Proton-Rich and Neutron-Rich Nuclei Produced by Heavy Ions

66 Proton-Rich and Neutron-Rich Nuclei Produced by Heavy Ions Ernst Roeckl

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Gesellschast für Schwerionenforschung Darmstadt, Postfach 110541, D-6100 Darmstadt, Federal Republic of Germany Recent nuclear-structure studies of proton-rich and neutron-rich nuclei, performed at the GSI on-line mass separator, are surveyed and an outlook is given towards a continuation of such investigations with heavy-ion beams of higher energies. In this report, recent nuclear-structure studies will be described as performed at the GSI mass-separator on-line to the heavy-ion accelerator UNILAC. We shall first discuss properties, such as masses, moments, charge radii and Gamow-Teller beta transitions, of very proton-rich nuclei obtained in fusion-evaporation reactions with O, Ca and Ni beams. Secondly, measured beta decay half-lives of neutron-rich isotopes, produced in multinucleon transfer reactions with (9-15) MeV/u beams of Ge, Se, Xe, W and U, will be presented in comparison with theoretical predictions. Finally, an outlook will be given to the extension of such experiments at the heavy-ion synchrocyclotron SIS and the experimental storage ring ESR being under construction at GSI. In order to be brief, details on the various topics are not given here, but should rather be taken from the references given at the end of this paper. 16

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PROTON-RICH NUCLEI The f ^-Shell Region Very recent experiments attempted to produce and investigate protonrich nuclei in the f^ region using Ca + C and S + Si fusion-evaporation reactions. The new T=-1 nucleus Mn was identified, using the p3n channel, with a half-life of 150110 ms and strong gamma-lines at 752.1 keV (2 -K) ) and 1106.1 keV (4 -2 ) [K0S85]. From gamma-gamma coincidence data, measured in particular for higher transition energies, higher-lying levels were identified including the 4 , T=l isobaric analogue state at 5792.4 keV in Cr. Preliminarily, beta-delayed proton emission was 7

40

12

32

2

48

z

+

+

+

+

+

48

0097-6156/ 86/ 0324-0439$06.00/ 0 © 1986 American Chemical Society

Meyer and Brenner; Nuclei Off the Line of Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

440

NUCLEI OFF THE LINE OF STABILITY 48

observed f o r Mn, which would extend the A=4n, Τ =-1 family of precursors 44 beyond the so f a r heaviest member

V [CER71]. The known Τ =-3/2

nucleus

45 C r

T

^ l/2

= 4

°

m s

^

w

a

s

P

r o d u c e d

through the 2p5n channel with an i n t e n s i t y of

approximately 1 atom/s, and there i s p r e l i m i n a r y evidence f o r beta-delayed 47 47 proton decay of T =-3/2 Mn, produced through the p4n channel. ( Mn would z

represent the heaviest T =-3/2, A=4n+3 nucleus observed experimentally.) z

Our

conclusions from

such as nuclei,

4 0

1 2

Ca + and

C

these p i l o t

experiments

are, that inverse reactions

are indeed s u i t a b l e f o r producing new p r o t o n - r i c h f . ^

that

sufficient

source

strength

separated samples can be reached even f o r h a l f - l i v e s as short as 40 "Southeast" of

1 Q 0

2

f o r spectroscopy of massms.

Sn

Nuclear-structure studies around the expected double s h e l l - c l o s u r e at 1 0 0

S n have concentrated recently to study "quenching" of Gamow-Teller (GT)

beta t r a n s i t i o n s , and to investigate moments and charge r a d i i by means of c o l l i n e a r l a s e r spectroscopy. A f t e r g i v i n g some recent examples from these investigations,

a novel ion source with bunched beam-release i s b r i e f l y

mentioned at the end of t h i s s e c t i o n . +

Within the s e r i e s of p r o t o n - r i c h N=50 and Z=50 n u c l e i , fJ /EC delayed y-rays

were

s t u d i e d recently

for

[RAT85] ; from measured 3 /(fJ +EC) +

+

the

decay

r a t i o s , Q__

of

9 6

Pd

[RYK85] and

1 0 4

Sn

values were deduced to be

EC

3450(150) keV

and 4 0 0 0 ± ^

keV,

r e s p e c t i v e l y . These Q values together

with the ones of neighbouring decays can be used to determine masses of very p r o t o n - r i c h isotopes, i n c l u d i n g the n u c l e i beyond the proton d r i p l i n e Z=50

show

that

this

[RAT85].

