Speaker
Description
We developed a new method for measuring the cross section of 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 $^{12}$C($\alpha,\gamma$) reaction by measuring the photodissociation of $^{16}$O contained in the CO$_2$ gas of the TPC; the $^{16}$O($\gamma,\alpha$)$^{12}$C reaction. Initial measurements were carried out using the UConn-TUNL-Weizmann-PTB optical readout TPC (O-TPC) [1] operating with 100 torr CO$_2(80\%)$ + N$_2(20\%)$ 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 N$_2$O gas [4]. We report angular distribution measured with unprecedented accuracy [3-5]. Specifically, we measured the E1-E2 mixing phase angle (f12) of the $^{12}$C($\alpha,\gamma$) reaction, that for the first time agrees with the prediction of unitarity [6]. 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).
$[3]$ 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).
$[4]$ 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
$[5]$ Kristian C.Z. Haverson and Mikolaj Ćwiok et al., Submitted to Nature Communication, 2026. https://doi.org/10.21203/rs.3.rs-10181237/v1
$[6]$ Moshe Gai. Phys. Rev. C 88, 062801(R) (2013).