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Physics (P1)
Radioactivity
| Question | Answer |
|---|---|
| What is an atom? | Positively charged nucleus, consisting of protons and neutrons surrounded by negatively charged electrons |
| Describe the nuclear radius in the atom. | Much smaller than that of the atom |
| Where is most of the mass of an atom concentrated? | In the nucleus |
| Give the size of an atom. | 1x10(-10) m |
| Give the relative mass for: Protons, Neutrons, Electrons & Positrons | 1, 1, 0.0005, 0.0005 |
| Give the relative charge for: Protons, Neutrons, Electrons & Positrons | +1, 0, -1, +1 |
| Why are atoms neutral? | The number of protons = The number of electrons |
| In each atom what do the electrons do? | Orbit the nucleus at different set distances from the nucleus |
| When will electrons move to a higher orbit? | If the atom has absorbed EM radiation |
| When will electrons move to a lower orbit? | If the atom has emitted EM radiation |
| How do atoms form positive ions? | Losing outer electrons |
| What is emitted from unstable nuclei in a random process? (5) | Alpha, Beta +(Positron), Beta -, Gamma rays and neutron radiation |
| What are 4 ionising radiations? | Alpha, Beta-, Beta+ and Gamma rays |
| What is meant by background radiation? | Radiation that is always present and in small non-harmful amounts |
| Give 4 examples of background radiation. | Cosmic rays, underground rocks, nuclear fallout, nuclear weapon testing |
| Method 1 for detecting radiation and how it works. | Photographic film - Goes darker when it detects radiation and is worn as a badge |
| Method 2 for detecting radiation and how it works. | Geiger-Muller tube - Transmits electrical pulse to the machine making a click sound, radiation can be detected by frequency |
| What is an alpha particle equivalent to? | Helium nucleus (4,2) |
| What is a beta particle? | An electron emitted from the nucleus |
| What is a gamma ray? | EM radiation |
| Describe Alphas: Penetrating and Ionising | Weakly penetrating, highly ionising |
| Describe Betas: Penetrating and Ionising | Medium penetrating, medium ionising |
| Describe Gammas: Penetrating and Ionising | Highly penetrating, lowly ionising |
| How did JJ Thomson describe the atom? | Plum Pudding - Positive sphere with scattered negative electrons to make it neutral |
| Describe Rutherford's model. | Positive nucleus at the centre, negative electrons existing in a cloud around the nucleus |
| What was the Bohr model? | He concluded the electrons exist in fixed orbitals |
| Describe the process of B- decay. | Neutron becomes a proton and releases an electron |
| Describe the process of B+ decay. | Proton becomes a neutron and releases a positron |
| What happens to the atomic and mass number when it undergoes alpha decay? | -4 from Mass number, -2 from Atomic number (+ a 4,2 alpha particle) |
| What happens to the atomic and mass number when it undergoes beta- decay? | Nothing happens to the mass number but the atomic increases by 1 (+ a 0,-1 beta particle) |
| What happens to the atomic and mass number when it undergoes beta+ decay? | Nothing happens to the mass number but the atomic decreases by 1(+a 0,1 beta particle) |
| What happens to the atomic and mass number when the nucleus emits a neutron? | Mass number decreases by 1, atomic stays the same (+ 1,0 n particle) |
| What happens in gamma decay? | They get rid of excess energy from the atom, mass and atomic number still stay the same when gamma is emitted. |
| How does the activity of a radioactive source decrease over time? | Activity decreases each time a radioactive nucleus decays |
| What is the unit of activity of a radioactive isotope? | Bq |
| What is meant by the half-life of a radioactive isotope? | The time taken for half the undecayed nuclei to decay or the activity of a source to decay by half |
| What can be said about our knowledge of a particular nucleus decaying? | It cannot be predicted when it will happen |
| What is good about half-life? | It enables the activity of a very large number of nuclei to be predicted during the decay process |
| If we are given the initial Bq, how do we work out each half-life? | Keep dividing each result by 2 |
| What is 1 danger of ionising radiation? | They can ionise atoms and molecules within them leading to tissue damage. |
| Give another danger of ionising radiation. | Damage without killing the cells, giving rise to mutant cells that divide uncontrollably (cancer) |
| Give 3 precautions to take when using ionising radiation. | Wear protective clothing, keep the radiation in lead containers and keep exposure time minimum |
| Give 3 precautions to reduce harm for doctors and patients that are using ionising radiation. | Small dose for the patient, radiation used has short half life, doctors and patients wear protective clothing |
| What is contamination? | Unwanted radioactive nuclei on other materials |
| What is irradiation? | Purposely exposing something to radiation but doesn't make it radioactive |
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