Performace of Gas Electrom Multiplier (GEM) As a neutron detector

=Abstract=

I propose to construct and measure the performance of a fission chamber instrumented with preamplifiers known as a  Gas Electron Multiplier (GEM). This fission chamber is a chamber filled with a 90/10 Ar/$$CO_2$$  gas mixture enclosing a fissionable target material, like Uranium or Thorium. A neutron of sufficient energy has the potential to interact with fissionable material producing heavy ions known as fission fragments. The fission fragments within 5 micron of the target's surface may escape the target as ions and ionize the gas in the chamber. Electrons freed from the ionization gas can enter the GEM preamplifier producing secondary electrons which are directed to collectors using strong electric fields.

Gas Electron Multiplier (GEM) invented by Fabio Sauli in 1997F. Sauli, et al, NIM A386, (1997) 531-534. The GEM preamplifier is a 50 micron sheet of kapton that is coated on each side with 5 micron of copper. The copper clad kapton is perforated with 50-100 micron diameter holes separated by 100-200 micron in a staggered array. Then, THGEM preamplifier is designed as a macroscopic version of GEM that uses a perforated fiberglass board (PC board) clad with a conducting material. A thick fiberglass sheet, that may have up to 10mm thickness, is perforated with holes with a diameter of  2 mm.

Strong electric fields are established by supplying a potential difference between the two sides of the kapton, or the fiberglass for the case of the THGEM. The electric field lines transport liberated electrons through the preamplifier holes. For the GEM foils, the smaller diameter of the hole can provide sufficient amplification using a potential difference of 350 V between the two sides. On the other hand, the THGEM with the larger hole diameter requires a higher potential difference of about 2000 Volts to achieve similar amplifications.

The objective of this work is to construct a GEM based ionization chamber. The GEM will follow a proven design (change the reference)G. Agocs, B. Clark, P. Martinego, R. Oliveira, V. Peskov,gand P. Picchi,JINST, 3, P020112, 2008 and use a resistive paste to reduce discharge events. The detector will be made sensitive to neutrons by doping the resistive paste with a fissionable material. The doping step will take place once a working GEM equipped detector has been demonstrated. This fission chamber-like device will have the advantage of measuring the location of the incident neutrons that induced a fission event within the chamber by measuring the ionization signal using a segmented charge collector.

Motivation
Fast neutron detectors have many applications in different disciplines of nuclear technology. Fast neutron detectors are used for Homeland security applications, such as neutron imaging for the large size cargo containers, high penetrating neutrons are desirable when efficient fast neutron detectors are available. They are also used for real time measurements of fast neutron beam flux which are used in nuclear reactors such as the Advanced Test Reactor (ATR). The goal of this research is to economically build and test the performance gaseous electron multipliers preamplifiers, as they are installed in detector's chamber that has a coated layer of fissionable material such as U-233.

=Theory=

Gaseous Medium Physical Concepts

Induced Neutron Fission Fragment

=References=