Structure of Very Heavy Elements:
GABRIELA
Introduction and Motivations
Current experimental set-up
Milestones and (subset) results
Perspectives : short/long term
A. Lopez-Martens for the GABRIELA collaboration
GABRIELA
GABRIELA is a project dedicated to spectroscopic studies of heavy elements
The project takes place at the Flerov Laboratory for Nuclear Reactions, JINR, Dubna
Advantages of Dubna:
- intense stable beams (~1 pμA)
- stable and radioactive targets (233-236,238U, 237Np, 239,240,242,244Pu, 241,243Am,
245-248Cm, 249Bk, 249Cf,...)
- beam time
Goals of the project:
- study of single-particle states and nature of their couplings along isotopic
and isotonic chains as N=152Æ162
- study of isotopes for which very little spectroscopic information exists
- study of the stability of heavy nuclei produced in fusion-evaporation reactions
Gamma Alpha Beta Recoil Investigations with the ELectromagnetic Analyser
2m concrete wall
VASSILISSA
separator
U400
3 μm Mylar foil
α
recoil
e-
K. Hauschild, A.V. Yeremin et al.,
Nucl. Instr. Meth. A 560 (2006) 388
Milestones
Dec 2003 and Jan 2004: project accepted by JINR and IN2P3 Scientific Councils
May 2004: 1 day beam time
tests at the focal plane, 2 Ge + 1 BGO
48Ca beam, 164Dy and 174Yb standing targets
June-July 2004: 6 days beam time
tests with new chamber, 2Ge, 1BGO and 1electron detector
40Ar beam, 164Dy, 174Yb and 181Ta rotating targets
Sept-oct 2004: 1 month beam time
full setup
48Ca beam, 207-208Pb and 209Bi rotating targets
207Pb(48Ca,2n)253No => 249Fm
Alpha Decay of 253No – Gabriela Expt. Alpha Decay of 253No – JYFL Expt.,
A. Lopez-Martens et al., Submitted to Phys. Rev. C R.-D. Herzberg et al, J. Phys G30 (2004) R123
F. Hessberger et al., Eur. Phys. J. A 22 (2004) 417
α-γ
5/2+[622]
211
α-e- M1
129
E2
N = 151 systematics : isomeric 5/2+
251Fm : ORNL annual report : no peer reviewed publication
more recently: α−γ coincidences measured at SHIP
208Pb(48Ca,1n)255No -> 251Fm
209Bi(48Ca,1n)255Lr -> 255No -> 251Fm
‘ToI’
K
L Fm X-rays
200-keV
M
Analysis still ongoing
Extending the N = 151 systematics to 253No
New measurement at SHIP and α-decay information from 257Rf : E(5/2+) = 180(30) keV
GABRIELA: delayed e- and X-rays observed, substancial population of 5/2+ state in reaction
Milestones
Dec 2003 and Jan 2004: project accepted by JINR and IN2P3 Scientific Councils
May 2004: 1 day beam time
tests at the focal plane, 2 Ge + 1 BGO
48Ca beam, 164Dy and 174Yb standing targets
June-July 2004: 6 days beam time
tests new chamber, 2Ge, 1BGO and 1electron detector
40Ar beam, 164Dy, 174Yb and 181Ta rotating targets
Sept-oct 2004: 1 month beam time
full setup
48Ca beam, 207-208Pb and 209Bi rotating targets
July 2005: 10 days beam time
48Ca and 22Ne transmission test
Oct-Nov 2005: 1 month beam time
thinner chamber, new e- electronics, 6 Ge + 2 BGO + 4 passive shields
22Ne beam, 238U rotating target
48Ca beam, 210Pb class III rotating target
48Ca beam, 208Pb and 209Bi rotating targets
N = 153 systematics
Abrupt change of alpha decay
pattern
Change in 257No ground state ?
210Pb(48Ca, 1n)257No -> 253Fm
Cross section ?
Asai et al PRL95(2005)
248Cm(13C, 4n) σ = 1100 nb
Just as we were getting prepared …
210Pb target ready, radioprotection clearance……
Unique oportunity to use 210Pb target and
look at γ-e- coincidences in 253Fm.
3 bombarding energies
120 hours, beam dose of 8x1017
=> no events
assuming 100 nb
=> target thickness limit < 5 μg/cm2
To persue this further : 244Pu(18O, 5n) σ > 100 nb
=> requires transmission tests with an 18O beam
Is the 3/2+[622] swapped with 7/2+[613] in 259Rf ?
242Pu(22Ne,5n)259Rf -> 255No
σ ~ 5 nb, IB ~ 1 - 1.5 μA
=> improvements to set-up
Improvements to experimental setup
1) Modified Ge detector
=> 2x array efficiency
2) New Si detectors : larger + more strips
3) New lower power preamplifier => Colder Si
=> better e- resolution
4) 37o magnet replaced by 8o
=> less dispersion
5) ToF : thinner foils
=> less straggling
shorter
=> less dispersion Tx * εD ~ 3x
These modifications should be tested before next campaign (oct-nov 2006)
=> tests in September 2006
Further into the future
Limited beam time available at U400 (1-2 months/year)
Vassilissa is in the same experimental hall as the Gas Filled Separator
=> limited access time to target area
The cyclotron U400M will soon be upgraded to extract low energy beams (5 AMeV)
There is enough space for a dedicated experimental hall
= > The GABRIELA collaboration has applied for funds to build an upgraded
separator (Separator for Heavy ELement Studies) at the U400M dedicated to
prompt and focal plane gamma-ray spectroscopy
At the target position:
Ge detectors equipped
with TNT2-D cards
and/or
BaF2 array
Upgraded
focal plane
setup
If application is successful, 3 year funding should start sept 06
=> 1st test beams : sept 09
The people
A.V. Belozerov, M.L. Chelnokov, V.I. Chepigin, V.A. Gorshkov, A.P. Kabachenko, O.N. Malyshev,
Yu.Ts. Oganessian, A.G. Popeko, R.N. Sagaidak, A.V. Shutov, A.I. Svirikhin, A.V. Yeremin
FLNR, JINR, Dubna, Russia
Ch. Briancon, P. Desesquelles, K. Hauschild, A. Korichi, A. Lopez-Martens, J. Robin
CSNSM, IN2P3-CNRS, F-91405 Orsay Campus, France
D. Curien, O. Dorvaux, B. Gall, F. Khalfallah, M. Rousseau, N. Rowley, L. Stuttgé
IReS, IN2P3-CNRS, F-67037 Strasbourg, France
M. Guttormsen, S. Siem, A-C Sunde, N. Syed
Department of Physics, Oslo University, 0316 Oslo, Norway
F. Hanappe, V. Bouchat
Université Libre de Bruxelles, 1050 Bruxelles, Belgium
A. Goergen, Ch. Theisen
DAPNIA/SPhN, CEA-Saclay, France
A. Minkova
Department of Atomic Physics, University of Sofia, Sofia, Bulgaria
S. Antalic, S. Saro, M. Venhart
Comenius University of Bratislava, Slovakia
G. De France, Ch. Stodel
GANIL, France
D. Pantelica, R. Borcea
NIPNE, Roumania
