The UNISOR nuclear orientation facility

Nuclear Instruments and Methods North-Holland, Amsterdam

in Physics

THE UNISOR NUCLEAR

ORIENTATION

I.C.

Research

B40/41

423

(1989) 423-428

FACILITY

GIRIT

Vanderbilt Uniuerslty, Department of Physics and Astronomy, Nashudle, Tennessee 37235, USA, UNISOR, Oak Ridge Associated Universities, Oak Ridge, Tennessee 37831, USA, and Joint Institute for Heauy Ion Research, HHIRF, Oak Ridge, Tennessee 37831, USA

The combination of an on-line isotope separator and a dilution refrigerator has increased the applicability of the nuclear orientation technique to a wide range of nuclei, especially those very far from stability. The UNISOR nuclear orientation facility (UNISOR/NOF) has recently become operational. The following is an overall view of the UNISOR system and recent results.

[6,7]

1. Introduction

and internal

systems The

major

developments

nuclear

orientation

decade

can be summarized

a dilution after

production

by this

relaxation

method

of

another

problems

associated of

eliminated.

There

type: at

NICOLE

been

second

in

FRG major

on oriented

tems.

are

of this

the DOLIS-

recent

[3]. The

development

only to long-lived

systems [l],

very

Switzerland

Up to this decade

applied

materials

addition,

FOLBIS

sys-

to an accelerator of the past decade

magnetic

resonance

spin

nuclear

field gradient

relaxation

hyperfine

the NMR/ON

technique

was

nance

was considered

(For

rightfully

tion of the nuclear with

nuclear

technique state

g-factor

of

in combination or isomeric

limitations

nuclei.

Furthermore, measurement The

of the ability

0 Elsevier Publishing

Science

this of the

last decade

has

to detect

(Y, p

Publishers

Division)

B.V.

correlations ments) spin ments

states)

and

for the first time and can in the rare-earth

stability.

of on-line

region.

in the solid-state

studies

is the nuclear This of

III. NUCLEAR

contri-

especially

spectroscopy

is due partly

to the

such

as angular

coincidence

measure-

(reduced

to extensive

isotope

the major

technique,

techniques,

intensity

and partly

field,

orientation

of traditional (low

the mea-

the double-reso-

[12] which was used to study

orientation,

or in-beam

Auo, of the

see ref. [13].)

nuclear

ground

the

field gradient,

that enables

g [ll];

spectroscopy

on-line

determining

include

on oriented

splitting,

technique

for studies

of the nuclear far from

spin

innova-

[lo] as a means of measur-

i6’TbTb,

bution

of nuclei

isotopes.

to 1985,

mag-

nuclear

passage

of the NO applications

In the nuclear

a powerful

also seen the development

Physics

applica-

field prior

provides

of the implanted

(North-Holland

method

a very accurate

0168-583X/89/$03.50

of

B and

dilute

recent

due to an electric

method

system,

field interac-

field

of NMR/ON,

quadrupole

spin echo

as a model

resonance

short-lived

provides

The success

that the on-line

orientation

magnetic

for directly

spins

technique

proved

systems.

the from

solid-state

hyperfine

The

adiabatic

of the sign of

NMR/ON

the

orientation,

developed

electric

a review

of

changes

of the low-temperature in

damage.

area

interaction

a rare-earth

times

[6] on some of the In and

in the

V_,; a novel

in on-line

the hyperfine

nuclear

of modulated

has

nuclei

eq), thermometry,

radiation

nuclei (MAPON),

serve

Ag isotopes

mostly

technique

of

a-detection

anisotropy

of static

(both

force

and

orientation

the

structural

technique

parameters

brute

in

nuclei.

the electric netism,

of

the

the application

tion (HFI)

ing the weak

(see review by Herzog

of

the measurement

surement

by KOOL

is a measure

[4]. tech-

that

A,

gives a

measurements

with oriented fact

orientation

included

e.g. higher and

importance

the

to daughter

sys-

with on-line

The

Traditionally,

and long search

the first NMR/ON

states.