measure

of

the

Alpha

1

0

ground-state 9

I and

1 1 3

Cs

decay-energy d i f f e r e n c e s f o r

proton s h e l l strength tends

to be

enforced by neutron s h e l l c l o s u r e s , with a d i s t i n c t e f f e c t o c c u r r i n g also at N=64 and N=66 due to d ^

2

and s ^

2

neutron subshell c l o s u r e s . We

shall

return to t h i s p o i n t when d i s c u s s i n g r e s u l t s from c o l l i n e a r l a s e r spectros copy.

The measured GT t r a n s i t i o n strengths of even N=50 isotones and t i n

(Z=50) isotopes are shown i n F i g . 1 i n comparison with p r e d i c t i o n s from shell-model c a l c u l a t i o n s [TOW85]: The experimental r e s u l t s f o r the N=50 94 96 nuclei the

Ru

and

measurements

Pd agree w e l l with the c a l c u l a t i o n s of Towner, whereas f o r even

t i n isotopes appear to c o n t r a d i c t the slope

expected from a standard p a i r i n g

approach.


66.

441

Proton-Rich and Neutron-Rich Nuclei

ROECKL

4

30

6

n=Z-40

10

8

2.3

h s i n g l e - p a r t i c l e shell model

i f "

20

10

-Ι2Λ

| 0 j = 1263

h

2.5

CD

2.6 i : en 2.7 ο

CQ

10 3.0

94

Ru

96

Pd

98

^100

Cd

Sn

ÏÔ2

Sn

ÏÔ4

Sn

ÎÔ6

Sn

ÏÔB

Sn

3.5 4.0

110

Sn

Fig. 1. C o m p a r i s o n o f t h e e x p e r i m e n t a l l y o b s e r v e d GT t r a n s i t i o n s t r e n g t h B(GT) o f even N=50 i s o t o n e s and t i n i s o t o p e s w i t h p r e d i c t i o n s . The c o r r e s p o n d i n g l o g f t v a l u e a r e g i v e n a t t h e r i g h t hand s c a l e . The f u l l l i n e r e p r e s e n t s p r e d i c t i o n s from t h e extreme s i n g l e - p a r t i c l e s h e l l model a s f u n c t i o n o f t h e number η o f p r o t o n s i n the qQf s h e l l . Lower t r a n s i t i o n p r o b a b i l i t i e s a r e o b t a i n e d b y t a k ing i n t o account ( a p p l y i n g i n s u c c e s s i v e o r d e r ) : r e n o r m a l i z a t i o n o f the f r e e n e u t r o n v a l u e o f t h e c o u p l i n g c o n s t a n t g ^ - t o a c c o u n t f o r "higher order e f f e c t s " (dashed l i n e ) , p a i r i n g c o r r e l a t i o n s o f p r o tons (dotted l i n e ) , p a i r i n g c o r r e l a t i o n s o f neutrons (dot-dash l i n e ) and c o r e p o l a r i z a t i o n f r o m p a r t i c l e - h o l e i n t e r a c t i o n s w i t h a f i n i t e and a z e r o range f o r c e ( t o p a n d b o t t o m d o u b l e - d o t d a s h l i n e , r e s p e c t i v e l y ) [6,7] See r e f s . [RYK85] a n d [KLE85] f o r d e t a i l s . X

In

c o l l a b o r a t i o n w i t h G. Huber e t a l . ( U n i v e r s i t y o f M a i n z ) , c o l l i

near l a s e r s p e c t r o s c o p y o f s h o r t - l i v e d indium and t i n i s o t o p e s

[KIR85,

ULM85, L0C85] was e x t e n d e d i n r e c e n t e x p e r i m e n t s , b o t h a t GSI and a t t h e ISOLDE f a c i l i t y a t CERN [ E B E 8 5 a ] . moments, e l e c t r i c the

Systematical data

on

magnetic

dipole

q u a d r u p o l e moments and i s o t o p e s h i f t s were o b t a i n e d i n

mass range A=105 t o A=127.

