B 769 pp. 549-553 Elsevier
We report the first experimental constraints on spectroscopic factors and strengths of key resonances in the 30P(p, ³)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 ³-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 TH0.10?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.
Shand CM, Wilson E, Podolyak Z, Grawe H, Brown BA, Fornal B, Janssens RVF, Bowry M, Bunce M, Carpenter MP, Carroll RJ, Chiara CJ, Cieplicka-Orynczak N, Deo AY, Dracoulis GD, Hoffman CR, Kempley RS, Kondev FG, Lane GJ, Lauritsen T, Lotay G, Reed MW, Regan PH, Rodriguez-Triguero C, Seweryniak D, Szpak B, Walker PM, Zhu S (2015) STRUCTURE OF Pb-207 POPULATED IN Pb-208+Pb-208 DEEP-INELASTIC COLLISIONS, ACTA PHYSICA POLONICA B 46 (3) pp. 619-622 WYDAWNICTWO UNIWERSYTETU JAGIELLONSKIEGO
Podolyak Z, Shand CM, Wilson E, Brown BA, Grawe H, Chiara CJ, Zhu S, Fornal B, Janssens RVF, Bowry M, Bunce M, Carpenter MP, Cieplicka N, Deo AY, Dracoulis GD, Hoffman CR, Kempley RS, Kondev FG, Lane GJ, Lauritsen T, Lotay G, Reed MW, Regan PH, Triguero CR, Seweryniak D, Szpak B, Walker PM (2015) Octupole transitions in the Pb-208 region, 11TH INTERNATIONAL SPRING SEMINAR ON NUCLEAR PHYSICS: SHELL MODEL AND NUCLEAR STRUCTURE - ACHIEVEMENTS OF THE PAST TWO DECADES 580 ARTN 012010 IOP PUBLISHING LTD
Simmons E, Trache L, Banu A, McCleskey M, Roeder B, Spiridon A, Tribble R, Saastamoinen A, Aysto J, Davinson T, Woods P, Lotay G, Wallace J (2010) Very low energy protons from the beta decay of proton rich nuclei for nuclear astrophysics, AIP Conference Proceedings 1304 pp. 415-419
The MARS group at TAMU has developed a new experimental technique to measure very low energy protons from ²-delayed proton-decay of proton-rich nuclei produced and separated with the MARS recoil spectrometer at TAMU. Recently we have investigated the ²-delayed p-decays of 23Al [1], and 31Cl [2], and obtained information on the resonances in the 22Na(p,³)23Mg and 30P(p,³) 31S reactions, respectively. These reactions are important in explosive H-burning in Novae [3]. Recently an experiment looking at the ²-delayed p-decay of 20Mg was also done in order to obtain information on resonances in the 19Ne(p,³)20Na reaction. A simple setup consisting of a telescope made of a thin double sided Si strip detector (p-detector) backed or sandwiched between two thick Si detectors (²-detectors) was designed. We studied different W1 and BB2 p-detectors made by MSL, and found that the thinner detectors with a small cell size are best to measure proton energies as low as 2-300 keV. © 2010 American Institute of Physics.
Pattabiraman NS, Jenkins DG, Bentley MA, Wadsworth R, Lister CJ, Carpenter MP, Janssens RVF, Khoo TL, Lauritsen T, Seweryniak D, Zhu S, Lotay G, Woods PJ, Krishichayan, Isacker PV (2008) Analog E1 transitions and isospin mixing, Physical Review C - Nuclear Physics 78 (2)
We investigate whether isospin mixing can be determined in a model-independent way from the relative strength of E1 transitions in mirror nuclei. The specific examples considered are the A=31 and A=35 mirror pairs, where a serious discrepancy between the strengths of 7/2-’5/2+ transitions in the respective mirror nuclei has been observed. A theoretical analysis of the problem suggests that it ought to be possible to disentangle the isospin mixing in the initial and final states given sufficient information on experimental matrix elements. With this in mind, we obtain a lifetime for the relevant 7/2- state in S31 using the Doppler-shift attenuation method. We then collate the available information on matrix elements to examine the level of isospin mixing for both A=31 and A=35 mirror pairs. © 2008 The American Physical Society.