a-radiation

by on-line

this technique

temperatures

in

in on-line term

for B-particles

advantages,

higher

lies

radiation

of the dipole

function

in connection

systems

[5]). Due to the need for high statistics to be incompatible

l/2

NMR/ON, isotopes

for the resonance,

at

tions,

[2], the UNISOR/NOF a

is not on-line

nuclei,

the

by diffusion

host

Belgium

and,

the use of the nuclear

nique

the

England

USA,

at CERN,

tem in Bonn,

the insolubility

at Leuven,

Ridge,

is that

of practical

effects

parent

the

by ion implan-

method

number

distribution

technique

The

> 10 s. Since

are now four on-line

at Daresbury,

Oak

The

with

method.

directly

of this

impurities

the KOOL

COLD

the

is due to the nuclear-spin

advantage

techniques

stability

T,,2 of nuclei which can

nuclei under study are produced tation,

far from

T,. which is typically

time,

the last

the use of

and electromagnetic

extension

limit on the half-lives

be studied

during First,

nuclei

at an accelerator

the angular

low-temperature

as follows.

to cool

is a major

principal

the

field that took place

refrigerator

selection,

in

bremsstrahlung

[8,9]. The occurrence

separators

population technical with

of lowdevelop-

accelerators

PHYSICS/ASTROPHYSICS

424

I. C. Girit / LJNISOR nuclear orientation facility

which made access Thus,

coupled

spectroscopy, ground-

to nuclei

far from stability

with gamma-ray nuclear

orientation

experiments

spin

static

and excited-level

dipole and electric and long-lived

quadrupole

isomers,

and,

most

tion multipolarities

of almost

decay.

A detailed

ments

of

magnetic

quadrupole

moments

techniques

respectively. ments The [16].

mixing

parameter because

phases

ability

depends things

of the electric

on can

square

spe-

principle

models

This

is

values,

a matrix

(b) tion,

tell

prob-

of

a spherical

A = 150 region

to those

of a deformed

Fig.

upon

crossing

the

of

host. a

Shape

coexistence

a structure

occurs

in the

boundary

needs

accurate

bands

of different

example,

bands

[19]. The

conversion possible

with

data

bands

examples

unambiguous

nucleus,

for

of the same

between

spin in these

multipolarity.

to resolve Such

Internal

ambiguities

EO transitions

[20] for transitions

above

and

precise in well

many

between

others

determination these the

can be done

in are

differ-

require of

is

errors

well to a certain

satisfied

if one of the two possible

rejected.

This is because

an de-

obtained

2, the of

3 contains

the

in the facility.

solutions

the

the host on the

in that the beam

access

of the refrigerator.

up to eight

detectors

to

This

to view

of the heat shields

the

enables

four at 45O, to view the target

with

field direc-

the axis of symmetry,

dual-plane

in fig.

lies in the

a modified

ion source by

the cold beam cryostat.

the activity

is implanted

the 3He-4He

a 90”

is focused

refrigerator

Fe)

dilution

magnet

(SM).

The

(typically

tube (CBT) is soldered refrigerator at about

magnetic

are polarized

pro-

on a target

bending (see

research (TM)

The ionized

in

reac-

at 50 kV)

magnet.

section

The

2.2)

before

which is part of the

The ferromagnetic

the temperature

open.

(IS).

are then accelerated beam

(usually

heavy-ion accelerator

beam which is focused

mass-separated

chosen-mass

Holifield

25 MV tandem

FEBIAD

tion products

view of the UNISOR/NOF

2. The

vides the primary

baffle

is that onto

plane.

