Comment on: Δ-excitation in nuclei

499c

Nuclear Physics A446 (1985) 499c-5OOc North-Holhd, Amsterdam

Connnent on

:

A-EXCITATIONIN NUCLEI

Michele ROY-STEPHAN IPN-Orsay,

BPl,

and Laboratoire

F-91406 Orsay National Saturne,

Going

A physics,

on

with

developments

I

CEN Saclay,

would like to say a few words

of a program concerning

at Saturne.

This program

has started

by an experiment

LNS collaboration. to spin-isospin

F-91191 Gif-sur-Yvette

Cedex on

further

A in nuclei via charge exchange reactions

is devoted to spin isospin excitation on (3He,t)

in a

Copenhagen,

in general, and

Lund, Lyon, Orsay,

In (3He,t) spectra, the complete response of the nucleus

probe

has shown

up

: nuclear particle-holes

time. Moreover

excited

at the same

13He,t)

: the A peak in nuclei is shifted 70 MeV down in energy with respect

to the free A excitation, collective

cancellation charge

between

exchange

is

The

(u,q)

various unique

region

the maximum

would

still

separated.

be The

measurements. deuteron

and

effects

by the virtual

if

step

response

Saturne.

our

The

It will

experimental

it

(AS = 1

1).

AL =

Another

be

will

A excitation

provide

ion physics. in an heavy

assume that A excitation

037%9474/85/$03.30

high

- and

where energy

precisely,

using

Very

2He)

sensitivity

thus

the

which

ion reaction

could

involve

tensor state

be

spin

polarized

interaction

at 0" or at small angle.

is

assignment

much

as an (z, c)

more

advantageous

n and p contributions. should

for

give

a

of Gamov-Teller spin

dipole

(n,p)

definitive strength.

transitions

of freedom has long remained unexplored,

recently,

dominate

is very close

The

responses

will

in S = 0 final

to separate

measured,

spin

process

matter.

nearly as much information (2,

domain opened to A degrees

heavy

reaction

answer to the question of the quenching

Furthermore,

one,

respect,

transverse

program

protons

will bring

will

and

in a spectrometer

be possible

strength

transverse

this

II:exchange

research

two

together

T22 measurements

Gamow-Teller

In

in nuclear

longitudinal

of

reaction and in the present situation

i.e.

occurs.

: n and p can both contribute

spanned

be detected

experimentally.

of the

sensitive to medium effects.

improved

of

in

in nuclei. Strong medium effects are expected

spin-isospin

next

has appeared

(fig. 1). It raises the question

We will study the (a, 2He)

beam

(2He), will T20

of

feature

response, but not in the z x G

virtual n are especially

to

pt3He,t)A++

nature of A excitation

in the a.{ longitudinal

a very intriguing

and A have been

we have observed, (fig. 2).

n production

QEkvie.r Science Publishen B.V. (North-Holland Physics Publishing Division)

It seems

for the first

time,

very reasonable

to

in heavy ion. It is also a very

M. Roy-Stephan / A-Excitation in nuclei

E=950

MeV/A

27AL(20Ne,

E=950

b)

0'

20Na)

MeV/A

0)

0”

T+,i,o,(GeV) FIGURE 1

FIGURE 2

important energy. the

mechanism

for thermal

We will thus undertake

very

peripheral

nature

equilibration a detailed

of this

in heavy

ion reactions

investigation

reaction,

we will

at high

of this process. Using have access

to density

effects. Another

problem

direct TI emission, would

deserves

give an answer.

intensities. injector,

This

: how does a A deexcite in a nucleus,

It would

further

holes ? Coincidence

need big solid angle detectors

direction

implies

operation

Mimas, which will also offer the possibility

reactions,

as

Relying

the

exchange

attention

coupling with 2 particle-2

on

for

we think

correlations.

example

very direct that

heavy and

ion

simple

H.I.D.C.I.

double

charge

character

should

of

measurements

and higher beam the

new

Saturne

of studying more exotic exchange

of heavy

be a sensitive

(H.I.D.C.I.).

ion single

charge

probe of short range