Heavy fragment emission in high energy reactions on heavy nuclei

HAL Id: jpa-00206874

https://hal.archives-ouvertes.fr/jpa-00206874

Submitted on 1 Jan 1970

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

Heavy fragment emission in high energy reactions on

heavy nuclei

G. Remy, J. Ralarosy, R. Stein, M. Debeauvais, J. Tripier

To cite this version:

HEAVY FRAGMENT EMISSION

IN HIGH ENERGY REACTIONS ON

HEAVY NUCLEI

By

G.

_REMY,

_J.

_RALAROSY,

R.

_STEIN,

M. DEBEAUVAIS et

_J.

_TRIPIER,

Département de _{Physique Corpusculaire.} Centre de Recherches Nucléaires, Strasbourg.

(Re(u

le 11

_{Y’ut’llet 1969.)}

Résumé. 2014 A l’ aide de détecteurs visuels _solides, nous avons étudié certaines réactions induites _par des

_protons

de haute

_énergie

_{(0,6 ;}

3 ; 18 ; et 23

_GeV)

dans des cibles d’uranium,

de

_plomb

et d’or.

Nous

_présentons

des résultats concernant la

_fréquence

relative de fission binaire et ternaire,

la

_fréquence

des événements ternaires

_coplanaires,

les distributions

_angulaires

et les distributions

en masse et en

_impulsions

concernant les

_fragments

de fission ternaire.

Abstract. 2014 Three

prong events,

registered

in

_plastic

visual detectors have been studied and

_calculated,

and their cross-sections for various

_targets

and various

_incoming

_energies

have been

_compared

to

_binary

fission cross-sections.

Angular,

energy and

fragment

mass distributions are also

_given.

Introduction.

-

During

the _{last years,} a _process

with nuclei

_{desintegrating symmetrically}

into three

fragments

has been

_{investigated by}

_many authors

_{[1, 2,}

6,

8].

This process can be induced

_by

fast

_protons

or

_heavy

ions,

the three emitted masses

_being

in both cases of the same size. These

_ternary

events have been called «

_Ternary

fission ». This nuclear inter-action must be

_{distinguished}

from the low _energy fission

[3, 4, 5, 7]

and from

_spontaneous

fission of transuranium nuclei into two

_heavy

_fragments

and a

lighter

one, for

example

lithium or helium.

Ternary

fission cross-sections at

_high

_energies

are

between a few millibarn and some ten millibarns. We must note that the

_majority

of these cross-sections have been obtained

_by

solid state track detectors. Their use seems to be the most accurate

_technique

to

study

ternary

(and binary)

fission at

_{high energies.}

In this

_work,

we

_emphasize

_ternary

fission,

but we

shall also

_give

some results

_concerning

_binary

fission and

_{fragmentation}

and

_point

out the relative

impor-tance of these

_phenomena.

Gold,

lead and uranium

_targets

have been

_exposed

to

_high

_energy

_protons

of

_0.6,

_3,

18 and 23 GeV

.at C.E.R.N. and in

_Saclay.

Our results concern :

1)

Relative

_frequency

of

_ternary

to

_binary

fission for various

_targets

and for various

_energies.

2)

The ratio of the number of

_coplanar

_ternary

events to the total number of

_ternary

events.

3)

The

_angular

distribution of two

_fragments

for

.coplanar

events.

4)

Mass distribution for

_coplanar

events. We have also calculated non

_coplanar

events

_by

means of some

supplementary

hypotheses.

5)

Momentum distribution of the emitted

_fragments.

6)

The distribution _{of total kinetic energy released.}

Experimental.

- Our

experimental technique

has

.already

been

_published

_[1].

The detector used is a

polycarbonate (makrofol).

Its main

_property

is a

critical

_registration

threshold of :

If an

ionizing particle

has at the

_point

of entrance into the detector an _energy loss _per unit

_path

_greater

than

this critical

_value,

its track can be made visible

_by

chemical treatment.

It can then be observed

through

an

_optical

micro-scope. A standard

development procedure

is

applied

and one can detect in makrofol

heavy particles

with masses

M >

16.

The

_{insensibility}

of this kind of detector to

_light

particles

allows the

_study

of rare events

_involving

heavy

particles.

The

_background

which would be due to the much more

_{frequent light particles,}

is not

registered

in

_plastics.

In _{this way solid}

_plastic

detec-tors are ideal

_{heavy particle}

detectors.

The sandwich

_technique

used has a 4~

_geometry.