The mean s q u a r e c h a r g e - r a d i i , deduced

from

m e a s u r e d i s o t o p e s h i f t s , show c l e a r l y o n s e t and d i s a p p e a r a n c e o f d e f o r m a t i o n , i f compared t o a s i m p l e t w o - p a r a m e t e r ter

ansatz

approximates

6

as

formula (see F i g . 2 ) .

the a d d i t i o n

of a f i r s t

The

term,

lat-

which

d e s c r i b e s t h e s m o o t h l y v a r y i n g change o f n u c l e a r c h a r g e r a d i i f o r s p h e r i c a l shape as g i v e n b y t h e d r o p l e t model [MYE83] , and a s e c o n d t e r m r e p r e s e n t i n g the

e f f e c t o f change i n q u a d r u p o l e d e f o r m a t i o n . A d i f f e r e n t i a l p l o t o f mean


442

NUCLEI OFF THE LINE OF STABILITY 54

56

58

60

62

64

68

70

72

74

'

76

1*1*1

0.6 0.4 0.2

-

0

y ^ " ^

0.0

k i l l * y' /

-0.2

Sn

-0.4

-0.4 -0.6

-0.6 -0.8 54

56

58

60

62

64

1.

66

68

70

72

74

76

» *

78

Neutron Number Ν 2 F i g . 2. Change of the nuclear mean square charge r a d i i 6 f o r indium and t i n isotopes r e l a t i v e to N=66. The s o l i d l i n e s correspond to the pure v o l ume e f f e c t at constant shape according to the droplet model [MYE83]. square c h a r g e - r a d i i of indium and

t i n isotopes (Brix-Kopfermann

diagram)

reveals a s u b s h e l l s t r u c t u r e around N=64 [L0C85], which r e l a t e s to s i m i l a r observations made on the b a s i s of mass d i f f e r e n c e s as mentioned above.

The

disappearance of quadrupole deformation f o r l i g h t indium isotopes, howev er, i s i n disagreement with the r e s u l t of constant deformation as deduced from experimental quadrupole moments, and the

r e l a t i o n to measured

B(E2)

values of l i g h t cadmium isotopes i s a l s o not understood at present. In order to improve the s i g n a l - t o - n o i s e r a t i o i n c o l l i n e a r l a s e r spec troscopy, an ion source with bunched beam release was t e s t e d s u c c e s s f u l l y . For t h i s purpose, the temperature of a " c o l d trap" i n s i d e the i o n source i s reduced f o r storage

of r e a c t i o n products, which are released from the trap

during a subsequent p e r i o d of i n c r e a s e d temperature. The release of indium was

found to occur with a FWHM of approximately 0.5s,

substantial spectrum of

improvement 108

i n signal-to-noise

ratio

corresponding to a

f o r the fluorescence

In [EBE85b] obtained during t h i s release p e r i o d .

Moreover,

such a storage-release o f f e r s the p o s s i b i l i t y of doing "ion-source chemis t r y " : S e t t i n g time windows due to the e l e m e n t - s p e c i f i c release p r o f i l e s , i t 104 was p o s s i b l e to e n r i c h secondary beams of e.g. 21-s Sn with respect to 104 104 the i s o b a r i c contaminants 1.5-min In and 58-min Cd.


66.


ROECKL

"Northwest" o f A

443

Gd

programme

region "northwest

of d e t a i l e d 1 4 6

of

decay-spectroscopic i n v e s t i g a t i o n s i n the

G d " i s pursued i n c o l l a b o r a t i o n with P. K l e i n h e i n z

et a l . (KFA J i i l i c h ) . These experiments,

which a l s o use the o n - l i n e separa-

tor ISOCELE at Orsay and ISOLDE at CERN, cannot be covered i n t h i s b r i e f report. I t may s u f f i c e

to mention here

the studies of protons

and gamma

rays emitted a f t e r beta decay o f N=81,82 n u c l e i , these decays being domi147 nated by ^ 1 1 / 2 ^ ^ 9 / 2 ^ i° ' decay o f Dy, d e e x c i t a t i o n 147 of h i g h - l y i n g l e v e l s i n the daughter nucleus Tb _ was i n v e s t i g a t e d by observing beta-delayed protons and gamma-rays. In a p r e l i m i n a r y e v a l u a t i o n G

T

t r a n s

t

n s

F

o

r

0

of corresponding proton and gamma energies, the proton separation energy o f + 147 1/2

Tb was determined

to be 1975 keV [SCH85] . This i s o f i n t e r e s t i n

view o f the d i s c r e p a n c i e s between recent mass measurements o f t h i s nucleus. NEUTRON-RICH NUCLEI In

collaboration

with

W.-D.

