Positronium formation: Interrelation with radiation chemistry

282

Symposium

43.

POSITRONIUH

FORMATION:

abstracts

INTERRELATION

WITH RADIATION

CHEYISTRY

YASUO IT0 Research

Center

When a positron materials

it

and the

(Ps:

with

high

o-Ps

the

I

intensity

processes times

and

the

of

10

scale

is

related place

to at

are

two basic

The Ore model abstracts

simply

from

reaction

Ps

model,

by reaction

of

terminal

is

test

the

which

is

effects

e+

validity the

of

study

of

spur

model,

charge

electron

with

be well

the

described

and fluorescence for

parameter Both

experiments

samples

CL

Ps were

containing

scavengers,

efficiencies

by

ecuation

efficiency.

performed

of

radiation

empirical

formation

concentration

in

scavenging

“reactivity”

of

the

recombination

studied

known to

indicator

scavenging

result

the

same

and the

were

are

formation the

be formed electron

was that

efficiencies

spur

compared.

in

scavenging

the

same for

and fluorescence.

fluorescence,

almost

the

almost

the

completely

both

(Especially

efficiency

described

could

by the

Ps

for be

WAS

(2) performed

two models,

electron

to

This

among

scavenger

Within

the

related

equation.)

been

the

closely

by

positron spur: + e +e + Ps have

the

is well

(WAS equation)

(1)

to

other

Warman-Asmus-Schuler’s

as an

substance

an excess

on Ps formation.

the

react

assumed

of

is

the

The

e+ with

Many experiments

The kinetics

efficiency

while

Ps formation.

the

Tokyo,

phenomena .

and the

+

model,called

of

of

chemistry,

process:

In an another

processes

carries

reactivity

that

the

the

in cyclohexane

-9 s,

of

e ++M-+Ps+H

the

electron

framework

surprising

that

the

very

close

result

Ps formation to

the

and has posed and geminate

scavenging

lead

time

us to

conclude

in cyclohexane

geminate

is

recombination

a new problem

time

why Ps formation

recombination

look

so similar.

ion, e -+s+s-

should

lead

to

an

probability

geminate

recombination

But

fact

this

evidence formed

for

scavenger thermal perform

this

to

ized

as

in

the

it

radiation

be regarded

model,

Ps

because

This

suggests

spur

is

becoming

reaction

thus

(I)

and

with

necessary

makes (2)

it

in

“hot-Ps”,

from

that

efficient

the

in

to

quantitatively

induced Monte

inhibiting

pair spurs.

processes.

at

the of

terminal

This

simulation

was

less

indeed of

the

as

they

recombination. positron

many ion pairs,

may overwhelm

in

low are

Ps formation

geminate

that

composed

Carlo

i.e.

difference

scavengers

intercepting

single-ion

possible

a slight

effects, the

are

be removed is

scavenger

as a direct

reacts

It

was actually

concentrations

chemistry.

also

Ps.

There the

intercepts

Ore model

experiments

compare

of

just

cannot

by the

(3)

inhibition

formation

to

two

Ps formation

considers

an electron

an epithermal

of

the

much earlier

models

with

Uni-varsity

measured

(
There

the

1s

and Technology. 319-11, Japan

13,

are

be easily

take

3

which

and form

intensity,

lifetime

state

time

insulating

ortho-Ps

can The

on the

on the

The

of

that

accuracy,

information of

,

rs

into

up an electron

e+e’).

1 ifetime,

parameters

Nuclear Science Toka i , Ibaraki,

injected

can pick

“positronium”

major

is

for

the

while Y-ray

confirmed intraspur

by a

Symposium abstracts

Another between shown

example

of

in Fig.

, of C6F6 are seen

intensity

the

binary

to

Ps formation

the

in

we found

that

very

that

the

mixture

S-shape

the

to

shows a peculiar

composition, of

with

those from

of

and

C F also 66 maxima and

the

Ps formation.

such parallelism

Ps formatfan

abstraction C6Ft:

fluorescent)

fluorescence

close

some of

state

is

component,

Is

on the

has been deduced

electron

parallelism

same trend.

the

dependence

shows a similar

L (one mixture

follow

S-shaped

minima

excellent

and fluorescence

1 in which I3 and the

fluorescence

It

the

Ps formation

283

from

takes

excited

a new mechanism

of

place

via

molecular

Fig.1

Ps formation.

Comparison

volume Further have

results

been

on the from

of

presented,

importance

studies

and emphasis

was made

of

a scientific

potential

Ps formation

the

viewpoint

applications

studying

in

not

but

fluorescence

yield,

I

a function

fraction

of

3’ C F 66

as

L, of

in cyclohexane.

only

also

as a tool

ultra-fast

processes

study

of

and Ps intensity,

for

of

(sub-picosecond)

radiation

spur.

44.

BEHAVIOR OF POLYMERIZED LIQUID CRYSTAL PHASES STUDIED BY POSITRON ANNIHILATIO#

RAFAEL LOPEZ, SONIA MILLAN. JUAN CARLOS ALVAREZ AND LUZ ALICIA FUCUGAUCHI lnstituto National de lnvestigaciones Nucleares. Unidad de lnvestigacidn Aplicada Sur 1073, 03720, N6xico. D. F. Ave. lnsurgentes

In earlier

work

annhilation

the

polymerization

of

In

study,

the

detect

phase

this

used

to

technique

was applied

liquid

crystal

water.

The

annihilation

of

a study

lyotropic

liquid

transitions sodium

changes

parameters

of

positron

temperature

of

this

the

crystals.

same technique

system

sharp

to

has been in the

ID-undecenatethe

positron

as a function

of

system.

samples hexagonal,

indicate

structural

chanqes

Photomicrographs

show the laminar

presence and

of

of

these

nematic,

isotropic

phases.

in