Nuclear physics flashcards

Nuclear physics covers the structure and behaviour of atomic nuclei. Students must understand proton number, nucleon number, and isotopes, as well as the four fundamental forces acting within the nucleus. Radioactive decay — alpha, beta-minus, beta-plus, and gamma — must be described in terms of changes to the nucleus, and decay equations must be balanced. The concept of half-life and its mathematical treatment using the decay constant are essential. Students also need to understand nuclear binding energy, mass defect, and how energy is released in fission and fusion reactions via Einstein's mass-energy equivalence E = mc squared. The stability of nuclei can be analysed using binding energy per nucleon curves. Radioactive decay follows an exponential pattern, and students should be comfortable applying and manipulating the relevant equations.

1. Card 1

   What is the nucleon number (mass number) of an atom?

   The nucleon number is the total count of protons and neutrons in the nucleus. It is also called the mass number and is given the symbol A.

2. Card 2

   Define isotopes.

   Isotopes are atoms of the same element that have the same proton number but different numbers of neutrons, giving them different nucleon numbers.

3. Card 3

   What changes in the nucleus during alpha decay?

   The nucleus loses 2 protons and 2 neutrons, emitting an alpha particle (helium-4 nucleus). The proton number decreases by 2 and the nucleon number decreases by 4.

4. Card 4

   What is emitted during beta-minus decay and what nuclear change occurs?

   A beta-minus particle (fast electron) and an antineutrino are emitted. A neutron converts to a proton, so proton number increases by 1, nucleon number unchanged.

5. Card 5

   What is the mass defect of a nucleus?

   The mass defect is the difference between the total mass of the separate nucleons and the actual mass of the assembled nucleus. This missing mass is converted to binding energy.

6. Card 6

   State Einstein's mass-energy equivalence equation.

   E = m x c squared, where E is energy in joules, m is the mass defect in kilograms, and c is the speed of light (3 x 10^8 m/s). This is called mass-energy equivalence.

7. Card 7

   What does binding energy per nucleon tell us about nuclear stability?

   A higher binding energy per nucleon means the nucleus is more stable. Iron-56 sits at the peak of the curve and is the most stable nucleus.

8. Card 8

   Define the decay constant.

   The decay constant (lambda) is the probability that a given nucleus will decay per unit time. It is related to half-life by lambda = ln2 / t(half-life).

9. Card 9

   Write the equation for radioactive decay activity.

   Activity A = lambda x N, where lambda is the decay constant and N is the number of undecayed nuclei present. Activity is measured in becquerels (Bq).

10. Card 10

    How does nuclear fission release energy?

    A heavy nucleus splits into two smaller nuclei with greater binding energy per nucleon. The increase in binding energy is released as kinetic energy of the products.

11. Card 11

    Why does nuclear fusion release energy?

    Light nuclei combine to form a heavier nucleus with higher binding energy per nucleon. The mass defect of the products is converted to energy via E = mc squared.

12. Card 12

    What is the exponential decay equation for the number of undecayed nuclei?

    N = N(0) x e^(-lambda x t), where N(0) is the initial number of nuclei, lambda is the decay constant, and t is time elapsed.

• Students often confuse binding energy with the energy needed to assemble a nucleus rather than correctly identifying it as the energy required to completely separate all nucleons, leading to errors in stability comparisons.
• A common error is forgetting to include the antineutrino when writing a beta-minus decay equation, or confusing it with the neutrino emitted in beta-plus decay, which costs marks in balanced decay equations.
• Many students incorrectly apply the half-life concept by halving the time rather than halving the number of nuclei, or they forget that activity and number of nuclei both decay exponentially with the same half-life.

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