Neutron-induced cross-section measurements by

activation technique and gamma-ray

spectrometry in the energy range up to 20 MeV.

Compilation of experimental nuclear reaction

data in EXFOR database

Valentina Semkova

Institute for Nuclear Research and Nuclear

Energy, Bulgarian Academy of Sciences, Sofia,

Bulgaria

Content

Neutron-induced activation reaction cross section measurements

Neutron source characterization

Irradiation geometry

HPGe detector characterization

Sample composition

Cross section uncertainties

True coincidence summing correction calculations and uncertainty

calculation

EXFOR compilation of experimental nuclear reaction data

JINR, DUBNA 6 November 2019

Neutrinics calculations Boltzmann: Neutron transport

Bateman: Nuclide evolution

1. Neutron flux distribution in space and

energy (slowing down through elastic

scattering and secondary particle emission

(n,nʹg), (n,xn))

2. Radioactivity inventory based on

irradiation history (low activation

materials required).

3. Sensitivity (SR=(∂R/∂σ)(σ/R)) and

uncertainty (including correlations) analysis

required to provide adequate estimation for

the uncertainty of the integral

characteristics.

4. Nuclear data evaluations based on

experimental data and model calculations

Activation cross sections and uncertainty propagation

• A is the number of counts, c flux in1i 1 1 exp ti

• n is the number of atoms in the exp texp n it

target per area, clow 1 iEm0ax breakupi E . fi E dE

• e is the detector efficiency

• I is the gamma ray intensity E max i E . f i E dE

• λ is the decay constant E 0

• ti, tc, tm, irradiation, cooling and

cabs 1 1 exp x

measurement time x

Uncertainty propagation

Linear function

The general formalism of propagation of the variance and the covariance of the

parameter xk to those of yi is based on up to first order Taylor expansion of yi around

the expectation value xk0 of xk.

Neutron source characterization I

Neutron production in the 2-3 MeV and 13.5-14.8 energy ranges using D-D

and D-T at Ed~kev

high intensity; low background; neutron emission in 4π; limited energy range, kinematics

well known, Zr/Nb ration method used to verify neutron energy at sample position.

0 degrees 90 degrees

Fluence (n/(cm2 MeV s) 7,0E+07

6,0E+07

5,0E+07 14,5 15 15,5

4,0E+07

3,0E+07 Neutron energy (MeV)

2,0E+07

1,0E+07

0,0E+00

14

Neutron source characterization II

Neutron production in the 13.8 - 20.5 MeV energy range from D-T

reactions at Ed=1 to 4 MeV (Van de Graaff accelerator)

wider energy range; neutron emission in 4π; quasi-monoenergetic neutrons

background of low-energy neutron distribution; relatively low intensity

o TOF spectra measurement

•Liquid scintillator (NE213):

•Pulsed VdG: 1.5 ns fwhm, long tails, 400 ns rep. period

•3 m flight-path

•Collimator to avoid scattered neutron contributions

o Reaction rate measurements for the

following dosimetry reactions:115In(n,n)115mIn,

58Ni(n,p)58m+gNi, 56Fe(n,p)56Mn, 27Al(n,p)27Mg,

27Al(n,)24Na and 93Nb(n,2n)92mNb

o Adjustment of ′k for 6 energy intervals by

GLSM bases on standard reactions group cross

sections and measured reaction rates

Neutron source characterization III

Neutron production in the 4 - 13 MeV energy range from D-D reactions

at Ed=4 to 11 MeV (Cyclotron accelerator)

Neutron emission predominantly in forward direction; quasi-monoenergetic

neutrons high background of low-energy neutron distribution.

Fig. 1. Evaluated cross sections and the 0-deg neutron

spectrum of the D(d,n)3He reaction at 9.02 MeV.

Cabral et al., Nucl. Sci. Eng. 106, 308-317 (1990).

Neutron source characterization IV

Deuteron beam on thick 9Be target: very high intensity; broad energy

distribution, respectively spectrum average cross sections

Irradiation geometry

T1/2 ≥ min 3 s ≤ T1/2

T1/2=15.663 s

:

T1/2=6.21 s

Samples characteristics: natural and enriched

(n,γ) (n,3n)

(n,2n)

(n,p) (n,n+p)

HPGe detector characterisation

The Monte Carlo simulation of the

detector response allows taking into

account the detailed characteristics of

the detector and samples (complex

shape, sample matrix, γ-ray self-

attenuation, volume activity

distribution, coincidence summing

effects, etc.

Application of MC calculated detector efficiency

Total efficiency (%) 30

25

20

15

10

5 W sample 0.25 mm thick

Point soirce

0

0 200 400 600 800 1000 1200 1400

Gamma-ray energy (keV)

Threshold

(n,t) 6.4 MeV

(n,nd) 19.3 MeV

(n,2np) 21.6 MeV

Decay constant:

T1/2 15.97 d

Eg 983.525 keV

Ig 99.89(4) %

Sample size:

ø 30 x 5 mm

Interference: No

Counting rate (cps)241Am(n,2n)240Am cross section measurements

4

3 988 keV

988 keV

889 keV

889 keV

2

1

0

0 20 40 60 80 100 120 140 160 180

Cooling time (h)

Cross section uncertainty calculations

not correlated

correlated

Isomeric cross section measurement by analysis of

complex decay curve

n p m p p m

g m m g

Ng

tc g m 1 egT egtc 1 emT emtc

g

Ng tc

~ Ae Begtc mtc 70

A 58gCo decay curve

B 68

m g m g 1 1 egT

g m 1 emT 66

Activity (cps) 5+ 24.889 9.15 h

c 64

1 emT IT

1 egT 62 2+ 0 70.8 d

EC 58Co

60

IR m Measured

Fitted

m g

m g 1 58 58Fe

g

c A B 1 0 5 10 15 20 25 30

Cooling time (h)

True coincidence summing (TCS) correction

TCS uncertainty propagation

Cs-134 b- decay

EXFOR: scope of compilation

total

neutrons

charged particles

photons

Incident energy range up to 1 GeV

Quantities:

Cross sections CS (51%); Partial differential with respect to angle DAP (19.4%)

Differential data with respect to angle DA (19.3%); Resonance parameters RP (8.89);

Partial cross section data CSP (8.53%); Polarisation data POL (5.15%);

Fission product yields FY (5.03%); Differential data with respect to angle and energy DAE (4.78%); Fission

neutron quantities MDQ (2.27%); Gamma spectra SP (2.14);

Resonance integrals RI (2.08); Differential data with respect to energy DE (1.74%);

Thick target yields TT (1.65%) etc.

Reaction fields:

SF1. Target Nucleus

SF2. Incident particle

SF3. Process

SF4. Reaction Product

Data type fields:

SF5. Branch

(partial reactions)

SF6. Parameter

SF7. Particle considered

SF8. Modifier

(rel. data; fitting coeffi.)

(SF1(SF2,SF3)SF4,SF5,SF6,SF7,SF8,SF9)

Summary

Activation data are needed in many fields of science and

applications.

All factors/corrections influencing the particular

interaction needs to be carefully studied in order to obtain

accurate data.

Uncertainty analysis including covariance data have to

improve precision.

The new experimental data improve the knowledge of the

excitation functions the parameterization model calculations.