Angular momentum population in fragmentation reactions

Zsolt PodolyákUniversity of Surrey

2

~15(+3)

>20(+7)

5(+5)

7

Isomers observed following fragmentation of 208Pb and 238U (Z>60)

No. of isomersknown(+new)

New isomers => nuclear-structureKnown isomers => reaction mechanism (angular momentum population

What is the production cross section for individual states?

I=43/2

Low spin

PROTON RICH

~1 ms

“Pow

er”

of fr

agm

enta

tion

● M. Pfützner et al., Phys. Lett. B444 (1998) 32. ■ M. Pfützner et al., Phys. Rev. C65 (2002) 064604.▲ K. Gladnishki et al., Phys. Rev. C69 (2004) 024617.

isomeric ratio:

total

isomerN

NR exp

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

M. P

fütz

n er e

t al .,

Ph y

s . R

e v. C

65

(20 0

2 ) 0

5 46 0

4.

ABRABLA

Analytical formulae

ρth -all states with spin higher than the isomer decay into the isomer

M. Pfützner et al., Phys. Rev. C 65 (2002) 054604.R

exp

/ρth

e

open symbol: known higher-lying isomer (not observed)

Nuclear structure has to be considered

φ = Iisomer/(I parallel+I isomer) = Iisomer / I total

ρexp=Rexp /φ

ρexp - the probability of populating states with higher spin than the isomer – can be compared with theory!

196Pb: A.K.Singh et al., Nucl. Phys. A707 (2002) 3186W(16O,6n) at 110 MeV; 170Er(30Si,4n) at 144 MeV fusion-evaporation reaction!

196Pb

270 ns 2.7 MeV 12+

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

The highlighted points: Higher lying isomers decay into our isomer

preliminary

preliminary

175Hf

176Ta179Ta

177Ta

The highlighted points: Higher lying isomers decay into our isomer

Conclusions on the reaction mechanism

• Good agreement between experiment and theory (within a factor of 2-3)

• predictions for radioactive beams seems to be possible

There are new data on:212Fr 15– 213Fr 29/2+

212Ra 8+

214Ra 17–

215Ra 43/2– <= HIGHEST SPIN from fragmentation215Ac 29/2+ 217Ac 29/2+

Future:

Background from the stopping down of the fast ions:

To be simulatedby P. Detistov Surrey/Sofia