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Papers by G Hit
Proceedings of 10th Symposium on Nuclei in the Cosmos — PoS(NIC X), 2009
Proceedings of 10th Symposium on Nuclei in the Cosmos — PoS(NIC X), 2009
Charge-exchange reactions on stable nuclei have been used frequently to study the spin-isospin re... more Charge-exchange reactions on stable nuclei have been used frequently to study the spin-isospin response on nuclei, which is, for example, crucial for estimating weak-transition rates in late stellar evolution. Because a large fraction of the relevant nuclei in such scenarios are unstable, there is a strong need to expand charge-exchange studies to unstable nuclei, which requires that experiments must be carried out in inverse kinematics. A promising probe for experiments in the ∆T z =-1 direction is the (p,n) reaction. The "Low Energy Neutron Detector Array" (LENDA) is currently under development at the NSCL (National Superconducting Cyclotron Laboratory). The array will consist of 24 plastic scintillator bars with dimensions of 300 × 45 × 25 mm. The neutron energy is measured using the time-of-flight technique. Position sensitivity along the bar is achieved by combining the timing and pulse height signals. In this work results of measurements using prototype modules and results of simulations are presented.
Proceedings of 10th Symposium on Nuclei in the Cosmos — PoS(NIC X), Jul 29, 2009
The half-life of 84 Mo, an even-even N = Z nucleus near the proton dripline created during explos... more The half-life of 84 Mo, an even-even N = Z nucleus near the proton dripline created during explosive hydrogen burning in Type I X-ray bursts in the rapid proton capture (rp) process, was remeasured and found to be more than 1σ shorter than the previously adopted value. The effect of the measured half-life on rp-process reaction flow is explored.
Proceedings of 10th Symposium on Nuclei in the Cosmos — PoS(NIC X), Jul 29, 2009
We have performed an experiment at NSCL to study the β-decay of N=Z isotopes 96 Cd, 98 In and 100... more We have performed an experiment at NSCL to study the β-decay of N=Z isotopes 96 Cd, 98 In and 100 Sn using the β-Counting system (BCS) and the Segmented Germanium Array (SeGA). The * Speaker.
AIP Conference Proceedings, 2010
The decay properties of rp-process nuclei in the vicinity of 100Sn have been studied at the Natio... more The decay properties of rp-process nuclei in the vicinity of 100Sn have been studied at the National Superconducting Cyclotron Laboratory (NSCL). The measured beta-decay half-life for 100Sn is 0.55-0.31+0.70 s, in agreement with a previous measurement. In 98In, the beta-decay of the ground state plus that of a long lived isomer were observed with half-lives of 47(13) ms and 0.66(40) s respectively. The half-life of 96Cd, measured for the first time, is 1.03-0.21+0.24 s however, the existence of a predicted isomeric state in this nucleus could not be confirmed. Additionally, a gamma cascade de-exciting a mu-isomer in the odd-odd nucleus 96Ag was observed. The implications of the measured half-life of 96Cd on the calculated rp-process final abundances are discussed.
Physical Review Letters, 2010
We report on the first successful extraction of a þ Gamow-Teller strength distribution from a rad... more We report on the first successful extraction of a þ Gamow-Teller strength distribution from a radioactive isotope in an intermediate-energy charge-exchange experiment in inverse kinematics. The (7 Li; 7 Be þ ð429 keVÞ) reaction at 100A MeV was used to measure Gamow-Teller transition strengths from 34 P to states in 34 Si. The results show that little mixing occurs between sd and pf shell configurations for the low-lying 0 þ and 2 þ states even though 34 Si neighbors the island of inversion and low-lying 2@! intruder states exist. Shell-model calculations in the sdpf model space are consistent with these findings.
Physical Review Letters, 2011
A new technique to measure (p,n) charge-exchange reactions in inverse kinematics at intermediate ... more A new technique to measure (p,n) charge-exchange reactions in inverse kinematics at intermediate energies on unstable isotopes was successfully developed and used to study the 56 Ni(p,n) reaction at 110 MeV/u. Gamow-Teller transition strengths from 56 Ni leading to 56 Cu were obtained and compared with shell-model predictions in the pf-shell using the KB3G and GXPF1A interactions. The calculations with the GXPF1A interaction reproduce the experimental strength distribution much better than the calculations that employed the KB3G interaction, indicating deficiencies in the spin-orbit and proton-neutron residual potentials for the latter. The results are important for improving the description of electron-capture rates on nuclei in the iron region, which are important for modeling the late evolution of core-collapse and thermonuclear supernovae.
