Measurements of spatial variations in response of ionization chambers

2012 ◽  
Vol 20 (1) ◽  
pp. 160-165 ◽  
Author(s):  
William E. B. Miller ◽  
Alan L. Kastengren
Keyword(s):  
Space Charge ◽  
Spatial Variation ◽  
Bias Voltage ◽  
Ionization Chamber ◽  
Significant Variation ◽  
Ambient Air ◽  
Spatial Variations ◽  
Ionization Chambers ◽  
Charge Effects ◽  
X Ray

Measurements of the spatial variations in the response of three ionization chamber (IC) designs were tested as a function of chamber bias voltage, incident X-ray flux and fill gas. Two components of spatial variation are seen. When the ionization chambers are near saturation, spatial variations exist that are tied to the chamber geometry. While the response of some chambers is relatively flat, others show significant variation across the IC. These variations appear to be inherent in the response of each IC at saturation. When the chamber is far from saturation, large spatial variations in response are present when N2is used as a fill gas, but not when ambient air is used as a fill gas. These appear to be tied to space charge effects.

Partial volume characteristics of ionization chambers in kilovoltage x-ray exposure measurements

2011 ◽  
Vol 11 (3) ◽  
pp. 184-188
Author(s):  
Syed F. Akber ◽  
Than S. Kehwar
Keyword(s):  
Ionization Chamber ◽  
Incident Radiation ◽  
Ionization Chambers ◽  
X Ray ◽  
Partial Volume ◽  
Spatial Response ◽  
Beam Output ◽  
Volume Characteristics ◽  
Made In ◽  
Lead Sheet

AbstractThe partial volume (spatial) response of four ionization chambers (Keithley) in kilovoltage X-ray beams, generated by the Philips Super 80CP X-ray unit, was assessed. The volume of the ionization chambers were of 10 cm3, 15 cm3, 150 cm3, and 600 cm3 used with Keithley electrometer Model 35040. The beam output was measured using a monitor chamber (Radcal 6.0 cm3) placed close to the collimator. The source to chamber distance was kept constant at 1 m. For the measurement of the response of ionization chambers of 15 cm3, 150 cm3, and 600 cm3, a slit of 2.0 mm width was made in a lead sheet of 3.2 mm thick and size of 30 × 30 cm2 and was placed on the ionization chamber. The measurements were made for 81 kVp, 400 mA, and 0.25 s and the slit was moved at an increment of 2.0 mm over the entire length of the chamber. For the measurements of the ionization chamber of 10 cm3 (CT chamber), the beams of 120 kVp, 200 mA and 0.2 s were generated, and a slit of 5 mm width was made in a similar lead sheet that was moved at an increment of 5.0 mm. From the result it appears that the sensitive volumes of the ionization chambers affect the response of the ionization chamber to incident radiation.

scholarly journals The influence of x-ray pulse length on space-charge effects in optical pump/x-ray probe photoemission

2019 ◽  
Vol 21 (7) ◽  
pp. 073042 ◽  
Author(s):  
Danilo Kühn ◽  
Erika Giangrisostomi ◽  
Raphael M Jay ◽  
Florian Sorgenfrei ◽  
Alexander Föhlisch
Keyword(s):  
Space Charge ◽  
Pulse Length ◽  
Space Charge Effects ◽  
Optical Pump ◽  
Charge Effects ◽  
X Ray

Space charge effects in the axis-photonique PX-1 x-ray streak camera

2007 ◽  
Author(s):  
M. H. Edwards ◽  
N. Booth ◽  
Z. Zhai ◽  
G. J. Tallents ◽  
T. Dzelzainis ◽  
...  
Keyword(s):  
Space Charge ◽  
Streak Camera ◽  
Space Charge Effects ◽  
Charge Effects ◽  
X Ray

scholarly journals Photoemission from the gas phase using soft x-ray fs pulses: an investigation of the space-charge effects

2020 ◽  
Vol 22 (12) ◽  
pp. 123029
Author(s):  
Adriano Verna ◽  
Giovanni Stefani ◽  
Francesco Offi ◽  
Tatsuo Gejo ◽  
Yoshihito Tanaka ◽  
...  
Keyword(s):  
Space Charge ◽  
Gas Phase ◽  
Space Charge Effects ◽  
Charge Effects ◽  
X Ray

Ionization chambers for monitoring the position and tilt of X-ray beams

2000 ◽  
Vol 33 (3) ◽  
pp. 986-987
Author(s):  
U. W. Arndt ◽  
M. P. Kyte
Keyword(s):  
Ionization Chamber ◽  
Ionization Chambers ◽  
X Ray

An air-filled ionization chamber with a three-way split anode can be used to measure the tilt and the translation of a collimated X-ray beam with respect to the chamber axis.

scholarly journals Vacuum space charge effects in sub-picosecond soft X-ray photoemission on a molecular adsorbate layer

2015 ◽  
Vol 2 (2) ◽  
pp. 025101 ◽  
Author(s):  
M. Dell'Angela ◽  
T. Anniyev ◽  
M. Beye ◽  
R. Coffee ◽  
A. Föhlisch ◽  
...  
Keyword(s):  
Space Charge ◽  
Space Charge Effects ◽  
Charge Effects ◽  
X Ray ◽  
Adsorbate Layer ◽  
Vacuum Space

scholarly journals Evaluation of using radiographic films in measurements of penumbra width for radiotherapy applications and stereotactic radiosurgery

2018 ◽  
Vol 14 (1) ◽  
pp. 5204-5212
Author(s):  
Ehab A Hegazy
Keyword(s):  
Stereotactic Radiosurgery ◽  
Ionization Chamber ◽  
Field Size ◽  
Physical Parameters ◽  
Ionization Chambers ◽  
X Ray ◽  
Radiation Fields ◽  
Economic Method ◽  
Width Measurements ◽  
Penumbra Region

The accuracy of treatment field size in is a success key in cancer radiotherapy. As Increase in dose may lead to overdose side effects, and decrease in dose lead to subtherapeutic effect which increased incidence of tumor recurrence or incomplete recovery of patient. Many physical parameters should be measured very accurately in order to predict the dose distribution as physical penumbra of radiation fields. Ionization chamber is considered as slandered tools for measuring penumbra. Mega voltage x-ray energy penumbra is measured using ionization chamber due to its high accuracy in measuring absolute dose. This technique can produce the gold standard for penumbra measurements; however, it is a very time consuming and demanding process. Aim of this work is to evaluate the using radiographic films in penumbra width measurements for radiotherapy applications and stereotactic radiosurgery by comparing results obtained by standard ionization chambers to radiographic films as new tool for penumbral width measurements. Comparison between penumbra region measured by ionization chamber and o-xmat v Kodak radiographic films were carried out under the same physical and dosimeteric conditions. Penumbra width differences were found to be less than 1 mm for 6 mev, 15 mev photon beam and 6 mv, 15 mv electron beam used in radiotherapy. Measured differences were considered very small and has no effect on penumbra width measurements however o-xmat v Kodak films provide fast .easy and economic method for penumbra measurement used in radiotherapy dosimetery. 

Sign in / Sign up

Export Citation Format

Share Document