ABSTRACT Thermal Activation cross-sections for the (n, γ) reaction were experimentally measured using NIRR-1 facilities

* Sadiq

Jonah

R Nasiru

Zakari

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Bajopas Volume 3 Number 1 June 2010 
  
 
 
Bayero Journal of Pure and Applied Sciences, 3(1): 210 - 214 
Received: September, 2009 
Accepted: June, 2010 
    
 
DETERMINATION OF NEUTRON-INDUCED ACTIVATION CROSS SECTIONS 
USING NIRR-1 
 
*Sadiq, U.1 Jonah, S.A.2  Nasiru, R.1 and Zakari, Y.I.1   
1Department of Physics, Ahmadu Bello University, Zaria 
2Reactor Engineering Section, Centre for Energy Research and Training, Ahmadu Bello University, Zaria 
Correspondence author: sadiqumarx@yahoo.co.uk 
 
ABSTRACT 
Thermal Activation cross-sections for the (n, γ) reaction were experimentally measured using 
NIRR-1 facilities. The irradiated target isotopes were 71Ga, 109Ag, 55Mn 94Zr; 96Zr; 238U, 74Se, 75As 
and 48Ca. In order to obtain reliable activation cross sections, careful attention was paid to neutron 
irradiation and to the measurement of induced activity.  The values obtained for the ten (n, γ) 
reactions were compared against the comprehensive evaluated values listed in Mughabghab, 
(2003) and other evaluated data libraries. The values were found to compare well with values 
evaluated by Mughabghab and those from other libraries.  
 
Keywords: RNAA, Thermal capture cross section, Resonance integral, k0-factors. 
 
INTRODUCTION  
A database of activation cross sections for neutron 
energies (of up to 20MeV) is required for the design of 
a D-T fusion reactor, neutron dosimetry and neutron 
shielding in a reactor facility, and for confirming 
predictions based on reaction calculations. The (n, γ) 
cross section σ0 is a basic constant and the reliability 
of the literature data should be a matter of concern; 
as the accuracy and consistency of σ0’s from different 
libraries are often troublesome (De Corte et al, 1987) 
thus making a selection of reliable data difficult. A 
number of the cross section data compiled, in several 
evaluated data libraries, are evaluated mainly on the 
basis of theoretical calculations. Experimental data, if 
available, are used to normalize the calculated values 
and to improve their accuracy and reliability. In cases 
where no measurements have been made, the 
systematics for the majority of the reactions are used 
to predict the cross sections.                                                                                                                                                 
 Recently, a number of investigations were 
conducted to measure activation cross sections σ0 and 
isomeric cross section ratios I0 of some nuclides whose 
σ0 and I0 are either doubtful or have never been 
measured (Andrej, 2002). More recently, the IAEA set 
up the Working Party on Evaluation Co-operation 
(WCEC) Subgroup-23 (SG-23)  to assemble, verify and 
validate an evaluated data library for the minor fission 
products by reviewing and making use of existing 
evaluations, running nuclear model calculations and 
performing partial re-evaluation work (Andrej, 2002). 
The purpose of the exercise was to compare the 
thermal capture cross sections and resonance 
integrals from the SG-23 library to the equivalent 
values in the k0 database. It was discovered that 12 
out of 30 nuclides studied showed differences from 
5% to greater than 20%.  
The Nigeria Research Reactor-1, NIRR1, is 
designed for use in NAA thus, its neutron flux remains 
stable and constant during both irradiations of the 
‘bare’ and the ‘Cd-covered’ foils.. The k0-standardized 
method is widely accepted for multi-element NAA with 
respect to variations in neutron spectrum parameters 
and gamma-ray counting geometry (De Corte, 1987).  
The k0-standardized method, developed in the 1970s 
by Simonits et al., (1975) involves the simultaneous 
irradiation of a sample and a neutron flux monitor, 
such as gold, and the use of a composite nuclear 
constant called k0-factor. The k0-factor is independent
of irradiation and measuring conditions thus, 
eliminating the problems of non-availability of 
standards for certain elements and the inaccuracy 
caused by poorly prepared in-house standards (Jonah 
et al, 2005). Our main objective is to determine 
activation cross section data in the framework of the 
IAEA Coordinated Research Project No.13728 entitled 
“Reference Database for NAA” using the NIRR-1 
Facilities.  
 
