Igcse physics:-
Explain briefly the following scientifically.
1. radioactivity.
2. radioactive decay
3. half life
4. Alpha particle
5. beta particle
6. gamma rays
7. Atomic model.
8. Isotopes
9.uses of radioisotopes.
10. Rutherford's experiment.
11. Safety precautions.
Please give high level answers.
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SHORT NOTE ON THE RADIOACTIVITY
27.5.14 0 Comments
Unstable atomic nuclei will spontaneously decompose to form nuclei with a higher stability. The decomposition process is called radioactivity. The energy and particles which are released during the decomposition process are called radiation. When unstable nuclei decompose in nature, the process is referred to as natural radioactivity. When the unstable nuclei are prepared in the laboratory, the decomposition is called induced radioactivity
The three types of radiation were named after the first three letters of the Greek alphabet: a(alpha), b(beta), and g(gamma)
ALPHA PARTICLE
è Alpha particles are made of 2 protons and 2 neutrons.
è This means that they have a charge of +2, and a mass of 4 (the mass is measured in "atomic mass units", where each proton & neutron=1)
We can write them as 2a4, or, because they're the same as a helium nucleus, 2He4.
è Alpha particles are relatively slow and heavy. They have a low penetrating power - you can stop them with just a sheet of paper. Because they have a large charge, alpha particles ionise other atoms strongly
è Remember, in Alpha decay:
à atomic number decreases by two
à atomic mass decreases by four.
BETA PARTICLE
è Beta particles have a charge of minus 1, and a mass of about 1/2000th of a proton.
è This means that beta particles are the same as an electron. We can write them as b- or, because they're the same as an electron, e-.They are fast, and light.
è Beta particles have a medium penetrating power. They are stopped by a sheet of aluminum or plastics such as Perspex. Beta particles ionize atoms that they pass, but not as strongly as alpha particles do.
èRemember, in Beta decay :-
àatomic number increases by one
à atomic mass unchanged
GAMMA PARTICLE
è Gamma rays are waves, not particles.
è This means that they have no mass and no charge. So we sometimes write 0g0.
è Gamma rays have a high penetrating power - it takes a thick sheet of metal such as lead, or concrete to reduce them significantly.
è Gamma rays do not directly ionize other atoms, although they may cause atoms to emit other particles which will then cause ionisation.
è We don't find pure gamma sources - gamma rays are emitted alongside alpha or beta particles. Strictly speaking, gamma emission isn't 'radioactive decay' because it doesn't change the state of the nucleus, it just carries away some energy.
è Remember, in Gamma decay:-
àatomic number unchanged
àatomic mass unchanged.
SUMMARY
Alpha particles are easy to stop, gamma rays are hard to stop.
Particles that ionise other atoms strongly have a low penetrating power, because they lose energy each time they ionise an atom.
Radioactive decay is not affected by external conditions.
Transmutation is the changing of an atom into another kind of atom that takes place during radioactive decay.
In the year 1896, Henri Becquerelof France discovered radioactivity.
The amount of time for half the atoms in a radioactive sample to decay is called the half-life..
The term radioactivity was coined by Marie Curie.
ISOTOPES
è These are the elements having same atomic number but different mass number. They have the same atomic number because the number of protons inside their nuclei remains the same. The difference in their mass number is due to the difference in their number of neutrons. Since they are neutral isotopes are elements having same number of electrons, which make them to possess identical chemical properties.
Examples of isotopes are 1H1, 1H2, 1H3 are all isotopes of hydrogen and 17Cl37, 17Cl35 are isotopes of chlorine.
ISOBARS
èIsobars are atoms of different elements having the same atomic mass but different atomic number. Since their number of electrons is different, their chemical properties are different.
Examples of isobars are
(i) 32Ce76 , 34Se76
(ii) 26Fe58, 27Ni58
ISOTONES
Isotones are elements having the same number of neutrons. Examples of isotones are Chlorine - 37 and Potassium - 39. Both have 20 neutrons in their nuclei.
DETECTION OF RADIATIONS
è Radioactivity is invisible, has no smell, makes no sound - in fact it cannot be detected by any of our senses.
However, because radioactivity affects the atoms that it passes, we can easily monitor it using a variety of methods:
à Geiger-Müller tube
àPhotographic Film
à Gold Leaf Electroscope
à Spark Counter
à Cloud Chamber
à Bubble Chamber
à Modern Detectors
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