NPL2611A Ion Chamber

The NPL2611A is a Secondary Standard Therapy Dosimetry Chamber produced by the National Physics Laboratory.

Construction of the NPL2611A chamber consists of a thin walled high purity graphite thimble, amber insulator and a hollow pure aluminum electrode and is supported by a thin walled aluminum stem. The stem terminates in a robust cable entry, by which the chamber can be mounted. A length of low noise triaxial cable connects to a TNC triaxial plug. Since the chamber is vented, air density corrections must be applied.

Please note: This chamber is manufactured at the National Physical Laboratory (NPL), in the UK, and support, both in terms of maintenance and calibration, are available from NPL directly.

Specification
Active Dimensions	Sensitive Volume—325mm³Length of volukme—9.22mm Thimble wall thickness– 0.5mm Diameter—7.35 mm
Exterior Dimensions	Length — 185mm Diameter — 12.5 mm
Materials	Thimble—high density (1.80b/cm³) high purity extruded graphite Collecting electrode – aluminium 99.99% pure Main insulator — amber stem insulators P.C.T.F.E. HV insulator – Delrin The chamber stem is guarded to a point 15mm from the measuring Volume
Reference Point	The effective measurement point for positioning the chamber should be taken to be the axis of the chamber 5mm from the tip of the graphite thimble
Venting	To ensure that the chamber is equilibrated with the atmosphere the measuring volume is vented giving pressure equilibration times for just a few seconds
Build up Cap	Delrin, with external diameter of 17.0 mm and wall thickness of 600mg/cm²
Cable	Suhner GO 233OHT connections Centre core—signal at HV Inner screen—guard at HV Outer screen—earth potential Length 10m