Variation of Flux and Energy of 14 Mev Neutrons With Variation of Matrix Around A Sample

Ranjita Mandal^1,2*, Anita Thanekar², G. R. Pansare^{2, 3}, V. N. Bhoraskar² and D. Sengupta¹

¹Department of Geology and Geophysics, I.I.T., Kharagpur - 721 302, India. 

²Department of Physics, University of Poona, Pune - 411 002, India.

³H.V. Desai College, Pune - 411 002, India.

DOI : http://dx.doi.org/10.13005/msri/080223

ABSTRACT:

Here a method has been described to study the attenuation of flux and energy of the neutrons passing through different materials. Variation of activity of the irradiated and activated sample by 14 MeV neutrons was observed by changing the matrix around it. The sample was a combination of Aluminium foil and copper powder placed at 0o position (position of maximum flux) and the matrices were Air, Water, Iron, sand and carbon powder.

KEYWORDS: Matrix; Cross-section; 14 MeV neutrons; Activation method; Neutron flux; Neutron energy

Copy the following to cite this article: Mandal R, Thanekar A, Pansare G. R, Bhoraskar V. N, Sengupta D. Variation of Flux and Energy of 14 Mev Neutrons With Variation of Matrix Around A Sample. Mat.Sci.Res.India;8(2)

Copy the following to cite this URL: Mandal R, Thanekar A, Pansare G. R, Bhoraskar V. N, Sengupta D. Variation of Flux and Energy of 14 Mev Neutrons With Variation of Matrix Around A Sample. Mat.Sci.Res.India;8(2). Available from: http://www.materialsciencejournal.org/?p=2686

Introduction

The 14 MeV neutron generator¹ used for the present work generates neutrons of energy 14.77 MeV and has a flux of 10⁸ n/cm²/sec. When a sample is irradiated then the induced activity ² in the sample is

A=N σ F

Where A, N, σ and F denote activity induced in the irradiated sample, the neutron flux, cross-section of the reaction through which activity is induced and flux of the neutrons respectively.

Now, if two samples 1 and 2 are irradiated simultaneously then the activity induced will be

A₁=N₁σ₁F  and  A₂=N₂σ₂F

F being same for both because of simultaneous irradiation. Taking the ratio of the two activities, we get 

A₁/A₂=Kσ₁/σ₂

Where K=N₁/N₂ is constant for constant weights of sample 1 and 2. A₁/A₂ is constant when σ₁/σ₂ is constant. And σ₁/σ₂ is constant when the energy of the incident neutrons is constant. As with the variation of energy both σ₁ and σ₂ vary, so does the ratio σ₁/σ₂. So knowing this ratio the value of the energy E can be found as σ₁/σ₂ has a constant value for a particular value of E. The actual neutron source is surrounded by an iron water cooling jacket. The results can help to understand the attenuation of the neutron energy and flux and corresponding corrections can be made in the cross-section values obtained from the neutron activation analysis method using these neutrons.

Material and Methods

For observing the variation of flux and energy of neutrons, experiment was done by irradiating two samples simultaneously and varying the matrix around it and noting the variation of activity.

The sample and matrix used along with the concerned data is given in Table 1 and 2.

Table 1: Samples used

Click on image to enlarge

 Table 2: Matrices used

Click on image to enlarge

The excitation curves^{3, 4} are shown in figures 1 and 2. The samples taken together, Copper in powder form and Aluminium as foil within a polythene bag were irradiated with different matrices around it one by one. The time of irradiation, cooling and counting were 10, 2 and 10 minutes respectively. These two samples were taken because of the following reasons:

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