SO I THINK IT IS KIND OF FUN…

Nuclear Chemistry&

Radioactivity

Who Am I?

Mark Vander Pol M.Div. Westminster Seminary California, 2009 Waiting for a call to the ministry Graduated from CCHS in 1995 I think I set a record in the Physics Olympics… I

wonder if it is still standing?

Why Am I Here?

B.A. Trinity Christian College, 1999 Minor: Biology Major: Chemistry

Where Was I?

S.E.T. Environmental, Inc., 1999-2002 Hazardous Materials Chemist

Argonne National Laboratory, 2002-2005 Chemical Technology Division Analytical Chemistry Laboratory Radiochemical Analysis Group

I was a radiochemist analyzing and working with radioactive materials

What is Nuclear Chemistry?

Study of the change/transformation of the atomic nuclei of isotopes What are isotopes?

Atoms of an element that differ in their atomic mass (same number of protons, different number of neutrons).

Radioactivity What is emitted from a change in an atom’s nucleus A material is “radioactive” when it is contains isotopes

which are decaying and emitting certain types of radiation. When I was working at Argonne my group determined what

isotopes were present in a sample. We usually did this by measuring the energies of the various types of radiation.

Radioactive Radiation

There are three main types of radiation that result from radioactive decay. Alpha - α Beta – β-

Gamma – γThere are other ways that nuclei can

transform Electron Capture – “K-Capture” Positron emission – β+ SF – Spontaneous Fission IT – Isomeric Transition

Measuring Radiation

Disintegration Events One decay per second = 1 Becquerel (Bq)

1 Curie = 3.7x1010 Bq Geiger Counters used to measure activity

Energies α, β, and γ radiation occur with various energies Specialized detectors are made for each type of

radiation The energies of a sample can be plotted on a

spectrogram

α Radiation

The biggest type of radiation Contains 2 protons and 2 neutrons

What would this be the nucleus of? Because of its size it can’t pass through much. Paper can stop α

radiation and even a few inches of air can cause it to loose its energy. However, because it is so big and heavy it can do a lot of damage.

Comes from the decay of the larger isotopes (106Te, really 144Nd)Causes the isotope to drop its atomic number by 2 and its

atomic weight by 4. 238U decaying by α would become… 234Th – why?

Uranium is atomic number 92. Loosing 2 protons gives it an atomic number of 90, which is Thorium.

Loosing 2 neutrons as well makes 4 nucleons lost. 238-4=234 which is the new atomic mass

β- Radiation

An electron being emitted Smaller than α so it isn’t as easily stopped, but it is

still a particle. Stopped by low density material (wood, plastic, etc.)

Essentially a neutron turns into a proton and emits an electron. The atomic number increases by 1, but the atomic mass stays the same 137Cs decaying by β- would become… 137Ba – why?

Cesium’s atomic number is 55. Adding a proton would make the atomic number 56 which is Barium.

The atomic mass stays the same because all that was lost was an electron (negligible difference)

γ Radiation

Electromagnetic Radiation Not a particle, but is a wave like light, x-rays, radio

waves, etc. Very hard to stop. Usually need heavy metals like

lead.Nothing “decays” by γ radiation—it is energy

emitted as a result of another nucleus transformation (i.e. α or β decay).

Half-Life

The amount of time it takes for a particular radioactive material to decrease by half Could be hundreds of thousands of years or milliseconds

(p.723) The shorter the half-life the more radiation the material

is emitting (because it is decaying faster).Example:

212Po : t1/2 = 45 seconds (decays to stable 208Pb) Start with 100 grams at 1:15:00

At 1:15:45 you will have how many grams? At 1:16:30? At 1:17:15? What about at 1:30:00?

What Isotopes Are Radioactive?

Easier/Quicker answer: What Isotopes aren’t radioactive? All the elements have isotopes that will undergo

radioactive decay Hydrogen only has one, 3H, tritium: t1/2 12.32 years, β- decay

The larger the nucleus the more unstable it is and the more likely to have decay properties. Decaying allows the nucleus to get to a more stable state.

Around 266 stable isotopesApproximately 650 isotopes with t1/2 > 60 min.At least 2,350 isotopes with t1/2 < 60 min.

Natural Radioisotopes

There are 65 radioactive isotopes that are found in nature Some are continually formed in the atmosphere by

interactions with cosmic rays Many are the part of “decay chains” from naturally

occurring 232Th, 235U, and 238U. (See p. 717) These decay to stable isotopes of Pb (208, 206, and 207

respectively) The remaining are just radioactive!

Foods with a lot of potassium have detectable amounts of β- radiation because of naturally occurring 40K! (The abundance of 40K is only o.0117% and the t1/2 is 1.27 billion years)

Man-Made Radioisotopes

Nuclear Fission Reactions Fission is the splitting of a large atom (235U or 239Pu) with

neutrons into smaller atoms along with enormous amounts of energy being released. (p.714)

The “Fission Products” generated are varied and very radioactive

Energy can be harnessed and converted to electricity (p. 716)

Bombardment In a fission reaction sometimes neutrons are absorbed and

larger elements are created (by β- decay) Other particles can be bombarded onto targets to create

other isotopes

Why Is Nuclear Chemistry Important?It’s practical

Smoke alarms use 241Am to ionize the airIt’s dateable

14C dating helps archeologists determine dates of organic materialIt’s for your health

Many radioisotopes can be used as tracers to determine the functionality of various bodily organs.

Also used to help kill cancer cells.It can keep the lights on

Nuclear fission reactions help produce electricityIt can keep you warm

Okay, not really. However, 238Pu heat sources provide electricity to unmanned spacecraft

Thanks!

Any Questions?