A coincidence method of measuring a flux of fast neutrons

1948 ◽  
Vol 44 (1) ◽  
pp. 96-113 ◽  
Author(s):  
B. B. Kinsey ◽  
S. G. Cohen ◽  
J. Dainty
Keyword(s):  
Cross Section ◽  
Ionization Chamber ◽  
Unit Area ◽  
Solid Angle ◽  
Fast Neutrons ◽  
Proton Scattering ◽  
Coincidence Method ◽  
Γ Rays ◽  
Thick Layers

A method is described in which the rate at which fast neutrons cross unit area is measured by counting protons projected into a small solid angle in the forwards direction from thin and thick layers of polythene. The protons are detected by triple coincidences between three proportional counters mounted coaxially behind the hydrogenous layers. The method is applicable to neutrons of energies from 1 MeV. upwards, and can be used in the presence of intense γ-rays. The flux of these neutrons is calculated in terms of the rate of detection of the protons, the solid angle for proton collection, the mass per unit area of the polythene layer, and the neutron-proton-scattering cross-section. A study of the behaviour of proportional co-axial counters, used in this manner, has been made. A determination of the angular distribution of fast neutrons produced by a deuteron-deuterium source has been made by our coincidence method, and the results compared with those obtained by the ionization chamber method by Bretscher and French. Absolute values agree to within 10%.

Determination of energy absorption in a mixed flux of fast neutrons and γ-rays by an ionization method

Atomic Energy ◽  
1961 ◽  
Vol 9 (2) ◽  
pp. 630-636
Author(s):  
Yu. I. Bregadze ◽  
B. M. Isaev ◽  
V. A. Kvasov
Keyword(s):  
Energy Absorption ◽  
Fast Neutrons ◽  
Ionization Method ◽  
Γ Rays

scholarly journals Scattering of slow neutrons

1937 ◽  
Vol 162 (908) ◽  
pp. 127-143 ◽  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Ionization Chamber ◽  
Percentage Increase ◽  
Quantitative Interpretation ◽  
Total Cross Sections ◽  
Paraffin Block ◽  
Γ Rays ◽  
Absorbing Elements ◽  
Slow Neutrons

The adsorption and scattering of slow neutrons have been studied by various methods. In their first survey, Amaldi, D'Agostino, Fermi, Pontecorvo, Rasetti and Segré (1935) investigated the absorption of slow neutrons by different elements inside a paraffin block. The number of slow neutrons capture in an indicator (e. g. silver). The values for the absorption coefficients which they obtained with this arrangement can be regarded as a measure of the ''true'' absorption of slow neutrons. Later, Dunning, Pegram, Fink and Mitchell (1935) measured the "total" cross-sections, i. e. the sum of the well-defined beam of slow neutrons, and a lithium-coated ionization chamber as indicator. Recently, Griffiths and Szilard (1937) have determined the cross-section of some strongly absorbing elements using the captured γ-rays from cadmium as indicator. The scattering of slow neutrons was studied for some elements by MItchell and Murphy (1935), Mitchell, Murphy and Whitaker (1936), Budnitzky and Kurtschatow (1935) Pontecorvo and Wick (1936), and others. In these experiments, the slow neutrons issuing from a paraffin block passed through an indicator (e. g. silver), and were scattered backwards from the substance under investigation. When thin scattered are used, the percentage increase of the radioactivity produced in the indicator gives a measure of the scattering cross-section. This method has the disadvantage, even in the case of good scatters, that the increase in the radioactivity of the indicator is usually small compared with the effect due to the primary neutrons. A quantitative interpretation of the results may be further complicated by the fact that the neutrons leave the surface of the paraffin block at angles from 0 to 90°. Also, multiple scattering is not avoided.

scholarly journals Resonance phenomena in the interaction of fast neutrons with beryllium and aluminium

1947 ◽  
Vol 192 (1028) ◽  
pp. 114-127 ◽  
Keyword(s):  
Energy Level ◽  
Cross Section ◽  
Neutron Energy ◽  
Cross Sections ◽  
Accurate Determination ◽  
Fast Neutrons ◽  
Transmission Method ◽  
The Cross ◽  
Scattering Cross Sections

The total scattering cross-sections of beryllium and aluminium have been measured by a transmission method for neutrons of energies between 0∙35 and 0∙55 MeV and 1∙8 and 4∙0 MeV. Resonances have been found in the scattering by beryllium at a neutron energy of 2∙6 MeV and in the scattering by aluminium at neutron energies of 2∙4 and 2∙9 MeV. It has been shown that the cross-section for the reaction 9 Be ( n , α ) 6 He also has a resonance at 2∙6 MeV, and an accurate determination of the cross-section for this reaction has been made. A discussion is given of the properties of the energy level in 10 Be responsible for the resonances in the case of beryllium.

scholarly journals The angular distribution of protons projected by fast neutrons

1937 ◽  
Vol 163 (913) ◽  
pp. 265-281 ◽  
Keyword(s):  
Angular Distribution ◽  
Binding Energy ◽  
Cross Section ◽  
Direct Evidence ◽  
Fast Neutrons ◽  
Proton Scattering ◽  
Potential Well ◽  
The Mean ◽  
The Cross ◽  
Square Hole

The nature of the interaction between neutron and proton has assumed great importance in modern nuclear theory, since it is now generally assumed that these two particles form the fundamental constituents of all nuclei. Little direct evidence exists, however, as to the nature of this interaction. The stable existence of the deuteron shows that the force between neutron and proton is attractive, and for purposes of calculation a “square hole” potential well has generally been assumed. With this model some success has been obtained* in correlating the magnitudes of a number of experimentally measurable quantities such as ( a ) the binding energy of the deuteron, ( b ) the total cross-section for neutron-proton scattering (Tuve and Hafstad 1936; Amaldi and Fermi 1936 a ), ( c ) the cross-section for photo­ electric disintegration of the deuteron (Chadwick and Goldhaber 1935), and ( d ) the cross-section for capture of neutrons by protons (Amaldi and Fermi 1936 b ). The interaction is not completely derivable from the above data, since the values of these quantities depend mainly upon r 2 V , where r is the mean radius and V is the depth of the potential hole.

