Naslov
Search for gamma-ray transitions between 12C-12C cluster states in 24Mg

Autori
Elanique, A. ; Haas, F. ; Freeman, R.M. ; Beck, C. ; Nouicer, R. ; Watson, D.L. ; Jones, C. ; Cowin, R. ; Lee, P. ; Basrak, Zoran

Vrsta, podvrsta i kategorija rada
Radovi u zbornicima skupova, cjeloviti rad (in extenso), znanstveni

Izvornik
Proceedings of the XXXVI International Winter Meeting on Nuclear Physics / Iori, I. - Milano : Universita degli Studi di Milano, 1998, 529-536

Skup
International Winter Meeting on Nuclear Physics (34 ; 1998)

Mjesto i datum
Bormio, Italija, 26.01.1998. - 31.01.1998

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
cluster states; magnesium-24; nuclear molecules; in band gamma-ray transitions; triple coincidences (fragment-fragment-gamma)

Sažetak
The formation of nuclear omolecules in ^24Mg is well supported by a large number of experimental results pointing to the existence of ^12C-^12C cluster states in this light nucleus. In particular, the pronounced resonances found in elastic and inelastic ^12C-^12C cross sections are frequently interpreted in terms of different rotational bands of the superdeformed dinuclear complex. However, such an explanation is not unique and remains much debated. A strong experimental signature for the existence of nuclear molecules would be the observation of enhanced E2 gamma-ray transitions connecting rotational cluster states. The corresponding short lived resonances are located at relatively high excitation energies well above the particle decay threshold. In fact, even with the enhancement of the radiative gamma_gamma width, due to a high deexcitation gamma-ray energy (6~7 MeV) and moreover to a large quadrupole moment of the system, gamma_gamma is still expected to be much smaller than the particle decay width making the observation of such gamma rays extremely difficult. The aim of the experiment performed at the Orsay Tandem accelerator was to search for collective E2 gamma-ray transitions between states corresponding to the 10^+ and 8^+ resonances in the ^12C+^12Cj collision. A bombarding energy E_lab.=32.9 MeV of the ^12C+^12C reaction has been chosen to populate a well known and isolated 10^+ resonance. The experiment has been carried out in a triple coincidence mode (fragment-fragment-gamma)with the outgoing binary fragments in the exit channels detected in two position sensitive Si detectors and the gamma rays in the 4Pi array Chateau de Cristal composed of 74 BaF_2 scintillators. A few events have been observed which could arise from the transitions we searched for. This would be the first time that such transitions have been seen and from the assumptions we have made, a value of 1.7x10^-5 for the (gamma_gamma/gamma_c)_10+ radiative branching ratio has been deduced which corresponds to an enhanced B(E2)=180 W.u. This value is quite consistent with the molecular state picture of the 10^+ and 8^+ cluster states in ^24Mg at excitation energies of 30.4 and ~23.5 MeV, respectively.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

POVEZANOST RADA