DETERMINATION OF NEUTRON-INDUCED ACTIVATION CROSS SECTIONS USING NIRR-1
DETERMINATION OF NEUTRON-INDUCED ACTIVATION CROSS SECTIONS USING NIRR-1
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Date
2007-06
Authors
Umar, SADIQ
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Abstract
The full-energy peak efficiency (FEP) curves of the gamma-ray spectrometry setup for use
with the newly commissioned Nigeria Research Reactor-1 (NIRR-1) have been determined
at three source-detector positions aimed at routine neutron activation analysis with the
reactor. Standard gamma ray sources were used to determine the efficiency curves in the
energy range of 59.5-2240.1 keV and a semi-empirical approach was used to extend the
efficiency data from 2204.1 keV to 4000 keV. The semi-empirical method has been found
to be reasonably accurate within experimental uncertainties.
The neutron spectrum parameters (i.e. the thermal-to-epithermal flux ratio, f, and
the epithermal flux shape factor, α) for one inner and one outer (A1 and A2) irradiation
channels of NIRR-1, required (or needed) for the extension of its applicability to k0-NAA,
were determined using the “Cd-ratio for multi-monitor method”. For the general
applicability of the k0-NAA to deal with “non-1/v” (n, γ) reactions, the modified spectral
index, r(α)√(Tn/T0), and Westcott’s g(Tn) factor for monitoring neutron temperature Tn
were also determined for the two irradiation channels. Neutron spectrum parameters
determined in the inner channel A1, are: α = -0.046 ± 0.005; f = 18.4 ± 0.34 ; r(α)√(Tn/T0) =
0.04878 ; Tn = 38.810(Holden) and g(Tn) = 11.30, 1.883. For the outer channel A2, the
values are: α = +0.024 ± 0.002;
f = 49.5 ± 0.96; r(α)√(Tn/T0) = 0.01786 ; Tn = 30.220(Holden) and g(Tn) = 13.89, 1.821.
The results are in good agreement with reported values from other reactor facilities with
similar core configuration.
The thermal radiative capture cross sections, σ0 and k0-factors for ten (n,γ) reactions
i.e. 197Au (n, γ) 198Au; 94Zr (n, γ) 95Zr ; 96Zr (n, γ) 97Zr ; 238U (n, γ) 239U ; 55Mn (n, γ) 56Mn ;
109
Ag (n, γ) 110mAg ; 48Ca (n, γ) 49Ca ; 71Ga (n, γ) 72Ga ; 74Se (n, γ) 75Se and 75As (n, γ) 76As
have been reevaluated and the results compare well with evaluated data from libraries and
Mughabghab, (2003). This work has been undertaken as part of an IAEA Coordinated
Research Project No.13728 entitled “Reference Database for NAA”.
Description
A DISSERTATION
SUBMITTED TO THE POST GRADUATE SCHOOL,
AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE AWARD OF
DOCTOR OF PHILOSOPHY DEGREE (PhD) IN PHYSICS.
DEPARTMENT OF PHYSICS,
AHMADU BELLO UNIVERSITY, ZARIA
JUNE, 2007
Keywords
DETERMINATION,, NEUTRON,, INDUCED,, ACTIVATION,, CROSS,, SECTIONS,, NIRR-1,