AUGUST, 2014

ATOM FOR PEACE, NOT FOR WAR Prof. Manashi Goswami ComeAugust,thewhole worldremembers Three otherplanes had left earlierin orderto two frightfuldays ofworld history,August 6th ascertain the weather condition over the and 9th, 1945. The atomic bombings of the possibletargets.On thehookinthe ceiling of cities of Hiroshima and Nagasaki in Japan the plane hung the ten- foot atomic bomb wereconducted onthesedays by theUnited "Little Boy". On 6th August,1945, the first States during the finalstageofWorld WarII. choice target Hiroshima, was having clear These two bombings werethefirst and remain weather.At 8:15(am) localtime, Enola Gay's theonly useofnuclearweapons in warfare. doorsprangopen and itdroppedthe little boy. By August1945, theallied Manhattan project had successfully tested an atomic deviceand had produced weapons based on two alternate designs.Auranium gun type atomic bomb (Little Boy) was dropped on Hiroshima on August 6,1945, followed by a Plutoniumimplosion-type bomb (Fat Man) onthecity ofNagasakionAugust 9. Within thefirsttwo to fourmonths of thebombing, The Mushroom Cloud acute effect killed 90,000 - 166,000 people Thebomb exploded 1,900feet abovethe in Hiroshima and 60,000 - 80,000 in city.The mushroom cloud itself was a Nagasaki. During the following months large number of people died various radiation spectacularsight.Abubbling mass ofpurple- effects and injuries. gray smoke with a hot red burning core estimated to have reached a height of 40,000 On the Day feet.Such was the description of dreadful At 2.45 amonMonday,August 6,1945a devastation that tookplaceon6th August1945 B-29 bomber plane,the Enola Gay tookoff at Hiroshima city. from Tinian, a north pacific island in the Why Hiroshima Marinianas,1500 miles south of Japan. Colonel Paul Tibbets, the pilot nick named TheU.S.A. beganinspring 1945studying B-29 as "Enola Gay"after his mother. Just targets for dropping of the atomic bomb.To beforethetake-offtheplane's nick namewas observe accurately the effect of atomic painted on its sides. The Enola Gay was bombing, the potentialcities required tohave escorted by two other bombers that carried an urban area ofat least 5 kmin diameter. On cameras and avarietyof measuringinstruments. July 25,1945, an orderwas issued calling for ScienceHorizon 3 AUGUST, 2014 thefirst atomic bomb to be dropped on one of tremendous amount of energy.Forexample the four cities Hiroshima,Kokura,Niigata & splitting of one atom of uraniumproduces Nagasaki. The name Hiroshima as the prime around 220 MeV of energy. The fission targetwasissued onAugust2. Onereason is process becomes self-sustaining as neutrons that Hiroshima was the only city thought to produced by the splitting of atom strike have noAllied-prisoner-of-warcamps. On6th nearby nuclei and produce more fission. August,the sky overHiroshima city was clear This is known as chainreaction which causes hence Hiroshima's fate was destined for nuclearexplosion. destruction. The Science Behind Atom Bomb A nuclear explosionis an explosionthat occurs as a result of the rapid release of energy from high speed nuclear fission or fusion reaction. Thedriving reaction may be nuclearfission,nuclearfusion ora multistage cascading combination oftwo. The immense destructive power of atomic weapons is derived from a sudden release of energy produced by splitting the nuclei of the fissileelements making up the bomb's core.TheU.S.developedtwo typesof fission based atomicbombs during the second worldwar.The first"LittleBoy"was aguntype weapon with a uranium core. The second weapon dropped onNagasakiwas called "Fat Man" and was an implosion -type device with Nuclear Chain Reaction a plutoniumcore. Natural uranium contains very less amount (0.7%) offissionable U-235isotopes Fission and rest is U-238isotopes.Whena uranium- The isotopes Uranium- 235 and 235atomabsorbs a neutron and splits into two Plutonium-239 readily undergo fission. newatoms , itreleases three new neutrons and Fissionoccurs when athermal neutronstrikes the sum total of mass lost in the process the nucleus of either isotope splitting the appears in the form of energy according to isotopes into fragments and releasing a Einstein's famous Mass-Energyequivalence

