CGS18

Measurement of the 12C(a,g) reaction by measuring the Photodissociation of 16O; a New Tool for Nuclear Astrophysics

Not scheduled

20m

Monterey, California (USA)

Oral Presentations Parallel

Speaker

Moshe Gai (University of Connecticut)

Description

We developed a new method for measuring the cross section of gamma capture reactions (that occur in stellar processes) by measuring the time reverse Photodissociation reaction occurring inside TPCs operating in gamma-beams. This measurement of the time reverse process is not an indirect measurement and certainly not a “surrogate measurement”. It relies on the well-recognized concept of Detailed Balance. We specifically discuss measurements of the 12C(a,g) reaction by measuring the photodissociation of 16O contained in the CO2 gas of the TPC; the 16O(g,a)12C reaction.

Initial measurements were carried out using the UConn-TUNL-Weizmann-PTB optical readout TPC (O-TPC) [1] operating with 100 torr CO2(80%) + N2(20%) gas mixture, placed in the gamma beam of the HIgS/TUNL at Duke University. Using the O-TPC we demonstrated [2] the validity of our new method and bench marked it against world data, with the measured total reaction cross section that agrees with the world data. During 2021 the O-TPC was decommissioned and replaced by the Warsaw electronic readout TPC (eTPC) [3].

We will discuss the new readout technologies and the setup of the TPC detectors and report on new results obtained using the Warsaw eTPC [3] and the O-TPC operating with N2O gas [4]. We report angular distribution measured with unprecedented accuracy [3,4]. Specifically, we measured the E1-E2 mixing phase angle (phi_12) of the 12C(a,g) reaction, that for the first time agrees with the prediction of unitarity [5].

• The material presented here is based on work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics grants Number DE-FG02-94ER40870.

References
[1] M. Gai, M.W. Ahmed, S.C. Stave, W.R. Zimmerman, A. Breskin, B. Bromberger, R. Chechik, V. Dangendorf, Th. Delbar, R.H. France III, S.S. Henshaw, T.J. Kading, P.P. Martel, J.E.R. McDonald, P.-N. Seo, K. Tittelmeier, H.R. Weller and A.H. Young, Jour. Instr. 5, 12004 (2010).
[2] R. Smith, M. Gai, S.R. Stern, M.W. Ahmed, Nature Communications 12, 5920 (2021).), https://www.nature.com/articles/s41467-021-26179-x
[3] M. Ćwiok, W. Dominik, A. Fijałkowska, M. Fila, Z. Janas, A. Kalinowski, K.Kierzkowski, M. Kuich,Ch. Mazzocchi, W. Okliński, M. Zaremba, M. Gai, D.K. Schweitzer, S.R. Stern, S. Finch, U. Friman-Gayer, S.R. Johnson, T. Kowalewski, D.L. Balabanski, C. Matei, A. Rotaru, K.C.Z. Haverson, R. Smith, R.A.M. Allen, M.R. Griffiths, S. Pirrie, and P.S.R Alcibia, EPJ Web Conf. 279, 04002 (2023). https://doi.org/10.1051/epjconf/202329001004
[4] Kristian C.Z. Haverson, Robin Smith, Moshe Gai, Deran K. Schweitzer, Sarah R. Stern and Sean W. Finch, Communications Physics, 9, 27(2026). https://doi.org/10.1038/s42005-025-02458-7
[5] Moshe Gai. Phys. Rev. C 88, 062801(R) (2013).