Grieser M, Litvinov YA, Raabe R, Blaum K, Blumenfeld Y, Butler PA, Wenander F, Woods PJ, Aliotta M, Andreyev A, Artemyev A, Atanasov D, Aumann T, Balabanski D, Barzakh A, Batist L, Bernardes A-P, Bernhardt D, Billowes J, Bishop S, Borge M, Borzov I, Bosch F, Boston AJ, Brandau C, Catford W, Catherall R, Cederkall J, Cullen D, Davinson T, Dillmann I, Dimopoulou C, Dracoulis G, Duellmann CE, Egelhof P, Estrade A, Fischer D, Flanagan K, Fraile L, Fraser MA, Freeman SJ, Geissel H, Gerl J, Greenlees P, Grisenti RE, Habs D, von Hahn R, Hagmann S, Hausmann M, He JJ, Heil M, Huyse M, Jenkins D, Jokinen A, Jonson B, Joss DT, Kadi Y, Kalantar-Nayestanaki N, Kay BP, Kiselev O, Kluge H-J, Kowalska M, Kozhuharov C, Kreim S, Kroell T, Kurcewicz J, Labiche M, Lemmon RC, Lestinsky M, Lotay G, Ma XW, Marta M, Meng J, Muecher D, Mukha I, Mueller A, Murphy ASJ, Neyens G, Nilsson T, Nociforo C, Noertershaeuser W, Page RD, Pasini M, Petridis N, Pietralla N, Pfuetzner M, Podolyak Z, Regan P, Reed MW, Reifarth R, Reiter P, Repnow R, Riisager K, Rubio B, Sanjari MS, Savin DW, Scheidenberger C, Schippers S, Schneider D, Schuch R, Schwalm D, Schweikhard L, Shubina D, Siesling E, Simon H, Simpson J, Smith J, Sonnabend K, Steck M, Stora T, Stoehlker T, Sun B, Surzhykov A, Suzaki F, Tarasov O, Trotsenko S, Tu XL, Van Duppen P, Volpe C, Voulot D, Walker PM, Wildner E, Winckler N, Winters DFA, Wolf A, Xu HS, Yakushev A, Yamaguchi T, Yuan YJ, Zhang YH, Zuber K (2012) Storage ring at HIE-ISOLDE Technical design report, EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS 207 (1) pp. 1-117 SPRINGER HEIDELBERG
Wilson E, Podolyak Z, Grawe H, Brown BA, Chiara CJ, Zhu S, Fornal B, Janssens RVF, Shand CM, Bowry M, Bunce M, Carpenter MP, Cieplicka-Orynczak N, Deo AY, Dracoulis GD, Hoffman CR, Kempley RS, Kondev FG, Lane GJ, Lauritsen T, Lotay G, Reed MW, Regan PH, Triguero CR, Seweryniak D, Szpak B, Walker PM (2015) Core excitations across the neutron shell gap in Tl-207, PHYSICS LETTERS B 747 pp. 88-92 ELSEVIER SCIENCE BV
David HM, Woods PJ, Lotay G, Seweryniak D, Albers M, Alcorta M, Carpenter MP, Chiara CJ, Davinson T, Doherty DT, Hoffman CR, Janssens RVF, Lauritsen T, Rogers AM, Zhu S (2013) Low-lying T=0 states in the odd-odd N=Z nucleus 62Ga, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 726 (4-5) pp. 665-669
New, low-lying levels in the odd-odd, N=Z nucleus 62Ga have been identified using a sensitive technique, where in-beam ³ rays from short-lived nuclei are tagged with ² decays following recoil mass identification. A comparison of the results with shell-model and IBM-4 calculations demonstrates good agreement between theory and experiment, with the majority of predicted low-lying, low-spin T=0 states now identified. There is a dramatic change in the level density at low excitation energies for the N=Z nucleus 62Ga when compared with neighbouring odd-odd Ga isotopes where, in contrast, the low-lying level structure is dominated by configurations with T=1 pairing interactions between excess neutrons. This illustrates the distinctively different aspects of nuclear structure exhibited by nuclei with N=Z. © 2013 Elsevier B.V.
