Recent progress in applications of high energy ion beams to nuclear structure and atomic physics

Nuclear Physics A447 (1985) 1570162~ North-Holland, Amsterdam

157c

RECENT PROGRESS IN APPLICATIONS STRUCTURE AND ATOMIC PHYSICS

OF HIGH ENERGY HEAVY ION BEAMS TO NUCLEAR

T.J.M. SYMONS Nuclear Science Division, Lawrence Berkeley California, Berkeley, California 94720*

Laboratory,

University

of

We discuss some recent experiments at the Bevalac which demonstrate the usefulness of relativistic heavy ion beams for study of the nuclear structure of radioactive isotopes.

In the three years that have passed since the first conference series, the study of relativistic

heavy ion collisions

in this

has come of age.

The

most striking manifestation

of this has been the steady stream of new data

obtained

such as the GSI-LBL Plastic Ball, the streamer

using 4n detectors

chambers at Berkeley and Dubna. and the new spectrometer The consequence experimental

DIOGENE at Saclay.

of this effort is that we are at last beginning

to see

results that can be related directly to parameters

equation of state. this conference

These results are discussed

and are summarized

with these developments, of relativistic

of the nuclear

in several contributions

in the talk by H. Stocker.'

another trend can be found.

to

In parallel

This is the application

heavy ion beams to other fields of physics that only a short

time ago would have been unexpected.

In this contribution,

we shall briefly

review the progress that has been made during the last year in the study of nuclear structure relativistic Projectile

and atomic physics using the unique properties

fragmentation

is a process that was studied in some detail in

the first years of Bevalac operation.* relatively

small momentum

separation

of different

consequences.

Firstly,

isotopes by magnetic

on the chemical

isotopes were discovered

produced,

and the ease of

rigidity has two important

isotopes far from stability can be produced with with low energy isotope separators properties

because of the very high detection extended

It was realized early on that the

spread of the fragments

yields that are competitive dependance

of

heavy ion beams.

of the isotope.

efficiency

and without

This comes about

that is possible.

Several new

at the Bevalac3 and these studies have been

using the intense beams that are now available

at GANIL.4

The

*This work was supported in part by the Director, Office of Energy Research, Division of Nuclear Physics of the Office of High Energy and Nuclear Physics of the U.S. Department of Energy under Contract DE-AC03-76SF0009B.

037.5-9474/86/$03.50 OEIsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

T.J.M. Symons /Applications

158~

of high energy heavy ion beams

second important aspect of the fragmentation

process is the copious production

of isotopes that are unstable but not necessarily Because of their small momentum fragments

can be transported

secondary

beams.

spread (Ap/p

at the limits of stability.

1% at 1 GeV/nucleon)

-

through a conventional

these

beam line and used as

Experiments

along these lines have now begun at the Bevalac. In the past year Tanihata and co-workers, 5.6 have carried out a series of

elegant measurements and Li isotopes.

of the reaction cross sections of the particle-stable

In discussing

this experiment,

the final results than on the question

we shall concentrate

of whether these measurements

He

less on

can be

used to extract reliable nuclear structure information. The experiments were 11 using BOO MeV/nucleon B and " Ne beams incident on a Be target

performed

to produce secondary beams which were transported Interaction targets.

cross-sections

Further details of the experimental

references

technique

can be found in

5 and 6.

To relate the measured quantities

to the HISS spectrometer.

were found for each isotope using Be, K and Al

cross-sections

to theoretically

calculable

such as the nuclear radius, the authors developed

procedure.

They first defined an interaction

geometrical

relation dI (p,t) = * [RI (P) + RI

where RI(p) and RI(t) are the interaction and target respectively.

the following

nuclear radius (RI) using the

(t)l

2

(1)

nuclear radii of the projectile

Using this relation, the authors

have deduced RI

for all the particle stable isotopes of He and Li relative to 4He. results are illustrated are clearly visible.

in figure 1.

The

nuclear structure effects 11 For example, the interaction radius of Li is very

much larger than that of 12C .

Significant

It can also be seen that for two nuclei of

the same mass number, the more neutron rich isotope invariably interaction

cross-section.

diffuseness

of the neutron skin as neutrons are added.

has the larger

These effects may be related to the increased

T.J.M. Symons /Applications

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of high energy heavy ion beams

159c

2.5

E -aa!2.0

1.5 1u

3 A

XBL 856-2809

FIGURE 1 Interaction nuclear radii RT are plotted for all the He and Li isotopes as well as for gE3e and 12C. The dotted lines in the figure indicate an AlI3 dependence on radius. (Taken from reference 6.) When the results of this experiment was expressed compared

suggesting

were first presented,

that it was unclear whether

in a reliable way to a nuclear structure

collaborators

one.