Physical Review Letters, 2005
We report on the first determination of the absolute BE2; 0 1 ! 2 1 excitation strength in the N ... more We report on the first determination of the absolute BE2; 0 1 ! 2 1 excitation strength in the N Z nucleus 72 Kr. 72 Kr is the heaviest N Z nucleus for which this quantity has been measured and provides a benchmark in a region of the nuclear chart dominated by rapidly changing deformations and shapes mediated by the interplay of strongly oblate and prolate-driving orbitals. The deduced quadrupole deformation strength is in agreement with a variety of self-consistent models that predict an oblate shape for the ground state of 72 Kr. Large-scale shell-model Monte Carlo calculations reproduce the experimental BE2 value and link the result to the occupation of the deformation-driving g 9=2 orbit.
Physical Review Letters, 2008
The β-decay properties of the N=Z nuclei 96 Cd, 98 In and 100 Sn have been studied. These nuclei ... more The β-decay properties of the N=Z nuclei 96 Cd, 98 In and 100 Sn have been studied. These nuclei were produced at the National Superconducting Cyclotron Laboratory (NSCL) by fragmenting a 120 MeV/nucleon 112 Sn primary beam on a Be target. The resulting radioactive beam was filtered in the A1900 and the newly commissioned Radio Frequency Fragment Separator (RFFS) to achieve a purity level suitable for decay studies. The observed production cross sections of these nuclei are lower than predicted by factors of 10 to 30. The 100 Sn production cross section is 0.25(15) pb, in sharp contrast with the 120 pb lower limit established at 63 MeV/nucleon incident energy of the same primary beam. The deduced half-life of 100 Sn is 0.55 +0.70 −0.31 s, in agreement with previous measurements. Two β-decaying states in 98 In were observed with measured half-lives of 47(13) ms and 0.66(40) s. The half-life of 96 Cd, which was the last experimentally unknown waiting point half-life of the astrophysical rp-process, is 1.03 +0.24 −0.21 s. The implications of the experimental T 1/2 value of 96 Cd on the abundances predicted by rp-process calculations and the origin of A=96 isobars such as 96 Ru are explored.
Physical Review C, 2008
The Gamow-Teller strength for the transition from the ground state of 13 C to the T=1/2, J π = 3/... more The Gamow-Teller strength for the transition from the ground state of 13 C to the T=1/2, J π = 3/2 − excited state at 3.51 MeV in 13 N is extracted via the 13 C(3 He,t) reaction at 420 MeV. In contrast to results from earlier (p,n) studies on 13 C, a good agreement with shell-model calculations and the empirical unit cross section systematics from other nuclei is found. The results are used to study the analog 13 N(e − , νe) 13 C reaction, which plays a role in the pre-explosion convective phase of type Ia supernovae. Although the differences between the results from the (3 He,t) and (p,n) data significantly affect the deduced electron-capture rate and the net heat-deposition in the star due to this transition, the overall effect on the pre-explosive evolution is small.
Physical Review C, 2011
The 150 Nd(3 He,t) reaction at 140 MeV/u and 150 Sm(t, 3 He) reaction at 115 MeV/u were measured,... more The 150 Nd(3 He,t) reaction at 140 MeV/u and 150 Sm(t, 3 He) reaction at 115 MeV/u were measured, populating excited states in 150 Pm. The transitions studied populate intermediate states of importance for the (neutrinoless) ββ decay of 150 Nd to 150 Sm. Monopole and dipole contributions to the measured excitation-energy spectra were extracted by using multipole decomposition analyses. The experimental results were compared with theoretical calculations obtained within the framework of Quasiparticle Random-Phase Approximation (QRPA), which is one of the main methods employed for estimating the half-life of the neutrinoless ββ decay (0νββ) of 150 Nd. The present results thus provide useful information on the neutrino responses for evaluating the 0νββ and 2νββ matrix elements. The 2νββ matrix element calculated from the Gamow-Teller transitions through the lowest 1 + state in the intermediate nucleus is maximally about half of that deduced from the half-life measured in 2νββ direct counting experiments and at least several transitions through 1 + intermediate states in 150 Pm are required to explain the 2νββ half-life. Because Gamow-Teller transitions in the 150 Sm(t, 3 He) experiment are strongly Pauli-blocked, the extraction of Gamow-Teller strengths was complicated by the excitation of the 2 ω, ∆L = 0, ∆S = 1 isovector spin-flip giant monopole resonance (IVSGMR). However, the near absence of Gamow-Teller transition strength made it possible to cleanly identify this resonance, and the strength observed is consistent with the full exhaustion of the non-energy-weighted sum rule for the IVSGMR.
