Radiactividad en potencia, Apuntes de Física

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RADIOCHEMISTRY

DR MAHMOUD NAJIM 2020/

RADIOACTIVITY – WHAT IS IT?

• ALL SUBSTANCE ARE MADE OF ATOMS. THESE HAVE ELECTRONS (E)

AROUND THE OUTSIDE, AND A NUCLEUS IN THE MIDDLE. THE

NUCLEUS CONSISTS OF PROTONS (P) AND NEUTRONS (N), AND IS

EXTREMELY SMALL. (ATOMS ARE ALMOST ENTIRELY MADE OF EMPTY

SPACE!)

• IN SOME TYPES OF ATOM, THE NUCLEUS IS UNSTABLE , AND WILL

DECAY INTO A MORE STABLE ATOM. THIS RADIOACTIVE DECAY IS

COMPLETELY SPONTANEOUS. THE ENERGY THAT IS RELEASED FROM

THE NUCLEUS OF THE ATOM IS RADIATION.

RADIOACTIVITY – ALPHA PARTICLES

 Alpha particles are made of 2 protons and 2 neutrons.

 This means that they have a charge of +2 , and a mass of 4

(the mass is measured in "atomic mass units", where each proton & neutron=1)

We can write them as , or, because they're the same as a helium nucleus,.

 Alpha particles are relatively slow and heavy.

 They have a low penetrating power - you can stop them with just a sheet of paper.

 Because they have a large charge, alpha particles ionize (pull electrons from) other atoms

strongly.

RADIOACTIVITY – BETA PARTICLES

 Beta particles have a charge of minus 1 , and a mass of about 1/2000th of a proton. This means that beta particles are the same as an electron. We can write them as or, because they're the same as an electron, , written in isotope notation as  They are fast , and light.  Beta particles have a medium penetrating power - they are stopped by a sheet of aluminum or plastics.  Beta particles ionize atoms that they pass, but not as strongly as alpha particles do.

RADIOACTIVITY – SUMMARY

Particles that ionize other atoms strongly have a low penetrating power , because they lose energy each time they ionize an atom. Therefore, alpha particles are easy to stop and gamma rays are hard to stop.

ISOTOPE NOTATION

• (^) ISOTOPE NOTATION INCLUDES ADDITIONAL INFORMATION ABOUT AN ISOTOPE. IN ADDITION TO THE CHEMICAL SYMBOL, THE MASS NUMBER AND THE ATOMIC NUMBER ARE INCLUDED. THIS ALLOWS INFORMATION ABOUT THE NUCLEUS TO BE DETERMINED.The isotope notation for an atom of uranium-238 is:  The mass number is 238. This is the sum of protons and neutrons in the nucleus. (Protons + Neutrons = Mass)  The atomic number is 92. This is the quantity of protons (and electrons) in the atom. It also leads to the chemical symbol for the isotope.  The chemical symbol “U” is obtained from the name or by looking up the atomic number on the periodic table.

IDENTIFYING ALPHA AND BETA DECAY

REACTIONS

Alpha Decay: Alpha decay is one process that unstable atoms can use to become more stable. During alpha decay, an atom's nucleus sheds two protons and two neutrons in a packet that scientists call an alpha particle. Since an atom loses two protons during alpha decay, it changes from one element to another. For example, after undergoing alpha decay, an atom of uranium (with 92 protons) becomes an atom of thorium (with 90 protons). The reaction above would be written as: (with the He representing the alpha particle)

IDENTIFYING ALPHA AND BETA DECAY

REACTIONS

Beta decay: During beta decay, a neutron turns into a proton and an electron. The electron is emitted and is called a beta particle. This reaction would be written as:

DECAY CHAIN OF U-

• (^) STEP 1: ALPHA DECAY OF URANIUM-

  ---

• (^) STEP 2: BETA DECAY REACTION

  ---

• (^) STEP 3: BETA DECAY REACTION

  ---

• (^) NOW YOU COMPLETE THE REST ………………………

FISSION AND FUSION

• (^) FISSION: FISSION IS THE PROCESS OF SPLITTING AN ATOM.
• (^) FUSION: NUCLEAR FUSION IS THE PROCESS BY WHICH MULTIPLE SMALL ATOMIC NUCLEI JOIN TOGETHER TO FORM A HEAVIER NUCLEUS.

HALF LIFE

• WHEN RADIOACTIVE ISOTOPES DECAY, THEY DO SO EXPONENTIALLY. THEIR RATE OF DECAY IS DETERMINED THROUGH AN UNDERSTANDING OF HALF-LIFE.
• (^) HALF-LIFE IS THE AMOUNT OF TIME IT TAKES FOR HALF OF THE ATOMS OF AN UNSTABLE ISOTOPE TO DECAY.
• (^) ATOMS WITH SHORT HALF-LIVES ARE MORE UNSTABLE THAN THOSE WITH LONG HALF-

HALF LIFE

• WHEN RADIOACTIVE ISOTOPES DECAY, THEY DO SO EXPONENTIALLY. THEIR RATE OF DECAY IS DETERMINED THROUGH AN UNDERSTANDING OF HALF-LIFE.
• (^) HALF-LIFE IS THE AMOUNT OF TIME IT TAKES FOR HALF OF THE ATOMS OF AN UNSTABLE ISOTOPE TO DECAY.
• (^) ATOMS WITH SHORT HALF-LIVES ARE MORE UNSTABLE THAN THOSE WITH LONG HALF-

HALF LIFE EXAMPLES

• (^) AN INITIAL SAMPLE OF ZINC-61 CONTAINS 215 GRAMS. AFTER 976 DAYS , THE SAMPLE SIZE HAS REDUCED TO 13.4375 GRAMS. WHAT IS THE HALF- LIFE OF ZINC-61 ATOMS?
• (^) SOLUTION  AMOUNT TIME 215 GRAMS 0 DAYS

HALF LIFE EXAMPLES

• (^) THORIUM-230 DECAYS WITH A HALF LIFE OF 80, YEARS. IF AN INITIAL SAMPLE HAS A MASS OF 10. GRAMS , HOW MUCH WILL REMAIN AFTER 320, YEARS?
• (^) SOLUTION  AMOUNT TIME 10 GRAMS ___ DAYS (YEARS)