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Nuclear Fission
Occasionally, an atomic nucleus breaks apart into smaller pieces in a radioactive process called spontaneous fission (or fission). Often, fission produces excess neutrons that will sometimes be captured by other nuclei, possibly inducing additional radioactive events. Uranium-235 undergoes spontaneous fission to a small extent. One typical reaction is
As with any nuclear process, the sums of the atomic numbers and mass numbers must be the same on both sides of the equation. Spontaneous fission is found only in large nuclei. The smallest nucleus that exhibits spontaneous fission is lead-208. (Fission is the radioactive process used in nuclear power plants and one type of nuclear bomb.)
Nuclear Fusion
Nuclear fusion is the thermal combining of light elements to form relatively heavier nuclei. The process requires very high temperatures for the reacting nuclei to combine upon collision.
These temperatures are provided by ordinary fission bombs.
These reactions sometimes known as thermonuclear reactions.
A fusion reaction releases energy at the rate of 3-23 MeV per fusion event i.e. two deuterium (heavy hydrogen) nuclei to form helium. ·
This 3.3 MeV (energy) produced is equal to 5.28 × 10-13 J.
Application of nuclear fusion
- Used in the production of hydrogen bomb. Possible reactions for an hydrogen bomb include;
Detecting Nuclear Radiation
- Geiger-Muller tube (GM tube)
This is a special instrument which tells us the number of particles detected per minute (“counts per minute”).
GM tubes work using the ionising effect of radioactivity. This means that they are best at detecting alpha particles, because -particles ionise strongly.Different models of GM tubes are available for detecting α,β and γ radiation.
The tube is filled with Argon gas, and around +400 Volts is applied to the thin wire in the middle.
When a particle enters the tube, it pulls an electron from an Argon atom. The electron is attracted to the central wire, and as it rushes towards the wire, the electron will knock other electrons from Argon atoms, causing an “avalanche”. Thus one single incoming particle will cause many electrons to arrive at the wire, creating a pulse which can be amplified and counted. This gives us a very sensitive detector.
- Photographic Film
Henri Becquerel (1896)is credited as the scientist who discovered the the science behind effects of the radioactive material on a photographic film. This was after he discovered that Uranium compounds would darken a photographic plate, even if the plate were wrapped up so that no light could get in
It is now a fact that Radioactivity will darken (“fog”) photographic film, . this effect can be used to measure how much radiation has struck the film.Workers in the nuclear industry wear “film badges” which are sent to a laboratory to be developed, just like your photographs. This allows us to measure the dose that each worker has received (usually each month).
The badges have “windows” made of different materials, so that we can see how much of the radiation was alpha particles, or beta particles, or gamma rays.
- 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.
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- 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.
- 5. 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.
- 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 -800 C 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