Proton and Two-Proton Decay of a High-Spin Isomer in 94 Ag Ernst ROECKL GSI Darmstadt and Warsaw University

Fusion-evaporation reactions 58 Ni( 40 Ca,p3n) 94 Ag Isotope separation on-line Detectors: ›Silicon strip detectors: ß particles, protons ›Germanium detectors: γ rays Experimental Techniques

Properties of the (21 + ) isomer of 94 Ag deduced from  -  and  -proton studies E* = 6.7(5) MeV T 1/2 = 0.39(4) s  fusion-evaporation = 350 pb *) *) Further parameters characterizing the experiment: 40 Ca intensity 75 particle-nA, 58 Ni-target thickness 3 mg/cm 2, ion-source efficiency 10%, intensity of the 94 Ag (21 + ) beam 10 atoms/min, measuring time 80 h I  = (21 + ) C. Plettner et al., Nucl. Phys. A 733, 20 (2004) I. Mukha et al., Phys. Rev. C 70, (2004)

(21 + ) isomer in 94 Ag: What was known by end of 2003 Population 0 + ground-state of 94 Ag (T 1/2 ~ 29 ms, A. Stolz, Ph D Thesis (2000)): not observed in fusion- evaporation reactions ! Comparison with shell-model predictions (up to 4p-4h excitations): inversion of 17 + and 21 + levels in 94 Ag ! 0.39(4) s 0.61(2) s Beta and  -delayed proton emission studied by using a multiple  -ray trigger ! N=Z=47

One-proton decay of the (21 + ) isomer of 94 Ag Search by measuring coincidences between charged particles and  -  cascades in 93 Pd Experiment: I. Mukha et al., Phys. Rev. Lett. 95, (2005) Theory: WKB estimate of proton widths à la Gamow

Si-  -  coincidence,  gates on 93 Pd lines *) Si singles spectrum scaled down by a factor (3) MeV 0.79(3) MeV *) 93 Pd  -rays identified by C. Rusu et al., Phys. Rev. C 69, (2004)

Data on the one-proton decay of the (21 + ) isomer of 94 Ag E p (MeV) ______ 0.79(3) 1.01(3) Intensity per 100 decays _______ 1.9(3) 2.2(4) T 1/2 (exp) (s) ______ 21(6) 18(4) L ___ (4) (3,5) T 1/2 (WKB) /T 1/2 (exp) _______________ 1  (L=4) 3  (L=5) Deformation effect? I  i  I  f __________ (21 + )  (33/2 + ) (21 + )  (33/2 –,35/2 – )

Two-proton decay of the (21 + ) isomer of 94 Ag Search by measuring coincidences between charged particles and  -  cascades in 92 Rh Experiment: I. Mukha et al., accepted for publication in Nature Theory: Three-body breakup model, L. Grigorenko et al., Phys. Rev. C 68, (2003)

Si-Si-  -  coincidence,  gates “shifted off” the 92 Rh lines Si-Si-  -  coincidence,  gates on 92 Rh lines *) *) 92 Rh  -rays identified by D. Kast et al., Z. Phys. 356, 363 (1997) 1.88(9) MeV

Experimental data on the two-proton decay of the (21 + ) isomer of 94 Ag E 2p = 1.88(9) MeV … and correlation data... I = 0.5(3) % per decay T 1/2 = 0.39(4)/0.5(3)% = 80(50) s I  i  I  f : (21 + )  (13 +,15 + ) L = (6,8)

Relative energy spectra... Predictions of the break-up model Experiment Expected for sequential 2p decay … for proton-proton correlations … for proton- 92 Rh correlations Expected for isotropic 2p decay

Di-proton ( 2 He) emission a = (long-to-short axis ratio) -1/2 Simultaneous emission of 2 protons Simultaneous emission of 2 protons

Summary and Outlook The proton decay of the (21 + ) isomer of 94 Ag has unprecedented features including discovery of one- and two-proton radioactivity from one and the same nuclear state, unambiguous identification of one- and two-proton by measuring coincidences with characteristic  rays, new kind of emission of protons from the poles of a prolate-deformed nucleus, tentatively deduced from correlation data. It is mandatory to try to improve the proton-proton correlation data with respect to statistics and angular resolution: Where can such a measurement be done ?

Si-Si-  -  coincidence,  gates on 93 Pd lines *) Singles spectrum scaled down by a factor (3) MeV 0.79(3) MeV “  gate” All  spectra gated by 93 Pd  - rays *) *) 93 Pd  -rays identified by C. Rusu et al., Phys. Rev. C 69, (2004)

L=(4) L=(3,5)

MeV MeV E Si1 + E Si2 gates: Si-Si-  -  coincidence,  gates “shifted off” the 92 Rh lines Si-Si-  -  coincidence,  gates on 92 Rh lines *) 1.88(9) MeV 92 Rh 94 Pd *) 92 Rh  -rays identified by D. Kast et al., Z. Phys. 356, 363 (1997)

This work Estimated by extrapolating systematical trends (G. Audi et al., Nucl. Phys. A 729, 337 (2003))

What this talk is about 1. In the odd-odd nucleus 94 Ag an isomer has been observed to have the following unique properties: excitation energy of 6.7 MeV, tentative spin/parity assignment of (21 + ), half-life of 0.4 s, one-proton and two-proton radioactivity 2. The one-proton decay is strongly hindered. 3. The two-proton decay is strongly enhanced.

Array of three silicon-strip detectors – High resolution and low energy-threshold for detecting charged particles (positrons, protons) – High granularity*)  position information I. Mukha et al., Nucl. Phys. A 745, 9285 (2004) *) Only 2 segments per detector used in this work