Isotop Geochemistry 1

Faculty of Agro Industry and Natural Resources

On Monday, August 6, 1945, at 8:15 AM, the nuclear bomb "Little Boy" was dropped on Hiroshima by an American B-29 bomber, the Enola Gay, directly killing an estimated 80,000 people. By the end of the year, injury and radiation brought total casualties to 90,000–140,000] . Approximately 69% of the city's buildings were completely destroyed, and about 7% severely damaged.

On August 9, 1945, Nagasaki was the target of the world's second atomic bomb attack (and second detonation of a plutonium bomb; the first was tested in central New Mexico, USA) at 11:02 a.m., when the north of the city was destroyed and an estimated 40,000 people were killed by the bomb codenamed "Fat Man." According to statistics found within Nagasaki Peace Park, the death toll from the atomic bombing totaled 73,884, as well as another 74,909 injured, and another several hundred thousand diseased and dying due to fallout and other illness caused by radiation.[7]

"Little Boy" was the codename of the atomic bomb dropped on Hiroshima on August 6, 1945 by the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul Tibbets of the 393d Bombardment Squadron, Heavy, of the United States Army Air Forces.[2] It was the first atomic bomb to be used as a weapon.

"Fat Man" is the codename for the atomic bomb that was detonated over Nagasaki, Japan, by the United States on August 9, 1945, at 11:02 AM (JSP). It was the second of the only two nuclear weapons to be used in warfare to date"Fat Man" was detonated at an altitude of about 1,800 feet (550 m) over the Japanese city of Nagasaki and was dropped from a B-29 bomber Bockscar, piloted by Major Charles Sweeney of the 393d Bombardment Squadron, Heavy.

Distribution Of Nuclear Reactors

FACULTY OF AGRO INDUSTRY AND NATURAL RESOURCES DEPARTEMENT GEOSCIENCE

Isotope geochemistry is an aspect of geology based upon study of the relative and absolute concentrations of the elements and their isotopes in the Earth.

1. The nucleus which contains:

2. Orbiting electrons.

protonsneutrons

The Atom

The atom consists of two parts:

.

The Atom

All matter is made up of elements (e.g. carbon, hydrogen, etc.).Atom of different elements contain different numbers of protons.The mass of an atom is almost entirely due to the number of protons and neutrons

XA

ZA = number of protons + number of neutrons

Z = number of protons

A – Z = number of neutrons

Number of neutrons = Mass Number – Atomic Number

Isotopes

Isotopes are atoms that contain the same number of protons but a different number of neutrons. The number of protons (the atomic number) is the same for each isotope

U235

92U

238

92

There are many types of uranium:

Isotopes of any particular element contain the same number of protons, but different numbers of neutrons.

A 235

Z 92

Number of protons 92

Number of Neutrons 143

A 238

Z 92

Number of protons 92

Number of neutrons 146

Most of the isotopes which occur naturally are stable. A few naturally occurring isotopes and all of the man-made isotopes are unstable.Unstable isotopes can become stable by releasing different types of particles.This process is called radioactive decay and the elements which undergo this process are called radioisotopes/radionuclides.

Radioactive Decay

Radioactive decay results in the emission of either:

an alpha particle (a)a beta particle (b)or a gamma ray(g).

.

Alpha Decay

An alpha particle is an emission of particle identical to that of a helium nucleus

It contains two protons and two neutrons.

XA

ZY

A - 4

Z - 2+ He

4

2

unstable atom

more stable atom

alpha particle

Alpha Decay

Ra226

88

Rn222

86

He4

2

Alpha Decay

XA

ZY

A - 4

Z - 2+ He

4

2

Ra226

88Rn

222

86+ He

4

2

Alpha Decay

Rn222

86He

4

2+Po

218

84He

4

2

Rn222

86+Y

A

ZHe

4

2

Alpha Decay

He4

2U

234

92+Th

230

90He

4

2

X A

Z+Th

230

90He

4

2

Alpha Decay

Th 230

90+Y

A

ZHe

4

2

He4

2+Ra

226

88He

4

2Th

230

90

Alpha Decay

X A

Z+Pb

214

82He

4

2

He4

2+Pb

214

82He

4

2Po

218

84

Alpha Decay

Beta DecayA beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay.

Beta decay occurs when a neutron changes into a proton and an electron.

