Experimental Determination of Neutron Cross Sections of Yttrium by Activation Method

Experimental Determination
of

Neutron Cross
Sections

of

Yttrium
by

Activation

Method

by

Barbara Geier


Supervisors:


Assoc
. Prof Dr. Wolfgang Sprengel



RNDr
.
Vladimír

Wagner
Csc
.



Ing.
Ondřej

Svoboda




Internship

at

the

Nuclear

Spectroscopy

Department
of

Nuclear

Physics

Internship


Organized

by

IAESTE Graz


6
weeks


Departement
of

Nuclear

Spectroscopy

in
Řež




Summary

1.
Irradiation of the yttrium foil by neutrons
to
produce

radioactive isotopes

2.
Analysing

of the gamma
emission

of the
daughter

nuclei

by a germanium
semiconductor

detector

3.
Determination

of the area of a gamma
peak

with

the program DEIMOS32

4.
Determination

of the
number

of
produced

nuclei

N
yield

out of the
peak

area

5.
Determination

of the cross section for the
single isotopes out of
N
yield




Introduction


Cross
section
:
probability

of

nuclear

reaction


Depends

on
the

neutron

energy

–

excitation

function




Example
:

Activation

Method


Reaction

of

a
neutron

beam
with

nuclei

to

produce

radioactive

isotopes


Daughter

nuclei

start

to

decay

by

gamma

emission


Semiconductor
detector

(
for

analysing

gamma

emission
)

◦
Compton
scattering

◦
Photoeffect

◦
Production

of

electron
-
positron

pairs


Experiment:
Production

of

the

Neutron Beam


E
Protons
: 35
MeV


Reaction
:
7
Li(
p,n
)
7
Be


E
Neutrons
: ~32
MeV


Yttrium sample was
irradiated

for

22 h



Quasi
-

monoenergetic

neutron

spectrum

for

a
7
Li(
p,n
)
7
Be
reaction
,
with

protons

at

an
energy

of

35
MeV


Experiment


Gamma
emission

of

yttrium

sample was
measured

in a
germanium

semiconductor

detector

for

different
distances
: 15, 23, 53, 70,
93, 173 mm





Evaluation
of

measured

gamma

spectrum

with

Deimos32

Determination
of

area

and

uncertainty

of

area

for

gamma

peaks

Corrections

N
yield
:
Number

of

produced

nuclei

in a
given

foil

Corrections

Weighted

average
:

Uncertainty

of

weighted

average
:

2

–
test
:

Possible

Reactions



Radioactive

potassium

isotope

40
K


Gamma
peak

at

an
energy

of

1460
keV


Analysed

for

reference

to

see

if

the

measurement

went

smoothly

The
ratio

between

the

area

of

the

gamma

peak

and

the

life

time
of

the

detector

should

be

constant

Number

of

produced

nuclei

N
yield

for

the

isotope
88
Y


Reaction
:
89
Y(n,2n)
88
Y


Half liveT
1/2

= 106.95 d


Comparison

between

the

different
measurements

of

the

23 mm
distance

between

sample
and

detector

for

the

gamma

line

at

an
energy

of

898.0
keV

898.0
keV

1836
keV

Number

of

produced

nuclei

N
yield

for

the

isotope
88
Y


The sample was
turned

to

the

other

side

after
each

measurement
.
There

is

a
slight

influence

on
the

results

between

side

(a) (
left
)
and

side

(b)
(
right
)
of

the

sample.

N
yield

for

the

isotope
88
Y

Comparison

between

the

different
measurements

at

different
distances

for

the

898.0
keV

gamma

line
:

N
yield

for

the

isotope
87
Y


Reaction
:
89
Y(n,3n)
87
Y


Half liveT
1/2

= 79.8 h



388.5
keV

484.8
keV

Comparison

between

the

different
measurements

of

23 mm
distance

between

sample
and

detector

for

the

gamma

line

at

an
energy

of

388.5
keV

N
yield

for

the

isotope
87
Y

Nearly

100%
decays

from

the

isomeric

state

87m
Y
to

87
Y









The
equation

for

the

change

of

radioactive

nuclei

after
irradiation

for

87
Y
is
:

Cross
section

Cross
section

for

88
Y

1
barn

= 10
-
28
m
2

Cross
section

for

the

89
Y(n,2n)
88
Y
reaction
:
(0.41
±
0.05)
barn

Cross
section

for

87m
Y

Cross
section

for

the

89
Y(n,3n)
87m
Y
reaction
:
(0.56
±
0.07)
barn

Cross
section

for

87
Y +
87m
Y

Cross
section

for

the

89
Y(n,3n)
87
Y +
89
Y(n,3n)
87m
Y
reaction
:

(0.77
±
0.08)
barn

Cross
section

for

87
Y

Cross
section

for

the

89
Y(n,3n)
87
Y
reaction
:
(0.21
±
0.03)
barn

Thank

you

for

your

attention
!


Questions
?

Calculation

of

the

peak

efficiency

correction

factor

for

the

distance

of

173 mm