(HHIRF)

maintain

systems

implanted

the bottom

four

The common

The UNISOR/NOF,

in design

allows

of the

systems.

on-line

the construction

A schematic

entering

comparison

foil (T) on which

to the cold finger of (DR)

which

should

12 mK with the 4 K

domains

in the target

foils

by a 1.5 T superconducting

degree, for

function

2. I. The ‘He- 4He dilution refrigerator

are

of S can only be

S is a quadratic

In section

mixing

measurements systematic

in the determination

these design

the operation

Section

is directly

tion, which determines

and

of neutron-deficient

in the same core.

how

This

but the certainty

the same

Existing

in some cases, by connect-

EO + Ml

precision by

eliminated.

states

unable

and

The

termined

where one

the sign of 6 changes

admixtures.

signatures

ently shaped

ratios.

are

multipole

considered The

within

are characterized,

transitions

instance

measurements.

in the case

[18] where

two bands ing

ratio

shape

can be seen

Au isotopes these

mixing

radia-

is the main

the same solid angle. The external

equatorial

between

[17].

is another

to nearly

to 99% Ml

underlie

orientation

of these

the eight detectors, essentially

facility

change

that

a side access.

Also,

of multipole (c)

three

is from

is shown

ratios

fact

a schematic

nuclear

ion beam

N = 88 and N = 90, where both the sign and magnitude mixing

of

setup

1 shows

fully on-line

the host

nuclear

characteris-

with

This

recently

other hand, differs

For example,

rotor

values

one corresponding

are discussed. results

separated

of informa-

with a level structure

vibrator

in terms

the

the UNISOR/NOF.

2. Experimental

feature

element.

us about

of nuclei.

the

and the other

principles

configuration

on the shape

from nuclei

described

behind

design

UNISOR/NOF

multi-

and shell closures.

especially

by

[Zl],

so

the mixing

The sign of S is also a good source

transition

extra

the arguments

transition

value.

by studying

can

ratios,

ref.

this

using

at this angle will help to distinguish

foil through model

2 of

unambiguously.

preliminary

of mixing ratios with the predictions

single-shell

collectivity

measurement two cases

of nuclei.

the

fig.

at an indefor

sensitive

a transition

of

In

mixing

mo-

have

and magnetic

whereas

be learned

(a) Comparison

tic

the

nuclear

matrix-element

are preserved,

Several

orien-

ratios

than a reduced

contains

6(E2/Ml)

basic

a more

or B(M1)

[21].

be clarified

need

tion, give the same W(90 “)/W(O o ) ratio but differ by 20% in their 45 o angular distribution. Thus only a

electric

below.

be

further

measurements

as 45 O. The

and

mixing

may

as a B(E2)

a S-value

the relative

of

6,

in

such

99% pure E2 radiation

the transition

E2/Ml

can

Krane

[14] and [15],

tests of different

ratio,

such

pole operators

ratios

of

angle

and this requires

angle,

the measurenuclear

in refs.

explained

in many instances

probability,

emitted

to use A,, pendent

transi-

on the other hand, deserves

very sensitive

The

moments

for the reasons

measurements

provided

on

to measure

unambiguously,

cial attention

importantly,

study

be found

yield

of ground states

by low-temperature

need

directional distribution coefficients, A,. In order to eliminate one of the two solutions, it is often necessary

magnetic

all radiatioins

dipole

can

The

values,

moments

radioactive

tation

possible.

and conversion-electron

6 is of the

The refrigerator

and the bottom

bly (fig. 3) were manufactured [22]. The refrigerator to allow bottom

is a standard

access,

access

by Oxford design,

the tail section

beam

assem-

Instruments but, in order

and the magnet

1. C. Gwit / UNISOR

O~-L~~E

NO 1 3 -

OF

0 90 TO

0 90

2 4 2 -

MAGNETIC

T

9 cm

FIELD

& DIRECTION

1.5 T horizontal FIRST 1981

ON-LINE

November

Fig. 1, A schematic

1.5 T horizontal

IMPLANTATION

1983 comparison

have been modified. The tails are cylindrical; the outer one is 18 cm in diameter, so the closest source-to-detector distance is 9 cm. At this distance, for detectors with 5 cm crystal diameter, the magnet allows 1.65, 1.29 and 1.07% solid angle for 0 O, 45” and 90” detectors, respectively. There is also a 2.2 cm opening at the bottom of the magnet for beam entrance. The refrigerator is

UNISOR

0 45 90

DISTANCE

7 cm MAX.

