Neutron self-shielding – Uma curva universal (II)

1. Este registo (para memória futura) é a continuação (e conclusão) da seguinte entrada anterior: http://tempoderecordar-edmartinho.blogspot.com/2012/02/autoproteccao-neutronica-neutron-self.html, entrada que era referente ao factor de perturbação do fluxo de neutrões de ressonância, G_res, e ao artigo: [1] 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 (2003) p.371. De salientar que, no seguimento deste trabalho, produzimos um outro em que se procedeu à extensão da curva universal a amostras com geometria cilíndrica: [2] I.F. Gonçalves, E. Martinho & J. Salgado, Extension of universal curve of resonance neutron self-shielding factors to cylindrical samples. Nuclear Instruments and Methods in Physics Research B 213 (2004) p.186.

2. Na entrada acima referida, dizia-se que, para interpretar adequada­mente os resultados da irradiação de uma amostra num reactor nuclear, é imprescindível conhecer não só G_res, mas também o factor de perturbação do fluxo de neutrões térmicos, G_th.  

O êxito da curva universal para o factor G_res levou-nos a supor que o mesmo poderia acontecer com o factor G_th, embora com outra variável adimensional. Efectuados os cálculos de G_th para 17 materiais distintos, com propriedades nucleares bem diferenciadas, e comparando os resultados obtidos com valores de G_th experimentais e teóricos encontrados na literatura, concluiu-se que a suposição tinha fundamento. O trabalho efectuado foi publicado no seguinte artigo: [3] 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, Vol. 261 – Issue 3 (2004) pp. 637-643.

Curva universal de G_th versus valores experimentais e teóricos

(F – folha; W – fio; E – experimental; T – calculado).

3. Segundo o Science Citation Index (ISI-WoK), o trabalho [3] foi citado até hoje nos seguintes artigos:

Title: Determination of self-shielding factors and gamma attenuation effects for tree ring samples

Author(s): Dagistan Sahin, Kenan Ünlü

The Pennsylvania State University, Radiation Science and Engineering Center, USA

Source: JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY  Volume: 291   Issue: 2   Pages: 549-553   Published: 2012

Title: Measurements of k(0) and Q(0) values for (64)Zn(n,gamma)(65)Zn and (68)Zn(n,gamma)(69m)Zn reactions with covariance analysis
M.S. Dias, V.Cardoso, M.F.Koskinas, I.M.Yamazaki, R.Semmler, M.Moralles, G.S.Zahn, F.A.Genezini, M.O. de Menezes, A.M.G.Figueiredo

Instituto de Pesquisas Energéticas e Nucleares, Centro do Reator de Pesquisas, São Paulo, Brazil

Source: APPLIED RADIATION AND ISOTOPES  Volume: 69   Issue: 7   Pages: 960-964    Published: 2011

Title: Evaluation of uncertainties for neutron activation analysis measurements using the comparator method of standardization
Author(s): Robert R. Greenberg, Richard M. Lindstrom, Elizabeth A. Mackey, Rolf Zeisler

National Institute of Standards and Technology, Analytical Chemistry Division, Gaithersburg, USA
Source: SPECTROCHIMICA ACTA PART B-ATOMIC SPECTROSCOPY  Volume: 66   Issue: 3-4   Pages: 208-232   Published: 2011

Title: Neutron self-shielding with k(0)-NAA irradiations
Author(s): Chilian C.; Chambon R.; Kennedy G.

Ecole Polytechnique, Montreal, Canada
Source: NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT  Volume: 622   Issue: 2   Special Issue: SI   Pages: 429-432   Published: 2010

Title: Distribution of spatial photoneutrons inside a 70 kg water phantom via neutron activation analysis
Author(s): Mu-Tai Liu ^a, Sing-ShengHuang ^a, Wen-ShanLiu ^b, Da-MingYea ^c,d Lung-Kwang Pan ^d, Chien-YiChen ^c,e

^a Department of Radiation Oncology, Changhua Christian Hospital, Taiwan, Republic of China

^b Department of Radiation Oncology, Chun Shan Medical University Hospital, Taiwan, Republic of China

^c Department of Medical Imaging, Chun Shan Medical University Hospital, Taiwan, Republic of China

^d Department of Medical Imaging and Radiological Sciences, Central Taiwan University of Science and Technology, Taiwan, Republic of China

^e School of Medical Imaging and Radiological Sciences, Chung Shan Medical University, Taiwan, Republic of China
Source: APPLIED RADIATION AND ISOTOPES  Volume: 68   Issue: 9   Pages: 1816-1821   Published:  2010

