Warsaw active target TPCs for studying astrophysical reactions

by Mikolaj Cwiok (University of Warsaw)

Thursday 12 Feb 2026, 10:00 → 12:00 Europe/Berlin

Abstract: 

In the seminar I will present a detector R&D programme carried out at the University of Warsaw (Poland) in collaboration with: University of Connecticut (USA), ELI-NP/IFIN-HH (Romania) and Sheffield Hallam University (UK) dedicated to study (proton,gamma) and (alpha,gamma) nuclear reactions of astrophysical interest, which regulate abundance of
carbon and oxygen elements in the Universe.

In particular, the production of Oxygen-16 and burning of Carbon-12 via the 12C(alpha,gamma)16O reaction takes place in stars at energies close to the Gamow peak. Typical direct measurements of this benchmark reaction suffer from maximal available ion beam currents and target deterioration. Instead, thanks to the principle of detailed balance in nuclear reactions, one can measure time-reverse reactions induced by intense semi-monochromatic gamma beams. For this purpose we have developed a Time Projection Chamber (Warsaw TPC) with active gaseous target kept at low pressure, in which collimated gamma-ray photons can react with nuclei of the gas. The kinematics of outgoing charged particles is reconstructed on event-by-event basis from specially arranged, redundant signal strip arrays (u-v-w).

First experiments were conducted in years 2020-2022 with gamma-ray beams from the High Intensity Gamma-Ray Source (HIgS) facility, Triangle Universities Nuclear Laboratory, Durham, NC, USA, as well as with the neutron beam from the IGN-14 neutron generator
at the Institute for Nuclear Physics, Polish Academy of Science, Cracow, Poland.

In the presentation I will focus on the results on Oxygen-16 photo-disintegration reaction from the experiment conducted at HIgS for the gamma beam energies corresponding to nominal centre-of-mass energies from 6.7 MeV down to 1.35 MeV. The relative contributions of E1 and E2 components and E1+E2 cross sections were extracted from the measured angular distributions at different gamma beam energies. The results are based on a simplified event reconstruction algorithm after analysing only partial statistics available, while work on more sophisticated data processing is still ongoing.

A new multi-purpose version of the TPC apparatus that can study nuclear processes with radioactive ion beams, in addition to gamma-ray and neutron beams, will be discussed as well.

 

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