The

_target

₍₃₀

to 50 is

_evaporated

on a 200 pm

plastic

sheet

₍₃₀

X 30

_mm).

It is

_partially

_glued

to

another

_plastic

foil and

_placed

into a small

_polyethylene

bag

which is sealed under vacuum. This

_procedure

insures

_good

contact between detector and

_target.

After

_irradiation,

the

_target

is dissolved and the tracks

are

developed

with 5N NaOH at 60 ~C for 40 mn.

By

observation with an

_{optical microscope,}

we can

distinguish

3 kinds of events.

A. SINGLE TRACKS. - Their

lenghts

lie between 0 and

_{approximatively}

_{30 ~m.}

_They

can be attributed

to

_spallation

or

_{fragmentation}

reactions

_(we

have taken

in account

_only

tracks which have

_projected

horizontal

lengths

greater than 2.5

_~m).

The

_incoming

_protons

enter the foil

_vertically.

28

B. Two CORRELATED TRACKS. - These

tracks,

generally

due to two _very

_heavy

_fragments,

are

corre-lated.

_They

_{correspond approximately}

to one half of

the mass of the

_target

nucleus. This means that

they

originate

from the same interaction. These events

can be attributed either to

_binary

fission or to double

fragmentation.

We can divide them into two _very

different classes :

Scheme 1

a)

If the

_trajectories

of both

_{heavy fragments}

and the

_incoming

_proton

direction are

_coplanar,

then the

projections of OM1

and

_OM2

on a

_{plane, perpendicular}

to the

_proton

direction,

3 are colinear. This

implies

that the momentum of the

_{fissioning moving}

nucleus is in the

_proton

direction.

b)

If the

_{projected angle of OM,}

and

_OM2

is not

_180°,

then a transverse momentum

_component

exists for the

moving

nucleus. This

_implies

that

_{lighter particles}

are

produced.

These

particles

are emitted

during

the cascade or

evaporation

_step

of the reaction and

cannot be observed with the used detector.

C. THREE CORRELATED

_TRACKS

_{( fig. 1).}

- Three

tracks

_originate

from the same

_target

_point.

We have

FIG. 1.

High

energy

proton

interactions with

_heavy

nuclei.

proved,

that these events can

_only

be

_genuine

_ternary

events

_[1].

_They

are classified under the name "ter-nary

fission",

without

implying

a

special

mechanism

of reaction

(the

dashed lines serves

_solely

to

_recognize

easily

the

_{corresponding}

_points).

Results and discussions. - 1. FRAGMENTATION.

-Figure

2 shows the

_SIB

ratio of

_single

to

_binary

tracks

FIG. 2. -

High

energy

proton

interactions with uranium,

lead and

_gold

targets,

ratio of

_single

events to

binary

events.

as a function of

_target

nucleus and

incoming

_proton

energy. It can be seen that :

a)

For a

_given

_target

nucleus,

increases

_by

a

factor of 10 when the

_incoming

_proton

_energy rises from 0.6 GeV to 25 GeV.

b)

For a

_given

incoming

_energy

SIB

decreases when

the

target

mass increases

(the

dashed lines serves

solely

to

_{recognize easily}

the

_{corresponding}

_points).

We can _compare our results to those obtained

_by

Hudis and Katcoff

_[8].

_{They employed}

mica

detec-tors and found a similar

dependence

for Our

results are of the same order as theirs.

2. TERNARY

_FISSION

_{(fig. 1).}

- The ratio of

ternary

fission relative to

_binary

fission is indicated in table I for _every

_target

nucleus and

_proton

_energy.

Figure

3 a shows versus

_incoming

_energy for

lead,

gold

and uranium. It can be seen that :

a)

For a

_given

_target

_nucleus,

seems to have

a maximum between 3 and 18 GeV :

- that the value at 600 MeV

is very small and thence the

_uncertainty

is

_large.

b)

For a

given

_energy the relative

_frequency

of

FIG. 3.

a) High

energy

proton

interactions with uranium, lead and

_{gold targets;}

ratio of

_ternary

events to

_binary

events.

b)

Fragment

mass distribution for

_coplanar

events.

(*) Indicates poor statistics. The represented error is _only the statistical one.

Our numerical results are

_higher

than those obtained

by

Hudis and Katcoff

_[8]

and Brandt et al.

_[2].

This is due to the

_following

reason :

- Makrofol is sensitive

to

_particles

of masses heavier

than 16

_(oxygen),

but mica is sensitive

_only

to

masses with M > 30. Thence our

_ternary

fission

events contain an

_important

contribution of

_lighter

fragments

than those which can be visualized in

mica.

