Radon:
4 types of radiation:
alpha: Helium nucleus He4/2 (charged, heavy)-stopped by skin, paper
beta: fast electron e- (charged, small)-stopped by foil
gamma: high energy photon, like light-stopped by lead
neutron: just a neutron n1/0 (heavy, no charge)-stopped by lots of lead and concrete

Review Isotopes:
Radon is 222/86: how many n, p and e?
How many for C 14/6?

Exponential decay and growth: decay for radioactive stuff, growth for populations and bacteria
Decay formula: At = Ao (0.5)^n
Growth formula: At = Ao (2)^n
At = amount some time later, time t
Ao = starting amount
n = number of half lives (t1/2) or doubling times (t2)

We'll use M&Ms as our "atoms" for this:
  1. pour out 32 M&Ms on a plate
  2. drop into a shaker, shake, pour out on the plate
  3. remove the ones with the M&M label facing up
  4. count the remainder
  5. repeat
  6. graph number of M&Ms (y) number of turns (x)
Questions:
  1. Does the number ever really get to zero in real live atoms?
  2. What is the change in atoms at each turn?
  3. How is this related to the amount of atoms left?
Problems:
  1. 64 grams of C14/6 with half life of about 5000 years decays.
    1. How much is left after 5000 years?
    2. 15,000 years?
    3. 30,000 years?
  2. Sr90/38 has a half life of about 30 years. If Ao is 200 grams,
    1. how much is left after 60 years?
    2. 120 years?
    3. 45 years?
Setup for each problem:
  1. find n (60/30 = 2)
  2. find Ao (200 grams)
  3. At = 200(0.5)^2 = 50 grams
n.b. 45 grams is not a whole number of half lives
so what? just use the number to get 70 grams (try this)

Exponential growth:
Same deal as with decay, only we use 2 instead of 0.5
Decay formula: At = Ao (0.5)^n
Growth formula: At = Ao (2)^n
n is called t2 or the doubling time (you may have seen this in AP bio)
Example: If bacteria population doubles every 6 hours, and Ao is 1000 bacteria, how many after 24 hours?
24/6 = 4 = n
At = 1000(2)^4 = 16,000 bacteria
This works for people, viruses, rhinos, even capybaras...
One reason antibiotics and antivirals attack the reproductive cycle, not existing viruses.

n.b. this depends on two things:
RATE: the reproductive or decay rate
BASE: how much you start with

Exponential Growth Lab:
  1. Start with 4 M&Ms, double until 32, graph
  2. On the same graph, repeat starting with 8 M&Ms
    1. What is the change in M&Ms at each turn?
    2. which graph has the steeper slope?
    3. how would birth control change t2?
    4. why did China have a one child policy had between 1980 and 2015?
Examples: (numbers are grossly estimated for comparison)
Each country starts with about 30 million in this example:
How many in each case after 42 years?
Canada t2=21 years
Nigeria t2=7 years
Japan t2 = -7 years (?)

Rule of 70
Countries use growth rate instead of t2
If growth rate is 7%, then 70/7 means 10 years is t2
if growth rate is 14% then 70/14 means 5 years for t2
if growth rate is 3.5% then 70/3.5 means 20 years for t2

Populations depends on BASE and RATE