Future Challenges Using Decay Spectroscopy with Projectile Fragmentation and In-Beam Deep Inelastic...

Future Challenges Using Decay Spectroscopy with Projectile

Fragmentation and In-Beam Deep Inelastic Reactions

Paddy Regan

Dept. of Physics

University of Surrey,UK

E-mail: p.regan@surrey.ac.uk

Outline of Talk• (Some) Physics questions in heavy neutron-rich nuclei.

• Thin target multinucleon transfer reactions:– 100Mo+136Xe : reaction mechanism info.– 198Pt+136Xe: 136Ba I=10+seniority isomers, effective charges.

• Projectile-fragmentation isomer spectroscopy.– The Stopped Beam RISING Campaign, some physics aims.– g-factors and BaF2 timing below isomers.

Main physics interest in neutron-rich nuclei is based on the EVOLUTION OF SHELL STRUCTURE and the appearance of

‘large gaps in the nuclear single-particle spectrum’.

Reasons to study neutron-rich nuclei

1) Evolution of collective modes (vibrations, rotations, superdef ?) from spherical states by altering (N,Z,I, Ex).

2) Identification of specific nucleonic orbitals, e.g. via isomeric decays, g-factors, B(E2:I->I-2), effective charges, shell model descriptions, seniority schemes, deformed (Nilsson) schemes etc.

3) Identifying new nuclear ‘exotica’, e.g., the unexpected, beta-decaying high-spin states, new symmetries (e.g., 32), neutron ‘skins’, new shell closures, shape changes etc.

How do we study the heavy neutron-rich ?• Multi-nucleon transfer reactions:

– Backed/thick target technique (made famous by Broda, Fornal, Krolas (Crakow group) + Daly, Janssens, Khoo, Lunardi et al.,)

• Projectile-fragmentation reactions:– Isomer spectroscopy (made famous by Pfützner, Rykaczewski,

Grzywacz, Janas, Lewitowicz et al., & the Warsaw Group).

In both cases, the reaction mechanism is not fullystudied and experiments are needed in order toset the limits of both of these techniques.

2)12( LModified from Introductory Nuclear Physics, Hodgson, Gadioli and Gadioli Erba, Oxford Press (2000) p509

Aim? To perform high-spin physics in stable and neutron rich nuclei. Problem: Fusion makes proton-rich nuclei.Solutions? (a)fragmentation (b) binary collisions/multi-nucleon transfer

See eg. Broda et al. Phys. Rev Lett. 74 (1995) p868Juutinen et al. Phys. Lett. 386B (1996) p80Wheldon et al. Phys. Lett. 425B (1998) p239 Cocks et al. J. Phys. G26 (2000) p23Krolas et al. Acta. Phys. Pol. B27 (1996) p493Asztalos et al. Phys. Rev. C60 (1999) 044307

CCMMAX

MAX

TB

TLF

VER

L

LAA

L

2

2

31

2

1

1

7

2

:limit Rolling

-1

cos-1

by calculated then is correctionDoppler The

coscoscoscossinsinsinsin)cos(

where

)cos(r.r

by given is angleray -fragment/ the

k )cos( , j )sin()sin( ,i )cos()sin(

k, and j i, rsunit vectoCartesian For

2

2,1'

2121212112

122121

1,2

1,2

EE

rr

rzryrx

z

x

y

Simon et al., Nucl. Inst. Meth. A452, 205 (2000)

BLF

TLF

beam tlftlf

blfblf

Ge

TOF ~5-10 ns.ns-s isomers can de-excite in bestopped by CHICO position detector. Delayeds can still be viewedby GAMMASPHERE.

Rochester Group

100Mo + 136Xe @ 700 MeV GAMMASPHERE + CHICOPHR, A.D. Yamamoto et al., AIP Conf. Proc. 701 (2004) p329

Can we use the data from the CHICO+Gammasphere expt. to understand the ‘DIC’ reaction mechanism ? A wide range of spins & nuclei are observed.

R.Broda et al., Phys. Rev. C49 (1994)

Wilczynski (‘Q-value loss) Plot A.D.Yamamoto, Surrey PhD thesis (2004)

Gating on anglegives a dramatic channel selection in terms of population.

Relative Intensitiesof 6+->4+ yrast transitions in TLFs (relative to 100Mo) for 136Xe beam on 100Mo target at GAMMASPHERE+ CHICO.

+2p

-2n

+2n

Fold distributions highlight different reaction mechanisms

PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313

Emission angle of TLFs can give information/selection on reaction mechanism (and maybe spins input ?)