Title: Determination of the neutron spectrum shape parameter alpha in k(0) NAA methodology using covariance analysis
Author(s): Mauro S. Dias , Vanderlei Cardoso, Marina F. Koskinas, Ione M. Yamazaki

Instituto de Pesquisas Energéticas e Nucleares (IPEN-CNEN/SP), Centro do Reator de Pesquisas - São Paulo, Brazil
Source: APPLIED RADIATION AND ISOTOPES  Volume: 68   Issue: 4-5   Pages: 592-595   Published: 2010

Title: Development and implementation of k(0)-INAA standardization at 10 MW Pakistan research reactor-1
Author(s): Wasim M.; Arif M.; Zaidi J. H.; Anwar, Y.

Pakistan Institute of Nuclear Science and Technology, Division of Chemistry, Islamabad, Pakistan
Source: RADIOCHIMICA ACTA  Volume: 97   Issue: 11   Pages: 651-655   Published: 2009

Title: Complete thermal and epithermal neutron self-shielding corrections for NAA using a spreadsheet
Author(s): Chilian C.; St-Pierre J.; Kennedy G.

Ecole Polytechnique, Downtown, Montreal, Canada
Source: JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY  Volume: 278   Issue: 3   Pages: 745-749   Published: 2008

Title: Production of medical radioactive isotopes using KIPT electron driven subcritical facility
Author(s): Talamo Alberto; Gohar Yousry

Nuclear Engineering Division, Argonne National Laboratory, Argonne, USA

Source: APPLIED RADIATION AND ISOTOPES  Volume: 66   Issue: 5   Pages: 577-586   Published: 2008

Title: Monte Carlo optimization of sample dimensions of an Am-241-Be source-based PGNAA setup for water rejects analysis
Author(s): Z. Idiri ^a, H. Mazrou ^a, S. Beddek ^a, A. Amokrane ^b, A. Azbouche ^a

^a Centre de Recherche Nucléaire d’Alger, Alger, Algérie

^b Faculté de Physique, Université des Sciences et de la Technologie Houari-Boumediene, Alger, Algérie

Source: NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT  Volume: 578   Issue: 1   Pages: 279-288    Published: 2007

Title: Standardization problems in INAA of large organic samples
Author(s): R. Gwozdz ^a, F. Grass ^b

^a Trace Chemistry, Copenhagen, Denmark

^b Atominstitut of the Austrian Universities, Vienna, Austria

Source: CZECHOSLOVAK JOURNAL OF PHYSICS  Volume: 56   Pages: D229-D240   Published: 2006

4. Uma pesquisa efectuada na internet conduziu às seguintes citações do artigo [3]:

Chih-Hao Chang

The measurement of neutron fluence rate for Tsing-Hua Open-pool Reactor boron neutron capture therapy beam.

Dissertation, National Tsing-Hua University, Taiwan, 2006

http://nthur.lib.nthu.edu.tw/handle/987654321/28718

N.J.J. Peters

Monte Carlo neutronic simulations for a new approach to parametric INAA and MO-99 production feasibility at MURR.

PhD Thesis, University of Missouri-Columbia, USA, 2009

https://mospace.umsystem.edu/xmlui/bitstream/handle/10355/9663/research.pdf?sequence=3

5. O conjunto de resultados obtidos no projecto Neutron Self-Shielding encontra-se sintetizado nos seguintes documentos:

http://edmartinho.files.wordpress.com/2010/08/universal-curve-of-gres-formulae1.pdf

http://edmartinho.files.wordpress.com/2010/08/universal-curve-of-gth-formulae5.pdf

http://edmartinho.files.wordpress.com/2010/08/universal-curves-of-gres-and-gth.pdf

6. Finalmente, é de notar que em 2010 uma equipa canadiana da Escola Politécnica de Montreal caracterizou o trabalho efectuado no Laboratório Nuclear de Sacavém como segue:

(…) The thermal and epithermal self-shielding factors, G_th and G_ep [equivalente a G_res], are very close to unity for most activation reactions in most samples and can be ignored. However, the self-shielding effect is important for elements with high thermal neutron absorption cross-sections or high resonance neutron activation cross sections if these elements are present in high concentrations and for large samples. For most elements, epithermal neutron self-shielding is more significant than thermal neutron self-shielding. Historically, the calculation of G_th and G_ep 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. [1–3](…)

in C. Chilian, R. Chambon, G. Kennedy, Neutron self-shielding with k₀-NAA irradiations. Nuclear Instruments and Methods in Physics Research Section A 622 (2) (2010) p.429.