November

-

DETECTOR

cm

0.5, 1.5 vertical

UNlSORfNOF

DETECTORS 2 2

SOURCE 5,6

SYSTEMS

DARESBURY /NICOLE

LEUVEN

425

nuclear orrentation facility

OLNO

/

July

1988

June

1988

of fully on-line systems.

equipped with a “top load” facility to change target material while the refrigerator is operational. The cooling power of the refrigerator at a circulation rate of 500 pmol/s is given by the power relation Q = 0.017(T2 44.9) pW, where T is the target base temperature. The target foils and thermometer sources are soldered on the face of a 1.0 cm diameter cylindrical copper

FACILITY

MS

Hor$on;tai

Vertical PIZIW

Fig. 2. An overall view of the UNISOR/NOF experimental setup. TM: HHIRF 25 MV tandem, IS: modified FEBIAD ion source, MS: mass separator 90 o bending magnet, ED: 90’ electrostatic deflector, QL: quadrupole triplet lens, CBT: cold beam tube, SM: superconducting pofarizing magnet, T: ferromagnetic target foil, DR: dilution refrigerator. III. NUCLEAR

PHYSICS/ASTROPHYSICS

I. C. Grit / UNISOR

426

nuclear orientation facility

it to the entrance of the 90 o electrostatic deflector. The transmission through the horizontal beam line is checked by a removable

Faraday

cup. An x-y

also be used to monitor up.

A 90°

equally

electrostatic

spaced

quadrupole

deflector

parallel

triplet

plates

lens just

vides the final focusing

before

control

deflectors

Faraday

the beam enters

target

ranges

striking

at this stage

cup mounted

The transmission

seven

beam.

the deflector

placed just before

of the beam

of

the

A pro-

the cold

of the beam is achieved

the size of the beam

intensity

can

it is bent

consisting deflects

beyond

beam line. The final steering a set of x-y

beam scanner

the beam shape before

by

an iris used to the target.

The

is monitored

by a

on the 4 K baffle. from the dispersion

chamber

from 70% to 96% for different

to the

beams.

2.3. Data acquisition system Currently

the UNISOR/NOF

tem is based linked

on a Tennecomp

to a Concurrent

CAMAC

interface.

transferred either

THE BOTTOM ACCESS

in the isotope holder

ber

which

of the dilution

is screwed unit

into the mixing

by the top

loading

sample

holder

is made of high-purity

lurium

copper

and lies at the center

holtz-type

superconducting

run in persistent and

the beam

refrigerator

magnet

cryostat

detection liquid

transfer

Recent baffles

which

surrounds

are closed,

can

also

be

field.

The

are accommod-

A separate

experimentalists

experiments

tel-

is horizontal,

to this

and the detectors

electronics,

platform and

for

cryogenic

shown

that,

a base temperature

when

all the

of 7.6 mK can be

reached.

first,

monitor

of

the

beam

A compressor

line narrows

is focused

separator

and a Faraday

sity of the beam line.

is controlled

by several lenses and deflector

the separated

before

in

which

cup check it enters

and

assemblies.

