"More than any other time in history, mankind faces a crossroads. One path leads to despair and utter hopelessness. The other, to total extinction. Let us pray we have the wisdom to choose correctly." Woody Allen Woody Allen

NUCLEAR ENERGY HOW MANY OF YOU HAVE SEEN A NUCLEAR REACTOR?

A DAY WITOUT FUSION IS LIKE A DAY WITHOUT SUNSHINE.

THERE ARE TWO SOURCES OF NUCLEAR ENERGY: 1)NUCLEAR FUSION – WHEN LIGHT NUCLEI ARE COMBINED TO MAKE HEAVIER NUCLEI – EXAMPLES ARE THE SUN, NUCLEAR FUSION REACTORS, AND HYDROGEN BOMBS 2)NUCLEAR FISSION – WHEN HEAVIER NUCLEI BREAK APART TO FORM LIGHTER NUCLEI – EXAMPLES ARE NUCLEAR REACTORS AND ATOMIC BOMBS BOTH SOURCES OF ENERGY INVOLVE THE STRONG AND WEAK NUCLEAR FORCES IN THE NUCLEUS.

BRIEFLY, THERE ARE FOUR FUNDAMENTAL FORCES IN NATURE: GRAVITY IS THE WEAKEST. IT ACTS BETWEEN PARTICLES HAVING MASS AND CAN ACT AT VERY LONG DISTANCES, BUT ITS FORCE DECREASES WITH DISTANCE. F g = (G x M 1 x M 2 ) / d 2 GRAVITY IS ALWAYS POSITIVE. ELECTROMAGNETISM CAN ALSO ACT AT VERY LONG DISTANCES. IT IS THE FORCE BETWEEN ELECTRICALLY CHARGED PARTICLES, AND IT CAN BE POSITIVE OR NEGATIVE. F E = kQ 1 Q 2 / d 2 IT IS THE FORCE INVOLVED IN CHEMICAL BONDS.

THE OTHER TWO FORCES ACT A VERY SMALL DISTANCES AND ARE INVOLVED IN THE NUCLEI OF ATOMS. THE WEAK FORCE IS RESPONSIBLE FOR BETA DECAY. IT ACTS AT VERY SHORT DISTANCES ( m). THE STRONG FORCE ALSO ACTS AT VERY SHORT DISTANCES ( m). IT IS RESPONSIBLE FOR HOLDING THE PARTICLES IN THE NUCLEUS TOGETHER. IT IS ALWAYS POSITIVE. SINCE IT ACTS AT VERY SHORT DISTANCES, THIS IS WHY IN NUCLEAR FUSION THAT YOU HAVE TO BRING POSITIVELY CHARGED NUCLEI VERY CLOSE TOGETHER IN ORDER TO GET THEM TO FUSE (AND TO OVERCOME THE REPULSION OF LIKE POSITIVE CHARGES).

NUCLEAR BINDING ENERGY IS VERY STRONG. NUCLEAR BINDING ENERGY IS DEFINED AS THE ENERGY REQUIRED TO BREAK A NUCLEUS DOWN INTO ITS RESPECTIVE NUCLEONS (NEUTRONS AND PROTONS). 63 Cu + Energy  29 p n o IT IS USUALLY GIVEN AS ENERGY PER NUCLEON. IF YOU THINK OF THE ABOVE EQUATION IN REVERSE, YOU COULD ALSO THINK OF IT AS THE ENERGY THAT WOULD BE RELEASED IN NUCLEUS FORMATION.

IF YOU LOOK AT A PLOT OF BINDING ENERGY VERSUS MASS NUMBER, YOU CAN GET A PRETTY GOOD IDEA OF WHERE THE ENERGY IN NUCLEAR REACTIONS COMES FROM. IRON HAS THE MOST STABLE NUCLEI.

TO FORM ELEMENTS FROM IRON AND BELOW, THE FUSION PROCESS WOULD RELEASE ENERGY. TO FORM ELEMENTS ABOVE IRON, ENERGY WOULD HAVE TO BE ADDED. ELEMENTS HEAVIER THAN IRON COULD RELEASE ENERGY THROUGH FISSION.

E = MC 2 THIS EQUATION IS ASSOCIATED WITH NUCLEAR ENERGY. IT IS USUALLY INTERPRETED AS MASS CAN BE CONVERTED INTO ENERGY. IN SOME EXTREME (VERY) CASES, THIS IS TRUE. HOWEVER, WHAT IT REALLY MEANS IS THAT ENERGY HAS MASS. LET’S GO BACK TO OUR EQUATION FOR COPPER. 63 Cu + Energy  29 p n o A NUCLEUS OF 63 Cu HAS A MASS OF amu. A PROTON HAS A MASS OF amu. A NEUTRON HAS A MASS OF amu.