Simmons E, Trache L, Banu A, McCleskey M, Roeder B, Spiridon A, Tribble R, Saastamoinen A, Aysto J, Davinson T, Woods P, Lotay G (2010) Very low energy protons from the beta decay of proton rich nuclei for nuclear astrophysics, AIP Conference Proceedings 1213 pp. 239-241
We have developed a new experimental technique to measure very low energy protons from ²-delayed p-decay of proton-rich nuclei produced and separated with the MARS recoil spectrometer at TAMU. Recently we have investigated the ²-delayed p-decays of 23Al[1] and 31Cl[2] and obtained information on the resonances in the reactions 22Na(p, ³)23Mg and 30P(p,³)31S, respectively. These reactions are important in explosive H-burning in Novae [3]. A simple setup consisting of a telescope made of a thin double sided Si strip detector (p-detector) backed or sandwiched between two thick Si detectors (²-detectors) was designed. We studied two different p-detectors and found that the thinner detectors with a small cell size are best to measure proton energies as low as 2-300 keV. © 2010 American Institute of Physics.
Wu J, Nishimura S, Lorusso G, Moller P, Ideguchi E, Regan PH, Simpson G, Soderstrom P, Walker PM, Watanabe H, Xu Z, Baba H, Browne F, Daido R, Doornenbal P, Fang Y, Gey G, Isobe T, Lee P, Liu J, Li Z, Korkulu Z, Patel Z, Phong V, Rice S, Sakurai H, Sinclair L, Sumikama T, Tanaka M, Yagi A, Ye Y, Yokoyama R, Zhang G, Alharbi T, Aoi N, Bello Garrote F, Benzoni G, Bruce A, Carroll R, Chae K, Dombradi Z, Estrade A, Gottardo A, Griffin C, Kanaoka H, Kojouharov I, Kondev F, Kubono S, Kurz N, Kuti I, Lalkovski S, Lane G, Lee E, Lokotko T, Lotay GJ, Moon C, Nishibata H, Nishizuka I, Nita C, Odahara A, Podolyak Z, Roberts O, Schaffner H, Shand CM, Taprogge J, Terashima S, Vajta Z, Yoshida S (2017) 94 -Decay Half-lives of Neutron-Rich 55Cs to 67Ho: Experimental Feedback and Evaluation of the r-Process Rare-Earth Peak Formation, Physical Review Letters 118 (7) 072701 American Physical Society
The -decay half-lives of 94 neutron-rich nuclei 144?151Cs, 146?154Ba, 148?156La, 150?158Ce, 153?160Pr, 156?162Nd, 159?163Pm, 160?166Sm, 161?168Eu, 165?170Gd, 166?172Tb, 169?173Dy, 172?175Ho and two isomeric states 174mEr, 172mDy were measured at Radioactive Isotope Beam Factory (RIBF), providing a new experimental basis to test theoretical models. Striking, large drops of -decay half-lives are observed at neutron-number N = 97 for 58Ce, 59Pr, 60Nd, 62Sm, and N = 105 for 63Eu, 64Gd, 65Tb, 66Dy. Features in the data mirror the interplay between pairing effects and microscopic structure. r-Process network calculations performed for a range of mass models and astrophysical conditions show that the 57 half-lives measured for the first time play an important role in shaping the abundance pattern of rare-earth elements in the solar system.
