ISOMERIC BEAMS

• Shell-model isomers in the 208Pb region

• Stopped isomeric beams: τ < 1 ms

• Stopped isomeric beams: τ > 1 ms

• Fast isomeric beams: purification

• Fast isomeric beams: reactions

Phil Walker – University of Surrey

212Po = 208Pb + α

2911 keV, (18+) τ = 65 s, α decay

ground state, 0+, 430 ns, α decay

wait for one second: isomer purity = 100 %

E > 1MeV, τ > 1 ms isomers

Walker and Dracoulis, Nature 399 (1999) 35

high-spin isomer chart

a Phil Walker special

long-lived, high-spin isomers

Walker and Dracoulis, Hyp. Int. 135 (2001) 83

hafnium (Z=72) isomers

Walker and Dracoulis, Hyp. Int. 135 (2001) 83

178Hf 188Hfexpt.

calc.

Super-FRS yields215Ra

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

217Ac level scheme

from (HI,xn) reactionsDecman et al., Nucl Phys. A436 (1985) 311

29/2+, T1/2 = 740ns217Ac

217Ac γ-ray spectrumZ. Podolyak, private communication

from 238U fragmentation

208Pb region

many μs isomersexpected

212Po, 18+, 65s

215Ra, 43/2-, 800ns

217Ac, 29/2+, 1μs

Summary217Ac: 1μs isomer purified by flight time through FRS (factor of 15 in 300 ns) good for RISING fast beam opportunity for (i) γ-gated Coulex (ii) knockout reactions …… and knockout to other isomers: RISING stopped beam

212Po: 65s isomer 100 % purified by flight time in ESR

N~126, Z<82: many new μs isomers expected good for RISING stopped beam test N=126 shell-gap stability approach r-process path ….