Publications

Publications by members of the Experimental Subatomic Physics group.

Compton scattering from 4He at 61 MeV

The Compton scattering cross section from 4He has been measured with high statistical accuracy over a scattering angle range of 40o−159o using a quasimonoenergetic 61-MeV photon beam at the High Intensity Gamma-Ray Source. The data are interpreted using a phenomenological model sensitive to the dipole isoscalar electromagnetic polarizabilities (αs and βs) of the nucleon. These data can be fit with the model using values of αs and βs that are consistent with the currently accepted values. These data will serve as benchmarks of future calculations from effective field theories and lattice quantum chromodynamics.

Author(s): 
Sikora, M. H. and Ahmed, M. W. and Banu, A. and Bartram, C. and Crowe, B. and Downie, E. J. and Feldman, G. and Gao, H. and Grie\ss{}hammer, H. W. and Hao, H. and Howell, C. R. and Karwowski, H. J. and Kendellen, D. P. and Kovash, M. A. and Li, X. and Mar
Journal Reference: 
Phys. Rev. C96 (2017) 055209

Photodisintegration of <sup>7</sup>Li with progeny nuclei in excited states

We study the reaction channels 7Li + γ → n + 6Li(2.19), 7Li + γ → n + 6Li(3.56), and 7Li + γ → d + 5He(1.27) → n + d + 4He by detecting neutrons produced by photodisintegration events. We find absolute cross sections and angular dependence for 7Li + γ → n + 6Li(2.19) at photon energies 13 and 15 MeV and for 7Li + γ → n + 6Li(3.56) at the photon energy 15 MeV. The incident photons are linearly polarized and we report dependence of the cross sections on polarization. For the reaction channel 7Li + γ → d + 5He(1.27) → n + d + 4He we obtain an upper bound on its cross section at photon energies 12, 13, and 15 MeV.

Author(s): 
W. A. Wurtz, R. E. Pywell, B. E. Norum, S. Kucuker, B. D. Sawatzky, H. R. Weller, S. Stave, and M. W. Ahmed
Journal Reference: 
Phys. Rev. C 92, 044603 (2015)

Performance test of a lead-glass counter for the J-PARC E36 experiment

The J-PARC E36 experiment will search for a violation of lepton universality by a precise measurement of the ratio of the kaon decay widths . Charged particles will be identified by the combination of three independent systems: a lead-glass Cherenkov counter, an aerogel Cherenkov counter, and a time-of-flight measurement. The performance of the lead-glass Cherenkov counter was investigated with e+, μ+, and π+ beams in the relevant momentum region from the decays. By using a polyethylene degrader to slow down the beam momentum in front of the lead-glass block, we succeeded in reducing the muon mis-identification probability down to 5% while maintaining a high e+ detection efficiency of 98%.

Author(s): 
Y. Miyazaki, S. Shimizu, S. Bianchin, C. Djalali, D. Gill, J. Jiang, M. Hasinoff, K. Horie, Y. Igarashi, J. Imazato, A. Ivashkin, M. Kohl, R. Narikawa, R. Pywell, S. Strauch, M. Tabata, A. Toyoda, H. Yamazaki, T. Yoshioka
Journal Reference: 
Nucl. Inst. Meth. in Phys. Res. A 779 (2015) 13–17

Photodisintegration of <sup>6</sup>Li

The cross sections for the photodisintegration of 6Li have been measured for all the available reaction channels that have neutrons in the final state, except the 6Li(γ,p0)5He(g.s.) channel. The cross sections were measured at the photon energies, 8, 9, 10, 11, 12, 13, 15, and 15.6 MeV using linearly polarized photons, and 20, 25, 30, and 35 MeV using circularly polarized photons. Associated Legendre function coefficients are extracted for the 6Li(γ,n0)5Li(g.s.) and 6Li(γ,n1)5Li(1.49) channels. For all observed reaction channels Legendre function parametrizations are used to determine total cross sections. Comparisons with recent theoretical calculations of the total photodisintegration cross section using various nucleon-nucleon interactions are inconclusive because of the large uncertainty in the cross sections for reactions channels that are not measured. We hope that the precision of our results for specific reaction channels will prompt calculations for those reaction channels.

Author(s): 
W. A. Wurtz, R. E. Pywell, B. E. Norum, S. Kucuker, B. D. Sawatzky, H. R. Weller, S. Stave, and M. W. Ahmed
Journal Reference: 
Phys. Rev. C 90 (2014) 014613

Monte-Carlo simulation of the photon-tagger focal-plane electronics at the MAX IV laboratory

Rate-dependent effects in the electronics used to instrument the tagger focal plane at the MAX IV Laboratory have been investigated using the novel approach of Monte Carlo simulation. Results are compared to analytical calculations as well as experimental data for both specialized testing and production running to demonstrate a thorough understanding of the behavior of the detector system.

Author(s): 
L.S. Myers, G.Feldman, K.G.Fissum, L.Isaksson, M.A.Kovash, A.M.Nathan, R.E. Pywell, B.Schröder.
Journal Reference: 
Nucl. Inst. Meth. in Phys. Res. A 729 (2013) 707

Measurement of the absolute and differential cross sections for <sup>7</sup>Li(γ,n<sub>0</sub>)<sup>6</sup>Li

We have measured the cross section of the photoneutron reaction channel 7Li + γ → 6Li (g.s.) + n where the progeny nucleus is the ground state of 6Li. We obtained the absolute cross section at photon energies 10, 11, 12, 13, 15, 20, 25, 30, and 35 MeV and also the dependence of the cross section on polar angle for all but the highest photon energy. For the energies 10 to 15 MeV we were able to use linearly polarized photons to obtain the dependence of the cross section on the photon polarization.

Author(s): 
W. A. Wurtz, R. E. Pywell, B. E. Norum, S. Kucuker, B. D. Sawatzky, H. R. Weller, M. W. Ahmed, and S. Stave
Journal Reference: 
Phys. Rev. C 84 (2011) 044601

An LED, fiber optic, gain monitoring system for a segmented scintillator array.

A gain monitoring system, which uses light emitting diode flashers and a fiber optic light distribution system, has been developed for use with a segmented, liquid scintillator neutron detector array. The system is designed to track neutron detector cell gains without relying on the stability of any system components. Tests show that the system is capable of tracking the gains of individual detector cells to the design accuracy of 3%.

Author(s): 
B.E. Bewer, R.E. Pywell, R. Igarashi, W.A. Wurtz
Journal Reference: 
Nucl. Inst. Meth. in Phys. Res. A 608 (2009) 417

Photon flux monitor for a mono-energetic gamma ray source

A novel photon flux monitor has been designed and tested for use at the Duke University High Intensity Gamma Source. The five-scintillator-paddle system detects recoil electrons and positrons from photoelectric, Compton and pair-production processes. It is designed to be insensitive to gain and detector threshold changes and is usable for photon energies above 5 MeV. It has been calibrated using direct counting with a NaI detector, and its efficiency has been shown to be well described by a GEANT4 simulation.

Author(s): 
R.E. Pywell, O. Mavrichi, W.A. Wurtz, R. Wilson
Journal Reference: 
Nucl. Inst. Meth. in Phys. Res. A 606 (2009) 517

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