Courtin S, Fruet G, Jenkins D, Heine M, Montanari D, Morris L, Lotay GJ, Regan PH, Kirsebom O, Della Negra S, Hammache F, De Sereville N, Bastin B, de Oliveira F, Randisi G, Stodel C, Beck C, Haas F (2017) Fusion Cross Sections of Astrophysics Interest Within the STELLA Project., Proceedings of the 14th International Symposium on Nuclei in the Cosmos (NIC2016) 2017 021001 Physical Society of Japan
Low energy fusion between light heavy-ions is a key feature of the evolution of massive stars. In systems of astrophysical interest, the process may be strongly affected by molecular configurations of the compound nucleus, leading to resonant S factors. In particular, the 12C+12C fusion reaction has been the object of numerous experimental investigations. The STELLA project has been developed to extend these investigations to lower energies towards the Gamow window.
Watanabe H, Zhang G, Yoshida K, Walker PM, Liu J, Wu J, Regan PH, Soderstrom P, Kanaoka H, Korkulu Z, Lee P, Nishimura S, Yagi A, Ahn D, Alharbi T, Baba H, Browne F, Bruce A, Fukuda R, Griffin C, Ideguchi E, Inabe N, Isobe T, Kanaya S, Kojouharov I, Kondev F, Kubo T, Kubono S, Kurz N, Kuti I, Lalkovski S, Lane; G, Lee C, Lee E, Lorusso G, Lotay GJ, Moon C, Nishizuka I, Nita C, Odahara A, Patel Z, Phong V, Podolyak Z, Roberts O, Sakurai H, Schaffner H, Shand CM, Shimizu Y, Sumikama T, Suzuki H, Takeda H, Terashima S, Vajta; Z, Valiente-Dobon J, Xu Z (2016) Long-lived K isomer and enhanced gamma vibration in the neutron-rich nucleus 172Dy: Collectivity beyond double midshell, Physics Letters B 760 (Sept) pp. 641-646 Elsevier
The level structure of 172Dy has been investigated for the first time by means of decay spectroscopy following in-flight fission of a 238U beam. A long-lived isomeric state with T1/2 = 0.71(5) s and K À = 8 ? has been identified at 1278 keV, which decays to the ground-state and ³-vibrational bands through hindered electromagnetic transitions, as well as to the daughter nucleus 172Ho via allowed ² decays. The robust nature of the K À = 8 ? isomer and the ground-state rotational band reveals an axially-symmetric structure for this nucleus. Meanwhile, the ³-vibrational levels have been identified at unusually low excitation energy compared to the neighboring well-deformed nuclei, indicating the significance of the microscopic effect on the non-axial collectivity in this doubly mid-shell region. The underlying mechanism of enhanced ³ vibration is discussed in comparison with the deformed Quasiparticle Random-Phase Approximation based on a Skyrme energy-density functional.
Söderström P, Walker PM, Wu J, Liu H, Regan PH, Watanabe H, Doornenbal P, Korkulu Z, Lee P, Liu J, Lorusso G, Nishimura S, Phong V, Sumikama T, Xu F, Lalkovski S, Lotay GJ, Patel Z, Podolyak Z, Shand CM (2016) K-mixing in the doubly mid-shell nuclide 170Dy and the role of vibrational degeneracy, Physics Letters B 762 pp. 404-408 Elsevier
A detailed study of the structure of the doubly mid-shell nucleus View the MathML source has been carried out, following isomeric and ² decay. We have measured the yrast band up to the spin-parity JÀ=6+ state, the K=2³ -vibration band up to the 5+ state, a low-lying negative-parity band based on a 2? state that could be a candidate for the lowest energy octupole vibration state within this nucleus, and a candidate for the KÀ=6+ two quasi-particle isomer. This state was determined to have an excitation energy of 1643.91(23) keV and a half life of 0.99(4) ¼s, with a reduced hindrance for its decay to the ground-state band an order of magnitude lower than predicted by NpNn systematics. This is interpreted as being due to ³ -vibrational mixing from a near degeneracy of the isomer and the 6+ state of the ³ band. Furthermore, the parent nucleus 170Tb has been determined to have a half-life of View the MathML source s with a possible spin-parity of 2?.
