P4 Flashcards
What’s the radius of an atom?
1 × 10-10 meters.
What’s the basic structure of an atom?
Positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons.
How big is the nucleus in comparison to an atom?
The radius of a nucleus is less than 1/10 000 of the radius of an atom.
Where in an atom is the most concentrated?
Most of the mass of an atom is concentrated in the nucleus.
What are different energy levels?
The electrons are arranged at different distances from the nucleus.
In an atom which 2 subatomic particles have the same number of particles?
Electrons and protons.
What is the atomic number?
Number of protons.
What is the mass number?
Number of protons and neutrons
What is an isotope?
Atoms of the same element that have different numbers of neutrons
Does the atom became positive or negative charged if it loses an electron?
Positive charged.
Why might a scientific model be changed or replaced?
New experimental evidence.
Before the discovery of the electron, what were atoms thought to be?
Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided.
What led to the plum pudding model of the atom?
The discovery of the atom.
What does the plum pudding model look like?
Sea of positive charge with negative electrons inside.
What knowledge did the alpha particle scattering experiment come out with?
Mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged. This nuclear model replaced the plum pudding model.
How was the nuclear model changed and by who?
Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances.
Who decided neutrons existed?
Chadwick.
What was the order in which subatomic particles were discovered?
- Electrons. 2. Protons. 3. Neutrons.
What is radioactive decay?
Some atomic nuclei are unstable. The nucleus gives out radiation as it changes to become more stable.
What is activity and what is it measured in?
Activity is the rate at which a source of unstable nuclei decays. Activity is measured in becquerel (Bq)
What is count - rate?
Count-rate is the number of decays recorded each second by a detector (eg Geiger-Muller tube).
What are the 4 things that can be emitted from a nucleus?
- Alpha particle. 2. Beta particle. 3. Gamma ray. 4. Neutron.
What is an alpha particle?
Consists of 2 protons and 2 neutrons (helium nucleus).
What is a beta particle?
A high speed electron ejected from the nucleus as a neutron turns into a proton
What is a gamma ray?
Electromagnetic radiation from the nucleus
What is an alpha particle’s penetration power and ionising power like?
It cannot penetrate through materials and is stopped quickly. Paper absorbs it. It’s highly ionising.
What is an beta particle’s penetration power and ionising power like?
They are absorbed by aluminium. Moderately ionising.
What is a gamma ray’s penetration power and ionising power like?
Travel far without being stopped and only absorbed by thick lead or concrete. As it passes through things and not collide with atoms; it is weakly ionising.
What’s an alpha particle equation?
4 / 2 He
What’s a beta particle equation?
0 / -1 e
What happens with the numbers with gamma rays?
The emission of a gamma ray does not cause the mass or the charge of the nucleus to change.
Is radioactive decay random?
Yes
What is the half - life?
The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level.
What is radioactive contamination?
Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials.
Compare the hazards associated with contamination and irradiation.
High levels of contamination of alpha is the most dangerous they can harm in one localised area. Gamma is the least dangerous as it’s weakly ionising so can pass through the body. High levels of irradiation from all sources are dangerous especially beta and gamma as they can penetrate the skin and get to your vital organs.
How to protect yourself from irradiation?
Gloves and tongs. Protective suits.
How is peer review going to protect us?
The more we understand means the more we can protect ourselves. Once peer reviews; info can be accepted and improvements can be made.
Where can background radiation come from? (2)
- Natural sources such as rocks and cosmic rays from space. 2. Man-made sources such as the fallout from nuclear weapons testing and nuclear accidents.
What is radiation dose measured in?
Radiation dose is measured in sieverts (Sv)
Gamma rays can kill what and why?
Cancer - high doses of it can kill the cells.
Nuclear radiations are used in medicine for the: (2)
- exploration of internal organs. 2. control or destruction of unwanted tissue
Radiation can do what?
Enter living cells and ionise them. This leads to tissue damage.
What is nuclear fission?
Nuclear fission is the splitting of a large and unstable nucleus (eg uranium or plutonium).
What happens in nuclear fission?
- Usually, for fission to occur the unstable nucleus must first absorb a neutron. 2. The nucleus undergoing fission splits into two smaller nuclei, roughly equal in size, and emits two or three neutrons plus gamma rays. 3. Energy is released by the fission reaction. 4. All of the fission products have kinetic energy. 5. The neutrons may go on to start a chain reaction. 6. The chain reaction is controlled in a nuclear reactor to control the energy released.
What causes a nuclear explosion?
An uncontrolled chain reaction.
What is nuclear fusion?
Nuclear fusion is the joining of two light nuclei to form a heavier nucleus. In this process some of the mass may be converted into the energy of radiation.
