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Spectroscopic studies around 48Ni (E312b) - 2000 : final results

date: Juin 2000



J. Giovinazzo, B. Blank, M. Chartier, S. Czajkowski, M.S. Pravikoff, J.-C. Thomas, CENBG Bordeaux, France

C. Borcea, Institute for Atomic Physics, Bucharest, Romania

G. de France, M. Lewitowicz, F. de Oliveira Santos, GANIL, Caen, France

R. Grzywacz, Z. Janas, M. Pfützner, Institute of Experimental Physics, Warsaw, Poland





- proton drip-line reached experimentally up to A = 50 (projectile fragmentation experiments: GSI/FRS, GANIL/LISE, ...)
- full shell-model calculations in the fp-shell possible (Caurier et al.)
- mass region with good candidates for 2-proton radioactivity: correlated 2p emission from ground state (1p emission energetically forbidden) predicted since 1960’s but not observed 39Ti, 42Cr, 45Fe, 49Ni, 48Ni are candidates


Experimental work

- spectroscopic studies of nuclei at the drip-line (Z = 22 to 28): decay of 39,40Ti, 42,43Cr, 46Mn, 45,46,47Fe and 49Ni
- all isotopes are (beta-delayed) proton emitters


Experimental set up

GANIL cyclotrons for acceleration of primary beam:

Primary beam: 58Ni26+, 74.5 MeV / A, 3 mAe
SISSI device for a secondary beam

Reaction: projectile fragmentation of beam in a nickel target LISE3 spectrometer for selection of ions

Decay: particule - gamma coincidences, pixel correlation with implantation

Experimental set-up of the GANIL cyclotrons for acceleration of the beam, with the SISSI device for secondary-beam production, the LISE3 spectrometer for the selection of fragments and the detection set up.



Detection Set up:

Selected ions loose energy in the Silicon telescope (DE, E) and then are implanted in a silicon strip detector where their positions are determined. The implantation point is surrounded by 4 germanium detectors to detect the gamma-rays from decay. A third silicon detector is used as a veto detector.



Identification of implanted ions:

- energy: DE1, DE2, E3
- time of flight: with cyclotron RF and MCP (located before the Wien filter)
- veto signals: for light ions going through the telescope
- position: X-Y sensitive silicon detector (E2)

-> ion-by-ion identification almost no background !



Proton-gamma spectroscopy

need for high enough conting rates for proton-gamma coincidences

proton + gamma energy





Search for 2p emission


Most exotic isotopes: 42Cr, 45Fe, 49Ni


Relation between proton energy and half-life: tunnel effect through Coulomb barrier

42Cr: Ep = 1.9 MeV ---> expected T1/2 10-12 s

49Ni: Ep = 3.7 MeV ---> expected T1/2 10-16 s

45Fe: too low statistics


Concluding Remarks


First half-life measurements for 42Cr, 45Fe and 49Ni

Improved precision for half-lives of 39Ti, 43Cr, 46Mn and 46,47Fe , deduced IAS position, proton branching ratios, ...

need for higher gamma efficiency

First decay scheme for the most produced isotopes 43Cr and 47Fe

limited by precision on mass excess of daughter nuclei need for a comparison with a theoretical approach

No evidence for a 2-proton radioactivity:

42Cr and 49Ni: indications of a beta-delayed proton emission (from half-life, proton energy) 45Fe: need for higher statistics

other candidates to be studied: 48Ni and 54Zn ...