MATERIALS AND METHODS 
In the k0 standardization of NAA, the concentration of the analyte ‘a’ is obtained from its measured 
isotope/gamma ray as 
 
( )
( ) aP
AuP
a
Au
AuAumP
amP
a xQf
Qf
x
ak
x
SDCwtN
SDCWtN
,
,
,0
,0
,0 )(
)(
)(
1
/
/
ε
ε
α
α
ρ
+
+
=    (1)   
where ‘Au’ refers to the co-irradiated gold monitor 
[197Au (n,γ) 198Au,  Eγ=411.8 keV] and  Np  is the 
number of counts in the full energy peak, W the 
weight of the gold monitor, W the weight of the 
sample,  S the saturation factor, D the decay factor, C 
the counting factor, td  the decay time, tur the 
irradiation time, tm the measuring time, f the thermal 
to epithermal neutron flux ratio, α the epithermal 
neutron flux distribution, approximated by a 1/ E1+α 
dependence, 
210 
Bajopas Volume 3 Number 1 June 2010 
 
Qo,= Io/σo is the ratio of resonance integral to thermal neutron capture cross section at  neutron velocity of 2200 
ms-1 and εP  the full energy peak detection efficiency. 
Furthermore, in Eq. (1), the k0,Aa (a) factor is defined as 
  
AuAuAua
aaaAu
Au M
M
ak
γσθ
γσθ
,0
,0
,0 )( =          (2) 
Where M is the atomic weight, θ is the isotopic abundance, σ0  is the 2200 m/s (n,γ) cross section, and γ is the 
absolute gamma ray intensity (emission probability). 
 Eq. (1) is written in the Hogdahl formalism  (modified for a 1/ E1+ α epithermal flux shape for which it is 
required that the cross section in the thermal neutron region varies as 1/v. This requirement is fulfilled to a good 
approximation by most analytically interesting (n, γ) reactions. 
The conversions from the Q0 values to Q0 (α) and from s0 values to s0 (α), is given by 
 
α
αα α
α )1(
))(12(
429.0
)(
429.0
)( 00 eVEE
Q
Q
Cdr
⎥
⎦
⎤
⎢
⎣
⎡
+
+
−
=      (3) 
where rE  is the effective resonance energy. The (1 eV)α term (numerically unity) originates from the definition 
of the epithermal neutron flux in a 1/E1+α  distribution. The above treatise holds for the case where the analytical 
isotope is directly formed by (n, γ) reaction. 
 As to the measurement of Q0 values, the well-known cadmium ratio method (in the Hogdahl formalism) 
was used, and  
  1
)(0 −
=
CdCd RF
fQ α        (4) 
followed by conversion of Q0 (α) to Q0 according to Eq. (3)  
 
Experimental 
The neutron-induced nuclear reactions, whose 
activation cross sections were measured include:- 71Ga 
(n, γ)72Ga;  109Ag (n, γ)110mAg;  55Mn (n, γ)56Mn;  
94Zr (n, γ)95Zr;  96Zr (n, γ) 97Zr;  238U (n, γ)239U;  74Se 
(n, γ)75Se;  75As (n, γ)76As;       48Ca (n, γ)49Ca. The 
thermal cross sections σ0;  resonance integrals, I0, or 
the ratio of resonance integrals to thermal cross 
sections Q0, from references, (Andrej, 2002) show 
large differences of between 5-20%. 
The description of the monitors and the nuclear data 
of the reactions measured or reevaluated are as given 
in Tables 1 and 2. 
 
Table 1: Description of monitor foils and oxides used. 
Target Material description Diameter, cm 
Range of 
mass, mg 
Au Al-0.1% Au; 0.1mm thick,  IRMM-530 0.8 12-14 
Mn Mn-1% Al foil, 0.1mm thick, SP89070 IRMM. 0.6 3-5 
Zr 99.8% Zr foil; 1mm thick, Goodfellow 0.6 42-45 
U U-0.2% Al foil, 0.1mm thick, NS2017 IRMM. 0.6 43-53 
Se SeO2 powder,  Merck KGaA - 51-63 
Ag Ag2O powder, Merck KGaA - 50-51 
Ga Ga2O3 powder, Riedel-de-Haën. - 52-62 
Ca CaO powder, Merck KGaA - 54-57 
As As2O3 powder, Riedel-de-Haën. - 52-54 
 
Table 2: uclear data of monitor foils and oxides used. 
Atomic Weight Target product T½ Er θ,% Eγ, keV γ, % 
74.92 75As 76As 26.32h 106 100 559.1 44.6 
      559.2 46.2 
      563.2 1.6 
      657.1 6.4 
      1212.9 1.8 
      1212.9 + 1216.1 5.5 
      1216.1 3.7 
196.97 197Au 198Au 2.695d 5.65 100 411.8 95.53 
54.94 55Mn 56Mn 2.579h 468 100 846.8 99 
      1810.7 27.2 
      2113.1 14.3 
91.22 95Zr 96Zr 34.97d 6260 17.28 765.8 99 
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Bajopas Volume 3 Number 1 June 2010 
  
