Exploring the alpha cluster structure of nuclei using the thick target inverse kinematics technique for multiple alpha decays. Marina Barbui June, 23 rd, 2015

Alpha clustering in nuclei Ikeda diagram (K. Ikeda, N. Takigawa, and H. Horiuchi, Prog. Theor, Phys. Suppl. Extra Number, 464, 1968.) Many theoretical works have brought to the picture of alpha cluster nuclei described as a diluted gas of alphas in the lowest S state. (PRL 87, ; PRC 75, ). Possible existence of alpha condensates in nuclear matter. Experimentally not yet identified in 16 O or heavier Look for states analogous to the 12 C Hoyle state using the thick target inverse kinematics technique Estimated limit N = 10  for self-conjugate nuclei( Yamada PRC 69, )

The Thick target inverse kinematics technique Allows covering a large range of incident energies in the same experiment. In the inverse kinematics, the reaction products are focused at forward angles. Allows measuring reaction products emitted at 0 o. This Method has been used several times to study resonant elastic scattering or transfer reactions and is used here for the first time to detect multiple alpha emission. Limit: The position of the interaction point inside the gas has to be reconstructed with some assumptions

228 Th  source Energy(a.u.) Counts 228 Th  source self coincidence Time(ns) Counts Experimental setup Beam Monitor detector 4  E-E telescopes 55 um (16x16 strips) -1mm (3-quadrant, 1-16x16 strips) Havar window - 64  E front strips High gain pre amp STRUCK digitizers SIS3316 Trigger and Good timing information Good Energy resolution - The other 108 channels go to shapers and ADCs Pressurized chamber 4 He gas, pressure sufficient to stop the beam before the detectors

2) Experiment with the new setup on December AMeV on 4 He (5 Atm). Data analysis still in progress, low statistics. 2 experiments at Cyclotron Institute 1) Test run with a simplified setup AMeV on 4 He (3.5 Atm)

Events with alpha multiplicity 3 24 Mg* 12 C 1 12 C 2    AMeV or 13 AMeV + 4 He 3 alphas in the same event are correlated in time  T<15 ns and space v_   _lab -> Ek( 12 C 1 ) E*( 12 C 1 ) = E cm _  1 +E cm _  2 +E cm _  3 + Qgg (7.26MeV) Since the 3 alphas have similar and quite large energy in the laboratory and travel similar flightpaths the energy loss correction almost cancels out when we calculate 12 C excitation energy. Reconstruction of the interaction point with a recursive calculation based on the assumptions: 1)The resonant scattering produces 24 Mg * 2)The 3 alphas come from a 12 C 3)The other 12 C is in the ground state

Events with alpha multiplicity 3 -Total events -Uncorrelated events, mixing of 3 random alphas -Subtraction 7.65 MeV (0+) Spurious from mixed alphas 9.6 MeV (3-) 11.8 MeV (2-) 12.7 MeV (1+) Test run December 2014 experiment 7.65 MeV (0+) 9.6 MeV (3-) 16.5 MeV (to be analyzed) 11.8 MeV (2-) 12.7 MeV (1+) Relative energy of the three couples of alpha particles -> Tells us if the decay is proceeding through the 8 Be ground state. Dalitz Plot -> Information about the energy and momentum of the emitted alpha particles.

7.65 MeV (0+) Hoyle State decays through 8 Be gs In agreement with Monte Carlo simulation of the Hoyle state decaying through the 8 Be ground state Relative energies Experiment Simulation

9.64 MeV (3-) decays through 8 Be gs In agreement with Monte Carlo simulation of a 3- state decaying through the 8 Be ground state Experiment Simulation

Dalitz Plot (2- at 11.8 MeV) not decaying through 8 Be gs Fynbo, calculation O.S. Kirsebom, experimental data

Dalitz Plot (1+ at 12.7 MeV) not decaying through 8 Be gs Fynbo, calculation O.S. Kirsebom, experimental data

24 Mg excitation energy

Conclusions Using the suggested technique it is possible to study excited states of 12 C decaying into 3 alpha particles including the Hoyle state. This study can be extended to 16 O, but we need higher statistics. Better system: 32 S produced with 28 Si 15AMeV on 4 He, looking for the decay into two 16 O. 4  events -> possible identification of 16 O state analogous to the Hoyle state (candidate 0+ state at Ex 15.1 MeV). Next experiment scheduled: August 2015

M. Barbui, K. Hagel, J. Gauthier, S. Wuenschel, V.Z. Goldberg, H. Zheng, G. Giuliani, G. Rapisarda, E-J. Kim, X. Liu and J.B. Natowitz (Cyclotron Institute, Texas A&M University, College Station, TX, USA ) R. T. deSouza, S. Hudan (Indiana University, Bloomington, IN, USA) D. Fang (Shanghai Institute of Applied Physics (SINAP), Chinese Academy of Sciences, Shanghai, China) Thank you for your attention!