荷重結合容量方式多線陽極比例計数管における増幅器雑音の影響
スポンサーリンク
概要
- 論文の詳細を見る
<I>This paper describes a theoretical analysis of the influence of amplifier noise on the energy resolution and spatial resolution of a multi-wire proportional chamber using "weighted coupling capacitor method" in position signal read-out. The weighted coupling capacitor method is a kind of the pulse dividing methods: each anode wire (or cathode strip) is coupled to two charge-sensitive amplifiers through two capacitors, the capacities of which are weighted linearly to the position coordinate of the wire.</I><BR><I>The analysis shows that the fluctuation of the position signal due to the amplifier noise is proportional to the fluctuation of energy signal. If we assume that only the i-th anode wire delivers a charge, the fluctuation of position signal expressed in terms of standard deviation, σX<SUB>A</SUB>, is given by:<BR>σX<SUB>A</SUB>/L<SUB>X</SUB>=√i<SUP>2</SUP>- (n+l) i+ (n+1) <SUP>2</SUP>/2/ (n+1) ⋅σE<SUB>A</SUB>/E (1)<BR>where Lx is the effective length of the chamber, E the energy imparted by radiation, σE<SUB>A</SUB> the fluctuation (standard deviation) of E, and n the total number of the anode wires.</I><BR><I>If we assume that the equivalent noise charge (rms-value) of the charge-sensitive amplifiers at the input is expressed approximately by A+B⋅C<SUB>ext</SUB>., where A and B are the characteristic constants of the amplifier and C<SUB>ext</SUB>. the capacity existing at the input, the fluctuation of energy signal, σE<SUB>A</SUB>, is given by:<BR>σE<SUB>A</SUB> =√2W/M⋅ [A⋅C<SUB>x</SUB>+C<SUB>d</SUB>/C<SUB>x</SUB>+B⋅ (1+ 1/n+1) ⋅n⋅C<SUB>x</SUB>/6+n⋅Cd/2 +λ⋅C<SUB>a</SUB>/n+1] (2)<BR>where W is the W-value of the counting gas, M the gas multiplication factor, C<SUB>x</SUB> the sum of capacities of the two coupling capacitors connected between an anode wire to the amplifiers (C<SUB>x</SUB> is constant for all the anode wires), C<SUB>d</SUB> the stray capacity between an anode wire and the cathodes, C<SUB>a</SUB> the stray capacity between two adjacent wires, and λ a constant near unity.</I><BR><I>It can be seen, from Eq. (1), that the degradation of spatial resolution due to amplifier noise depends on the position of radiation incidnece and is minimal at the center of the chamber and maximal at both the end of it. It is also seen, from Eq. (2), that the effect of C<SUB>a</SUB> is usually neglected when n>>1. It is important to note that C<SUB>x</SUB> has an optimal value with which σE<SUB>A</SUB> and σX<SUB>A</SUB> are minimized. The optimal value of C<SUB>x</SUB>, obtained from d (σE<SUB>A</SUB>) /dC<SUB>x</SUB>=0, is equal to [6A⋅Cd⋅ (n+1) / (n+2) ⋅n⋅B] <SUP>1/2</SUP></I>.
- 社団法人 日本アイソトープ協会の論文
社団法人 日本アイソトープ協会 | 論文
- Distortion of Pulse Height Spectra Due to Absorbers in the Measurement of Low-energy .BETA.-rays with a Silicon Detector.
- タイトル無し
- Estimation of Angular Distributions of the Low-Energy .BETA.-Ray Emission from a Sealed Source.
- Comparison of SPECT images with four kinds of 99nTc collimators.
- Cross Talks on to 201Tl- and 123I-Photopeak Windows with Simultaneous Administration of Them, Using of a Gamma Camera.