Beta Decay

As a result of beta decay, the nucleus has one less neutron, but one extra proton.

The atomic number, Z, increases by 1 and the mass number, A, stays the same.

Po218

84

b0

-1

At218

85

Beta Decay

XA

ZY

A

Z + 1+ b

0

-1

Po218

84Rn

218

85+ b

0

-1

Th234

90Y

A

Z+ b

0

-1

Beta Decay

Th234

90Pa

234

91+ b

0

-1

X A

ZPb

210

82+ b

0

-1

Beta Decay

Tl210

81Pb

210

82+ b

0

-1

Bi210

83Y

A

Z+ b

0

-1

Bi210

83Po

210

84+ b

0

-1

Beta Decay

X A

ZBi

214

83+ b

0

-1

Pb214

82Bi

214

83+ b

0

-1

Beta Decay

Gamma DecayGamma rays are not charged particles like a and b particles. Gamma rays are electromagnetic radiation with high frequency. When atoms decay by emitting a or b particles to form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable. This excess energy is emitted as gamma rays (gamma ray photons have energies of ~ 1 x 10-12 J).

Exponential Decay

Decay of 226Ra

Half-Life

There are a large range of half-lives seen in natureHalf-lives are unaffected by the nuclei’s surroundings and only depend on what goes on inside the nucleus238U has a half-life of 4.5 billion years

Half-Life

To summarize, one-half of the sample will decay in one half-fifeOne-half of that one-half will decay in the next half lifeOne-half of that one-fourth will decay in the next half life

Half-Life

Transmutations

The changing of one element to another is called transmutationThis occurs whenever there is an alpha decay or a beta decayRemember, that for a gamma decay, the nucleus just changes internal energy levels, but doesn’t change the identity of nucleons

Transmutations

Artificial Transmutation

First example was Rutherford bombarding nitrogen with alpha particles4He + 14N -> 17O + 1HHe viewed the reaction with a cloud chamberThe particles left a vapor trail in the mist

Cloud Chamber

When you pull the piston down suddenly, you reduce the air pressure in the chamber. This means vapor is now super-saturated. A charged particle acts as a nucleation seed to condense the liquid from the vapor. This is the same principle as cloud-seeding to make it rain.

Isotopic Dating

Cosmic rays (mostly high energy protons) strike upper atmosphere and cause transmutations that result in many protons and neutrons being sprayed outProtons tend to grab electrons from other atoms and become simple hydrogenNeutrons keep going and smash into other atoms

Isotopic Dating

When a neutron strikes nitrogen1n + 14N -> 14C + 1HIn the atmosphere, 14C is about 1 part in 1011

Reacts with plants just like 12C14C decays via beta emission14C -> 14N + beta half life of 5730 years

Carbon Dating

When a plant dies, it stops the intake of carbonSince the 14C decays, after 5730 years, half of it will be goneWe can just weigh a piece of dead wood, calculate how much 14C it originally had and measure to how much it has now to get the age

Uranium Dating

We know the half -life of 238U and 235UThey have series that end in 206Pb and 207PbCompare how much U vs. special lead and calculate the age of the rock!!Carbon dating only good for about 50,000 yearsUranium rock dating good for millions of years

Nuclear Fission

1n + 235U -> 91Kr + 142Ba + 31n

Chain Reaction

Chain Reaction

The key to keeping the reaction going is that at least one of the neutrons given off, must cause another fissionControlled reaction in a nuclear reactorIf two or three cause fissions, you can get a bomb!Idea of critical mass

Critical Mass

Atom Bomb

Nuclear Reactor

Mass-Energy Relationship

So, where does the mass go?It is the binding energy that is holding the nucleus togetherInteresting to look at the mass per nucleon as we change the atomic number (change which element we look at)

Fusion Reactions

BERITA CHERNOBYLPada 26 April 1986, penduduk Kiev dikejutkan oleh sebuah ledakan besar. Ledakan ini memuntahkan potongan inti reaktor sampai 1500 meter ke langit dan menebarkan awan beracun ke 70 persen daratan eropa. Radioaktivitas total ledakan Chernobyl, menurut WHO, ditaksir 200 kali radiasi bom atom Hiroshima dan Nagasaki.