At

in the dispersion a beam

the shape

profile

and inten-

the horizontal

lens at the beginning

the beam;

accesses

the anisotropy

of interest.

of spec-

Thus,

to be

the data on the of the refrigera-

of up to three peaks the experimenters

of the sample

In on-line ber of counts

nuclear

orientation

observed

can

in real time.

beam

of the beam

an einzel lens at the end focuses

experiments

by a detector

the num-

at a given angle

0

is given by N( 0, T) = &&W(@, where

N,

T)&(7),

is the beam

rate

of the intrinsic

angle

0, the solid

angle

0, branching

angle

of the detector

at

by the detector

at

factors

counting

time at temperature

decay

etc.;

W(0,

is the

T) refers

to the

of a y-ray

T as defined

and

T,(T)

at an angle

in ref. [23].

orientation

experiments

where the

of the isotope

of interest

is constant,

and since

orientation

temperature

experiments, due

current

T;

function

coefficients,

(T = 1 K),

NT& can be determined tion

in the decay

dewars

nuclear

the nuclear high

involved

through

distribution

T, je is a

efficiency

attenuation

In off-line

(I) at temperature

subtended

radiation

0 and host temperature The 50 kV beam from the separator

chamber

and length

2.4. Data analysis

directional

2.2. The beam line

monitored

stored tapes.

allows the collection

the base temperature

the alignment

function

the inner one. have

are

of a 1.5 T Helm-

is vertical

ated by a 6 m high platform.

monitor

they

and the type of data storage program

a be

rod. The

oxygen-free

mode. The field direction direction

cham-

through

automatically

where

the number

A separate

disk and monitors

sys-

which is

computer can

of both computers

tra to be transferred controlled.

acquisition

disk drives or magnetic

time of the acquisition,

tor, and calculates sample

spectra

mainframe

on high-capacity

The software

Fig. 3. The bottom beam access to a ‘H~G~H~ refrigerator: (1) mixing chamber, (2) target, (3) superconducting magnet (1.5 T), (4) room temperature shield, (5) 77 K shield, (6) 4 K shield, (7) iris, (8) iris controller.

mainframe

The

to the

data

TP 5000 system

go to zero at

at high temperature.

the variations

to the fluctuations or changes

B,,

the normalization

factor

In on-line

in the rate of ion implantain the

in the extraction

accelerator

beam

efficiency

of the

I. C. Gird / UNISOR

isotope

separator

“warm”

(T-

this case,

will cause

1 K)

the normalization

the ratio

N( 0, T)/N(

R = B”(e,

will no longer

data.

cancel

The nuclide symmetry

(2)

on-line

[24] was chosen

experiment

spectrum The

c)N,/N,,

(3)

HHIRF

the ratio:

R,=R/R,,

(4)

eliminated.

unknown

Then,

A(B)

= l-

NJN,,,

at an angle

T)/W(O,

is

0 can be

in the following

(5) to choose

the ratio

of

way:

where

[NC@,c>/t(e> c>l [N(O, c>/f(O,c>l [N(Q, w>,‘t(e, w)] [N(O>w)/‘t(O, w)] ’ (6) 0 refers to six possible

45 o or 90 o positions

0 means 0 ’ or 180 O. Due to differences each

detector,

rately.

live times

The errors

tainties

correction system

to directly

and

B,U,A,) distribution

detectors,

with movement ak calculated

on a natural

The

data

were

K and was deposited

controlling

this temperature, were

from

for movement

in

of

and

A,

U,

for

to directional respectively.

effects

associated

For example,

A(45 o ) and A(90 o ) with A(270 o ), we correct

the line connecting

In the six-detector to obtain tectors

ak from

(0”

system eight

or 180a;

the 90°

and

these

eight

times,

so in the final

values, final known

combinations,

from A,,

each

information then

source would

of de-

45O or 225’).

detector average

is increased

if the orientation

the main

combinations

or 270”;

statistical

the uncertainty analysis,

now in use, it is possible

different

90°

in eight

at the

cycles.

Beam

h in each cycle.

the beam

access

from

buildup

was closed At

for two hours.

six detectors

placed

at 0 O,

runs, each of

At the end of each cycle,

the sample

by a new iron foil in order to avoid the

of daughter

end of this period

activity.

The activity

was collected taken.

