Proton and Two-Proton Decayof a High-Spin Isomer in 94Ag

Ernst ROECKL 

GSI Darmstadt and Warsaw University

• Fusion-evaporation reactions 58Ni(40Ca,p3n)94Ag

• Isotope separation on-line

• Detectors:

› Silicon strip detectors: ß particles, protons

› Germanium detectors: γ rays

Experimental Techniques

Properties of the (21+) isomer of 94Agdeduced from - and -proton studies

E* = 6.7(5) MeV

T1/2 = 0.39(4) s

fusion-evaporation = 350 pb *)

*) Further parameters characterizing the experiment: 40Ca intensity 75 particle-nA, 58Ni-target thickness

3 mg/cm2, ion-source efficiency 10%, intensity of the

94Ag (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, 044311 (2004)

(21+) isomer in 94Ag: What was known by end of 2003

Population 0+ ground-state of 94Ag (T1/2 ~ 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 94Ag !

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 94Ag

Search by measuring coincidences between charged particles and - cascades in 93Pd

Experiment:I. Mukha et al., Phys. Rev. Lett. 95, 022501 (2005)

Theory:WKB estimate of protonwidths à la Gamow

Si-- coincidence, gates on 93Pd lines *)

Si singles spectrumscaled down by a

factor 240

1.01(3) MeV

0.79(3) MeV

*) 93Pd -rays identified by C. Rusu et al., Phys. Rev. C 69, 024307 (2004)

Data on the one-proton decayof the (21+) isomer of 94Ag

Ep (MeV)

______

0.79(3)

1.01(3)

Intensityper 100 decays_______

1.9(3)

2.2(4)

T1/2(exp)

(s)

______

21(6)

18(4)

L

___

(4)

(3,5)

T1/2(WKB) /T1/2

(exp)

_______________

110-6 (L=4)

310-7 (L=5)

Deformation effect?

Ii If

__________

(21+) (33/2+)

(21+) (33/2–,35/2–)

Two-proton decay of the (21+) isomer of 94Ag

Search by measuring coincidences between charged particles and - cascades in 92Rh

Experiment:I. Mukha et al., accepted for publication in Nature

Theory:Three-body breakup model,L. Grigorenko et al., Phys.Rev. C 68, 054005 (2003)

Si-Si-- coincidence, gates “shifted off”

the 92Rh lines

Si-Si-- coincidence, gates on 92Rh lines *)

*) 92Rh -rays identified by D. Kastet al., Z. Phys. 356, 363 (1997)

1.88(9) MeV

Experimental data on the two-proton decayof the (21+) isomer of 94Ag

E2p = 1.88(9) MeV

… and correlation data ...

I = 0.5(3) % per decay

T1/2 = 0.39(4)/0.5(3)% = 80(50) s

Ii If : (21+) (13+,15+)

L = (6,8)

Relative energy spectra ...

Predictions of thebreak-up model

Experiment

Expected for sequential 2p decay

… for proton-protoncorrelations

… for proton-92Rhcorrelations

Expected for isotropic 2p decay

Di-proton (2He) emission

a = (long-to-short axis ratio)-1/2

Simultaneous emissionof 2 protons

Simultaneous emissionof 2 protons

Summary and Outlook

The proton decay of the (21+) isomer of 94Ag 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 ?

… if you want to see the field of exotic-beam research‘in full glory’, please feel invited to the following reading

The Euroschool Lectures on Physics with Exotic Beams, Vol. 1Lecture Notes in Physics Vol. 651 (2004), J. Al-Khalili and E. R. (Eds.)

Table of Contents: ‘The Why andHow...’ (M. Huyse), ‘Practioner’sShell Model’ (H.Grawe), ‘Halo Nuclei’(J. Al-Khalili), ‘In-flight Separation’(D.J. Morrissey, B.R. Sherrill),‘Stored Exotic nuclei’ (F. Bosch) …‘Precision Weak-interaction Studies’(N. Severjins), ‘Nuclear Astrophysics’(K. Langanke, F.-K. Thielemann, M.Wiescher), ‘Medical Applications ofAccelerated Ions’ (W. Kraft-Weyrather)

www.springeronline.com/3-540-22399-1

Si-Si-- coincidence, gates on 93Pd lines *)

Singles spectrum scaleddown by a factor 240

1.01(3) MeV

0.79(3) MeV

“ gate”

All spectra

gated by 93Pd - rays *)

*) 93Pd -rays identified by C. Rusu et al., Phys. Rev. C 69, 024307 (2004)

L=(4)

L=(3,5)

1.4 - 1.6 MeV

1.8 - 1.95 MeV

ESi1+ ESi2 gates:

Si-Si-- coincidence, gates “shifted off”

the 92Rh lines

Si-Si-- coincidence, gates on 92Rh lines *)1.88(9) MeV

92Rh

94Pd

*) 92Rh -rays identified by D. Kastet al., Z. Phys. 356, 363 (1997)

This work

Estimated by extrapolatingsystematical trends(G. Audi et al., Nucl. Phys.A 729, 337 (2003))

What this talk is about

1. In the odd-odd nucleus 94Ag 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