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 Form 4 Physics: Radioactivity online lessons

How to Detect nuclear radiation

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Answer Text:
Detecting nuclear radiation
1. Gold leaf electroscope–the rate of collapse of the leaf depends on the nature and intensity of radiation. The radioactive source ionizes the air around the electroscope. Beta particles discharges a positively charged electroscope with the negative charge neutralizing the charge of the electroscope. Alpha particles would similarly discharge a negatively
charged electroscope. To detect both alpha and beta particles a charged electroscope may not be suitable because their ionization in air may not be sufficiently intense making the leaf not to fall noticeably.
2.The spark counter – the detector is shown below
This detector is suitable for alpha sources due to the inadequacy of the ionization by both beta and gamma radiations. By putting the source away from the gauze or
placing a sheet of paper between the two one can determine the range and penetration of the alpha particles.

3. Geiger Muller (GM) tube– it is illustrated as below
The mica window allows passage of alpha, beta and gamma radiations. The
radiations ionize the gas inside the tube. The electrons move to the anode while the positive ions move to the cathode. As the ions are produced there are collisions which produce small currents which are in turn amplified and passed to the scale. The scale counts the pulses and shows the total on a display screen. After each pulse the gas returns to normal ready for the next particle to enter.
A small presence of halogen gas in the tube helps in absorbing the positive ions to reduce further ionization and hence a quick return to normal. This is called quenching the tube.
4. The solid state detector– this detector can be used to detect alpha, beta and gamma radiations where the incoming radiation hits a reverse biased p-n junction diode momentarily conducting the
radiation and the pulse of the current is detected using a scaler.
5. The diffusion cloud chamber– this chamber is simplified as shown below
The bottom of the chamber is cooled by solid carbon (V)
oxide to around #-80^0C# and the alcohol vapour from the felt ring spreads downwards. It is cooled below its normal condensing temperature. As a particle enters the chamber it ionizes the air in its path and alcohol condenses around the path to form millions of tiny alcohol droplets leaving a trail visible because it reflects light from the source. Alpha particles leave a thick, short
straight tracks. Beta particles leave thin irregular tracks. Gamma particles do not produce tracks and since they eject electrons from atoms the tracks are similar to those of beta particles.