Chapter 8.1.3-4 Radioactive Decay and Nuclear Instability

23 flashcards · Physics · by TheoTyson

1. What makes predicting the decay hard?

   Radioactive decay is random, so only the overall pattern for a large number of nuclei can be predicted.

2. What is the activity of a sample?

   The number of nuclei ( NNN ) that decay each second.

3. What is the activity of a sample proportional to?

   The activity of a sample is proportional to the size of the sample.

4. What is the unit for activity?

   Becquerels ( BqBqBq ) = 1 decay per second.

5. What is the decay constant ( λ\lambdaλ )?

   The probability of a given nucleus decaying per second.

6. What is the equation that links the number of nuclei ( NNN ), the decay constant ( λ\lambdaλ ) and time ( ttt )?

   ΔNΔt=−λN\frac{\Delta N}{\Delta t} = - \lambda NΔtΔN​=−λN

7. What is the equation that links the number of nuclei ( NNN ), the decay constant ( λ\lambdaλ ) and the activity ( AAA )?

   A=λNA = \lambda NA=λN

8. In what fashion does the number of undecided particles change?

   Decreases exponentially.

9. What is the half life of an isotope?

   The average time it takes for the number of unstable nuclei to halve.

10. What happens with the background radiation?

    The background radiation needs to be subtracted from the activity readings to give the source activity.

11. What is the gradient of a log⁡N\log{N}logN against ttt graph?

    The gradient is −λ- \lambda−λ .

12. What is the yyy -intercept of a log⁡N\log{N}logN against ttt graph?

    The yyy -intercept is N0N_0N0​ .

13. What is the equation for half life?

    T12=ln⁡2λT_{\frac{1}{2}} = \frac{\ln{2}}{\lambda}T21​​=λln2​

14. What is the equation for the number of unstable nuclei remaining?

    N=N0e−λtN = N_0e^{-\lambda t}N=N0​e−λt

15. What is the equation for activity at a specific time?

    A=A0e−λtA = A_0 e^{- \lambda t}A=A0​e−λt

16. How do you calculate the number of atoms from the molar mass and number of moles?

    Mass\text{Mass}Mass = Mr\text{Mr}Mr x mol\text{mol}mol NNN = mol\text{mol}mol x NAN_ANA​

17. Explain radioactive dating of objects

    All living matter take in the radioactive isotope carbon 14, and when they die, the activity of the carbon starts to fall, with the half life and activity, they can work out the age.

18. Explain the use of technetium-99m\text{technetium-99m}technetium-99m as a medical tracer

    Technetium-99m\text{Technetium-99m}Technetium-99m emits γ\gammaγ radiation that can be detected and is not too damaging to the person, the half life is 6 hours which is long enough to be detected, and not too long to cause damage, and decays to a stable isotope.

19. What force holds the nucleus together?

    The strong nuclear force hold the nucleus together.

20. What force pulls the nucleus apart?

    The electromagnetic force pulls the nucleus apart.

21. In which kind of unstable nuclei does beta minus emission happen?

    Beta minus happens in nuclei that have too many neutrons so one of the neutrons is changed into a proton.

22. In which kind of unstable nuclei does alpha emission happen?

    Alpha emission only happens in very heavy atoms with too many protons and neutrons.

23. In which kind of unstable nuclei does gamma emission happen?

    Nuclei that have undergone alpha or beta decay and so have excess energy.