Gurgi LA, Regan PH, Söderström P, Watanabe H, Walker PM, Podolyak Z, Nishimura S, Berry TA, Doornenbal P, Lorusso G, Isobe T, Baba H, Xu Z, Sakurai H, Sumikama T, Catford WN, Bruce A, Browne F, Lane G, Kondev F, Odahara A, Wu J, Liu H, Xu F, Korkulu Z, Lee P, Liu J, Phong V, Yagi A, Zhang G, Alharbi T, Carroll R, Chae K, Dombradi Z, Estrade A, Fukuda N, Griffin C, Ideguchi E, Inabe N, Kanaoka H, Kojouharov I, Kubo T, Kubono S, Kurz N, Kuti I, Lalkovski S, Lee E, Lee C, Lotay GJ, Moon C, Nishizuka I, Nita C, Patel Z, Roberts O, Schaffner H, Shand CM, Suzuki H, Takeda H, Terashima S, Vajta Z, Kanaya S, Valiente-Dobón J (2017) Isomer Spectroscopy of Neutron-rich 165,167Tb, Acta Physica Polonica B 48 (3) pp. 601-608
We present information on the excited states in the prolate-deformed, neutron-rich nuclei 165;167Tb100;102. The nuclei of interest were synthesised following in-flight fission of a 345 MeV per nucleon 238U primary beam on a 2 mm 9Be target at the Radioactive Ion-Beam Factory (RIBF), RIKEN, Japan. The exotic nuclei were separated and identified event-by-event using the BigRIPS separator, with discrete energy gamma-ray decays from isomeric states with half-lives in the s regime measured using the EURICA gamma-ray spectrometer. Metastable-state decays are identified in 165Tb and 167Tb and interpreted as arising from hindered E1 decay from the 7 2 [523] single quasi-proton Nilsson configuration to rotational states built on the 3 2 [411] single quasi-proton ground state. These data correspond to the first spectroscopic information in the heaviest, odd-A terbium isotopes reported to date and provide information on proton Nilsson configurations which reside close to the Fermi surface as the 170Dy doubly-midshell nucleus is approached.
Gurgi Laila, Regan Patrick, Söderström P-A, Watanabe H, Walker Philip, Podolyak Zsolt, Nishimura S, Berry Thomas, Doornenbal P, Lorusso G, Isobe T, Baba H, Xu ZY, Sakurai H, Sumikama T, Catford Wilton, Bruce AM, Browne F, Lane GJ, Kondev FG, Odahara A, Wu J, Liu HL, Xu FR, Korkulu Z, Lee P, Liu JJ, Phong VH, Yag A, Zhang GX, Alharbi T, Carroll RJ, Chae KY, Dombradi Zs, Estrade A, Fukuda N, Griffin C, Ideguchi E, Inabe N, Kanaoka H, Kojouharov I, Kubo T, Kubono S, Kurz N, Kuti I, Lalkovski S, Lee EJ, Lee CS, Lotay Gavin, Moon C-B, Nishizuka I, Nita CR, Patel Z, Roberts OJ, Schaffner H, Shand Callum, Suzuki H, Takeda H, Terashima S, Vajta Zs, Yoshida S, Valiente-Dòbon JJ (2016) Isomer spectroscopy of neutron-rich 168Tb103, Radiation Physics and Chemistry 140 pp. 493-496 Elsevier
In-flight fission of a 345 MeV per nucleon 238U primary beam on a 2 mm thick 9Be target has been used to
produce and study the decays of a range of neutron-rich nuclei centred around the doubly mid-shell nucleus
170Dy at the RIBF Facility, RIKEN, Japan. The produced secondary fragments of interest were identified eventby-
event using the BigRIPS separator. The fragments were implanted into the WAS3ABI position sensitive
silicon active stopper which allowed pixelated correlations between implants and their subsequent ²-decay.
