transmutation and decay series

TRANSMUTATION AND DECAY SERIESHOW URANIUM CHANGES TO LEAD

or

WHAT HAPPENS IN BETWEENKevin Lavarnway Schroon Lake Central School

START WITH A RADIOISOTOPEAn isotope is an atom of the same element with the same number of protons and a different number of neutronsSome isotopes are naturally unstable and spontaneously change to another isotope of a different elementThis change from one element to another is called TRANSMUTATION.

THIS IS NOT A CHEMICAL CHANGE!Chemical reactions involve atoms rearranging by breaking and forming bonds involving electronsTRANSMUTATION involves changes in the nucleus that change the actual identity of the elementThese reactions are called NUCLEAR because they involve the atoms nucleus

NOTATION Uranium 238

238 mass number ( p + n ) U 92 atomic number ( # p )

TRANSMUTATION INVOLVES THE RELEASE OF RADIATIONA Radioisotope emits, or gives off, radiation from its nucleus

Each isotope emits a certain type of radiation; it has a specific decay mode

The radiation can be in the form of particles or rays

ELECTROMAGNETIC SPECTRUMLOWER ENERGY HIGHER ENERGY

TYPES OF RADIATIONPure energy given off as rays is called gamma radiation

Radiation particles could be alpha or beta particles

ALPHA PARTICLEThe same as a helium nucleus2 protons and 2 neutrons

4 mass of 4 amu He 2 Has a 2+ charge because of 2 protons LOWEST PENETRATING POWER

BETA PARTICLEThe same characteristics as an electron(not from an energy levelemitted from the nucleus)0 essentially no mass e -1 charge of -1

HIGHER PENETRATING POWER

GAMMA RADIATIONPure electromagnetic energy with high frequency and short wavelength

No mass or charge associated with it

MOST PENETRATING POWER

PENETRATING POWER OF NUCLEAR RADIATION

NUCLEAR TRANSMUTATION(natural) Original NewRadioisotope Isotope + Radiation

238 234 4 U Th + He 92 90 2

A CLOSER LOOK U-238 has alpha decay Total mass before and after must be equal

238 234 4 U Th + He 92 90 2

Total of atomic numbers must also balance

How can you use decay mode information?Can you determine the new isotope if you know the decay mode?For example, Th-232 is an alpha emitter.

232 4 Th ? + He 90 2

STRATEGY *mass numbers must balance 232 = 228 + 4 Th ? + He 90 = 88 + 2 *atomic numbers must balance How do we know what the new isotope is?

CHECK THE PERIODIC TABLE!The new isotope has a mass number of 228 and an atomic number of 88.228 ? 88 each element has a unique atomic number The new isotope is Radium-228 which is a beta emitter!

What happens to Ra-228?

228 0 Ra ? + e 88 -1 (beta particle) Balance the mass numbers and the atomic numberscareful of that -1)

And the result of the decay is

mass number stays same 228 Ac atomic number increases by 1 89

Actinium a new element with a greater atomic #

This is a beta emitter as well! When will it stop???

not until a stable isotope is formed!The change from one radioisotope to another in a specific sequence is called a decay seriesWe will explore some transmutations that are part of the uranium-238 decay series...You will be given two radioisotopes and their decay modes. Determine what the product of each transmutation will be

Start off examples are:U-238 is an alpha emitter: 238 234 4 U Th + He 92 90 2

Th-234 is a beta emitter: 234 234 0 Th Pa + e 90 91 -1

Take your time and think it outWrite the symbol of the radioisotope in the proper notation on the reactant sideWrite the notation for the radiation type emitted on the product sideTotal up the mass numbers on top so the total mass is balanced on each sideTotal up the atomic numbers on the bottom so they are balanced as wellUse Periodic Table to identify the element by its atomic number

Some practice for youYou and a partner will receive a sheet of paper with two sample transmutations---tear in half so you each have two reactionsComplete each transmutation individually and then compare the results with your partnerDecide on the correct answers and we will share them with the entire class by completing the decay series

U-238 decay seriesU-238 Th-234 Pa-234 U-234 Th-230 Ra-226 Rn-222 Po-218 Pb-214 Bi-214 Po-214 Pb-210 Bi-210 Po-210 Pb-206 (stable)

One very special isotopeU-238 Th-234 Pa-234 U-234 Th-230 Ra-226 Rn-222 Po-218 Pb-214 Bi-214 Po-214 Pb-210 Bi-210 Po-210 Pb-206 (stable) Rn-222 is a gas!

Are all of the steps just alike?It looks like all transmutations are identical to every other when it is written out in a straight line or sequence

but some are alpha and some are beta decays they are not all the same.

Is there a better way to show what is really happening?

Lets try an x-y axis to show itAtomic numberMass numberFollow the directions on the hand-out to change the linear picture into a 2-dimensional display.Use the results to get the range of atomic numbers you need and the range of mass numbers you need to fit on your graph.Once you figure it out, place your Post-It note for your radioisotope on the wall chart in the right location.

Now for some practice on your ownYou have just worked with the decay series for U-238 and discovered a sequence of radioisotopes (including radon gas!)U-235 is a different isotope of uranium. It has its own decay series as it too eventually changes to lead.Give the U-235 decay series a try and practice your skills good luck!

Radon is released into the air and it becomes an environmental health hazard. The radioisotopes that follow radon are called radon progeny and they are very harmful when inhaled into the lungs.