The physical basis of capturing the ionizing radiation’s energy:
Ionizing radiation is a broad term for all the particles and quants that are capable of knocking away electrons from shells of atoms an molecules. There are a few of classified ionizing corpuscules and quants like:
- α - alpha particle which is doubly ionized atom of helium
- β - beta particle that may be an electron β− or positron β+
- γ - gamma radiation consisting of quants that are high energy photons.
There are more particles that are capable of ionizing matter by various interactions: muons, neutrons, protons but for the early stage of the research I would like to focus on the most common ones.
All those particles and quants carry energy, which is receding as they move through matter. This overall energy is lost due to various collisions and affections. As a result ions and electrons are liberated, which form tiny electric charge. The amount of the charge is directly proportional to energy of the particle to some extent.
Under special conditions this residue of charge left after passing of a particle may be collected and applied to estimate the energy and trajectory of it. The only thing required to do this is to measure the generated charge or current and analyse the results.
In this research project the medium to measure the radiation particles will be PIN diode. It is a flat slice of 3 semiconducting materials. Following the order P – positivly doped, I- intrinsic (undoped) and N – negatively doped semiconductor. When the energetic particle or quant strikes the I – undoped region, it easily conveys the energy to the silicon atoms creating electrons and holes. Those two opposite kinds of charged particles then are attracted by the electric field coming from the biasing voltage applied to the diode.
As those opposing clouds of charge are separated a pulse of current occurs, which can be measured using ultra low noise and precise amplifier circuits.
The whole instrument will be consisting of a few functional blocks, which will be tested and designed individually, but with consistency to provide high end results.
- Sensing matrix – in the first stage it will consist of an array of common BPW34 PIN diodes. As the project develops I will test some larger ones I found on the Internet under the misterious name 2DU10 (10x10mm). If those common diodes fail to meet the expectations I may even move to professional detectors produced by First Sensor or photo multiplier diodes or replace the semiconducting area with a high voltage PMT and a chunk of scintillator.
- Booststrapping circuit – while using larger diodes, their capacitance significantly reduces the charge generated by each event. There is a proposed solution that can be found on the website of Analog Devices. The simulations conducted for the detector in LTspice confirm the utility of this simple circuit, which will enable to use greater sensing areas....