romualdo desouza, ckg symposium, oct. 8, 2015 this work was supported by the u.s. doe office of...

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This work was supported by the U.S. DOE Office of Science under Grant No. DEFG02-88ER-40404Indiana University: T. Steinbach, M.J. Rudolph, Z.Q. Gosser, K. Brown,V. Singh, J. Vadas, B. Wiggins, S. Hudan, RdSFlorida State: I. Wiedenhover, L. Baby, S. Kuvin, V. TripathiGrappling with in nuclear fusion to overcome barriers

Romualdo deSouza, CKG Symposium, Oct. 8, 2015

This work was supported by the U.S. DOE Office of Science under Grant No. DEFG02-88ER-40404Indiana University: T. Steinbach, M.J. Rudolph, Z.Q. Gosser, K. Brown,V. Singh, J. Vadas, B. Wiggins, S. Hudan, RdSFlorida State: I. Wiedenhover, L. Baby, S. Kuvin, V. TripathiGrappling with in nuclear fusion to overcome barriers

Look! I know exactly how to get out of this damn valley!FRIBRomualdo deSouza, CKG Symposium, Oct. 8, 2015MotivationFusion reactions in the outer crust result in X-ray bursts and superburstsProblem: At the temperature of the crust, the Coulomb barrier is too high for thermonuclear fusion of carbon another heat source is needed.

Nuclear astrophysics: Nuclear reactions in outer crust of a neutron star Nuclear science: dynamics of fusing two neutron-rich nucleiHorowitz et al. proposed that 24O + 24O or 28Ne + 28Ne might be the heat source. More recently mid-mass nuclei have been suggested.


Energy output of a single burst equal our suns solar output for a decade!Romualdo deSouza, CKG Symposium, Oct. 8, 2015R.T. deSouza, et al Phys. Rev. C88 014602 (2013)

Density constrained TDHF calculationsIf valence neutrons are loosely coupled to the core, then polarization can result and fusion enhancement will occur16O Core16O Corevalence neutronsHorowitz et al., Phys. Rev. C 77, 045807 (2008)Umar et al., Phys. Rev. C 85, 055801 (2012)

Romualdo deSouza, CKG Symposium, Oct. 8, 2015What do we want to measure?Evaporation residuesEvaporated particles

TargetBeamEvap. ResidueAs the excited nucleus decays, emission of evaporated particles kicks evaporation residues away from zero degrees

To measure the fusion cross-section we need to count the number of evaporation residues relative to the number of incident O nucleiRomualdo deSouza, CKG Symposium, Oct. 8, 2015Experimental Setup: Florida State TandemIncident Beam: 18O + 12C @ 1-2 MeV/AIntensity of 18O: 3x105 ppsTarget: 100 g/cm2 carbon foil T2: Lab = 3.5 - 10.8; T3: Lab = 11.3 - 21.8Time-of-Flight (TOF) between target-MCP and Si (T2, T3)T.K. Steinbach et al., PRC90, 041603 (2014).


Identifying Evaporation ResiduesT.K. Steinbach et al., Phys. Rev. C 90, 041603(R)(2014)Evaporation residues are well separated from elastic and slit scattered beam particlesAlpha particles are also cleanly resolved

Romualdo deSouza, CKG Symposium, Oct. 8, 201518O + 12C Fusion Excitation FunctionWell described by Wong formalism (parabolic barrier) Rc = 7.34 0.07 fmV = 7.62 0.04 MeVh/2 = 2.86 0.09 MeV Measured the cross section for ECM ~ 5.3 14 MeV matches existing dataExtends cross-section measurement down to ~800 b level (~30 times lower than previously measured)

Romualdo deSouza, CKG Symposium, Oct. 8, 2015Comparison of 18O + 12C Fusion Excitation Function with DC-TDHF

Above the barrier, DC-TDHF with pairing predicts a larger cross-sectionIn this energy regime the quantity expt./DC-TDHF is roughly constant at 0.8Below the barrier the experimental cross-section falls less steeply with decreasing Ec.m. than the DC-TDHF predictions.Below the barrier the quantity expt./DC-TDHF increases from 0.8 to approximately 15 at the lowest energy measured.