The fact that increases with

_proton

_{energy, and}

that,

as it is well

_known,

_binary

cross-section decreases

slowly

in the same

conditions,

confirmes the idea that

ternary

fission cross-section increases with

_incoming

proton energy and this may be the result of a

_larger

fragmentation

contribution to this _{ternary process.}

Mass calculation for

ternary

events. - We have taken a

_part

of all found

_ternary

fission events and made a first

_approach

in

_calculating

the mass and

energy distribution for the

particles

emitted in ternary fission.

For this calculation one needs all

_geometrical

para-meters

_concerning

these events, as well as an

accurately

30

FIG. 4. -

Fragment

mass distribution for non

_coplanar

events.

for

_heavy

and

_lighter

elements from common fission

fragments

to _oxygen.

The

_projected

_ranges and the

_dip

_angles

of the three prongs are measured with the

_help

of an

_optical

microscope.

The error is

0.5 ~t

for

path

measurements

and 1 f.L for

_dip

measurements. The

_projected

azimu-thal

_angles

must also be determined

_{(AO == 20)}

for each track. The

_knowledge

of these

_quantities,

for

every event, allows a

spatial representation

of each

interaction. The

_{largest experimental}

error is due to

the

_dip

measurements.

An other

_aspect

is the

_necessity

of

_getting

a well

determined range-energy relation for ions in our

detec-tor, as a function of their mass and

charge

numbers.

This range-energy relation

gives

accurate results for

masses between 32 and 160 A.M.U. However for low masses the formula has been found

_by

_{extrapolation}

and is therefore

_inaccurately

known. The closer

to _oxygen we are the

larger

is the mass-error.

This results from the fact that for lower _masses, the theoretical

_relationship

cannot be used because we are near the

_registration

threshold in

_plastics.

We must

_point

out, that for

_light

ions

_registered

in

plastics,

the

_imperfect

_knowledge

_{of the range-energy}

relationship

disturbs also the mass

_spectrum

for heavier masses due to calculation

_procedures

used here.

In this first

_rough

_calculation,

we have assumed

that

_MfZ

is

_equal

to

_{the P- stability}

value

_given

_by

the nuclear chart

_tables,

instead of the classical well known E.C.D. or U.C.D. values. This

approximation

increases also the error in the

_resulting

masses.

In our

calculations,

a

_hypothesis

is needed

concer-ning

the mass of the

_fissioning

nucleus. We have assumed in our calculations that the cascade and the

evaporation

take

_place

before fission and lower the target mass for 10 A.M.U.

_(this

_arbitrarely

choiced

number is assumed to be

_independent

of the

_incoming

assump-FiG. 5. -

Fragment

momentum distribution for

_coplanar

events.

tion increases also the error we make in

_calculating

masses.

But we must note that our method is the

_only

pos-sible _one, which

_{nowadays permits}

a mass

determina-tion for

_ternary

events.

Presently,

we are

_carring

out new

_experiments

con-cerning experimental

range-energy determinations for visualized

_fragments

in makrofol.

In

_future,

when we have an accurate determination for the relation _{between range, energy,} mass, and

charge,

we shall _try an other

_calculation,

where the

assumption

that the

_products

are beta-stable will be

eliminated. We may also take in our future

calcula-tion the

_fissioning

mass as a

_parameter

which will vary

between certain

_limits,

and see in this _way the influence

of this

_parameter

on the mass results.

At 3 and at 23

GeV,

we have observed a

_large

number of events, but we must note that at 18

_GeV,

for technical _reasons, our statistics are _poor.

There-fore,

we

regard

the 18 GeV results as less

_important.

We

_employed

momentum and mass conservation

laws for the mass calculation. The

_geometrical

para-meters of each event are determined

experimentally.

The

_following

relations hold :

: the recoil momentum

_components

of the

_{moving nucleus,}

Pl’ P~, P3

: the momentum of the three emitted

particles,

lvlv

the

_{corresponding}

_masses,

A : the mass of the

_fissioning

nucleus. In order to solve these

_equations

and to calculate

and

_{P,, P2, P 3’}

we need a well determined

cal-32

FIG. 6. -

Fragment

momentum distribution for non

_coplanar

events.

culations,

we have fitted the

semi-experimental

mo-mentum-range-mass

relationship by

fourth

deegre

polynoms :

(P~

=

momentum,

Mi =

the mass,

(a, P, Y; oc’, P’, y’)

=

constants)),

Ri

is the range of the track in our

detector,

the

_computer

is then able to resolve our

equations (1).