198Pt +136Xe, 850 MeV

J.J. Valiente-Dobon, PHR,C.Wheldon et al., Phys. Rev.C69 (2004) 024316

67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85

59585756555453525150

757473

76

8483828180797877

N/Z compound

nano and microsecond isomerson gated 198Pt+136Xe withGAMMASPHERE+CHICODIC 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124

J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004) 024316

J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313136Xe+198Pt reaction beam-like fragment isomers.

131I

133I

128Te

130Te 136Xe

132Xe

138Ba

137La

136Xe+198Pt Target-like fragment isomers

J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313

184W

185Re

191Os

192Os

195Os

192Pt

198Pt

193Au

Identification of new ‘seniority’ isomer in 136Ba, N=80 isotone.

J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004) 024316

T1/2=91(2) ns

N=80 isotonic chain, 10+ isomers, (h11/2)-2I=10+

Q. Why does Ex(10+) increase while E(2+) decreases ? 91(2) ns

Structure of 8+ final state changes from 134Xe -> 136Ba ?See Valiente-Dobon, PHR, Wheldon et al., PRC69 (2004) 024313

Isomer decayalso depends on structureof final state

N=80, (h11/2)-210+ isomers

Energy of N=80 I=10+ isomers correlates with energy increaseof 11/2- singleneutron in N=81 isotones.

Increase in 10+ energy, plusexpansion of proton valencespace means8+ yrast state now (mostly)NOT (h11/2)-2

for Z>54

N=81

N=80

Ex, I=11/2 -

Ex, I=10

Pair Truncated Shell Model

Calculations (by Yoshinaga,Higashiyama et al. Saitama)predict yrast 8+ in 136Ba no longer mostly (h11/2)-2

but rather, (d5/2)2(g7/2)2

0.000

0.963

2.760

g7/2

d5/2

h11/2 Protons, max. seniority 2spin = 6 ħ (from (g7/2)2.

Seniority 4 states though can have up to7/2 + 5/2 + 5/2 +3/2 = 10 ħ

Expect neutron ‘seniority scheme’for (h11/2)-2 ‘j2’ mutlipletconfiguration at N=80 (e.g. 130Sn).

132Te, 134Xe have proton excitationsdue to g7/2, d5/2 at 0+,2+,4+,6+ but not competing 8ħ and 10ħ states.

Extra collectivity for higher-Z pushes down 0+ and 2+.

Proton s.p. energiesused in 136Ba SM calcs

primary beamPb @ 1GeV/u

Production target

Central focus, S2Final focus, S4

E(Z2)

cu

eB

Q

A

FTO

catcher

degraderdegrader

dipole, B

scintscint

MW=x,y

scint(veto)Use FRS@GSI or LISE3@GANIL to ID nuclei.

Transport some in isomeric states (TOF~ x00ns).Stop and correlate isomeric decays with nuclei id.

eg. R. Grzywacz et al. Phys. Rev. C55 (1997) p1126 -> LISE C.Chandler et al. Phys. Rev. C61 (2000) 044309 -> LISE M. Pfützner et al. Phys. Lett. B444 (1998) p32 -> FRS Zs. Podolyak et al. Phys. Lett. B491 (2000) p225 -> FRS M. Pfützner et al. Phys Rev. C65 (2002) 064604 -> FRS

In-Flight Technique Using Projectile Fragmentation

8+ isomer in 78Zn, real evidence of 78Ni shell closure.

J.M.Daugas et al. Phys. Lett.

B476 (2000) p213

Heaviest odd-odd,N=Z gammas, isobaric analog states ? 86Tc, C. Chandler et al. Phys. Rev. C61 (2000) 044309

Can perform spectroscopy at rates of few ions per hour.

136Sb

135TeUse FRS to select projectile fission products (forward boosted ones). Note transmission a few %.

T1/2=565(50) ns state in 136Sb (Z=51, N=85)

M. Mineva et al. Eur. Phys. J. A11 (2001) 9

Prompt ‘flash’ is a limiting problem for isomer Fragmentation.

Reduces effective Ge efficiency by factor of 3-4 !

(Partial) Solution ?

Use a low-Z (e.g., plastic stopper)

Background from the stopping down of the fast ions:

Simulated by P. Detistov Surrey/Sofia

M.Pfutzner,M.Hellstrom et al.

208Pb region

many μs isomersexpected

212Po, 18+, 65s

215Ra, 43/2-, 800ns

217Ac, 29/2+, 1μs

N=126, holes in 208Pb

(g9/2)-2 ‘2j’ multiplet(and isomer) in 130Cd (Z=48, N=82) should look like 98Cd (Z=48, N=50)

A real test of valence anaolgue scheme.

Do with fission fragments.