SO, IF WE DO THE MATH 29 protons( amu/proton) + 34 neutrons( amu/neutron) or amu THE MASS DEFICIT IS amu – amu = amu IF YOU PLUG THIS INTO THE E = MC 2 EQUATION, YOU END UP WITH THE BINDING ENERGY OF THE NUCLEUS. THE EQUATION WOULD HOLD FOR CHEMICAL REACTIONS, TOO. HOWEVER, THE ENERGIES INVOLVED ARE SO MUCH LOWER, THAT THE MASS CHANGES WOULD NOT BE EASILY MEASURABLE.

LET’S CONSIDER FUSION FIRST. IN FUSION, WE ARE FUSING LIGHTER NUCLEI TO MAKE HEAVIER NUCLEI. AGAIN, WE CAN GET ENERGY OUT OF THIS PROCESS UP TO IRON. BEYOND IRON, WE HAVE TO PUT ENERGY IN.

NOW, KEEP IN MIND THAT THE STRONG NUCLEAR FORCE ONLY WORKS AT VERY SHORT DISTANCES, M. SO, TO GET FUSION TO OCCUR, YOU HAVE TO OVERCOME THE ELECTROSTATIC FORCES OF REPULSION OF THE POSITIVE NUCLEI TO GET THEM CLOSE ENOUGH TO FUSE. TO GET THE NUCLEI MOVING FAST ENOUGH TO DO THIS REQUIRES VERY HIGH TEMPERATURES. MOTHER NATURE IS VERY GOOD AT DOING THIS IN THE CORES OF STARS.

THE FORCE OF GRAVITY IS TENDING TO COLLAPSE THE HUGE MASS OF A STAR INWARD TOWARDS THE CORE. THIS GENERATES VERY HIGH TEMPERATURES. THIS IGNITES FUSION REACTIONS WHICH GENRATE HUGE AMOUNTS OF ENERGY. THIS ENERGY TENDS TO PUSH THE MASS BACK OUT, AND EQUILIBRIUM IS REACHED.

THE CORE OF OUR SUN IS AT 15,000,000 o PLUS. OUR SUN IS FUSING HYDROGEN TO HELIUM. THIS IS A GREAT SOURCE OF ENERGY, BUT HOW WOULD WE ACHIEVE THIS ON EARTH. THERE ARE TWO PROBLEMS: 1)HOW DO YOU REACH START UP TEMPERATURE 2)HOW DO YOU CONTAIN THE HOT MATERIAL IN EXPERIMENTAL FUSION REACTORS, WE HAVE USED MAGNETIC FIELDS TO CONTAIN THE REACTIONS. IN EXPERIMENTAL FUSION REACTORS, WE ARE CURRENTLY USING HIGH ENERGY LASERS TO INITIATE THE REACTIONS. WE ARE PROBABLY 20 TO 50 YEARS AWAY FROM A COMMERCIAL FUSION REACTOR.

NUCLEAR FISSION OCCURS WHEN HEAVY NUCLEI BREAK APART TO FORM SMALLER NUCLEI. THIS CAN OCCUR WHEN NUCLEI BECOME SO LARGE THAT THEY BECOME UNSTABLE. ALL ELEMENTS WITH ATOMIC NUMBER 92 AND ABOVE ARE RADIOACTIVE. IT CAN ALSO OCCUR WHEN THE RATIO OF PROTONS TO NEUTRONS IS TOO HIGH. THE IDEAL RATIO IS 1:1. INSTABILITY OCCURS ABOVE THIS. NUCLEAR FISSION CAN ALSO BE INDUCED. WHEN A NEUTRON COLLIDES WITH A NUCLEUS AT THE RIGHT SPEED, THE NUCLEUS CAN BECOME UNSTABLE AND DISINTEGRATE. THIS CAN HAPPEN IN U235 AND Pu239.

The size of the nucleus is limited 1) The nucleus cannot hold a very large number of protons together. 2) There cannot be an unlimited number of neutrons. 2) There cannot be an unlimited number of neutrons.

ISOTOPES WITH UNSTABLE NUCLEI CAN NATURALLY UNDERGO FISSION BY GIVING OFF ALPHA PARTICLES, BETA PARTICLES OR NEUTRONS. THE AMOUNT OF ENERGY GIVEN OFF PER UNIT TIME DEPENDS ON HALF LIFE AND THE TYPE OF DISENTIGRATION. USUALLY, IT IS NOT GREAT.

IF YOU WANT LOTS OF ENERGY, YOU HAVE TO RESORT TO INDUCED FISSION. IN THIS CASE, YOU BOMBARD AN ISOTOPE WITH NEUTRONS TO CAUSE FISSION TO OCCUR.