Discrete ³-ray transitions emitted following decays from either metastable states or excited states populated
following beta decay were identified using the 84 coaxial high-purity germanium (HPGe) detectors of the
EURICA spectrometer, which was complemented by 18 additional cerium-doped lanthanum bromide (LaBr3)
A handful of nuclear reactions have been identified as vital for our understanding of explosive stellar phenomena and the nucleosynthesis associated with these scenarios. The
22Ne(±, ³)26Mg reaction in massive stars is responsible for using the neon fuel required for the 22Ne(±, n) 25 Mg, which is a key source of neutrons in these environments.
Cl(p, ³) 35 Ar reaction affects the final abundance of 34
S which could be used as an identifier of nova origin of presolar grains. The rate of these reactions is predicted to be dominated by a number of resonant states above the ±- and proton-emission thresholds, respectively. Consequently, by determining the nuclear properties of such resonant states
it is possible to estimate the 22 Ne(±, ³) 26 Mg and 34Cl(p, ³)35Arreaction rates.
In this thesis work, the 11B(16O,p)26Mg and 9Be(28Si,2n)35Ar fusion-evaporation reactions were used to populate excited states in the 26Mg and 35Ar nuclei, respectively.
The beams of 16O and 28Si were produced by the Argonne Tandem Linear Accelerator System and prompt electromagnetic radiation was detected using the GAMMASPHERE detector array, which, in the case of the 35Ar experiment, was used in coincidence with recoil selection provided by the Argonne Fragment Mass Analyzer. The two ³-ray spectroscopy studies performed in this work allowed a determination of the nuclear properties of astrophysically important ³-decaying states, which, in turn, were used to re-evaluate the 22
Ne(±, ³)26Mg and 34Cl(p,³)35Ar stellar reaction rates.
Christian G, Lotay G, Ruiz C, Akers C, Burke D, Catford W, Chen A, Connolly D, Davids B, Fallis J, Hager U, Hutcheon D, Mahl A, Rojas A, Sun X (2018) Direct measurement of astrophysically important resonances in 38K( p,³ )39Ca, Physical Review C 97 (2) 025802 American Physical Society
Background:

Classical novae are cataclysmic nuclear explosions occurring when a white dwarf in a binary system accretes hydrogen-rich material from its companion star. Novae are partially responsible for the galactic synthesis of a variety of nuclides up to the calcium (
A
40
) region of the nuclear chart. Although the structure and dynamics of novae are thought to be relatively well understood, the predicted abundances of elements near the nucleosynthesis endpoint, in particular Ar and Ca, appear to sometimes be in disagreement with astronomical observations of the spectra of nova ejecta.

Purpose:

One possible source of the discrepancies between model predictions and astronomical observations is nuclear reaction data. Most reaction rates near the nova endpoint are estimated only from statistical model calculations, which carry large uncertainties. For certain key reactions, these rate uncertainties translate into large uncertainties in nucleosynthesis predictions. In particular, the
38
K
(
p
,
³
)
39
Ca
reaction has been identified as having a significant influence on Ar, K, and Ca production. In order to constrain the rate of this reaction, we have performed a direct measurement of the strengths of three candidate
?
=
0
resonances within the Gamow window for nova burning, at
386
±
10
keV,
515
±
10
keV, and
689
±
10
keV.

Method:

The experiment was performed in inverse kinematics using a beam of unstable
38
K
impinged on a windowless hydrogen gas target. The
39
Ca
recoils and prompt
³
rays from
38
K
(
p
,
³
)
39
Ca
reactions were detected in coincidence using a recoil mass separator and a bismuth-germanate scintillator array, respectively.

