L.M. Robledo et al., J. Phys. G:Nucl. Part. Phys. 36 (2009) 115104

Main physics aim is to studythe best cases of nuclear triaxial rotation to finite spin.

190,192W are predicted to beamong the most gamma-soft, deformed nuclei in the entirenuclear chart.

Calculations suggest almost gamma-flat potential for N=116 190W

188W 190W 192W

TRS calculations for = 0 MeV / ħ are also consistent with 2~0.15; gamma=flat

N. Alkhomashi et al., Phys. Rev. C80 (2009) 064308

Stopped RISING Experiments @ GSI (2006-8): 27 ‘new’ isomers (48 total) measured in a wide range of neutron-rich nuclei. Beta-delayed studies also….

RISING: isomeric and beta decays

AGATA+PRISMA: prompt192Os target DIC

208Pb target DIC(see proposal by Zsolt Podolyak)

S.Steer, Zs. Podolyak, P.H. Regan et al., Int. Jour. Mod. Phys. E18 (2009) 1002

Knowledge to date ?

188Ta →188W

190Ta →190W

192Ta →192W

N. Alkhomashi et al., Phys. Rev. C80 (2009) 064308

bubble!

R.B.Cakirli & R.F. Casten Phys. Rev. C78 (2008) 041301 (R)

Evidence for a ‘sub – shell’ closure for Z=74 (or lighter ?)

192W

190W

Minimization of gamma-softness at N=116 ?

W isotopes

Davydov-Fillipov Model, low-lying I=2+

2 is evidence for large degree of ‘deformation’.Wilet-Jean (soft rotor) for flat also have low-lying 2+

2 state.

Knowledge to date on 190W is from - and isomer delayed spectroscopy. Spins are limited

Higher Spins in 190W ?

2qp states included

vacuum only

Prediction of a GIANT BACKBEND associated with abrupt prolate-to-oblate transition around 10 ħ. Favoured oblate collective rotations predicted for spins above this…..

Proposal to identify near-yrast states in 190,2W to >10ħ.

Suggested reaction parameters:

136Xe +192Os → 136-yBa + 192-xW E(136Xe) = 809 MeV from PIAVE; I(136Xe) ~2pna;

192Os target thickness = 0.5mg/cm2

BLF ~ 8% v/c; TLF ~ 6.7%; lmax(TLFroll)~39 ħ; lmax(BLFroll)~35 ħ

Gate on

• Barium (Z=56) binary partners in PRISMA and

• Barium (134,136,138Ba) isomers stopped in DANTE.

• Use 2-body kinematics for W isotope Doppler correction.

(assumes 20% above Coulomb barrier; can run with 900 MeV for better transmission / id in prisma.)

Reaction of choice would be192Os+136Xe -> 192-XW+136Ba Prompt and delayed gammas in 136Ba have been identified and can be used for tagging.

136Ba Isomer gate in 136Xe+198Pt ‘in-beam’ DIC reaction, clearly identifies (all previouslyreported) 198-xOs isotopes. Would expect the same from 136Ba isomer gate at target position from ions stopped in DANTE.

Note, can also use 134Ba & 138Ba isomers as ‘tungsten tags’ too.

Rate estimate / beam-time request:

Expect using the estimates on the previous page:

~ 4k ‘useful’ PRISMA – (190,2W)-(190,2W) 2 coincidences per day

+

~9.5k ‘useful’ DANTE-Ba-isomer- (190,2W)-(190,2W) 2 per day.

TOTAL ~ 70,000 190,2W 2 clean coincidences from a 5 day run.

Request 5 days beam-time

plus

one day for PRISMA calibrations and setting up.