 
 
Table 2 Continue 
Atomic Weight Target product T½ Er θ,% Eγ, keV γ, % 
238.03 238 U 239 U 23.45m 16.9 99.2746 74.7 50 
78.96 74Se 75Se 119.8d 29.4 0.9 121.1 16.41 
      136 56.02 
      264.7 58.6 
      279.5 24.73 
      400.7 11.13 
107.87 109Ag 110mAg 249.76d 6.08 48.17 446.8 3.657 
      620.4 2.776 
      657.8 94.74 
      677.6 10.8621 
      687 6.49 
      706.7 17.0242 
      744.3 4.661 
      763.9 22.36 
      818 7.323 
      884.7 72.86 
      937.5 34.31 
      1384.3 24.35 
      1475.8 3.989 
      1505 13.11 
      1562.3 1.184 
69.72 71Ga 72Ga 14.1h 154 39.9 630 24.37 
      834 99.55 
      894.2 9.842 
      1050.7 6.921 
      2201.7 26.06 
      2491 7.472 
      2501.8 20.52 
      2507.9 13.05 
40.08 48Ca 49Ca 8.718m 1330000 0.187 3084.4 91.7 
 Source: DeCorte et al. (986) 
 
Fig.1. Graphical comparison of Mughabghab with our result and other 
evaluated data
   76As    75Se   72Ga   110mAg   56Mn    239U     97Zr     95Zr     198Au 49Ca0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 1 2 3 4 5 6 7 8 9 1 0
Nuclides
Re
la
tiv
e 
m
ag
ni
tu
de
Mughabghab
This work
Jendl
SG-23
k0-Nudat
 
 212 
Bajopas Volume 3 Number 1 June 2010 
  
 
 
Table 3: Comparison of Calculated Activation cross section  σ0 and libraries. 
Target Product Mughabghab SG-23 k0/Nudat Jendl This work 
197Au 198Au 98.65 ±  0.09 - - - 98.74 ± 0.10 
94Zr 95Zr 0.0499 ± 0.0024 0.04992 0.051 0.04981 0.0433 ± 0.01 
96Zr 97Zr 0.0229 ±  0.001 0.02118 0.0197 0.0228 0.0213 ± 0.01 
238U 239U 2.68 ±  0.019 2.75* - 2.717 2.7252 ± 0.03 
55Mn 56Mn 13.36 ±  0.05 13.2* - 13.41 13.3055 ± 0.14 
109Ag 110m Ag 4.7 ±  0.20 3.90* - 90.53 4.2403 ± 0.26 
48Ca 49Ca 1.09 ± 0.07 1.12* - 1.093 0.8502 ± 0.24 
71Ga 72Ga 4.73 ± 0.15 4.735(1.8) 4.650(0.8) 3.709 4.7857 ± 0.05 
74Se 75Se 51.8 ± 1.2 51.86(2.7) 50.50(4.8) 51.8 77.418 ± 9.14 
75As 76As 4.23 ±  0.08 4.092(6.3) 3.85(4.8) 4.5 4.3776 ± 0.03 
 