(g9/2)-2

,

1

21

exp

21

WT

Tf

Best K-isomer?Doubly-mid-shell nucleus, 170DyN=104, Z=66 (Np.Nn=352=Maximum!).Appears to be a correlation betweenf values and NpNn for K=6+ isomers in A~180 region.(see PHR, Oi, Walker, Stevenson & Rath, Phys. Rev. C65 (2002) 037302)

Extrapolation suggestsisomer in 170Dy lives forhours….could be beta-decay candidate.

172Hf, 174Yb, 174Hf, 176Hf, 178Hf, 178W K=6+ isomers

170Dy ?

N=104 isotones, K=6+ energy

Xu, Regan, Walker et al

33 ns isomer in 195Os (last stable 192Os), useful test of structure in prolate/oblate shape coexistence region. 194Os Wheldon et al. Phys. Rev. C63 (2001) 011304(R)

First id of ‘doubly mid-shell’ nucleus, 170Dy (N=104, Z=66).

Data from M.Caamano et al.

BaF2 ‘fast timing’ data from H. Mach et al. Contribution to ENAM 2001

Allows an ordering of the gammas under isomer from their (~ps) lifetimes.

From Henryk Mach et al., 96Pd.

Use (BaF2,BaF2) coincidences below isomers to get B(E2) values ( & order gamma-transitions)

96Pd H. Mach et al.,

g-factors from fragmentation isomers

Basic idea, put isomer in B-field. Perturbation of gamma-ray angular distribution depends on induced Torque.

Rate of precession gives Larmor frequency, which gives g-factor.

‘Wiggles’ in count ratio between different angles from 13/2+ isomer, T1/2= 354(2)ns in 69Cu.

G.Georgiev EPJA20 (2004) p93;

J. Phys. G28 (2003) p2993 See poster by Steve Mallion

Stopped Beam Physics Workshop, Guildford 29-30th March 2004

50 delegates, ~ 20 presentations, 4 working groups…..

Major campaign using ‘retired euroball’ detectorsfor fragmentation-based nuclearspectroscopy.

Stopped-Beam Campaign to study decays from isomers and following beta-decay.

First call for proposals (deadline was last week), three proposals initially submitted for ‘isomer only’ study

1) A~110 neutron-rich Zr,Mo,Ru,Pd (Alison Bruce)2) A~140 proton drip-line, proton decay daughters (Dave Cullen)3) N=126, ‘south’ of 208Pb (Zsolt Podolyak) + g-factor letter of intent (Gerda Neyens)

‘Active stopper’ experiment planned for next EA (170Dy, 130Cd, etc.)

International ConferenceOn NUclear STructure, Astrophysics & Reactions University of Surrey, Guildford, UK5-8 January 2005

http://www.ph.surrey.ac.uk/cnrp/nustar05

Happy Birthday Rafal !!

PHR, Valiente-Dobon, Wheldon et al., Laser Phys Letts. 1 (2004) 317

Crossing and alignments well reproduced by CSM, although AHVs

Smith, Walker et al., Phys. Rev. C68 (2003) 031302

0

10

20

30

40

50

%>Ecoul

Ltlf (roll)

v/c graz tlf

Linear(%>Ecoul)

0

10

20

30

40

50

60

620 648 677 705 733 761 790E_beam (MeV)

blf_graz

tlf_graz

lmax/10

Kinematics and angular mom. input calcs (assumes ‘rolling mode’) for 136Xe beam on 100Mo target.

Estimate ~ 25hbar in TLFfor ~25% above Coul. barrier. For Eb(136Xe)~750 MeV, in labblf~30o and tlf~50o.

100Mo +136Xe (beam) DIC calcs.

Gamma-gamma analysis on 200Pt isomer (21 ns!), M. Caamano et al. Nucl. Phys. A682 (2001) p223c; Acta Phys. Pol. B32 (2001) p763 stripping effect to extend lifetime

I=43/2

Low spin

PROTON RICH

~1 ms

“Pow

er”

of f

ragm

enta

tion

Z. Podolyak et al.,

Chandler et al. Phys. Rev. C61 (2000) 044309

67Ge

69Se

76Rb

Search for long (>100ms) K-isomers in neutron-rich(ish) A~180 nuclei.

low-K high-K mid-K j

K

:rule sel. -K

Walker and Dracoulis Nature 399 (1999) p35

(Stable beam) fusion limit makes high-K in neutronrich hard to synthesise

also a good number for K-isomers.

