الكشف عن الجسيمات المشحونة - الطاقة النووية .. الفيزياء

Detection of charged particles - Nuclear energy .. Physics

Detection of charged particles

There are many methods aimed at tracking the interaction processes between fine particles and studying their decay. One of these methods is that which takes place inside a device called a bubble chamber where the traces left behind by the displaced body are seen, just as you see bubbles in a certain liquid. This process requires placing a liquid inside the chamber and raising its pressure in a way that raises its boiling point and thus allows it to be heated to a temperature slightly higher than the boiling point without boiling. Then the pressure is suddenly lowered, shortly before entering the liquid, approximately one hundredth of a second, so its atoms are displaced and energy is generated that results in rapid and local boiling that does not exceed the location of the particle trace itself. After about one thousandth of a second, the size of the bubbles left behind becomes large enough to be photographed and the trace of the particle and the results of its decay can be seen. After that, the boiling liquid is pressured back to its original value to avoid the process called swelling.

The scattering chamber is used to measure the energy of charged particles such as alpha rays, beta rays and X-rays. It contains a thin wire that acts as an anode and forms the axis of a cylinder that acts as a cathode. Then a low voltage is applied between the wire and the cylinder.

Once the particle passes through the chamber, the atoms of the surrounding gas are scattered, so the electrons head towards the anode and the positive ions go towards the cathode. This results in an electrical pulse proportional to the energy of the rays themselves. It is worth noting that the Geiger counter works according to this method with one difference, which is that the voltage in it is relatively large, which increases the energy of the formed ions and causes a flood of ion pairs that give a charge proportional to them and collect on the device's electrodes and allows for the counting of thousands of particles per second. The amplification in this counter is so great that it becomes capable of detecting even one beta particle.

The scintillation counter is used to detect and count the scattered particles. It consists of a scintillation crystal and a photomultiplier. A particle falls on a scintillation crystal, sodium iodate, and glows, giving off flashes of light that are captured by the photomultiplier and amplified, causing electrons to be emitted from its surface. It is possible to count each particle individually by this counter because of the short period between its passage and the production of an electric current.

(Effects in the bubble chamber)
Displacement chamber (above) and scintillation counter (below).