학술논문
Photoelectron Track Length Distributions Measured in a Negative Ion Time Projection Chamber
Document Type
Periodical
Author
Source
IEEE Transactions on Nuclear Science IEEE Trans. Nucl. Sci. Nuclear Science, IEEE Transactions on. 61(2):894-900 Apr, 2014
Subject
Language
ISSN
0018-9499
1558-1578
1558-1578
Abstract
We report photoelectron track length distributions between 3 and 8 keV in gas mixtures of ${\rm Ne} + {\rm CO}_2 + {\rm CH}_{3}{\rm NO}_2$ (260:80:10 Torr) and ${\rm CO}_2 + {\rm CH}_{3}{\rm NO}_2$ (197.5: 15 Torr). The measurements were made using a negative ion time projection chamber (NITPC) at the National Synchrotron Light Source (NSLS) at the Brookhaven National Laboratory (BNL). We report the first quantitative analysis of photoelectron track length distributions in a gas. The distribution of track lengths at a given energy is best fit by a lognormal distribution. A powerlaw distribution of the form, $f(E) = a(E/E_{o})^n$, is found to fit the relationship between mean track length and energy. We find $n = 1.29\pm 0.07$ for ${\rm Ne} + {\rm CO}_2 + {\rm CH}_{3}{\rm NO}_2$ and $n = 1.20\pm 0.09$ for ${\rm CO}_2 + {\rm CH}_{3}{\rm NO}_2$. Understanding the distribution of photoelectron track lengths in proportional counter gases is important for optimizing the pixel size and the dimensions of the active region in electron-drift time projection chambers (TPCs) and NITPC X-ray polarimeters.