RESULTS AND DISCUSSIONS 
For these determinations, the cadmium ratio was 
used. The nuclear data for the nuclides used and the 
cross section for gold, which is the universal 
comparator, were taken from DeCorte et al., (2003). 
The resulting activation cross sections of the 10 (n, γ) 
reactions  obtained were compared to the evaluated 
values by Mughabghab, 2003,  the SG-23 library, 
2002, k0/Nudat as well as other nuclear data libraries 
and is as presented in Table 3 and discussed in 1 to 
10 below. 
1. 197Au (n, γ) 198Au reaction. 
  Though this is not among the reactions whose 
activation cross section is in doubt, but our 
result is in excellent agreement with the 
evaluated data from the nuclear data libraries, 
SG-23 and Mughabghab within a range of 
0.1%. 
2. 94Zr (n, γ) 95Zr reaction. 
 Although the evaluated data from the 
libraries and Mughabghab agree with our 
results to within 13%, the values from the 
different libraries agree with each other to 
within almost the same margin. 
3. 96Zr (n, γ) 97Zr reaction. 
 Our result completely agrees with the results 
of the SG-23 but differ slightly with results 
from JENDL-3.3 and Mughabghab to within 
7%. The k0-Nudat value differs from JENDL-
3.3  and Mughabghab by about 14%. 
4. 238U (n, γ) 239U reaction. 
 Our result completely agrees with the 
evaluated data reported in the libraries and 
are also in excellent agreement with 
Mughabghab within a range of 2% 
5. 55Mn (n, γ) 56Mn reaction. 
The evaluated data reported by Mughabghab 
are in agreement with our results to within 
0.4%. The results from JENDL-3.3 also differ 
from Mughabghab by about the same 
margin. 
6. 109Ag (n, γ) 110mAg reaction. 
The evaluated data reported by Mughabghab 
is in agreement with our result to within 
10%., but differs significantly from results 
listed by JENDL-3.3. 
7. 48Ca (n, γ) 49Ca reaction. 
The evaluated data reported by Mughabghab 
and JENDL-3.3  vary significantly with our 
results to within 22%. The results from IAEA-
TECDOC, 1990 also differ from our results by 
about 26%. 
8. 71Ga (n, γ) 72Ga reaction. 
The evaluated data reported by Mughabghab 
and the other nuclear data libraries are in 
excellent agreement with our results to 
within 1.2%. Only the results from JENDL-3.3 
differ from our result by about 22%. 
9. 74Se (n, γ) 75Se reaction. 
The most significant difference from 
evaluated data reported by Mughabghab and 
the other nuclear data libraries is in this 
reaction, where the agreement with our 
results is to within 49%.  
10. 75As (n, γ) 76As reaction. 
The evaluated data reported by Mughabghab 
and JENDL-3.3  are in excellent agreement 
with our results to within 3.5%. The results 
from SG-23 and k0-Nudat differ from our 
result by about 7% and 14% respectively. 
A graphical comparison of our results with 
reported values from evaluated data libraries is also 
presented in Figure 1. The k0-values for the various 
gamma energies of these 10 isotopes were also 
calculated and presented along with the other 
calculated parameters as shown in Table 3. The 
results also compare favorably with the evaluated 
values by Mughabghab and other compilations by De 
Corte et al, 2003.  A graphical comparison of our 
values with Mughabghab is also given in Figure 1.  
 
213 
Bajopas Volume 3 Number 1 June 2010 
  
 
 
 
CONCLUSION 
The cadmium ratio was used to determine the thermal 
cross sections of ten (n, γ) reactions. Using the 
reaction 197Au (n, γ)198Au  as the standard, the results 
from seven of the nine reactions were found to be in 
excellent agreement to within 7% of those reported 
from evaluated data libraries. The results from the 
reactions 48Ca (n, γ) 49Ca and 74Se (n, γ) 75Se, were 
found to differ significantly (22% and 49%) from the 
evaluated data libraries.  
 
REFERENCES 
Andrej, T.(2002): Validation of thermal cross sections 
and resonance integrals of SG-23 evaluated 
nuclear data library;  SG-23_ validation doc., 
IAEA. 
De Corte F.; Simonits, A.; De Wispelaere, A.; Hoste, 
J.; (1986): Compilation of k0-factors and 
related nuclear data for 94 radionuclides of 
interest in NAA.; INW/KFKI interim 
report(1986) 
De Corte, F.  (1987): The k0- Standardization Method -
A Move to the Optimization of NAA; Ph.D 
Thesis; University of Gent, Belgium 
De Corte F.; Simonits, A.; De Wispelaere, A.; Hoste, 
J.; (1987): Accuracy and  applicability of k0-
standardization method, Journal of 
Radioanalytical Chemistry, vol. 113, pp145-
161. 
De Corte F.; Simonits, A. (2003): Recommended 
Nuclear Data for Use in the k0-
Standardization of Neutron Activation 
Analysis: Atomic Data and Nuclear Data 
Tables 85, pp.47-67. 
IAEA TECDOC, (1990): Practical aspects of operating a 
neutron activation analysis Laboratory; 
International Atomic Energy Agency IAEA-
TEC DOC 564. 
Jonah, S.A.; Balogun, G.I.; Umar, I.M.; Mayaki, M. C. 
(2005): Neutron spectrum parameters in 
irradiation channels of the Nigeria Research 
Reactor-1 (NIRR-1) for the k0-NAA 
standardization. Journal of Radioanalytical 
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Mughabghab, S. F. (2003): Thermal neutron capture 
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Shibata, K., Kawano, T., Nakagawa, T., Iwamoto, O., 
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Ohsawa, T., Nakajima, T., Yoshida, T., 
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DETERMINATION OF NEUTRON-INDUCED ACTIVATION CROSS SECTIONS USING NIRR-1

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DETERMINATION OF NEUTRON-INDUCED ACTIVATION CROSS SECTIONS USING NIRR-1

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