High-precision mass measurements below 48Ca and

in the rare-earth region to investigate

the proton-neutron interaction

Proposal to the ISOLDE and NToF Committee P267

Masses and nuclear structure

One- or two- neutron and proton separation energies

Shell closures

Deformation

Double differences (Vpn values)

Collectivity/deformation

Shell effect

=average interaction of the last proton and neutron J.-Y. Zhang et al, PLB89Cakirli et al., PRL05

Small p-noverlap

large p-noverlap

Unlike p-n orbits

Similarp-n orbits

Collectivity grows slower where proton-neutron interaction is small (=Vpn is small)

Single-particlestructure

Cakirli, Casten, PRL06

Masses and (collective) excited levels

Structure:deformation/collectivity

168Er

0+ 1217 keV

0+ 1422 keV

Which one is the lowest collective

excitation?

168Er

0+ 1217 keV

0+ 1422 keV collective

Cakirli et al,PRL09 in print N

IBA calculations for structure and

binding energies

Masses and nuclear structure:recent results from ISOLTRAP

Separation energies

mass of 82Zn: derived from systematic trends

FRDM: no shell quenching

ETFSI-Q: shell quenching

Neutron separation energy

No evidence for shell quenching: N=50 is a good magic number

80,81Zn

S. Baruah et al., PRL08

neutron shell gap

132Sn

Restoration of N=82 gap

M. Dworschak et al,PRL08

132,134Sn

Vpn

122 124 126 128 130 132

380

400

420

440

460

480

500

520

540

V

pn /

keV

Sn nuclides

ISOLTRAP AME 2003

n-rich Cd

Vpn trend smoothens

N

Z

11 new masses4 studied 1st time directly

n-rich Xe

n-rich RnNew nuclide identified: 229Rn

Unique Vpn behaviour around N=135:Connection to octupole deformation?

Neidherr et al,PRL09, accepted

Physics interest and the proposed mass measurements

Flattening of S2n values around Z=70 and N=108

Deformations: known shape-

transition region

subshell closure or other structural changes?

Vpn values in the 48Ca region

unique feature of shell structure: no sudden change from low-j to high-j orbits when crossing magic N=28 => no sudden dVpn drop expected

Possible sub-shell effect Nature of Vpn in light nuclei

Even-even Even-odd

South-east of 28Ca: Peak inVpn followed by a sudden drop

22 24 26 28 30 32 34Z/N

26

24

22

20

18 7 5 5 7

5 5 5 6

6 3 1 3 4

4 2 5 2

3 4 5 5

3

4

5

7

6

400-500500-600600-700700-800800-900900-1000>1000

Vpn (keV)f7/2 p3/2, f5/2f7

/2d

3/2

1

2

Vpn in neutron-rich rare-earth nuclides

N N

Even-even Even-odd

N

Z

Exceptionally high values away from the diagonal

Required mass uncertainty <10keV

158Sm: surprisingly low value at the diagonal

A systematic peak followed by a drop for N=Z+34

Much larger than for neighbours, also followed by a drop?

Even-even

Nuclides with unknown masses but known R4/2 or E(21+) values

Deformation region in neutron-deficient

rare earths

And n-rich 138Te and 160Sm

N80757065Z

62

64

66

68

shapes are expected to change rapidly

(MINIBALL proposal, P257)

Help determine the structure

Experimental setup

ISOLTRAP

B = 4.7 T

B = 5.9 T

2 m

determination of cyclotron frequency

(R = 107)

removal of contaminant ions

(R = 105)

Bunching of thecontinuous beam

Bm

qc

2

1

10 cm

1071195 1071200 1071205 1071210 1071215 1071220 1071225

200

220

240

260

280

300

320

340

Measurement Theoretical Fit

85Rb

Tim

e-o

f-fli

ght

[s]

Excitation frequency [Hz]

c = Bqm

Tim

e o

f fli

gh

t [

s]

Important setup features

Precision: routinely <5e-8 relative uncertainty (= 7 keV for A=150)Present residual systematic limit: 8e-9*m

Half-lives: time spent in the setup: 0.1 – several s;Shortest t1/2 at ISOLTRAP: 65 ms (74Rb)Shortest t1/2 at a Penning trap mass spectrometer: 11Li (9ms)

Yields: single-ion resonanceswith 1-10% efficiency: measurements with 100 particles/s

Discovery potential: The case of 229Rn

Contamination: Resolving power 105-106

up to 100-1000 times more of the contaminant than the beam

ISOLDE yields

39-44S: requested in another LOI (t1/2 of 30S)- Molecular beam (SCO+) with a FEBIAD plasma ion source or negative ions- 2003: 8e3 ions/C of 38S (ZrO2 target + plasma ionization)

46-48Ar: new efficient arc-discharge ion source (VADIS), used by ISOLTRAP in Aug08 for Xe and Rn isotopes- Expected yields >1e4 ions/C

138Te: official Te yields only from SC ISOLDE -COMPLIS (UCx+ hot plasma): 131-134Te: >1e9 ions/C; 135,136Te also studied; isobars: Cs, I, Sb with yields lower than Te- A=138 – expected isobar 138Cs (t1/2=33 min), required resolving power 7500

Rare earths: Ce, Nd, Sm, Gd, Dy, Er, Yb-Available at ISOLDE: surface ionization, a lot of contaminants-Improvement in efficiency and purity: laser ionization and low work-function cavities- 150Ce, 154,156Nd, and 158,160Sm requested by us in 2007: development list-RILIS schemes known for Nd, Sm, Gd, Dy, and Yb-Nd: the ionization scheme tested in 2008, Sm: to be tested in spring 2009-Cavity test planned for 2009

186Hf: SC yield for 180Hf (Ta target) 3e6 ions/CPSB, NICOLE: 177,179-184Hf (hot plasma Ta/W/Ir target + CF4), 185Hf observed

Beam-time request

Studies to be performed over 2-3 years

dVpn values

.

.

.

Vpn in neutron-rich rare-earth nuclides

N N

Even-even Even-odd

Microscopic interpretation of the peaks:n in the specific Nilsson orbits have increasingly higher overlaps with mid-shell p orbits as N grows from 92 to mid shell

Oktem et al, PRC06

Reasonable agreement

Nuclides with unknown masses but known R4/2 or E(21+) values

Nuclides with unknown masses but known R4/2 or E(21+) values

Masses and (collective) excited levels

Structure:deformation/collectivity

168Er

0+ 1217 keV

0+ 1422 keV

Which one is the lowest collective

excitation?

168Er

0+ 1217 keV

0+ 1422 keV collective

Cakirli et al,PRL09 in print N

IBA calculations for structure and

binding energies

Yields

223-229Rn

-600-500-400-300-200-100

0100200300400

222 224 226 228 230A

mas

s diff

eren

ce to

AM

E (k

eV)

AME03

ISOLTRAP

A new isotope of radon discovered: 229Rn7 new masses with <20keV,All never measured directly before

Neidherr et al., submitted to PRL

Nuclear structure: • residual proton-neutron interaction (dVpn values)• possible octupole deformation