The

_following

_hypotheses

have also been made :

1)

In all

_{calculations,}

we _{suppose that}

7~

_{= P~}

=

0,

i.e. the recoil momentum is in the

_incoming

direction.

2)

We consider

_{especially coplanar}

events, so that

the recoil momentum is _very small or _zero, but the

calculation has been

_performed

with the same

assump-tions for all

_coplanar

and non

_coplanar

events.

It is very difficult to determine the errors in the mass

calculations. Here are a few sources of error :

1) Experimental

errors on

path

length

measure-ments are of the order of 1 p,. This

corresponds

to 3

or 4 A.M.U. after calculation.

2)

The error introduced

_{by assuming Z JM}

to be

equal

to

_{the 03B2 stability}

value _{in range-energy} deter-minations may be of the order of 1 A.M.U. for

heavy

fragments

and 3 for

_lighter

ones.

3)

The

_uncertainty

in our

knowledge

of the mass

of the

_fissioning

nucleus can lead to an error of 3 or

4 A.M.U. on each

_fragment

mass.

To

_conclude,

the total error in mass determinations

is then

_roughly

of the order of 10 A.M.U. For non

coplanar

events, the results are

_{only given}

to be

compared

to

_coplanar

ones. The results are shown

in

_figures

3 to 8. We can note that :

1)

With

_increasing

_proton

_energy the mass

distri-butions becomes broader.

2)

With

_increasing

_proton

_energy the

_velocity

of the

_moving

nucleus decreases.

3)

The

_FIB

ratio decreases with

_increasing

energy

(FIB

defined

_by

the

_sign

_{of Pz}

while

_P~

=

0;

7. - Total kinetic energy.

FIG. 8. -

34

IIIVU IIIB.NMðV/C

FIG. 9. - Momentum of the

moving

target

nucleus

_(coplanar

and non

_{coplanar events).}

Conclusion. - This

paper was to

_{provide only}

a

general

view on the use of

plastic

track detectors for

the

_{study of high}

_energy fission. It is _easy to determine

accurately

some relative cross-sections and mass and

energy distributions. Rare events can be not

_only

registered

and counted but also studied

_{kinematically,}

if one knows

accurately

the different

geometrical

parameters.

Concerning

fission induced

_{by charged}

_particles,

we

plan

to continue our

_work,

especially

in

determi-nations of cross-sections of rare events and in calcula-tions of mass and energy _{distribution.}

Acknowledgements.

- It is

a

_pleasure

to

acknow-ledge

many

helpful

discussions with our

colleagues

from

_{C.E.R.N.-Heidelberg-Napoli-Warsaw}

collabo-ration

_{(see preceding publication).}

BIBLIOGRAPHY

[1]

DEBEAUVAIS

_(M.),

STEIN

(R.),

RALAROSY

_(J.)

and

CÜER

_(P.),

Nucl.

_Phys.,

1967, A 90, 186-198.

[2]

BRANDT

_(R.),

CARBONARA

_(F.),

CIE015BLAK

_(E.),

DAKOW-SKI

_(M.),

GFELLER

(Ch.),

PIEKARZ

_(H.),

PIEKARZ

_(J.),

RIEZLER

_(N.),

RINZIVILLO

(R.),

SASSI

_(E.),

So-WINSKI

_(M.)

and SAKRZEWSKI

_(J.),

Nucl.

_Phys.,

1967, A 90, 177-185.

[3]

DUTTA

_{(S. P.),}

Ind.

_J.

Phys.,

1953, 27, 547.

[4]

Ho

_{(Z. W.),}

TSIEN

(S. T.),

VIGNERON

_(L.)

and

CHAS-TEL

_(R.),

C. R. Acad. Sci., 1946, 223,

1119 ; Phys.

Rev., 1947, 71, 382.

[5]

MUGA

(M. L.),

BOWMANN

_(H.

_R.)

and

THOMP-SON

_{(S. G.),}

_{Phys. Rev., 1961,} 270.

[6]

FLEISCHER

(R. L.),

PRICE

_(P.

_B.),

WALKER

(R.

M.)

and HUBBARD

_{(E. L.),}

_Phys.

_{Rev., 1966,} 143, 943.

[7]

HYDE

(E.),

Nuclear

_Properties

of the

_Heavy

Ele-ments, vol. III, p. 131

(Prentice

Hall, Inc.,

En-glewood Cliffs/New

Jersey).

[8]

HUDIS

_(J.)

and KATCOFF

_(S.),

BNL 13 124

_(submitted