Next generation Geiger-Müller counters with enhanced sensitivity to
gamma-rays
The Geiger-Müller (GM) counter is one of the oldest and simplest ionizing radiation detectors;
however, it still remains as a very frequently utilized radiation detector in many industrial
applications such as level and thickness gauging [1]. Recently, there has been an interest in
further extending the application areas of these detectors to include e.g. gamma-ray dual
modality densitometry (DMD) and industrial gamma-ray process tomography. The use of
cylindrical, small diameter GM counters in such applications has been and still is considered as
these are applications that do not require the use of energy sensitive detectors. Also, the
robustness of GM counters in harsh environments, their relatively low cost and the fact that
they require relatively simple read-out electronics [2] makes their use a very attractive option
in gamma-ray densitometry and tomography with commercial potential. However, a major
drawback that limits the use of GM counters in such applications is their relatively poor gammaray stopping efficiencies. It is a well-known fact that the intrinsic gamma-ray stopping
efficiency in these detectors is only about 1.0% for a wide range of photon energies.
Fig. 1. Cross sectional view of the ZP1200 GM counter picked for this work. All dimensions are given in mm
Previously, methods to enhance the intrinsic gamma-ray stopping efficiency in these detectors
have been investigated through a series of benchmarked Monte Carlo (MC) modeling efforts.
The detector considered in the previous work is a Centronic, ZP1200 type GM counter which
is shown in Fig. 1. In particular, a method based on the insertion of electrically insulating disk
structures (see Fig. 2.) between the cathode and the anode of the counter has been considered.
MC simulations predict a three-fold increase in the efficiency [3].
Fig. 2. On the left: The electric field lines in the ZP1200 counter as calculated by the COMSOL Multiphysics
simulation platform. On the right: The electric field intensities plotted as a function of the radial distance from the
anode wire; with and without a 10 μm thick hafnium oxide disk.
The main purpose of the current project is to benchmark the results of MC simulations whereby
a ZP1200 counter will be cut open and electrically insulating disks will be inserted inside the
counter. The counter will then be placed in a vacuum chamber, and the chamber will be filled
with appropriate fill gases (mixtures of noble gases and halogens) at pressures between 100 and
200 mbar. At this initial stage, the experiments will be performed using relatively thick (~ 0.5
mm) polyoxymethylene (POM) disks which are easier to machine in-house. However, during
the course of the project, measurements may be repeated using different fill gases, gas pressures
and disk materials. Primarily, the change in the response of the counter to gamma-rays will be
studied using a bare counter and as a function of the number of disks inserted. The results of
these experiments will then be compared with Monte Carlo predictions.
Specifically, the student is expected to perform the following tasks:
1. construction and verification of the vacuum system to be used in the experiments
2. production of the electrically insulating POM disks to be fitted inside the counter with
the help of project advisors
3. setting up a simple read-out circuitry adequate for GM counters
4. performing measurements with the modified counters using different fill gases and
different fill gas pressures to determine their characteristics at different conditions
5. analysis of the data collected in the experiments
6. developing simple Monte Carlo1 models of the experiments for benchmarking purposes
The results of this work will be of novel nature and thus may be published in scientific journals.
The project is to be carried out in collaboration with the Department of Electrical Engineering
at Bergen University College.
Through working with this project, the student will gain knowledge and experience in
nuclear/radiation physics instrumentation, ionization based radiation detectors, numerical
modeling of signal generation in such detectors as well as Monte Carlo simulations of radiation
transport.
Project advisors:
1. Georgi Genov ([email protected]), University of Bergen
2. Ilker Meric ([email protected]), Bergen University College
[1] G.A. Johansen, P. Jackson, Radioisotope Gauges for Industrial Process Measurements, John Wiley & Sons
Ltd, Wiltshire, UK, 2004.
[2] G.A. Johansen, O. Vagle, Ø. Olsen, M.B. Holstad, I. Meric, Geiger Müller detectors for gamma-ray
tomography, in: Proceedings of the Fifth International Symposium on Process Tomography, Poland, Zakopane,
2008.
[3] Meric I., Johansen G.A., Holstad M.B., Calderon A.F., Gardner R.P., 2012. Enhancement of the intrinsic
gamma-ray stopping efficiency of Geiger–Müller counters, Nuclear Instruments and Methods in Physics Research
A 696, p. 46.
1
The specific Monte Carlo package to be used will be decided upon the project start