The (Li 6, Li ∗ 6 [3.56 MeV]) reaction at 100 MeV/u as a probe of Gamow-Teller transition strengths in the inelastic scattering channel

C. Sullivan, R. G.T. Zegers, S. Noji, Sam M. Austin, J. Schmitt, N. Aoi, D. Bazin, M. Carpenter, J. J. Carroll, H. Fujita, U. Garg, G. Gey, C. J. Guess, T. H. Hoang, M. N. Harakeh, E. Hudson, N. Ichige, E. Ideguchi, A. Inoue, J. IsaakC. Iwamoto, C. Kacir, T. Koike, N. Kobayashi, S. Lipschutz, M. Liu, P. Von Neumann-Cosel, H. J. Ong, J. Pereira, M. Kumar Raju, A. Tamii, R. Titus, V. Werner, Y. Yamamoto, Y. D. Fang, J. C. Zamora, S. Zhu, X. Zhou

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Background: Inelastic neutrino-nucleus scattering is important for understanding core-collapse supernovae and the detection of emitted neutrinos from such events in earth-based detectors. Direct measurement of the cross sections is difficult and has only been performed on a few nuclei. It is, therefore, important to develop indirect techniques from which the inelastic neutrino-nucleus scattering cross sections can be determined. Purpose: This paper presents a development of the (Li6,Li∗6[T=1,Tz=0,0+,3.56MeV]) reaction at 100 MeV/u as a probe for isolating the isovector spin-transfer response in the inelastic channel (ΔS=1,ΔT=1,ΔTz=0) from which the Gamow-Teller transition strengths from nuclei of relevance for inelastic neutrino-nucleus scattering cross sections can be extracted. Method: By measuring the Li6 ejectile in a magnetic spectrometer and selecting events in which the 3.56 MeV γ ray from the decay of the Li∗6[3.56MeV] state is detected, the isovector spin-transfer selectivity is obtained. High-purity germanium clover detectors served to detect the γ rays. Doppler reconstruction was used to determine the γ energy in the rest frame of Li6. From the Li6 and 3.56 MeV γ-momentum vectors the excitation energy of the residual nucleus was determined. Results: In the study of the C12(Li6,Li∗6[3.56MeV]) reaction, the isovector spin-transfer excitation-energy spectrum in the inelastic channel was successfully measured. The strong Gamow-Teller state in C12 at 15.1 MeV was observed. Comparisons with the analog C12(Li6,He6) reaction validate the method of extracting the Gamow-Teller strength. In measurements of the Mg24,Nb93(Li6,Li∗6[3.56MeV]) reactions, the 3.56 MeV γ peak could not be isolated from the strong background in the γ spectrum from the decay of the isoscalar excitations. It is argued that by using a γ-ray tracking array instead of a clover array, it is feasible to extend the mass range over which the (Li6,Li∗6) reaction can be used for extracting the isovector spin-transfer response up to mass numbers of ∼25 and perhaps higher. Conclusions: It is demonstrated that the (Li6,Li∗6[3.56MeV]) reaction probe can be used to isolate the inelastic isovector spin-transfer response in nuclei. Application to nuclei with mass numbers of about 25 or more, however, will require a more efficient γ-ray array with a better tracking capability.

Original languageEnglish
Article number015804
JournalPhysical Review C
Issue number1
Publication statusPublished - 2018 Jul 31


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