Determination of ionization cross section by electron spectroscopic imaging

1988 ◽  
Vol 46 ◽  
pp. 536-537
Author(s):  
G.T. Simon ◽  
Y.M. Heng ◽  
F.P. Ottensmeyer
Keyword(s):  
Energy Loss ◽  
Cross Section ◽  
Ionization Cross Section ◽  
Unit Area ◽  
Core Loss ◽  
Ionization Cross ◽  
Image Position ◽  
Electron Energy Loss ◽  
Ionization Edge

Electron energy loss spectroscopy (EELS) has become a significant technique for high resolution elemental microanalysis and mapping. Theoretically, quantitative analysis requires only one simple equation:Eqn.(1)where N is the number of atoms per unit area analysed; I(net)(a,δ) is the core loss intensity integrated over an energy range δ beyond the ionization edge and with a collection angle a; I(total) is the total intensity integrated beneath the whole spectrum; σ(a,δ) is the corresponding ionization cross section.To obtain I(net) according to current convention and some theoretical justification, the simplest way of removing the background beneath an ionization edge is simply fitting at least two pre-edge measurements to the equation of I=AE-r, where I is the intensity of electrons that have energy loss E; A and r are constants to be determined from the fitted pre-edge region. Several other methods have also been derived for better accuracy in specific applications.

scholarly journals 234U(n,f) cross section with the FIC detector at CERN (n TOF)

2020 ◽  
Vol 16 ◽  
pp. 175
Author(s):  
D. Karadimos ◽  
... Et al.
Keyword(s):  
Cross Section ◽  
Ionization Chamber ◽  
Reaction Cross Section ◽  
Fission Cross Section ◽  
Reaction Cross ◽  
Analog To Digital ◽  
Analysis Technique ◽  
Induced Fission ◽  
Line Analysis

The analysis technique applied to the data and the reaction cross section 234U(n,f) from the FIC (Fission Ionization Chamber) detector at the n TOF facility is pre- sented here. A comparison of the measured neutron induced fission cross section of 234U nucleus is given with the available data from the bibliography. The measure- ments took place at the installation of CERN in Geneva. The detector was placed in front of the neutron beam for the determination of the neutron induced fission cross section of various isotopes of the Th cycle. For the data acquisition, several flash Analog to Digital Converter (fADC) channels were used. This facilitated the detailed off-line analysis of data since all information was stored in the computer. The automation of the process was required because the high amount of stored data. The data analysis aimed at the discrimination of fission events. For this end we had to deal with three main issues: i) The subtraction of the background, ii) the fitting of the pulses and iii) the automation of the process.

scholarly journals Installation of NEOPTOLEMOS, the new sum spectrometer for cross section measurements of capture reactions at the ΤANDEM Accelerator Laboratory of NCSR “Demokritos”

2019 ◽  
Vol 24 ◽  
pp. 134
Author(s):  
V. Lagaki ◽  
V. Michalopoulou-Petropoulou ◽  
M. Axiotis ◽  
V. Foteinou ◽  
A. Lagoyannis ◽  
...  
Keyword(s):  
Cross Section ◽  
Large Volume ◽  
Solid Angle ◽  
Nuclear Astrophysics ◽  
Nuclear Level ◽  
Level Densities ◽  
Γ Rays ◽  
Integrated Cross Section ◽  
The University

Cross-section measurements of capture reactions are of key importance in understanding the contribution of the uncertainties of nuclear properties, such as the nucleon-nucleus potential and the nuclear level densities, entering in astrophysics abundance calculations. During the recent years, the Nuclear Astrophysics group of NCSR “Demokritos” has been conducting angle-integrated cross-section measurements using a large-volume NaI(Tl) detector installed at the Dynamitron Tandem Laboratory of the University of Bochum in Germany. Thanks to LIBRA funds a brand new cylindrically shaped NaI(Tl) detector, coined NEOPTOLEMOS, was acquired that is axially segmented in two, covering a solid angle of almost 4π for γ rays emitted at its center.

A quantitative approach to inner shell losses

1978 ◽  
Vol 36 (1) ◽  
pp. 526-527 ◽  
Author(s):  
R.D. Leapman ◽  
P. Rez ◽  
D.F. Mayers
Keyword(s):  
Energy Transfer ◽  
Cross Section ◽  
Cross Sections ◽  
Accurate Determination ◽  
Background Intensity ◽  
Core Excitation ◽  
Quantitative Basis ◽  
Cross Section Differential ◽  
Bound Electrons

Microanalysis by EELS has been developing rapidly and though the general form of the spectrum is now understood there is a need to put the technique on a more quantitative basis (1,2). Certain aspects important for microanalysis include: (i) accurate determination of the partial cross sections, σx(α,ΔE) for core excitation when scattering lies inside collection angle a and energy range ΔE above the edge, (ii) behavior of the background intensity due to excitation of less strongly bound electrons, necessary for extrapolation beneath the signal of interest, (iii) departures from the simple hydrogenic K-edge seen in L and M losses, effecting σx and complicating microanalysis. Such problems might be approached empirically but here we describe how computation can elucidate the spectrum shape.The inelastic cross section differential with respect to energy transfer E and momentum transfer q for electrons of energy E0 and velocity v can be written as

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