4 ScienceHorizon AUGUST, 2014 formula E= mc2.Two neutrons donot continue U-238, the isotope often captures the neutron the chain reaction because they are lost or to become U-239,failing to fission,and thus absorbed by U-238 atom. However, on an failing to instigate a chain reaction that would average one neutron does collide with a detonatea bomb.Hencethefirst challengeof neighbouring atomofU-235,which thensplits theproject was todeterminethe most efficient andreleases again neutronsand someenergy. way to separate and purify U-235 from the Thiscauses a nuclearchain reaction. overly abundant U-238. Criticality Inorder todetonateanatomic weapon,a criticalmass offissionablematerial is needed. This means enough uranium-235orplutonium- 239is required to ensurethat neutrons released by fission will strike another nucleus, thus producing a chain reaction. The more fissionable material is available the more is thechancethat suchan eventwilloccur.Critical mass is defined as the amount of materialat whicha neutronproducedbya fissionprocess will,on an averagecreateanother fission event. Difference between Little Boy& FatMan Little Boy Little Boy and Fat Man utilized different Once enough Uranium-235was obtained elementsand completely separatemethods of to power the bomb, the bomb was assembled construction in orderto function as nuclear withagun type design.Inthis specialdesignan weapons. Little Boy detonateddue to a fission amount ofU-235 is fired atanother tocombine chain reaction involving the isotope U-235of the two masses. This combination created a uranium,while Fat Man used Pu-239isotope critical mass that sets off a fission chain ofplutonium. reaction to eventually detonate a bomb. The Little Boy two masses ofU-235had to combine quickly LittleBoy was powered by theUranium to avoid the spontaneous decay ofthe atom isotope U-235.Most Uraniumfoundnaturally whichwould cause thebombtofizzle and thus in the world exist as U-238, leaving only failto explode. Little Boy was carrying around 0.7%of naturally existing Uranium as the 64kg ofpure U-235ofwhich only 0.6kg was U-235isotope. Whena neutron bombards on detonated during the explosion.

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Fat Man Powered by Plutonium, Fat Man could not use thesamegun-typedesign that allowed Little Boy to explode effectively. The form ofPlutoniumcollected was containing traces ofPu-240 isotope,asopposed to thedesired Pu-239. Pu-240's higher decay rate would causespontaneous decaybeforethe gun type Fat Man design could bring twomasses ofplutonium Atom for Peace together. This process lowers the energy Itwas unfortunate thatthe atomic energy involved in theactualdetonationof the bomb. beforebeing utilizedforthebenefit ofmankind Hence,a newdesign was constructed atLos was used fordestructionofmankind.In 1950s Alamoslaboratory ofU.S.A.The newdesign the attention was shifted to harnessing the used conventionalexplosives arounda central power of the atom in a controlled manner to Plutonium mass to quickly squeeze and apply the steady heat yield for generating consolidate Plutonium, increasing pressure electricity throughnuclear reactors.However, and density of the substance.An increased by 1942 the first artificial nuclear reactor, density allowed the Plutonium to reach its Chicago Pile -1had been already constructed critical mass, firing neutrons and allowing at the University ofChicago bya team led by fission chain reaction to proceed. To Enrico Fermi. Buttheprimary purpose ofthose detonate the bomb the explosives were reactors was themass production ofPlutonium ignited, releasing a shock wave that isotopes for nuclear weapons. Besides the compressed the inner Plutonium core and military use of nuclear power, there were led to its explosion.Fat Man was carrying politicalreasons topursue civilianuse ofatomic 6.2kg of plutonium,of which only 20% was energy.U.S.A. president Dwight Eisenhower detonated during explosion. madehis famous ATOM FORPEACEspeech to the UN general assembly on December 8, 1953. This diplomacy led to the dissemination of reactor technology to all institutions worldwide including those in U.S.A. Before 1950s, radiation from Radium was the only source for treatment of cancer. Nownuclear reactorhas opened uppossibilities formaking other elements radioactive. These

6 ScienceHorizon AUGUST, 2014 radioactiveisotopes are nowusedextensively At present 30 countries worldwide are in medicine, agriculture and industry. operating435nuclearreactors providing12.3% Radioactiveisotopes have helpedindiagnosis of the world's electricity. The use of nuclear and prevention ofmanycritical diseases.They power in domestic and commercial purpose are ofimmense use in the field of agriculture has become a reality in France since 1976. for betterproduction of crops,high yielding France has been stilldominatingthe world in variety of seeds,pest control and fertilisers. nuclear power with 73.3% share of its total Radiation alternatedvaccine has immunised powerconsumption.AfterKudankulamreactor sheep fromlungwormdiseases.In Indiaunder of India being fully operational with almost UNDP (United Nation Development Programme)collaboration such vaccines are going to be produced commercially in a laboratory locatedin Kashmir Valley. Bhabha Atomic Research Centre at Trombay is well known in the world for production of many usefulradioisotopes.It produces nearabout 325radioisotopes.

Kudankullan Reactor Centre

1000MW poweroutput,thenumber ofreactors in India has been raised to 21,with nuclear power capacity of 5308 MW and nuclear powersharehas enhancedto 3.5%. Thewhole BhabhaAtomic Research Centre (Trombay). world has now realised that nuclear energy is Perishable food stuffs, if exposed to the ultimate sourceofenergywhich can reduce radiation, are found to remain fresh beyond thegreenhouse gases andsave ourearth from theirnormal time. Hence radiation is used for global warming, which is pushing it to a big canningoffoodandpreservation.In a tropical catastrophe. So it is well justified that atom country like India, self- life of fruits and only canbring peace to the world intruesense, vegetables are short.Small dose of radiation if immensely available energy from its core prevents sprouting ofpotatoand onion while can be judiciously harnessed and utilised for higherdose can delay the ripening ofmango, the well being ofthe entire mankind. apple,banana etc. BARC,Trombay has a semi  Regional InstituteofEducation,Bhubaneswar-22 commercialfood processing plant. Mob.- 9439615558

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