People say you can’t live without love. I think oxygen is more important.

NUCLEI BECOME UNSTABLE WHEN THE RATIO OF PROTONS TO NEUTRONS IS NOT EXACTLY RIGHT AND WHEN THE NUCLEUS IS TOO LARGE.

ALL ELEMENTS ABOVE ATOMIC NUMBER 92 ARE RADIOACTIVE.

RADIOACTIVITY RESULTS WHEN THE UNSTABLE NUCLEUS EITHER BREAKS APART TO FORM SMALLER, STABLE NUCLEI OR IT GIVES OFF RADIATION IN ORDER TO STABILIZE OR BOTH.

HALF LIFE IN NUCLEAR CHEMISTRY IS THE TIME REQUIRED FOR HALF THE UNSTABLE NUCLEI TO UNDERGO RADIOACTIVE DECAY.

THE SHORTER THE HALF LIFE, THE FASTER DECAY OCCURS, AND MORE RADIATION PER UNIT TIME WILL BE PRODUCED.

THE FOLLOWING KINDS OF RADIATION CAN BE GIVEN OFF:

•ALPHA PARTICLES, a – HIGH SPEED HELIUM NUCLEI (2 PROTONS AND 2 NEUTRONS)

•BETA PARTICLES, b – HIGH SPEED ELECTRONS

•GAMMA RAYS, g - HIGH ENERGY, SHORT WAVELENGTH RADIATION SIMILAR TO X-RAYS

•NEUTRONS

IN TERMS OF DANGER TO HUMAN HEALTH:

ALPHA PARTICLES WILL NOT PENETRATE THE SKIN. THEY COULD BE STOPPED BY A COUPLE OF SHEETS OF PAPER AND A FEW FEET OF AIR. ALPHA EMITTERS WOULD ONLY BE A DANGER IF INGESTED.

BETA PARTICLES CAN PENETRATE THE SKIN, SO BETA EMITTERS WOULD BE AN INTERNAL AND EXTERNAL HAZARD. THEY COULD BE STOPPED BY A SHEET OF ALUMINUM OR SEVERAL FEET OF AIR.

GAMMA RAYS ARE VERY PENETRATING AND WOULD BE THE MOST HAZARDOUS. SEVERAL FEET OF CONCRETE OR SHEETS OF LEAD WOULD BE NEEDED TO STOP THEM.

NEUTRONS WOULD BE SIMILAR TO BETA PARTICLES.

MUCH OF THE HAZARD OF RADIOACTIVE MATERIALS WOULD BE DETERMINED BY THE HALF LIFE OF THE ELEMENT.

SOMETHING WITH A SHORT HALF LIFE IS GOING TO DECAY RAPIDLY, WHILE SOMETHING WITH A LONG HALF LIFE WILL NOT.

THE CHEMICAL NATURE OF THE ELEMENT WILL ALSO PLAY A PART IN HOW HAZARDOUS THE MATERIAL IS.

FOR EXAMPLE, ONE RADIOACTIVE ISOTOPE GIVEN OFF IN A NUCLEAR EXPLOSION IS STRONTIUM-90. STRONTIUM IS VERY SIMILAR TO CALCIUM. IF IT WERE SCATTERED OVER A WIDE AREA, SOME WOULD END UP ON GRASS EATEN BY COWS AND, IN TURN, WOULD END UP IN MILK. SINCE IT IS SIMILAR TO CALCIUM, IT COULD BE ABSORBED INTO BONES.

ANOTHER VERY IMPORTANT ISOTOPE IS IODINE-131. IT ACCOUNTS FOR ABOUT 3% OF ALL FISSION PRODUCTS OF URANIUM. IT HAS A HALF LIFE OF 8 DAYS, SO IT IS PRETTY HOT, AND IT IS A BETA EMITTER.

IODINE IS TAKEN UP BY THE THYROID GLAND, AND SMALL AMOUNTS OF IODINE-131 CAN CAUSE THYROID CANCER.

PEOPLE IN NUCLEAR ACCIDENTS ARE GIVEN IODINE TABLETS TO PREVENT THE UPTAKE OF IODINE-131.

WE CAN REPRESENT ISOTOPES OF ELEMENTS AS FOLLOWS:

U

THE SUPERSCRIPT REPRESENTS THE ATOMIC MASS, AND THE SUBSCRIPT REPRESENTS THE ATOMIC NUMBER.

SOMETIMES IN WRITING, YOU MAY SEE IT AS URANIUM 238.

238

92

IN NUCLEAR REACTIONS, THE RADIATION GIVEN OFF CAN CHANGE THE NUCLEUS, SO THE ATOM BECOMES A DIFFERENT ELEMENT.

AN ALPHA PARTICLE, , a IS A HELIUM NUCLEUS, SO WE COULD THINK OF IT AS

a = 42He

A BETA PARTICLE, b, IS A HIGH SPEED ELECTRON, SO WE COULD THINK OF IT AS

b = e-

IF A NUCLEUS LOSES A BETA PARTICLE, A NEUTRON IS CONVERTED TO A PROTON.

SOME EXAMPLES OF NUCLEAR REACTIIONS:

23292U 228

90Th + a

74Be 7

4Be + g

31H 3

2He + b