Paddy Regan Dept. of Physics University of Surrey, UK E-mail: [email protected]

Deep-Inelastic and Multinucleon Reactions with Discrete

Gammaray Spectroscopy: A Brief Review

Paddy Regan

Dept. of Physics

University of Surrey, UK

E-mail: [email protected]

Physics of neutron-rich nuclei is the evolution of shell structure related to large energy gaps in the nuclear single-particle spectrum.

Reasons to study neutron-rich nuclei include:

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

2) Identification of specific orbitals, e.g. via isomers; g-factors; B(E2:I->I-2); shell model, seniority, Nilsson schemes etc.

3) Identifying new nuclear ‘exotica’, e.g., -/proton/-decaying states; new symmetries (e.g., 32), shell closures, shape changes..etc.

• (Some) DIC basics. – Thick or thin targets ? (I, Ex,N, Z) ; isomer gating etc.

• Thin target multi-nucleon transfer reactions:– Neutron-rich C nuclei (Berlin BRS).– N~20, Island of Inversion.– N=32,34 (sub)-shell closures, Se (Z=34, N=50). – 48Ca magic number(s).– N=50 robustness and shell closure.– Rotation/vibration evolution in A~100.– 132Sn region

• Seniority I=10+ isomers, h11/2 neutron hole migration ?• Surface diffuseness, weakening of N=82 shell ?

– A~170-190 K-isomerism and nuclear shape symmetry.– 208Pb at high spins; octupole collective vibrations etc. – U, Th octupole states, (very) high-j intruders (k17/2 etc.)– DIC with RIBs (24Ne beam at GANIL)– TIARA (d,p) etc. in inverse kinematics….

Courtesy,Bogdan Fornal

Courtesy,

Bogdan

Fornal

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

W. Krolas et al., Nucl. Phys. A724, 289 (2003).

208Pb

64Ni

Advantages and limitations of -ray thick target measurements with DIC

ADVANTAGES

Gamma rays from all reaction products

Gamma rays from the stopped nuclei – narrow lines – easy analysis of coincidences

Detection of cross-coincidences – some potential for identification

LIMITATIONS

Gamma spectra very complicated(hundreds of sources)

Gamma rays from the short lived states smeared out by the Doppler effect (emitted before a product is stopped)

Difficulties of identifications withouta starting point.

Angular distribution of rays almost isotropic

186W186W

3.5 MeV, >3 ms, 16+3.5 MeV, >3 ms, 16+

Off-beam singles, 7h

Total singles, 15 min.

Deep-inelastic reactionsFor K-Isomers with

238U beams

Out-of-beam conditionyields only lines from

the new isomers.

Out-of-beam conditionyields only lines from

the new isomers.

Without an off-beamtiming condition, only

Coulomb excitationlines are seen.

Without an off-beamtiming condition, only

Coulomb excitationlines are seen.

238U at 1600 MeV 186W (16 mg cm-2) μs →ms beam pulsing Argonne/Notre-Dame

array of 12 Ge dets. 1.5 MeV, 18 μs, 7–1.5 MeV, 18 μs, 7–

Courtesy, Carl Wheldon

-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

M . 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

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

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

nano to microsecond isomer tagging ?

Isomer gating very useful in DIC experiments.

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

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

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

What about the spin input ?

max

3

1blfmax

3

1tlf

max

3/13/1

0

221

max

1

1

7

2

1

1

7

2

fragments. twoebetween th mom. ang. relative the

and , intosplit is limit, mode rolling In the

25.12

cosec1.4

where, approach,closest of distance by thegiven is

max. issection -cross DIC the whereangle The

. and 219.0

is mom. ang. peripheral max. y theclassicall-Semi

l

AA

ll

AA

l

lll

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eZZd

d

grazing

AA

AAVERl

B

T

T

B

blftlf

TBgraz

k

TB

TBCMCM

R. Bock et al., Nukleonika22 (1977) 529

+2p

-2n

+2n

Fold distributions highlight different reaction mechanisms

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

TLFs

BLFs

elastics

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

Emission angle of TLFs can give information/selection on reaction mechanism (and spin input).

198Pt +136Xe, 850 MeV

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

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

Temporal separation can clearly identify ‘prompts’ and isomer decays

136Xe + 198Pt

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

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

information and lifetime determination of 195Os isomer decay

New isomer in 195Os identified in GSI projectile fragmentation confirmed ‘in-beam’ CHICO+GAMMASPHERE data.