At the

the beam was shut off by a gate valve

and the target was allowed The

1

Then

down to base temperature.

cold data were collected

acquired

the

ion/s

was about

on the target while warm data were being

102 transitions

to cool for about

observed

30-40

min.

in 19’Au are currently

under analysis.

4. Conclusion The

ur( =

from pairs of diamet-

A(45 o ) and

along

values

are reduced.

from

was 2 X lo5

- l/2

the

The advantage

radiation,

results

for

from

Throughout

when the target

and the target was cooled Data

W target.

collected

on the target

= 51 min)

C beam

uncer-

270 o detectors.

cients.

target.

a 110 MeV

(Tl,2

accu-

introduced

coefficients,

systematic

of the beam

uk calculated

the

where

for gamma

by averaging

opposite

averaging

obtain

and deorientation

Furthermore,

classification by radioactive

isomer

the beam intensity

was allowed

is that, from any pair of A(90”),

u4( = BJJ,A,),

k = 2 and 4 refer,

quite

statistical

uncertainties

and peak fitting.

it is possible

cients,

experiment

and

of dead time of

be known

on N(t7, T) include

of the present

rically

should

as well as additional

background

state,

tandem

10 min duration.

_

state

a O(6)

its low-lying

this

of 19’Au, studied

by using

foil was replaced 1

by

45 O, 90 O, 180 O, 225 o and 270 o in 12-14

A(e)

=

whether

described

states

the gate valve

T).

it is convenient

this function

ratio

to 0 ‘, as shown below:

W(t9,

Experimentally

beam-rate

the anisotropies

given with respect

with

for the first UNISOR/NOF

r91Hg high-spin

of the

Instead,

the

be

excited

decay

where c and w refer to cold and warm data respectively.

that

nuclei

to determine

could

were produced

so

of even-even

scheme.

to:

we define

t9’Au, which has a Z = 3/2 ground

and lies in a region

’

Nwje

=

3. The on-line nuclear orientation of 19’Hg

In

from

NcfeW0, c>

w)/te(w)

which will reduce

in NT between

(T < 20 mK)

0, T -+ co). So we will have

NC@, c)/b(c>

R= N(B,

variations

and “cold”

421

nuclear orientation facility

is used of the eight

by fi

In four nk

= 2. In the

coefficients,

B,,

based

on the parent

ground

on distribution

coeffi-

of

tion refrigerators angles around ments as

the beam

The option

the target,

count

rate

in distance

bottom

90°

due

between

feature number

of detectors

available.

to achieve

this extra

means affect they affect

the performance

detectors,

multiple

mixing

will enhance

but ratios

with

technical

changes

did not by any

of an NMR

nor will

system

and

determination

of

a high degree

our understanding

and the

etc. This due to the

of the refigerator,

unambiguous

such

movement,

holder

feature

mo-

errors,

due to contractions, the counting statistics

the incorporation

particle

transition

beam

The

at 45 o

of the system,

the to

orienta-

the system

detectors

the sample

detector also enhances

necessary

enters

feature

uniquely

successfully

nuclear

some of the systematic

fluctuations

changes

now

of placing

a unique

us to determine and reduces

has

for on-line

whereby

from the bottom. enables

system

a new design

of nuclear

of accuracy structure.

are

of error

be due to those

UNISOR/NOF

demonstrated

U, coeffi-

The work at Vanderbilt supported Contract 760R00033,

by nos.

the

US

University

Department

DE-AS05-76ER05034

respectively.

UNISOR

III. NUCLEAR

and UNISOR of

Energy and

is

under

DE-ACOS-

is a consortium

PHYSICS/ASTROPHYSICS

of

428

I. C. Girit / UNISOR

universities, State of Tennessee, Oak Ridge Associated Universities, Oak Ridge National Laboratory, and is partially supported by them and by the US Department of Energy. The Joint Institute for Heavy Ion Research has as member institutions the University of Tennessee, Vanderbilt University, and the Oak Ridge National Laboratory; it is supported by the members and by the Department of Energy through Contract no. DE-FGOS87ER40361 with the University of Tennessee.

nuclear orientation facdity [7] J. Wouters, [8] L.

