Archive for March, 2010

09 Universal curve of Gth

March 31, 2010

09 2004 Universal curve of thermal neutron self-shielding factors (foils, wires, spheres, cylinders)

The interpretation of the sample activation in a nuclear reactor requires the knowledge of two corrective parameters: the thermal neutron self-shielding factor, Gth, and the resonance neutron self-shielding factor, Gres. The authors established a universal curve of Gres for isolated resonances and various geometries. The present paper deals with the description of Gth in foils, wires, spheres and cylinders by means of a universal curve on the basis of a dimensionless variable which includes the physical, nuclear and geometrical properties of the sample. The universal curve is in good agreement with the experimental and calculated values obtained from the literature.

08 Thermal neutron self-shielding factors

March 31, 2010

08 2003 Thermal neutron self-shielding factors in foils – A universal curve

The presence of a sample in the neutron field of a nuclear reactor creates a perturbation of the local neutron fluxes. In general, the interpretation of the sample activation due to thermal and epithermal neutrons requires the knowledge of two parameters: the thermal neutron self-shielding factor, Gth, and the resonance neutron self-shielding factor, Gres. In recent works, the authors established an universal curve of Gres for isolated resonances and various geometries. The present paper deals with the description of Gth in foils by means of an universal curve on the basis of a dimensionless variable which includes the physical, nuclear and geometrical properties of the sample. The universal curve is in very good agreement with experimental and calculated values obtained from the literature. The study of other geometries (spheres, wires and cylinders) is in progress.

07 Resonance neutron self-shielding factors

March 31, 2010

07 2004 Resonance neutron self-shielding factors in foils for collimated beams

An epithermal neutron self-shielding factor must be introduced to take into account the absorption of a neutron beam crossing a sample. This factor depends on the geometry and dimension of the sample, as well as on the physical and nuclear properties of the nuclides. On the basis of a dimensionless variable, which includes the relevant characteristics of the sample, universal curves for monoenergetic and 1/E collimated neutron beams are proposed, which enable the determination of the self-shielding factor for isolated resonances of high absorber nuclides.

06 Resonance neutron self-shielding factors

March 31, 2010

06 2004 Calculation of neutron self-shielding factors of a group of resonances

The resonance neutron self-shielding factor, Gres, is required in neutron metrology and activation data analysis. In a previous paper, the authors have shown that a dimensionless variable can be introduced which converts the dependence of Gres on the physical and nuclear properties of the material samples into an universal curve, valid for the isolated resonances of any nuclide. This work presents a methodology based on the universal curve, which enables to calculate Gres for a group of isolated resonances by weighting its individual contributions. A good agreement was reached with results calculated by the MCNP code and with experimental values for Mo foils and wires.

05 Universal curve of Gres (cylinders)

March 29, 2010

05 2004 Extension of universal curve of resonance neutron self-shielding factors to cylindrical samples

Resonance neutron self-shielding factors for cylindrical samples of nuclides used as activation detectors or as targets for radionuclide production have been calculated using the MCNP code. These factors depend on the sample dimensions, as well as on the physical and nuclear properties of the nuclides. However, defining a dimensionless variable, which includes the relevant characteristics of the samples, it is possible to extend to cylinders a previously deduced universal curve for isolated resonances of any nuclide and samples of other geometries (foils, wires and spheres).

04 Universal curve of Gres (foils, wires, spheres)

March 29, 2010

04 2003 Universal curve of resonance neutron self-shielding factors (foils, wires, spheres)

The presence of a nuclide sample in an epithermal neutron field of a nuclear reactor creates a perturbation of the local neutron flux. This effect can be very important, especially if the nuclide cross-section exhibits a prominent resonance peak. To take into account the effect of the neutron flux perturbation in the sample activation, a resonance neutron self-shielding factor (Gres) must be considered. This factor depends on the geometry and dimension of the sample, as well as on the physical and nuclear properties of the nuclide. On the basis of a dimensionless variable which includes the relevant characteristics of the sample, an universal curve is proposed, which enables the determination of the factor Gres for isolated resonances of any nuclide and samples of various geometries (foils, wires and spheres). The proposed universal curve is in very good agreement with experimental and calculated values obtained from the literature.

03 Resonance neutron self-shielding factors

March 29, 2010

03 2002 Calculation of resonance neutron self-shielding factors in foils

Epithermal neutron resonance self-shielding factors in foils of materials used as activation detectors or as targets for radionuclide production have been calculated using the MCNP code. Two irradiation conditions have been considered: (a) foils immersed into an isotropic neutron flux and (b) foils submitted to a collimated neutron beam. The self-shielding factors, Gres, for gold, indium, manganese and cobalt have been compared with available published values. The self-shielding factor depends on various physical and nuclear parameters. However, it is shown that for the isotropic case and for high absorber elements submitted to a collimated beam, a dimensionless variable could be adopted that describes the self-shielding factors of different materials by quasi ‘‘universal curves’’. Gres for the collimated beam are always higher than those for the isotropic case.

02 Resonance neutron self-shielding factors

March 29, 2010

02 2001 Calculation of resonance neutron self-shielding factors in wires

Epithermal neutron resonance self-shielding factors in wires of materials used as activation detectors or as targets for radionuclide production have been calculated using the MCNP code. The energy dependent self-shielding factor depends on the ratio scattering/capture cross sections. The self-shielding factors for cobalt and gold have been compared with available values. The self-shielding factor depends on various physical and nuclear parameters. However, an adimensional variable can be adopted that describes the self-shielding factors of different materials by a quasi ‘‘universal curve’’.