Dobon, Wheldon, Regan et al.,

M.Caamano, P.M.Walker, PHR et al., Eur. Phys. J. A (2005)

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

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

N=80isotone

10+

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

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

Energy of N=80 I=10+ isomers correlates with energy increaseof 11/2- singleneutron hole 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

Valiente-Dobon, PHR, Wheldon et al., PR C69 (2004) 024313

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

BRS+EUROBALL

Energy

Z

Carbon gate

Doppler correction from energy in BRS

Add-back included

1818O at 90 O at 90 MeV on on 99Be (98 Be (98 μg.cmμg.cm-2-2)) BRSBRS= = ±12.5±12.5° ° → ±45.5→ ±45.5°° Euroball: 15 clusters, 26 clovers (209 crystals)Euroball: 15 clusters, 26 clovers (209 crystals) Unique-Z id., position to 1 mm, energy of recoilUnique-Z id., position to 1 mm, energy of recoil Particle-γ, particle-γ-γ and particle-particle-γ-γParticle-γ, particle-γ-γ and particle-particle-γ-γ

coincidencescoincidences

Courtesy, Tzany Kokolova

S. Lunardi, Acta. Phys. Pol. B36 (2005) 1301

CLARA

S. Lunardi, Acta. Phys. Pol. B36 (2005) 1301A. Gadea et al., J. Phys. G (2005) in press

S. Lunardi, Acta. Phys. Pol. B36 (2005) 1301

H

He

Li

Be

B

C

N

O

F

Ne

Na

Mg

24Ne

Deep Inelastic Collision reaction with light exotic beamPopulation of exotic Ne-F-O isotopes

Report of the E421S experiment (spokeperson F.Azaiez):aim of the experiment

• cross section measurements• spectroscopy Ne-O-F

DIC with RIBs!A new era ?

courtesy, Giovanna Benzoni

Report of the E421S experiment:Experimental details

• reaction: 24Ne @ 7.923 MeV/A + 208Pb (10.9 mg/cm2) 24Ne5+ , Ibeam ~ 1.5 . 105 pps

beam on target for 7 days

• setup: Vamos + EXOGAMVamos @ 45°

EXOGAM 11 detectors(2 without Compton shield)

Typical count rates:

• Ions: 30/min Total Ion counts: 7*24*60*30 = 302400 cross section determination is feasible

• Ion-gamma coincidence 70/h Total Ion-gamma coinc. 7*24*70 = 11760

only spectroscopy of inelastic ch.

courtesy, Giovanna Benzoni

Report of the E421S experiment:very preliminary spectraID-plot

E

E (a.u)

NeFONaE

(a.

u.)

Ne (inelastic)

3 days of statistics (~ 1/2)

Conditions:-Si-gamma coincidence- Prompt gamma peaks- calculated v/c

Ana

lysi

s in

pro

gres

sWorking on mass separation

courtesy, Giovanna Benzoni

Report of the E421S experiment:future

F

Ne

24Ne ~ 500 mb

26Ne ~ 80 mb(2n pick up)

23F ~ 20 mb(1p removal)

Beam intensity required to study weaker channels

• to get to more exotic Ne isotopes ~ 106

• to get to F 5.106

• to get to O ~ 107

courtesy,

Giovanna Benzoni

TIARA

courtesy, Wilton Catford

Experimental Results for 24Ne(d,p)25Ne Transfer with TIARA

TIARA

25Ne

(d,p)

10 MeV/u

Courtesy, Wilton Catford

• DIC physics…. – Neutron-rich C nuclei (Berlin BRS).– N~20, Island of Inversion.– N=32,34 (sub)-shell closures, Se (Z=34, N=50). – 48Ca magic number(s).– N=50 robustness and shell closure.– Rotation/vibration evolution in A~100.– 132Sn region

• Seniority I=10+ isomers, h11/2 neutron hole migration ?• Surface diffuseness, weakening of N=82 shell ?

– A~170-190 K-isomerism and nuclear shape symmetry.– 208Pb at high spins; octupole collective vibrations etc. – U, Th octupole states, (very) high-j intruders (k17/2 etc.)– DIC with RIBs (24Ne beam at GANIL)– TIARA (d,p) etc. in inverse kinematics….