Vanneste,

[lo]

P.J. Back,

[ll]

W.D.

[12]

H. Marshak,

D. Vandeplassche, Nuytten

L. Vanneste,

and E. van Walle,

Instr.

J. Geenen, and Meth.

C. 186

Hamilton,

Hyperfine

Interactions

10

Green,

Hyperfine

S.J. Robinson, Interactions

[31 K. Schlosser, Workshop, tember

Conf. St.

N.J.

15/16 Proc.

Edmunds

Stone

(1983)

On-Line Hall,

4, 1988, to be published

Oxford,

Orientation-l

August

in Hyperfine

Interactions.

Hamilton

E.F. Zganjar,

[20]

E.F.

E. van Walle,

J. Wouters,

Phys. Rev. Lett. 57 (1986)

N. Severijns 2641.

[23]

M.O.

Stability,

Phys.

Interactions

Int.

Conf. Rosseau

Proc. (1988)

Wood,

1567. 4th Den-

p. 630.

Kortelahti,

5th

(1979)

Helsingor,

D. Vandeplassche,

Hyperfine

N. Severijns

22 (1985)

J.L.

Wood

on

Nuclei

507.

and Far

Lake, Ontario,

CD. From

Canada

p. 313.

ref. [3].

Instruments

K.S. Krane,

[24] J.L.

97.

and M.A. Grimm,

Ltd., Osney Mead, Oxford

England.

p. 731.

Inter-

Rev. Mod.

J. Phys. Gil

81-09)

ed. I.S. Towner,

Krane,

[22] Oxford

Hamilton,

Far From

J. Wouters,

Papanicolopulos,

[21] KS.

Hyperfine

22 (1985)

Cole, J.L. Wood

1981 (CERN

Zganjar,

Stability,

and J.H.

on Nuclei

1987, AIP Conf.

Nuclear Orientation, eds. H. 151 P. Herzog, Low Temperature Postma and N.J. Stone (North Holland, Amsterdam, 1986)

Interactions

and K. Kumar, J.D.

and L. Vanneste,

421.

[61 D. Vandeplassche. and L. Vanneste,

Hyperfine

[19] E. van Walle,

31-Sep-

K. Frei-

1764;

119.

mark, June

979. Nuclear

E. Klein,

59 (1987)

ref. [5] p. 199.

Int. Conf.

and P.M. Walker,

W. Vander-

ref. [3].

P. Roman,

and N. Mutsoro,

K. Kumar

(171 W.D.

W.

1583.

193.

ref. [5] p. 527.

A. KIuge, M. Reu141 P. Herzog, H.R. Folle, K. Freitag, schenbach and E. Bodenstadt, Nucl. Instr. and Meth. 155 (1978)

1. Berkes,

Chaplin,

Phys. Rev. Lett.

[16] J. Lange,

[18]

1219;

and

33 (1988)

J. Vanhaverbeke,

Brewer,

K. Nishimura 39 (1988)

54 (1982)

N.J. Stone and W.D.

Vanhaverbeke

ref. (81 p. 1583.

and D.H.

W.D.

[15] E. Hagn,

211.

(1981) V.R.

H. Pattyn,

Nucl.

J.

N. Severijns 1901.

ref. [3].

Hutchison

tag and P. Herzog,

[14]

PI

N. Severijns,

[13] B.G. Turrel,

References

Severijns,

56 (1986)

Bull. Am. Phys. Sot.

and J. Wouters,

S. Ohya,

(1981)

N.

[9] L. Vanneste, poorten

E. van Walle,

Phys. Rev. Lett.

Vanderpoorten,

actions

PI

D. Vandeplassche,

and L. Vanneste,

ref. [5] p. 31. Phys. Rev. C24 (1981)

1788.

OX2 ODX,