Schmidt-Ott

et a l .

(University of

Gottingen), decay p r o p e r t i e s of n e u t r o n - r i c h isotopes were i n v e s t i g a t e d i n the

manganese-to-zinc

region

[RUN83,RUN85],

[KIR82,RYK83,ESC84], and f o r radium

f o r rare-earth

and actinium

elements

[GIP85]. The beta decay

h a l f - l i v e s , measured i n these experiments and i n p a r t i c u l a r i n a recent one [B0S85],

are compared

chromium-to-nickel

to t h e o r e t i c a l

region,

the measured

predictions half-lives

i n F i g . 3. In the are s y s t e m a t i c a l l y

shorter than the p r e d i c t e d ones. This observation i s c a l l i n g f o r improved half-life

c a l c u l a t i o n s , and i t i s also of i n t e r e s t to study the i n f l u e n c e

of t h i s e f f e c t on the a s t r o p h y s i c a l r a p i d neutron-capture

(r) process. Pre-

l i m i n a r y conclusions from such c o n s i d e r a t i o n s [B0S85] are, that even with shorter from

half-lives

iron-group

the A~80 r-process abundance peak cannot nuclei

during

explosive helium burning cannot

explosive

helium

burning,-

be b u i l t - u p therefore

be the only s i t e o f the r-process, and a

s i g n i f i c a n t l y higher neutron density i s r e q u i r e d i n order to reproduce the observed A~80

r-process abundance peak.

STUDIES OF FAR-UNSTABLE NUCLEI AT SIS-ESR In May 1985,

the GSI proposal [KIE85] of b u i l d i n g an 18 Tm synchrotron

(SIS) and a 10 Tm experimental The

storage r i n g (ESR) was f o r m a l l y accepted.

plans o f u s i n g t h i s a c c e l e r a t o r complex f o r studying n u c l e i f a r from

stability

[R0E84] are thus becoming more r e a l i s t i c .

Heavy i o n beams from


444

NUCLEI OFF THE LINE OF STABILITY

59

63

64

67

69

73

177 180

183

232

234

MASS NUMBER OF HEAVIEST MEASURED ISOTOPE Fig.

3.

Ratio between measured beta

decay h a l f - l i v e s

(T^

e X p

) and

pred-

t h

i c t i o n s ( T ^ ) from a microscopic model [KLA84] (open c i r c l e s ) and from the gross theory of beta decay [TAK73] ( f u l l c i r c l e s ) . For the l a t t e r c a l c u l a t i o n s , beta decay energies were used from the mass formula of [MÔL81]. SIS and i n ESR between neon and uranium with energies up to 2 GeV/u, 2 ' l u s

1

and 1 GeV/u, 4 · 1 0

ties

at

lower

the

beta

offer

stability

in

a

studies

possibilities to

to extend

the

regions even f u r t h e r away

l i n e . This statement i s made on

somewhat shaky

( t a i l s of the) production cross s e c t i o n d i s t r i b u t i o n s ,

t h e i r dependence on the N/Z

measured

interesting

nuclear-structure

ground, since the and

s *, r e s p e c t i v e l y , and considerably higher i n t e n s i -

energies,

above-mentioned from

1 0

1 1

quite

r a t i o of p r o j e c t i l e and target, have been

incomplete

way

so

f a r . On

the other hand, recent

r e s u l t s obtained with 30 to 200 MeV/u beams at GANIL, LBL and MSU

show great

promise i n t h i s respect. In p a r t i c u l a r the most recent experiments at GANIL have

proven

s u c c e s s f u l l y that heavy-ion induced

fragmentation

combined with r e c o i l separation can be used f o r producing new impressive of with

numbers and y i e l d s , both of neutron-rich (carbon-to-cobalt)

proton-rich secondary

recoil

reactions

isotopes, i n

(T =-5/2)

species

[LAN85, GUI85, BER85]. I n v e s t i g a t i o n s

of unstable

n u c l e i are being planned downstream a

z

beams

separator

and

[GEI85],

using

this

fascinating possibilities

with

stored, cooled and slowed-down beams [KIE85] , but a l s o applying f i x e d ( s i n gle-turn)

target-detector

arrays.

