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The Determination of Saturation Currents in Free-air Ionization Chambers by Extrapolation Methods

Patricia B Scott and J R Greening

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The usual method of determining saturation currents in free-air chambers is to plot the reciprocal of the current, j, against the reciprocal of the collecting electric field, E, and extrapolate linearly to 1/E=0. It is shown that this method is valid only if the recombination taking place is initial recombination within ion clusters. Experimental and theoretical evidence is produced to show that in such chambers, at dose rates of 1 r/min or more, it is general (volume) rather than initial recombination which is taking place. Theory shows that under these circumstances one should plot 1/j against 1/E2, or more accurately against j/E2, and extrapolate to 1/E2 or j/E2=0.


PACS

87.56.Da Ancillary equipment

02.60.Ed Interpolation; curve fitting

Subjects

Computational physics

Medical physics

Dates

Issue 1 (April 1963)

Received 5 December 1962



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