February 12-15,2003 PROCON 2003, Legnaro-Padova, Italy Jean Charles THOMAS University of Leuven / IKS, Belgium University of Bordeaux I / CENBG, France Spectroscopic studies of neutron deficient light nuclei  decay properties of 21 Mg, 25 Si and 26 P nuclei

Decay properties of neutron deficient light nuclei Selection rules: Fermi:  T=   J=0 ;  f =  i Gamow-Teller:  T=0±1;  J=0±1 ;  f =  i   + (C.E.) emission Reduced transition probability:  Global properties Short half-lives (  ms) High Q  values Low S p values  -delayed charged particle emission

21 Mg, 25 Si and 26 P nuclei stable nuclei  emitters  emitters  p emitters  p emitters T z = -3/2T z = P 21 Mg 25 Si 22 Al 20 Na 27 S 20 Mg 22 Si 23 Na 26 Mg 27 Al 30 Si 31 P 32 S 11

target ion source degrader ( 9 Be) magnetic dipoles velocity filter Detection set-up Production of neutron deficient nuclei at GANIL (fragmentation) Production target Accelerator 36 Ar 95 MeV/u Fragment separation

Detection set-up  detection  Identification time of flight: E1D6, E2 energy loss: E1D6, E1, E2, E3  Spectroscopic study  -(2)p spectrum: E3  coincidence: E4  spectrum: germanium detector  Acquisition trigger implantation: E1D6 radioactivity: E2, E3, E4  coincidence  -(2)p radioactivity Implantation BEAM

Identification and counting rate : 26 P example Identification matrix (  E,T.o.F) Counting rates  Implantation: 65 ions/s ( 26 P) 300 ions/s ( 21 Mg, 25 Si)  Contamination: 10 % (for 26 P) < 1 % (for 21 Mg, 25 Si)

Analysis of  -delayed proton spectra  coincidence in E4 Counts Energy (keV)  energy deposit in E3 Counts  coincidence with E4 E 3 (keV)

Identification of  transitions 26 P  -decay scheme  Need for a good  detection efficiency  Use of in-beam experimental results  spectrum in 26 P decay Counts Energy (keV)

21 Mg decay scheme Experiment Theory

25 Si decay scheme Experiment Theory

26 P decay scheme ExperimentTheory

 - : n → p + e - + np ft -  + : p → n + e + + E.C. : p + e - → n + np ft + Mirror asymmetry principle  Charge independence hypothesis of nuclear interactions: symmetry of analog  transitions  Isospin symmetry breaking: asymmetry in mirror  -decays

Systematics of experimental  values (A  40) Average asymmetry  : 11 (1) % in the 1p shell (A<17) 0 (1) % in the (2s,1d) shell (17<A<40)  = 4.8 (4) %  Allowed Gamow-Teller transitions (log(ft)<6)  17 couples of nuclei  46 mirror transitions

Mirror asymmetry in the  decay of A=21 & A=25 nuclei Experiment Theoretical calculations N. A. Smirnova & C. Volpe INC + HOIC + WSINC + WS ± ± 30 0 ± 40 0 ± ±  (%)

Spectroscopic studies of neutron deficient nuclei  Suitability of the fragmentation production method associated with the spectroscopic study of neutron deficient light nuclei  good agreement between experimental results and shell model calculations (nuclear structure and  decay strength)  good selectivity and production rates  access to decay properties of exotic nuclei ( 21 Mg, 25 Si, 26 P, 22 Al, 27 S)  Perspectives  complementarity with in-beam studies  Rare decay modes: study of the 2p radioactivity  Fundamental symmetries: study of the mirror asymmetry phenomenon evaluation of the Coulomb correction in super-allowed Fermi  decays Need for high precision experiments

L. Achouri, LPC Caen - France J. Äystö, P. Dendoveen, J. Honkanen, J. Jokinen, University of Jyväskylä - Finland R. Béraud, A. Ensallem, IPN Lyon - France A. Laird, University of Edinburgh – United Kingdom M. Lewitowicz, F. de Oliveira-Santos, M. Stanoiu, GANIL Caen – France B. Blank, G. Canchel, S. Czajkowski, J. Giovinazzo, CENBG Bordeaux - France C. Longour, IReS Strasbourg – France Collaboration

21 Mg, 25 Si and 26 P nuclei  (MeV) Z N 26 P 25 Si 21 Mg

Half-life of 26 P Time correlation procedure implantation radioactivity Correlation intervals T rad (ms) Counts E 4 > 0 Energy (keV) counts

Analysing procedure N impl : number of implanted ions E ff , E ff p : detection efficiencies   detection: radioactive sources  p detection: simulations, nuclei implantation depth C  and C p : corrections on N  and N p   detection: acquisition triggering  p detection: fitting procedure + coincidence condition N  and N p : number of counts in spectra detector calibration (  sources, known  -  and  -p transitions) B.R.  Measurement of absolute transition intensities:  Transition assignment (energy):

Identification of  -(2)p transitions (2)p transition identification via total decay energy  in coincidence with (2)p emitted from the I.A.S. Counts Energy (keV) Counts Energy (keV)

Mirror asymmetry sources Origin and consequences of the isospin non-conservation in nuclear interactions  Nature: Coulomb effects second class currents in weak interaction calculation of  -decay transition probabilities  Effects: nucleon-nucleon interaction description shell structure of nuclear states beyond the V-A model of  decay theory

Coulomb effects Mirror asymmetry in allowed Gamow-Teller transitions: with isospin configuration mixing radial overlap of nucleon wave functions: “binding energy effects”

Binding energy effects The last proton of the  + emitting nucleus is less bound than the last neutron of the  - emitting nucleus : S p + < S n -  radial overlap mismatch of wave functions in the  + decay:  + 0

Systematic approach of binding energy effects How to see the binding energy effects on the radial overlap of the nucleon wave functions?  increasing of  with R - /R + where: R - = S n - - S p - + E - * R + = S p + - S n + + E + * i.e.  R - /R +   - /  +  decreasing of  as J i is increasing i.e. as the centrifugal barrier is increasing Behaviour of  with the total angular momentum of the emitting nucleus Behaviour of  with the binding energy difference of the initial and final nucleons