Prompt flash knocks out a large portion of the detectors….effectively reduces the gamma efficiency by upto 80%! Need digital electronics and time stamping

2

3/22

22

2

)1(exp

ratio,isomer predicts model off-cut sharp

1

3

3

210178.0

, 2

)1(exp

2

12

fJ jth

p

ppf

ffjj

JJdJPR

A

AAAA

JJJP

m

M. de Jong et al. Nucl. Phys. A613 (1997) p435

M. Pfutzner et al. Phys Rev. C65, 064604 (2002)

iitot

i

fii

qq

effimp

tot

b

ttG

TOFTOF

FGbN

NR

1

expexp

11

expF

, )1(

0

2

2

22

1

11

Isomeric Ratio Calculations

M. Pfutzner et al. Phys Rev. C65, 064604 (2002)

Pfutzner, Hellstrom, Mineva et al.

24

24

2 :Rotor

0 : Vibrator

)2(

242

),1(2

:Rotor

,2

:Vibrator

22

22

J

J

J

n

JR

JR

J

JJER

JEJJE

EJ

nE

PHR, Beausang, Zamfir, Casten, Zhang et al., Phys. Rev. Lett. 90 (2003) 152502

E-GOS plot appears to indicate that Vibrator-Rotator phase change is a feature of near stable (green) A~100 nuclei.

BUT….what is the microscopic basis ?

‘Rotational alignment’ can be a crossing between quasi-vibrational GSB & deformed rotational sequence.(stiffening of potential by population of high-j, equatorial (h11/2) orbitals).

PHR, Beausang, Zamfir, Casten, Zhang et al., Phys. Rev. Lett. 90 (2003) 152502

50

82

[550]1/2-

1h11/2

1g9/2

[541]3/2-

See PHR, Yamamoto, Beausang, Zamfir, Casten, Zhang et al., AIP Conf. Proc. 656 (2002) p422

‘Weak Coupling’

E/(I-j) E-GOS extension for odd-A

Suggests 11/2- band is anharmonic, -soft rotor?

BUT seems to work ok for +ve parity bandsvib ->rotor following(h11/2)2 crossing.

What about odd-A nuclei….are the h11/2 bands ‘rotational’ ?

case. 0 even)-(even for the toreduces which

22

2

24 by, simplified becan This

24

24

2

24

2

2

2

2

2

22

jI

E

jI

jRER

RKIRjI

jjIE

jIRjI

jE

jI

jI

I

I

I

EIR

jGOSE

j

jII

Carl Wheldon (HMI-Berlin) has suggested extension of E-GOS by ‘renormalising’ the rotational energies at the bandhead.

If the band-head spin of a sequence is given by j then substituting Ij in place of I, one obtains,

PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313

Can see clearly to spins of 20ħ using thin-target technique.

seems to work ok, h11/2 bands now look like rotors,

Even-Even yrast sequences and odd-A +ve parity only show rotational behaviour after (h11/2 )2 crossing….

215Ra

Stuchbery et al.Nucl. Phys. A641 (1998) 401

τ = 800 ns, 43/2-, 3.8 MeV

407 keV γ-ray

from 206Pb(13C,4n)

215Ra γ-ray spectrum

from 238U fragmentation

Z. Podolyak, private communication

Abrasion-ablation model

(1-2/3)

k = 2 A>10

“sharp cut-off” approximation:

De

Jong

, Ign

atyu

k, S

chm

idt,

NP

A61

3 (1

997)

435

.

]2

)1(exp[)(

2

mJ f

mmth

JJdJJPR

179W populated in: fragmentation of 208Pb at 1 GeV/u fusion evaporation: 170Er(13C,4n) at 67 MeV

M. Pfutzner, PHR et al. Phys Rev. C65, 064604 (2002)Higher spins for greater A.

208Pb beam at 1 GeV/u allows production of ( high-spin isomers,

M. Pfützner et al. Phys Rev. C65 (2002) 064604

High spins (>35/2) populated

Projectile Fragmentation Reactions

hotspot

Excited pre-fragment

Finalfragment

projectile

target

Energy (velocity) of beam > Fermi velocity inside nucleus ~30 MeV/uCan ‘shear off’ different combinations of protons and neutrons.Large variety of exotic nuclear species created, all at forward angleswith ~beam velocity. Some of these final fragments can get trapped in isomeric states.

Problem 1: Isotopic identification. Problem 2: Isomeric identification.

TLFs

BLFs

elastics

PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313

Can see 184-194Os in binary partner channels. i.e.in 2p transfer, up to 14 neutrons evaporated. ( 4n -> 194Os is heaviest known).

198Pt, 2+

136Xe, 2+

J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313

138Ce 125Sb

J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313

Super-FRS yields215Ra

170Dy, double mid-shell, ‘purest’ K-isomer ? (see PHR, Oi, Walker, Stevenson and Rath, Phys. Rev. C65 (2002) 037302)

Max at 170Dy

K=6+state favoured