Physical Review C, 2011
The isomeric and β decays of the N = Z + 2 nucleus 96 Ag were investigated at NSCL. A cascade of ... more The isomeric and β decays of the N = Z + 2 nucleus 96 Ag were investigated at NSCL. A cascade of γ-ray transitions originating from the de-excitation of a µs isomer was observed for the first time and was found in coincidence with two previously-known transitions with energies of 470 and 667 keV. The isomeric half-life was determined as 1.45(7) µs, more precise than previously reported. The existence of a second, longer-lived µs isomer, associated with a 743-keV γ transition, is also proposed here. Shell model results within the (p 3/2 p 1/2 f 5/2 g 9/2) model space, using the jj44b interaction, reproduced level energies and isomeric decay half-lives reasonably well.
IEEE Transactions on Nuclear Science, 2009
... G. Perdikakis, Sam M. Austin, D. Bazin, C. Caesar, JM Deaven, CJ Guess, GW Hitt, RT Meharchan... more ... G. Perdikakis, Sam M. Austin, D. Bazin, C. Caesar, JM Deaven, CJ Guess, GW Hitt, RT Meharchand, DT Nguyen, Y. Shimbara, K. Thorne, and RGT Zegers ... 469, p. 125, 1987. [4] RGTZegers et al., Extraction of weak transition strengths via the ( He, t) reaction at 420 MeV, Phys. ...
Electron capture and beta decay play important roles in the evolution of pre-supernovae stars and... more Electron capture and beta decay play important roles in the evolution of pre-supernovae stars and their collapse. Recent predictions for weak interactions in modern large-scale shell model calculations that include residual interactions differ greatly from earlier rates determined from independent particle models. We report preliminary results for the measurement of the GT strength in ^58Co via the ^58Ni(t,^3He) reaction with
Bulletin of the …, 2008
Charge-exchange reactions have long been used as a probe of the spin-isospin response of stable n... more Charge-exchange reactions have long been used as a probe of the spin-isospin response of stable nuclei, in particular the Gamow-Teller transitions. Gamow-Teller strengths can be extracted model-independently, providing detailed information on nuclear structure and key inputs ...
Bulletin of the American Physical Society, Nov 6, 2010
Although charge-exchange reactions at intermediate energies with a variety of probes on stable nu... more Although charge-exchange reactions at intermediate energies with a variety of probes on stable nuclei have long been the preferred tool to extract Gamow-Teller strengths beyond the Q-value window available for beta\betabeta-decay, the implementation of such reactions for rare isotopes has proven to be an experimental challenge. Here, we report on the first successful extraction of a beta\beta beta+ Gamow-Teller strength distribution from a radioactive isotope in an intermediate-energy charge-exchange experiment in inverse kinematics. The ($^{7}$Li,$^{7}$Be+$\gamma )$ ...
Proceedings of 10th Symposium on Nuclei in the Cosmos — PoS(NIC X), 2009
β-decay nuclides in the immediate neighborhood of 100 Sn were studied at the NSCL using the β-Cou... more β-decay nuclides in the immediate neighborhood of 100 Sn were studied at the NSCL using the β-Counting System (BCS) and the Segmented Germanium Array (SeGA). The nuclei of interest were implanted into the BCS and properties from both, implantations and subsequent β-decays, were recorded on an event-by-event basis, allowing for the direct observation of half-lives, β-delayed proton emission branching ratios, and β-end point energies. In addition the use of SeGA in conjunction with the BCS allows the observation of the prompt γ radiation from implantations and as well as photons emitted following β and β-delayed proton decay.
