Neutron-induced cross-section measurements by activation technique by V. Semkova

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  in1i 1  1 exp ti 
• n is the number of atoms in the exp texp n  it

target per area, clow 1 iEm0ax breakupi 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  egT egtc 1 emT emtc

g

   Ng tc
~ Ae  Begtc mtc 70

 A 58gCo decay curve

 B 68
  m  g m g  1 1  egT
g m 1  emT 66
Activity (cps) 5+ 24.889 9.15 h
 c  64
1  emT IT
1 egT 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.