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• Atomic Structure:

  • Positively charged nucleus surrounded by negatively charged electrons.

  • Subatomic particles:

    • Proton: Relative mass = 1, Relative charge = +1.

    • Neutron: Relative mass = 1, Relative charge = 0.

    • Electron: Relative mass = 0 (0.0005), Relative charge = -1.

  • Typical radius of an atom: 1 × 10−10 metres.

  • Radius of the nucleus is 10,000 times smaller.

  • Most of the mass of the atom is concentrated at the nucleus.

• Electron Arrangement:

  • Electrons lie at different distances from the nucleus (different energy levels).

  • Electron arrangements may change with the interaction with EM radiation.

• Isotopes and Elements:

  • All atoms of the same element have the same number of protons.

  • Neutral atoms have the same number of electrons and protons.

  • Isotopes are atoms of the same element with different masses.

  • Isotopes have the same number of protons but different number of neutrons.

  • Example: Carbon-12, Carbon-13, and Carbon-14.

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• How and why the atomic model has changed over time:

  • 1800: Dalton proposed that everything was made of tiny spheres (atoms) that could not be divided.

  • 1897: JJ Thomson discovered the electron, leading to the Plum Pudding Model.

  • 1911: Rutherford realized most of the atom was empty space through the Gold Foil Experiment.

  • 1913: Rutherford Model with a positive nucleus at the center and negative electrons in a cloud around it.

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• 1913: Bohr produced the final model of the atom.

• Positive charge of the nucleus could be subdivided into smaller particles called protons.

• James Chadwick provided evidence for the existence of neutrons.

• Some atomic nuclei are unstable and give out radiation as they change to become more stable.

• Radioactive decay is a random process.

• Activity is the rate at which a source of unstable nuclei decays, measured in Becquerel (Bq).

• Count-rate is the number of decays recorded by a detector per second.

• Forms of decay: Alpha (α), Beta Minus (β), Gamma (γ), Neutrons.

• Nuclear equations are used to represent radioactive decay.

• Electrons exist in fixed 'orbitals' to prevent the collapse of the atom.

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• Emission of different types of nuclear radiation may cause a change in the mass and/or charge of the nucleus.

• Alpha Decay: Decreases both the mass and charge of the nucleus.

• Beta Decay: Does not change the mass but increases the charge of the nucleus.

• Gamma Decay: Does not cause a change in mass or charge.

• Half-Life:

  • The time taken for half the nuclei in a sample to decay or for the activity/count rate to decay by half.

  • It cannot be predicted when any one nucleus will decay.

  • Short half-life: Less long-term risk, quickly becomes less radioactive.

  • Long half-life: Remains weakly radioactive for a long period of time.

  • Example: Americium has a half-life of 432 years, used in smoke alarms.

  • The number of atoms over time tends to 0.

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Net Decline

• Calculate the ratio of net decline of radioactive nuclei after X half-lives

• Half the initial number of nuclei, and keep doing so X number of times

• Formula: 𝐍𝐍𝐞𝐞𝐞 𝐃𝐃𝐞𝐞𝐞𝐞𝐞𝐞𝐞𝐞𝐞𝐞𝐞𝐞 = 𝐢𝐢 𝐧𝐧𝐧𝐧𝐧𝐧 𝐧𝐧 − 𝐧𝐧𝐧𝐧𝐧𝐧 𝐧𝐧 𝐚𝐚 𝐗𝐗 𝐡𝐡 𝐥𝐥 𝐥𝐥 𝐢𝐢 𝐧𝐧𝐧𝐧𝐧𝐧 𝐧𝐧

Contamination

• Lasts for a long period of time

• The source of the radiation is transferred to an object

• Unwanted presence of radioactive atoms on other materials

• Hazard is the decaying of the contaminated atoms releasing radiation

• Example: radioactive dust settling on your skin (your skin becomes contaminated)

Irradiation

• Lasts only for a short period of time

• The source emits radiation, which reaches the object

• Exposing an object to nuclear radiation, but does not make it radioactive

• Example: radioactive dust emitting beta radiation, which "irradiates" your skin

• Medical items are irradiated sometimes to kill bacteria on its surface, but not to make the medical tools themselves radioactive

Scientific Reports Published need to be peer reviewed

• Peer review is essential for studies on the effects of radiation on humans

• Incorrect measurements in initial studies can lead to safety levels that may cause harm

Background Radiation (Physics only)

• Weak radiation that can be detected from natural/external sources

• Sources include cosmic rays, radiation from underground rocks, nuclear fallout, and medical rays

• Occupation and location can affect the level of background radiation and radiation dose

• Measurement of Radiation Dose: Sieverts (Sv)

• Uses of Radiation: Tracers

• Technetium is used as a medical tracer

• It has a half-life of 6 hours and decays into a safe isotope that can be excreted by the body

• It is injected/swallowed and can flow through the body and be detected before it decays away

• It is a gamma emitter, so it can pass through body tissue without being absorbed

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Chemotherapy

• Gamma emitters are used to emit gamma rays onto certain areas of the body with cancerous cells

• Gamma rays are absorbed by the cancerous cells, causing them to die and controlling the disease

• It is also used to control other unwanted tissue

• Surrounding healthy cells may also be irradiated, causing unhealthy side effects

Nuclear Fission (Physics only)

• Nuclear fission is the splitting of a large and unstable nucleus (e.g., uranium or plutonium)

• Spontaneous fission is rare, usually requires the absorption of a neutron by the unstable nucleus

• The unstable nucleus splits into two smaller nuclei, emitting two or three neutrons and gamma rays

• Energy is released by the fission reaction

• This neutron may collide with another radioactive nucleus, causing it to split and release more energy

• This chain reaction can increase at an exponential rate if not controlled, as in a nuclear weapon

• Uranium nuclei are used in nuclear fission

Nuclear Fusion (Physics only)

• Two small nuclei fuse to form a heavier nucleus, releasing a large amount of energy

• The sum of the masses of the two nuclei is more than the mass of the heavier nucleus

• Some of the mass is converted into energy, released as radiation

• The sun is a natural fusion reactor

• Fusion is a more efficient way of producing energy compared to fission, but no design has achieved