Physical Review Letters, 2007
Proceedings of 10th Symposium on Nuclei in the Cosmos — PoS(NIC X), 2009
Proceedings of 10th Symposium on Nuclei in the Cosmos — PoS(NIC X), 2009
Charge-exchange reactions on stable nuclei have been used frequently to study the spin-isospin re... more Charge-exchange reactions on stable nuclei have been used frequently to study the spin-isospin response on nuclei, which is, for example, crucial for estimating weak-transition rates in late stellar evolution. Because a large fraction of the relevant nuclei in such scenarios are unstable, there is a strong need to expand charge-exchange studies to unstable nuclei, which requires that experiments must be carried out in inverse kinematics. A promising probe for experiments in the ∆T z =-1 direction is the (p,n) reaction. The "Low Energy Neutron Detector Array" (LENDA) is currently under development at the NSCL (National Superconducting Cyclotron Laboratory). The array will consist of 24 plastic scintillator bars with dimensions of 300 × 45 × 25 mm. The neutron energy is measured using the time-of-flight technique. Position sensitivity along the bar is achieved by combining the timing and pulse height signals. In this work results of measurements using prototype modules and results of simulations are presented.
Proceedings of 10th Symposium on Nuclei in the Cosmos — PoS(NIC X), Jul 29, 2009
The half-life of 84 Mo, an even-even N = Z nucleus near the proton dripline created during explos... more The half-life of 84 Mo, an even-even N = Z nucleus near the proton dripline created during explosive hydrogen burning in Type I X-ray bursts in the rapid proton capture (rp) process, was remeasured and found to be more than 1σ shorter than the previously adopted value. The effect of the measured half-life on rp-process reaction flow is explored.
Proceedings of 10th Symposium on Nuclei in the Cosmos — PoS(NIC X), Jul 29, 2009
We have performed an experiment at NSCL to study the β-decay of N=Z isotopes 96 Cd, 98 In and 100... more We have performed an experiment at NSCL to study the β-decay of N=Z isotopes 96 Cd, 98 In and 100 Sn using the β-Counting system (BCS) and the Segmented Germanium Array (SeGA). The * Speaker.
AIP Conference Proceedings, 2010
The decay properties of rp-process nuclei in the vicinity of 100Sn have been studied at the Natio... more The decay properties of rp-process nuclei in the vicinity of 100Sn have been studied at the National Superconducting Cyclotron Laboratory (NSCL). The measured beta-decay half-life for 100Sn is 0.55-0.31+0.70 s, in agreement with a previous measurement. In 98In, the beta-decay of the ground state plus that of a long lived isomer were observed with half-lives of 47(13) ms and 0.66(40) s respectively. The half-life of 96Cd, measured for the first time, is 1.03-0.21+0.24 s however, the existence of a predicted isomeric state in this nucleus could not be confirmed. Additionally, a gamma cascade de-exciting a mu-isomer in the odd-odd nucleus 96Ag was observed. The implications of the measured half-life of 96Cd on the calculated rp-process final abundances are discussed.
Physical Review Letters, 2010
We report on the first successful extraction of a þ Gamow-Teller strength distribution from a rad... more We report on the first successful extraction of a þ Gamow-Teller strength distribution from a radioactive isotope in an intermediate-energy charge-exchange experiment in inverse kinematics. The (7 Li; 7 Be þ ð429 keVÞ) reaction at 100A MeV was used to measure Gamow-Teller transition strengths from 34 P to states in 34 Si. The results show that little mixing occurs between sd and pf shell configurations for the low-lying 0 þ and 2 þ states even though 34 Si neighbors the island of inversion and low-lying 2@! intruder states exist. Shell-model calculations in the sdpf model space are consistent with these findings.
Physical Review Letters, 2011
A new technique to measure (p,n) charge-exchange reactions in inverse kinematics at intermediate ... more A new technique to measure (p,n) charge-exchange reactions in inverse kinematics at intermediate energies on unstable isotopes was successfully developed and used to study the 56 Ni(p,n) reaction at 110 MeV/u. Gamow-Teller transition strengths from 56 Ni leading to 56 Cu were obtained and compared with shell-model predictions in the pf-shell using the KB3G and GXPF1A interactions. The calculations with the GXPF1A interaction reproduce the experimental strength distribution much better than the calculations that employed the KB3G interaction, indicating deficiencies in the spin-orbit and proton-neutron residual potentials for the latter. The results are important for improving the description of electron-capture rates on nuclei in the iron region, which are important for modeling the late evolution of core-collapse and thermonuclear supernovae.