Energy and angular distribution of ERs in 18O + 12CEnergy and angular distributions of evaporation residues (ERs) reveal a clear component associated with alpha emission. This component is under-predicted by the statistical model codes PACE4 and evapOR.Romualdo deSouza, CKG Symposium, Oct. 8, 2015

Decay channels following fusion The large angle part of the ER angular distribution is populated almost exclusively by and +n decay with the largest angles populated by single emission only. The small angle region of the distribution is dominated by nucleon emission, principally 2n and n+pIn order to explain the observed angular distribution it is necessary to increase the single emission by a factor of 11 and the n+ by a factor of 1.9;Due to the increase in the emission channels, it is necessary to reduce the nucleon emission channels by 0.825 to reproduce the small angle portion of the spectrumRomualdo deSouza, CKG Symposium, Oct. 8, 2015

Direct measurement of the cross-section The increased emission indicated by the energy and angular distribution of ERS is directly confirmed by the extraction of the cross-section.The statistical model codes significantly under-predict the measured cross-section.At the lowest energies the measured cross-section is under-predicted by a factor of three.A stronger energy dependence is exhibited by the experimental data as compared to the model predictions.Romualdo deSouza, CKG Symposium, Oct. 8, 201519O produced by: 18O(d,p) @ ~68 MeVIntensity of 19O: 1-2x104 ppsBeam tagging by E-TOFTarget: 100 g/cm2 carbon foil T2: Lab = 3.5 - 10.8; T3: Lab = 11.3 - 21.8Time-of-Flight (TOF) between target-MCP and Si (T2, T3)Radioactive beams at Florida State : The RESOLUT facility

18O7+19O7+18O6+

Ion chamberRomualdo deSouza, CKG Symposium, Oct. 8, 201519O + 12C Fusion Excitation Function

Wong formalism (parabolic barrier)Fusion excitation functions for 19O + 12C and 18O + 12C were simultaneously measuredThe excitation function for 18O matches the results of the high resolution measurement previously performed within the statistical uncertainties.At all energies 19O + 12C is associated with a significantly large cross-section.18O19ORc7.34 0.07 fm8.00 0.40 fmV7.62 0.04 MeV7.64 0.61 MeVh/2 2.86 0.09 MeV 6.47 2.50 MeV Romualdo deSouza, CKG Symposium, Oct. 8, 2015 Fusion Enhancement in 19O + 12CAbove the barrier, the fusion cross-section for 19O is roughly 20% larger than that for 18OJust above the barrier at ~9 MeV the fusion cross-section for 19O increases dramatically as compared to 18O.At the lowest energy measured the cross-section for 19O exceeds that for 18O by approximately a factor of three.

Romualdo deSouza, CKG Symposium, Oct. 8, 2015Conclusions Developed an efficient method to measure the fusion excitation function for low intensity radioactive beams at energies near and below the barrier.

For 18O + 12C:We have measured the fusion cross-section down to the 800 b level a factor of ~30 lower than previously measured.In the sub-barrier regime the cross-section is substantially larger than that predicted by the DC-TDHF model suggesting a narrower barrier. Alpha emission is substantially enhanced over the predictions of the statistical model codes.

For 19O + 12C: First measurement of fusion in this system indicates a significant enhancement of fusion due to the presence of a single extra neutron as one approaches the barrier.Romualdo deSouza, CKG Symposium, Oct. 8, 2015Conclusions Developed an efficient method to measure the fusion excitation function for low intensity radioactive beams at energies near and below the barrier.