01 Resonance neutron self-shielding factors

March 29, 2010

01 2001 Calculation of resonance neutron self-shielding factors

In this work, the resonance self-shielding factor is calculated by means of the Monte Carlo technique for different materials (Au, Co, Mn), geometries (circular foils and wires) and incidence of neutrons (isotropic field and collimated beam). The results are compared with the values obtained by other authors.

Introduction

March 28, 2010

The main objective of this website is to make available scientific articles written by  Eduardo J. C. Martinho, José F. Salgado and Isabel Maria F. Gonçalves, from the Instituto Tecnológico e Nuclear, Sacavém, Portugal.

The research, published between 2001 and 2004, was about a relevant phenomenon in reactor and neutron physics called neutron self-shielding, which comprises resonance neutron self-shielding (Gres) and thermal neutron self-shielding (Gth). The practical importance of our work resides in the final conclusion that the phenomenon can be quantified by a universal law of Gres and Gth for foils, wires, spheres and cylinders.

BLOG Gráfico 03 Neutron flux profile resulting from the self-shielding effect in a sample

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The innovation of our final results has been summarized by a Canadian team* as follows:

«(…) Historically, the calculation of Gth and Gep [or Gres] was extremely difficult, and it was recommen­ded to dilute the samples to avoid self-shielding. Fortunately, reactor physicists recently showed that the amount of epithermal as well as thermal self-shielding could be expressed by the same analytical function, a sigmoid, for all nuclides [2–4]**. (…)»

* C. Chilian, R. Chambon, G. Kennedy: Neutron self-shielding with k0NAA irradiations. Nuclear Instruments and Methods in Physics Research A 622 (2) (2010) 429-432].

** CITED REFERENCES:

[2] E. Martinho, I.F. Gonçalves, J. Salgado, Universal curve of epithermal neutron resonance self-shielding factors in foils, wires and spheres. Applied Radiation and Isotopes 58(3) (2003) 371-375;

[3] I.F. Gonçalves, E. Martinho, J. Salgado, Extension to cylindrical samples of the universal curve of resonance neutron self-shielding factors. Nuclear Instruments and Methods in Physics Research B 213 (2004) 186-188;

[4] E. Martinho, J. Salgado, I.F. Gonçalves, Universal curve of thermal neutron self-shielding factors in foils, wires, spheres and cylinders. Journal of Radioanalytical and Nuclear Chemistry 261 (3) (2004) 637-643.

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Scientists from several countries [Algeria, Argentina, Australia, Austria, Bangladesh, Belgium, Brazil, Bulgaria, Canada, Chile, China, Cuba, Denmark, Egypt, France, Germany, Greece, Hungary, India, Indonesia, Iran, Italy, Japan, Kazakhstan, Malaysia, Mexico, Pakistan, Peru, Portugal, Romania, Slovenia, South Korea, Switzerland, Taiwan, The Netherlands, Turkey, United Kingdom, United States of America, Uzbekistan and Vietnam] and international institutions [Joint Research Centre/EU (Geel, Petten, Ispra) and International Atomic Energy Agency (Vienna)] are using our results in works related to various­ domains, namely reactor neutron metrology, determination of nuclear parameters (thermal neutron cross-sections and resonance integrals), neutron activation analysis, production of radioisotopes for medical applications.

CITATIONS: http://tempoderecordar-edmartinho.blogspot.pt/2015/11/neutron-self-shielding-citations.html

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CONTENTS:

https://edmartinho.files.wordpress.com/2010/03/01-2001-calculation-of-resonance-neutron-self-shielding-factors3.pdf

https://edmartinho.files.wordpress.com/2010/03/02-2001-calculation-of-resonance-neutron-self-shielding-factors-in-wires1.pdf

https://edmartinho.files.wordpress.com/2010/03/03-2002-calculation-of-resonance-neutron-self-shielding-factors-in-foils1.pdf

https://edmartinho.files.wordpress.com/2010/03/04-2003universal-curve-of-resonance-neutron-self-shielding-factors-foils-wires-spheres.pdf

https://edmartinho.files.wordpress.com/2010/03/05-2004-extension-of-universal-curve-of-resonance-neutron-self-shielding-factors-to-cylindrical-samples.pdf

https://edmartinho.files.wordpress.com/2010/03/06-2004-calculation-of-neutron-self-shielding-factors-of-a-group-of-resonances.pdf

https://edmartinho.files.wordpress.com/2010/03/07-2004-resonance-neutron-self-shielding-factors-in-foils-for-collimated-beams.pdf

https://edmartinho.files.wordpress.com/2010/03/08-2003-thermal-neutron-self-shielding-factors-in-foils-a-universal-curve.pdf

https://edmartinho.files.wordpress.com/2010/03/09-2004-universal-curve-of-thermal-neutron-self-shielding-factors-foils-wires-spheres-cylinders.pdf

https://edmartinho.files.wordpress.com/2010/04/10-2004-development-of-a-unique-curve-for-gth-in-spherical-scattering-materials.pdf

https://edmartinho.wordpress.com/2010/04/09/comparison-of-the-universal-curve-uc-with-published-results-3/

https://edmartinho.files.wordpress.com/2010/04/2004-gf-uma-inesperada-curva-universal.pdf (in portuguese)

https://edmartinho.wordpress.com/2010/08/29/universal-curves-of-gres-and-gth/

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edmartinho@gmail.com