Neutron Capture Cross Sections from 1 MeV to 2 MeV by Activation Measurements

Korea Institutes of Geoscience and Mineral Resource

G.D.Kim, T.K.Yang, Y.S.Kim, H.J.Woo, H.W.Choi, and W. Hong

Korea Atomic Energy Research Institutes

J.H.Chang

Introduction

Activation method : Historically first means of measurement of NCCS in MeV range

relatively simple to carry out

completely selective for a given nuclide in a mixture of target isotopes

Energies : 1 MeV to 2 MeV fusion reactor material research

Material : 63Cu and 186W

Mono-energetic fast neutrons source : 3T(p,n)3He reaction.

In KIGAM NCCS are being measured by activation method

In KIGAM neutron facility

Proton energy stability of the used accelerator : within 1keV

Producible maximum neutron energy : 2.6 MeV

Target Analysis

RBS ERD

T : 4.6 x 1018 atoms/cm2 , Ti : 1.4 x 1019 atoms/cm2

TiT target

Neutron Energy Spread

Calculated neutron energy [keV]1950 2000 2050 2100 2150 2200 2250 2300 2350

Nor

mal

ized

yie

ld [C

ount

s/10

0uC

]

2.0e+4

4.0e+4

6.0e+4

8.0e+4

1.0e+5

1.2e+5

1.4e+5

1.6e+5

=12.2

En = 2077 keV

background

12C(n,tot)

fitting data

Calculated neutron energy [keV]1500 1550 1600 1650 1700 1750 1800

Nor

mal

ized

yie

ld [c

ount

s/10

0uC

]

40000

45000

50000

55000

60000

65000

70000

75000

80000

1669

=1416O(n,tot)

measured2 =resonance

2 + tithick2 , : NES 1.3 % at 2.1 MeV

NES 1.7 % at 1.67 MeV

Neutron Pulse Shape and Height Spectrum

KIGAM neutron facility

detector

sample beam

Cooling system

monitor

Target chamber

D =No act

(1-e e 1-e R d

-t1 -t3 )( )(

Dgamma counts per unit time, No : areal density of sample

: neutron flux, act : neutron captured cross section

: decay constant of activated sample

t1 : neutron irradiation time

t2 : elapsed time from irradiation to measurement

t3 : measured time of gamma ray, R : transition probability

d : absolute gamma ray efficiency

-t2 )

Neutron Captured Cross Section

f(t) ;time dependence factor, subscript“o” refers to standard reaction

Do = No o o Ro o fo/o …… (1)

D = N R f/…… (2)

(1)/(2) =

Do N R f o

D No o Ro o fo o

=0.693/t ½ , / = (pho/to)/(ph/t) , t :neutron irradiation time

= Do N (ph) to R f t1/2,0

D No (ph)o t Ro o fo t 1/2 o

Characteristics of Sample

Purity(%) Weight(g) diameter Thickness(cm)

Density(g/cm3)

Molecular weight(g)

ArealDensity(1022 ions/cm2)

Au-1 99.99 117.34 5.090 0.310 19.282 196.97 1.7633

Au-2 99.99 122.84 5.115 0.315 19.282 196.97 1.8280

Cu 99.99 111.85 5.050 0.604 8.92 63.546 5.3800

W 99.95 223.54 5.015 0.595 19.35 183.85 3.7299

Abundance : 63Cu = 69.2 %of Cu, 186W=28.6 % of W

Absolute Efficiency of HPGe detector

species Gamma energy[keV]

Thickness[mm]

Calculatedefficiency

Au 411 3.1 or 3.15

0.0285 or 0.0280

Cu 511 6.04 0.0290

W 686 5.95 0.0183

By MCNP code and standard mixed source

Transition Probability

Z

n

Z-1 Z+1

Z

A

A+1

A+1A+1

Z A+1*

Z+1* A+1

Z-1 A+1*

EC

transition Gamma energy[keV]

Transitionprobility

198Au-198Hg(-) 411 0.9503

64Cu-64Ni(+) 511 0.1750187W-187Re(-) 686 0.1499

By Table of Isotopes

Gamma Spectrum of 198Au

411 keV

Gamma Spectrum of 64Cu

511 keV

Gamma Spectrum of 187W and Background

686

479

Neutron energy(MeV) Irradiationtime(hr)

Elapsed timefrom

irradiationto

measurement(hr)

Neutron flux

Gamma

counts

(n,)cross section(mb)

Statis-tical

Error(%)

2.015 197Au 0.982 0.040 9,542,379

5,057 53.4

63Cu 0.792 0.144 9,578,893

1,811 5.44 2.91

1.813 197Au 0.584 0.071 9,793,896

5,315 59.6

63Cu 0.413 0.374 9,720,648

1,760 5.49 2.93

1.611 197Au 0.549 0.128 8,319,212

4,663 66.5

63Cu 0.625 0.050 8,460,925

1,814 7.21 2.91

1.409 197Au 0.682 0.243 6,444,751

4,479 69.4

63Cu 0.869 0.031 6,014,762

1,630 7.67 3.10

Measured Data Table

Neutron energy (MeV) 0 1 2 3 4R

adia

tive

capt

ured

cro

ss s

ectio

n [m

b]

0

4

8

12

16

20

63Cu(n,g)

P.White et. els

ENDF-6

OURS

V.A.TOLSTIKOV

Neutron Captured Cross Sections of 63Cu

Neutron energy [MeV]

0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8

Neu

tron

cap

ture

cro

ss s

ectio

n [m

b]

15

20

25

30

35

40

45

50

55

M.Lindner (J.NSE.59,381,197604)

P. White (J.NE. 19,325,1965)

ours

ENDF-6

Neutron Captured Cross Sections of 186W

t

ln IoI

( )

No

I : neutron counts in sample–in

Io : neutron counts in sample-out

No: areal density of sample

In scattering correction factor

Dt = (/4) (DL/L1L2)2 n(0o)

n(0o)= (kR +1)4/4k2 : diffraction theory based on a continuum model

R = 1.33 A1/3 10-13 cm, D is diameter of detector

L is distance from target to detector, L1 is distance from target to sample

L2 is distance from detector to sample

Total Cross Section

Neutron energy [MeV]0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

Tot

al n

eutr

on c

ross

sec

tion

[bar

n]

0

1

2

3

4

5

6

Cu(n,tot)

Ours

Miller (52)

JEF-2.2

Total Cross Sections of Cu

Channel number

0 200 400 600 800 1000

Cou

nts

0

300

600

900

1200

1500

1800

Gamma Neutron

Sample in

Sample out

Total Cross Sections of W

Neutron energy [MeV]

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0

Tot

al c

ross

sec

tion

[bar

n]

5.5

6.0

6.5

7.0

7.5

8.0

ours

P.W.Miller

ENDF-6

Results

Neutron capture cross sections of 63Cu and 186W

Total scattering cross section of Cu and W

Geometric Efficiency of HP Ge detector