Results:

For the 689 keV resonance, we observed a clear recoil-
³
coincidence signal and extracted resonance strength and energy values of
120
+
50
?
30
(
stat
.
)
+
20
?
60
(
sys
.
)
meV
and
679
+
2
?
1
(
stat
.
)
±
1
(
sys
.
)
keV
, respectively. We also performed a singles analysis of the recoil data alone, extracting a resonance strength of
120
±
20
(
stat
.
)
±
15
(
sys
.
)
meV, consistent with the coincidence result. For the 386 keV and 515 keV resonances, we extract
90
%
confidence level upper limits of 2.54 meV and 18.4 meV, respectively.

Conclusions:

We have established a new recommended
38
K
(
p
,
³
)
39
Ca
rate based on experimental information, which reduces overall uncertainties near the peak temperatures of nova burning by a factor of
250
. Using the rate obtained in this work in model calculations of the hottest oxygen-neon novae reduces overall uncertainties on Ar, K, and Ca synthesis to factors of 15 or less in all cases.

Sun Y, Zhang G, Watanabe H, Kondev F, Lane G, Regan P, Söderström P, Walker P, Kanaoka H, Korkulu Z, Lee P, Liu J, Nishimura S, Wu J, Yagi A, Ahn D, Alharbi T, Baba H, Browne F, Bruce A, Carroll R, Chae K, Dombradi Z, Doornenbal P, Estrade A, Fukuda N, Griffin C, Ideguchi E, Inabe N, Isobe T, Kanaya S, Kojouharov I, Kubo T, Kubono S, Kurz N, Kuti I, Lalkovski S, Lee C, Lee E, Lorusso G, Lotay G, Moon C, Nishizuka I, Nita C, Odahara A, Patel Z, Phong V, Podolyak Z, Roberts O, Sakurai H, Schaffner H, Shand C, Shimizu Y, Sumikama T, Suzuki H, Takeda H, Terashima S, Vajta Z, Valiente-Dóbon J, Xu Z (2018) ²-³ and isomeric decay spectroscopy of 168Dy, EPJ Web of Conferences 178 pp. 02023-1 - 02023-3 EDP Sciences
This contribution will report on the experimental work on the level structure of 168Dy. The experimental data have been taken as part of the EURICA decay spectroscopy campaign at RIBF, RIKEN in November 2014. In the experiment, a 238U primary beam is accelerated up to 345 MeV/u with an average intensity of 12 pnA. The nuclei of interest are produced by in-flight fission of 238U impinging on Be target with a thickness of 5 mm. The excited states of 168Dy have been populated through the decay from a newly identified isomeric state and via the ² decay from 168Tb. In this contribution, scientific motivations, experimental procedure and some preliminary results for this study are presented.
Wilkinson Ryan, Lotay Gavin, Lennarz A., Ruiz C., Christian G., Akers C., Catford W. N., Chen A. A., Connolly D., Davids B., Hutcheon D. A., Jedrejcic D., Laird A. M., Martin L., McNeice E., Riley J., Williams M. (2017) Direct Measurement of the Key Ec.m.=456 keV Resonance in the Astrophysical Ne19(p,³)Na20 Reaction and Its Relevance for Explosive Binary Systems, Physical Review Letters 119 (24) American Physical Society
We have performed a direct measurement of the 19Ne(p,³)20Na reaction in inverse kinematics using a beam of radioactive 19Ne. The key astrophysical resonance in the 19Ne+p system has been definitely measured for the first time at Ec.m.=456+5?2 keV with an associated strength of 17+7?5 meV. The present results are in agreement with resonance strength upper limits set by previous direct measurements, as well as resonance energies inferred from precision (3He, t) charge exchange reactions. However, both the energy and strength of the 456 keV resonance disagree with a recent indirect study of the 19Ne(d, n)20Na reaction. In particular, the new 19Ne(p,³)20Na reaction rate is found to be factors of