First, they have demonstrated

and target RI values that is assumed

RI value is typically comparison

Tanihata and

that the separability

in equation

well except for the very lightest nuclei such as 4He. Secondly,

RI could in fact be

calculation.

have since gone a long way towards proving that the technique

indeed a powerful projectile

some criticism

1 holds very

The stability

of the

better than 0.1 fm when the target is varied.

they have made a detailed

study of the measured

RI values in

to the rms radii of the stable isotopes 4He, 5Li, 7Li. 'Be

and " C measured

by electron

scattering.

The results are shown in figure 2.

is of

160~

TJM.

Symons /Applications

of high energy heavy ion beams

I

6Li 7Li

1%

gBe

XBL

856-2808

FIGURE 2 The interaction radius, RI, and the rms radius, RF,, (measured bv electron scattering) are plotted for 4He, 6Li 7Li % and 12C. _ Triangles in the figure show the rms radii, RI,, oi Gaussian matter distributions which reproduce the present RT values as discussed in the (Taken from reference 6.) text.

e

The first point to note is that the absolute This is not particularly

not in agreement. disturbing

has now been explained

using a semi-classical this calculation

by the authors

they calculated

Using gaussian wave functions,

optical model.7

What is much more

the nucleon-nucleon

As can be seen. this calculation increases ones confidence

way.

cross-section

parameters

in

and the width parameter to R,,,.

Fixing

at the free nucleon value and adjusting

cross-section.

radius deduced from electron scattering!

nuclear structure.

cross-section

which can be related directly

cross-section

radius to fit the interaction

in a quantitative

the interaction

The only adjustable

are the nucleon-nucleon

of the gaussian distributions

greatly

surprising.

is that the variation with mass number is also quite different.

This difference

figure.

values of RT and RFms are

reproduces

nicely the variation

This is a striking

in the technique

in

result that

as a quantitative

probe of

The next step will be to perform similar calculations

using shell model wavefunctions.

the

they obtain the results in the

T.J.M. Symons /Applications

These pioneering secondary

experiments

are just the beginning

beams and many other possibilities

Minamisono,

These are discussed

Another quite different atomic physics. producing

of nuclei in

opportunities

for secondary

by Kienle in these proceedings.8

application

of relativistic

heavy ion beams is to

High energy heavy ion beams offer the unique possibility

few electron

systems of very high 2 atoms in the laboratory,

example, a beam of "+ U can be prepared Uranium atom in a foil.

However,

needed to do this efficiently. studied the stripping by the Bevalac.'

by stripping the electrons

energies

of

For

from the

in excess of 100 MeV/nucleon

are

As a first step in these studies, Gould et al.

and pick-up of electrons

With this knowledge

shift in He-like Uranium experiment

In particular,

Looking farther into the future, the

project at GSI will provide outstanding

beam studies.

161~

of studies using

are open.

et al. plan to measure ground state magnetic moments

the fp shell using NMR techniques. SIS18/ESR

of high energy heavy ion beams

from high Z atoms accelerated

in hand, a measurement

is now being attempted.

of the Lamb

The first test run for this

has recently taken place and results can be expected within the

next year.

The measurement

will allow high order QED effects to be tested

that are inaccessible

by studies of lighter atoms even

of these measurements

may be very much higher.

these measurements

are without

though the precision

As with the secondary

doubt the beginning

of a new generation

experimental

studies that will be made at our present accelerators 10 those that are just now being constructed.

beams, of

and at

REFERENCES 1) H. Stdcker, this volume. 2) D. E. Greiner et al. Phys. Rev. Lett. 35 (1975) 152. 3) G. D. Westfall

et al. Phys. Rev. Lett. 43 (1979) 1859.

4) M. Langevin et al. Phys. Lett. 1508 (1985) 71. D. Guillemaud-Mueller et al. GANIL Preprint, p.85.08 5) I. Tanihata et al. Phys. Lett. B., in print. I. Tanihata et al., Measurements of Interaction of He Isotopes LBL-18821 (1984). 6) I. Tanihata et al., Measurements of Interaction Radii of Li Isotopes LBL-19904 (1985).

(1985).

Cross Sections and Radii

Cross Sections

and Nuclear

7) P. J. Karol Phys. Rev. Cl1 (1975) 1203. 8) P. Kienle, this volume. 9) H. Gould et al. Phys. Rev. Lett. 52 (1984) 180. 10) H. Gould, New Experiments

on Few-Electron

Very Heavy Atoms LBL-19884

(1985).