This

may

lead

to

novel

expeditions

towards and beyond the nucléon d r i p l i n e s , which allow r e f i n e d studies of i n t e r e s t i n g phenomena i n known decay modes (e.g. GT quenching, studied then f o r l a r g e r beta-decay windows) as w e l l as search f o r new

modes of r a d i o -

activity.


66.

445


ROECKL

REFERENCES [BER85] M. Bernas, private communication (1985). [BOS85] U. Bosch et al., "Beta Half-Lives of Neutron-Rich Chromium-to-Nickel Isotopes Used for New Calculation of the Astrophysical r-Process", to be published. [CER71] J. Cerny et al., Phys. Lett. 37B 380 (1971). [EBE85a] J. Eberz, private communication (1985). [EBE85b] J. Eberz et al., "Collinear Laser Spectroscopy on g, Ιn using an Ion Source with Bunched Beam Release", to be published. [ESC84] W. Eschner et al., Ζ. Phys. A317 281 (1984) [GEI85] H. Geiβel, "Fragment Separation at SIS", contribution to the Accelerated Radioactive Beam Workshop, Parksville, September 5-7, 1985. [GIP85] K.-L. Gippert, "Kernspektroskopie projektilähnlicher Produkte aus U-induzierten Kernreaktionen", Ph. D. Thesis, University of Göttingen, GSI-85-20 (1985). [GRA84] I. S. Grant et al., in Proc. 7th Intern. Conf. on At. Masses and Fundamental Constants (AMCO-7), Darmstadt-Seeheim (1984), ed. O.Klepper, p. 170. [GUI85] D. Guillemaud-Mueller et al., "Production and Identification of New Neutron-Rich Fragments from 33MeV/u Kr Beam in the 18≤Z≤27 Region", GANIL P.85.08 (1985). [KIE85] P. Kienle,"The SIS-ESR Project of GSI", GSI-85-16 (1985). [KIR82] R. Kirchner et al., Nucl. Phys. A378 549 (1982). [KIR85] R. Kirchner et al., Nucl. Instr. and Meth. A234 224 (1985). [KLA84] H. V. Klapdor et al., At. Nucl. Data Tables 31 81 (1984). [KLE85] O. Klepper, in Proc. XXIII Intern. Winter Meeting on Nucl. Phys., Bormio (1985), p. 747. [KOS85] V. T. Koslowsky et al., in GSI Scientific Rep. 1984, GSI 1-85 (1985),p. 90. [LAN85] M. Langevin et al., Phys. Lett. 150B 71 (1985). [LOC85] H. Lochmann, "Kernmomente undÄnderungender mittleren quadratischen Kernladungsradien bei Zinn und Indium", Ph. D. Thesis, University of Mainz, GSI-85-8 (1985). [MÖL81] P. Möller and J. R. Nix, Nucl. Phys. A361 117 (1981). [MYE83] W. D. Myers and K.-H. Schmidt, Nucl. Phys. A410 61 (1983). [RAT85] G.-E. Rathke et al., Ζ. Phys. A321 599 (1985). [ROE84] Ε. Roeckl, in Proc. of the TRIUMF-ISOL Workshop, Mont Gabriel, TRI-84-1 (1985), p. 6. [RUN83] E. Runte et al., Nucl. Phys. A399 163 (1983). [RUN85] Ε. Runte et al., Nucl. Phys. A441 237 (1985). [RYK83] K. Rykaczewski et al., Ζ. Phys. A309 273 (1983). [RYK85] Κ. Rykaczewski et al., Z. Phys. A321 (1985),in print. [SCH85] D. Schardt et al., in Proc. XX Winter School on Physics, Zakopane (1985). [TAK73] K. Takahashi et al., At. Nucl. Data Tables 12 101 (1973). [TOW85] I. S. Towner, "A Mass Dependence in Hindrance Factors for Favoured Gamow-Teller Transitions", to be published. [ULM85] G. Ulm et al., Ζ. Phys. A321 395 (1985). 108

108m

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July 29, 1986


Proton-Rich and Neutron-Rich Nuclei Produced by Heavy Ions

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