Physical Review Letters, 2005
We report on the first determination of the absolute BE2; 0 1 ! 2 1 excitation strength in the N ... more We report on the first determination of the absolute BE2; 0 1 ! 2 1 excitation strength in the N Z nucleus 72 Kr. 72 Kr is the heaviest N Z nucleus for which this quantity has been measured and provides a benchmark in a region of the nuclear chart dominated by rapidly changing deformations and shapes mediated by the interplay of strongly oblate and prolate-driving orbitals. The deduced quadrupole deformation strength is in agreement with a variety of self-consistent models that predict an oblate shape for the ground state of 72 Kr. Large-scale shell-model Monte Carlo calculations reproduce the experimental BE2 value and link the result to the occupation of the deformation-driving g 9=2 orbit.
Physical Review Letters, 2008
The β-decay properties of the N=Z nuclei 96 Cd, 98 In and 100 Sn have been studied. These nuclei ... more The β-decay properties of the N=Z nuclei 96 Cd, 98 In and 100 Sn have been studied. These nuclei were produced at the National Superconducting Cyclotron Laboratory (NSCL) by fragmenting a 120 MeV/nucleon 112 Sn primary beam on a Be target. The resulting radioactive beam was filtered in the A1900 and the newly commissioned Radio Frequency Fragment Separator (RFFS) to achieve a purity level suitable for decay studies. The observed production cross sections of these nuclei are lower than predicted by factors of 10 to 30. The 100 Sn production cross section is 0.25(15) pb, in sharp contrast with the 120 pb lower limit established at 63 MeV/nucleon incident energy of the same primary beam. The deduced half-life of 100 Sn is 0.55 +0.70 −0.31 s, in agreement with previous measurements. Two β-decaying states in 98 In were observed with measured half-lives of 47(13) ms and 0.66(40) s. The half-life of 96 Cd, which was the last experimentally unknown waiting point half-life of the astrophysical rp-process, is 1.03 +0.24 −0.21 s. The implications of the experimental T 1/2 value of 96 Cd on the abundances predicted by rp-process calculations and the origin of A=96 isobars such as 96 Ru are explored.
Physical Review C, 2008
The Gamow-Teller strength for the transition from the ground state of 13 C to the T=1/2, J π = 3/... more The Gamow-Teller strength for the transition from the ground state of 13 C to the T=1/2, J π = 3/2 − excited state at 3.51 MeV in 13 N is extracted via the 13 C(3 He,t) reaction at 420 MeV. In contrast to results from earlier (p,n) studies on 13 C, a good agreement with shell-model calculations and the empirical unit cross section systematics from other nuclei is found. The results are used to study the analog 13 N(e − , νe) 13 C reaction, which plays a role in the pre-explosion convective phase of type Ia supernovae. Although the differences between the results from the (3 He,t) and (p,n) data significantly affect the deduced electron-capture rate and the net heat-deposition in the star due to this transition, the overall effect on the pre-explosive evolution is small.
Physical Review C, 2011
The 150 Nd(3 He,t) reaction at 140 MeV/u and 150 Sm(t, 3 He) reaction at 115 MeV/u were measured,... more The 150 Nd(3 He,t) reaction at 140 MeV/u and 150 Sm(t, 3 He) reaction at 115 MeV/u were measured, populating excited states in 150 Pm. The transitions studied populate intermediate states of importance for the (neutrinoless) ββ decay of 150 Nd to 150 Sm. Monopole and dipole contributions to the measured excitation-energy spectra were extracted by using multipole decomposition analyses. The experimental results were compared with theoretical calculations obtained within the framework of Quasiparticle Random-Phase Approximation (QRPA), which is one of the main methods employed for estimating the half-life of the neutrinoless ββ decay (0νββ) of 150 Nd. The present results thus provide useful information on the neutrino responses for evaluating the 0νββ and 2νββ matrix elements. The 2νββ matrix element calculated from the Gamow-Teller transitions through the lowest 1 + state in the intermediate nucleus is maximally about half of that deduced from the half-life measured in 2νββ direct counting experiments and at least several transitions through 1 + intermediate states in 150 Pm are required to explain the 2νββ half-life. Because Gamow-Teller transitions in the 150 Sm(t, 3 He) experiment are strongly Pauli-blocked, the extraction of Gamow-Teller strengths was complicated by the excitation of the 2 ω, ∆L = 0, ∆S = 1 isovector spin-flip giant monopole resonance (IVSGMR). However, the near absence of Gamow-Teller transition strength made it possible to cleanly identify this resonance, and the strength observed is consistent with the full exhaustion of the non-energy-weighted sum rule for the IVSGMR.
