Angular momentum population in fragmentation reactions Zsolt Podolyák University of Surrey

Isomers observed following fragmentation of 208 Pb and 238 U (Z>60) 7 ~15(+3) 5(+5) 2 >20(+7) No. of isomers known(+new) New isomers => nuclear-structure Known isomers => reaction mechanism (angular momentum population What is the production cross section for individual states?

Low spin PROTON RICH ~1 ms I=43/2

R

isomeric ratio: exp 

N iso mer N to ta l

● ■ ▲ 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.

Abrasion-ablation model

(1-2  /3) k = 2  A>10 “sharp cut-off” approximation:

R th

  

J m P

(

J

)

dJ

 exp[

J m

(

J

2 

m

2

f

 1 ) ]

Analytical formulae ABRABLA

ρ th -all states with spin higher than the isomer decay into the isomer

M. Pfützner

et al

., Phys. Rev. C 65 (2002) 054604.

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

Nuclear structure has to be considered 196 Pb 270 ns 2.7 MeV 12+ 196 Pb: A.K.Singh

et al.

, Nucl. Phys. A707 (2002) 3 186 W( 16 O,6n) at 110 MeV; 170 Er( 30 Si,4n) at 144 MeV fusion-evaporation reaction!

φ

= I

isomer

/(I

parallel

+I

isomer

) = I

isomer

/ I

total

ρ

exp

=R

exp

/φ

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

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

The highlighted points: Higher lying isomers decay into our isomer

177Ta 179Ta 176Ta 175Hf 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 Future: There are new data on: 212 Fr 15 – 213 Fr 29/2 + 212 Ra 8 + 214 Ra 17 – 215 Ra 43/2 – 215 Ac 29/2+ 217 Ac 29/2 + <= HIGHEST SPIN from fragmentation

Background from the stopping down of the fast ions: To be simulated by P. Detistov Surrey/Sofia