Lab 8 - Nuclear stability and decay

The kinds of particles emitted when a nucleus decays include...

 Alpha Beta
electron
Beta
positron
Gamma neutron
 ${}_2^4\alpha$ ${}_{-1}^0\beta=\beta^-$ ${}_{+1}^0\beta=\beta^+$ ${}_0^0\gamma$ ${}_0^1 n$
charge $+2e$ $-e$ $+e$ $0$ $0$

Radiation decays

${}_{92}^{238}U \rightarrow {}_{90}^{234}Th + {}_2^4 \alpha$

${}_6^{14}C\rightarrow {}_7^{14}N + {}_{-1}^0 \beta$

Write down the decays below in the same form as above. Use conservation of mass number and conservation of charge (atomic number) to figure out the daughter nucleus atomic number and mass number, then use the periodic table to figure out what element the daughter nucleus is.

  1. ${}_{38}^{90}Sr$ emits a ${}_{-1}^0\beta$ particle.

     

  2. ${}_{84}^{214}Po$ emits an ${}_2^4\alpha$ particle.

     

  3. ${}_{86}^{222}Rn$ emits an $\alpha$ particle.

     

  4. ${}_{37}^{75}Rb$ emits a positron

     

Patterns in nuclear decay?

In previous labs you have seen that some isotopes are more likely to give off one kind of radiation than another. Does the kind of radiation given off obey any kind of pattern? There are some isotopes that are stable. Can we predict which ones?

In what follows, you'll use the International Atomic Energy Agency's

Open up the chart and you will find a bunch of colored squares, each representing one isotope. The $x$-coordinate of one square is the number of neutrons, and the $y$-coordinate is the number of protons for that isotope.

You can navigate by draggine the chart around, and zooming in and out (with the scroll wheel). Hovering with your mouse over a square reveals the isotope. You can search for a particular isotope from the search box.

Take in the color-coding first. The black squares represent stable isotopes which do not decay. What is the lightest isotope that is stable? The heaviest one?

 

The stable isotopes (in black) seem to lie roughly on a line. The colors of the other squares are related to the half-lives (given in seconds) of each unstable isotope.

Is there any pattern or tendency? What happens to the half-lives as you move up & left or down & right, moving away from the line of stable isotopes?

 

Now click on the "Decay radiation" tab. Now, if you search for, or click on a particular square you will see the half-life ($T_{1/2}$) of the isotope, and information about how the isotope decays. What are the half-lives of these...

${}^{238}U$

${}^{14}C$ (used in "Carbon dating")

${}^{222}Rn$ (Radon-- a heavy gas: health concern in basements)

What is the decay radiation listed for the isotopes we looked at in class as $\alpha$, $\beta$, and $\gamma$ sources?

${}^{210}Po$

${}^{204}Tl$

${}^{133}Ba$

Look at a few of the stable, light isotopes in the region from $Z=1..20$. What is the approximate ratio of neutrons to protons in this region?

 

Repeat this in the heavy region from $Z=70..80$. What is the approximate ratio for stable isotopes in this region?

 

Nuclear decays

Now, imagine that you start at the x with an isotope of $n$ neutrons and $p$ protons on this diagram of $p$ ($y$-axis) vs $n$. After the nucleus decays, show where the daughter nucleus is relative to the starting nucleus, x, for (label these) $\alpha$, $\beta^+$ and $\beta^-$ decays?

   

In the light region (below about $Z=30$) click on a couple of isotopes below the stability line. Is there one kind of decay radiation that is more common than others? Broadly speaking what direction does this move the isotope in the table (referring back to your diagrams above)?

 


In this same region, click on a couple of isotopes above the stability line. Is there one kind of decay radiation that is more common than others? Broadly speaking what direction does this move the isotope in the table (referring back to your diagrams above)?

 


Based on the pattern that you've observed above, predict two different nuclei that you think will decay by giving off an alpha particle. Give your reasons why, and then check whether your predictions are right.