For 18O + 12C:We have measured the fusion cross-section down to the 800 b level a factor of ~30 lower than previously measured.In the sub-barrier regime the cross-section is substantially larger than that predicted by the DC-TDHF model suggesting a narrower barrier. Alpha emission is substantially enhanced over the predictions of the statistical model codes.

For 19O + 12C: First measurement of fusion in this system indicates a significant enhancement of fusion due to the presence of a single extra neutron as one approaches the barrier. just like a single valence neutron, a single individual can make a big difference!Romualdo deSouza, CKG Symposium, Oct. 8, 2015Grappling with Konrad

Grappling hook (aka valence neutron)Clueless postdoc (RdS)Romualdo deSouza, CKG Symposium, Oct. 8, 2015Additional slidesRomualdo deSouza, CKG Symposium, Oct. 8, 2015

Gridless MCP DetectorMinimize extraneous material in the beam path

Crossed electric and magnetic field transports electrons from secondary emission foil to the microchannel plate (MCP)

20 neodymium permanent magnets produce magnetic field (~85 gauss)

6 grid plates produce electric field (~101,000 V/m)

C foil frame biased to -1000 VMCP with 18 mm diameterTime resolution (MCP-MCP) ~ 350 ps

BeamBE

Bowman et al., Nucl. Inst. and Meth. 148, 503 (1978) Steinbach et al., Nucl. Inst. and Meth. A 743, 5 (2014)

Romualdo deSouza, TAMU, Dec. 2, 2014Add bowman reference as well and briefly mentioned 10/8/2015 7:35 AM 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

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18O + 12C Measurement at Florida State U.

21Tracy K. SteinbachApril 5, 2014Time-of-flight of beam measured between US and Tgt gridless MCP detector

Elastically scattered beam particles and evaporation residues: Time of flight measured between Tgt MCP and Si detectorsEnergy measured in annular Si detectors (T2, T3)18O BEAMUS MCP DetectorTgt MCPDetectorT2~ 130 cm~ 13 cmPMTT3LCP Det.Array

7 CsI(Tl)/photodiode detectors used to measure light charged particles

PMT (coupled to plastic scintillator) measures zero degree beam particles10/8/2015 7:35 AM 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

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Si DetectorNew design (S5) from Micron Semiconductor

Single crystal of n-type Si ~ 300 m thick

Segmented to provide angular resolution

Used to give both energy and time information

S5 (T2) Si DesignPies16Rings624 ring segmentsInter-strip width50 mEntrance widow thickness0.1-0.2 mwww.micronsemiconductor.co.ukSteinbach et al., Nucl. Inst. and Meth. A 743, 5 (2014)deSouza et. al., Nucl. Inst. and Meth. A 632, 133 (2011) Fast timing electronics gives timing resolution of ~ 450 ps

(Need ~ 1 ns time resolution)

Romualdo deSouza, ACS, Indianapolis 201350 um is chosen/needed to provide isolation between segments (it this interstrip is too thin than segments will no longer be isolated from each other)

Residues only penetrate the Si detectors a few microns so any reduction in entrance window thickness is helpful

10/8/2015 7:35 AM 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

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Is fusion of neutron-rich light nuclei enhanced relative to -stable nuclei?R.T. deSouza, S. Hudan, V.E. Oberacker, S. Umar Phys. Rev. C88 014602 (2013)Density constrained TDHF calculationsTDHF provides good foundation for describing large amplitude collective motion3D cartesian lattice without symmetry restrictionsSkyrme effective nucleon-nucleon interaction (SLy4)Ion-ion potential calculated as:V(R) = EDC (R) EA1 EA2Romualdo deSouza, TAMU, Dec. 2, 2014Romualdo deSouza, CKG Symposium, Oct. 8, 2015


Comparison of emission in similar systemsRomualdo deSouza, CKG Symposium, Oct. 8, 2015

romualdo desouza, ckg symposium, oct. 8, 2015 this work was supported by the u.s. doe office of...

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