Physical Review C, 2011
The isomeric and β decays of the N = Z + 2 nucleus 96 Ag were investigated at NSCL. A cascade of ... more The isomeric and β decays of the N = Z + 2 nucleus 96 Ag were investigated at NSCL. A cascade of γ-ray transitions originating from the de-excitation of a µs isomer was observed for the first time and was found in coincidence with two previously-known transitions with energies of 470 and 667 keV. The isomeric half-life was determined as 1.45(7) µs, more precise than previously reported. The existence of a second, longer-lived µs isomer, associated with a 743-keV γ transition, is also proposed here. Shell model results within the (p 3/2 p 1/2 f 5/2 g 9/2) model space, using the jj44b interaction, reproduced level energies and isomeric decay half-lives reasonably well.
IEEE Transactions on Nuclear Science, 2009
... G. Perdikakis, Sam M. Austin, D. Bazin, C. Caesar, JM Deaven, CJ Guess, GW Hitt, RT Meharchan... more ... G. Perdikakis, Sam M. Austin, D. Bazin, C. Caesar, JM Deaven, CJ Guess, GW Hitt, RT Meharchand, DT Nguyen, Y. Shimbara, K. Thorne, and RGT Zegers ... 469, p. 125, 1987. [4] RGTZegers et al., Extraction of weak transition strengths via the ( He, t) reaction at 420 MeV, Phys. ...
Electron capture and beta decay play important roles in the evolution of pre-supernovae stars and... more Electron capture and beta decay play important roles in the evolution of pre-supernovae stars and their collapse. Recent predictions for weak interactions in modern large-scale shell model calculations that include residual interactions differ greatly from earlier rates determined from independent particle models. We report preliminary results for the measurement of the GT strength in ^58Co via the ^58Ni(t,^3He) reaction with
Bulletin of the …, 2008
Charge-exchange reactions have long been used as a probe of the spin-isospin response of stable n... more Charge-exchange reactions have long been used as a probe of the spin-isospin response of stable nuclei, in particular the Gamow-Teller transitions. Gamow-Teller strengths can be extracted model-independently, providing detailed information on nuclear structure and key inputs ...
Bulletin of the American Physical Society, Nov 6, 2010
Although charge-exchange reactions at intermediate energies with a variety of probes on stable nu... more Although charge-exchange reactions at intermediate energies with a variety of probes on stable nuclei have long been the preferred tool to extract Gamow-Teller strengths beyond the Q-value window available for beta\betabeta-decay, the implementation of such reactions for rare isotopes has proven to be an experimental challenge. Here, we report on the first successful extraction of a beta\beta beta+ Gamow-Teller strength distribution from a radioactive isotope in an intermediate-energy charge-exchange experiment in inverse kinematics. The ($^{7}$Li,$^{7}$Be+$\gamma )$ ...
Proceedings of 10th Symposium on Nuclei in the Cosmos — PoS(NIC X), 2009
β-decay nuclides in the immediate neighborhood of 100 Sn were studied at the NSCL using the β-Cou... more β-decay nuclides in the immediate neighborhood of 100 Sn were studied at the NSCL using the β-Counting System (BCS) and the Segmented Germanium Array (SeGA). The nuclei of interest were implanted into the BCS and properties from both, implantations and subsequent β-decays, were recorded on an event-by-event basis, allowing for the direct observation of half-lives, β-delayed proton emission branching ratios, and β-end point energies. In addition the use of SeGA in conjunction with the BCS allows the observation of the prompt γ radiation from implantations and as well as photons emitted following β and β-delayed proton decay.
Physical Review Letters, 2007