Kelompok pecinta lingkungan Greenpeace bahkan menaksir, 160 ribu kilometer persegi tanah terkontaminasi bahan radioaktif. Sementara Mantan Sekretaris Jenderal PBB Boutros Boutros Ghali mengatakan, "Kecelakaan Chernobyl tidak dapat dianggap sebagai masalah beberapa abad saja, tapi juga masalah kekinian karena banyak program sosial, ekonomi, dan lingkungan yang harus didefinisikan kembali."

Yang pasti, fakta menunjukkan lima juta orang di sekitar Chernobyl terkena radiasi. Sekitar 650 ribu diantaranya adalah para buruh yang bertugas membersihkan muntahan ledakan Chernobyl. Dan sekitar 200 ribu dari 650 buruh tersebut, merupakan kelompok kunci beresiko tinggi terpapar radiasi. Mereka berada dalam zona penyingkiran, atau sekitar 30 kilometer dari pusat ledakan Chernobyl.

Sepuluh tahun kemudian tercatat, 60 ribu buruh pembersih yang kebanyakan berusia 30 tahunan, meninggal dunia. Sementara 30 persen laki-laki pekerja pembersih yang masih hidup menderita impotensi. Yang menjadi masalah, sebagian besar buruh ini ditolak dalam kehidupan sosialnya. Penyebabnya, mereka dicurigai akan menularkan radiasi dari reaktor PLTN kepada orang-orang di sekitarnya. Hal inilah yang memicu mereka meninggal akibat kecanduan alkohol, mati dalam kemiskinan, serta bunuh diri.

Dokter spesialis penyakit -yang berkaitan dengan tragedi Chernobyl- Natalya Preobrashenskaya mengatakan, selain pekerja pembersih muntahan radioaktif, jutaan anak-anak yang tetap hidup pasca ledakan merupakan kelompok berisiko tinggi terpapar radiasi. Preobrashenskaya bahkan menyatakan, jutaan anak-anak yang lahir di masa mendatang juga akan terkena cemaran radiasi Chernobyl, sesuai prilaku radioaktif yang dipakai sebagai bahan bakar PLTN, jutaan tahun!

Penyakit akibat Radiasi

Apa saja penyakit yang timbul setelah tragedi Chernobyl? Boutros Boutros Ghali menyebutkan, lebih dari 300 anak-anak terdiagnosis kanker gondok, kesuburan pria wanita menurun drastis, dan angka kematian naik.

Secara lebih terperinci, 60 persen anak-anak Ukraina atau sejuta orang lebih menderita kanker gondok, sepuluh persen lainnya yang masih duduk di bangku SD mengalami rusak mental, serta sebagian besar anak-anak Ukraina menderita penyakit tulang. Preobrashenskaya mengatakan, kekebalan tubuh anak-anak Ukraina pun menurun drastis sehingga disebut pula AIDS-Chernobyl.

Penelitian Preobrashenskaya senada dengan penelitian WHO. Badan Kesehatan Dunia itu menyatakan, setelah peristiwa Chernobyl terjadi peningkatan kasus kanker gondok anak, 100 kali dibanding prakecelakaan Chernobyl. Kenyataan lainnya, penduduk Kiev banyak yang terkena kanker paru-paru dan jantung. Dan banyak dokter memperkirakan, dalam waktu mendatang, epidemi berbagai penyakit menular akan meningkat di sekitar lokasi kejadian, dan di kalangan mereka yang terpapar radiasi nuklir.

Tragisnya, terapi kimia normal tidak efektif (mempan-red) pada penderita kanker akibat radiasi Chernobyl. Menurut Dr Andrei Butenko dari rumah sakit nomor satu di Kiev, dipastikan kanker gondok ganas yang menimpa anak-anak Ukraina akibat kontaminasi isotop iodium-131, isotop iodium yang radioaktif. Imbasnya, dengan terapi kimia di atas normal, kepala para pasien membotak dan wajah mereka bengkak-bengkak.

Horor yang kurang lebih sama dialami anak-anak Yunani. Anak-anak di negara tersebut berisiko terkena kanker dua hingga tiga kali akibat Chernobyl. Bahkan, anak-anak Yunani yang terpapar radioaktif ketika masih dalam kandungan ibunya berisiko menderita leukimia 2,6 kali lipat dibanding anak-anak lainnya. Hal ini karena adanya mutasi gen yang diberi nama 11q23.

Mutasi Gen

Mutasi gen merupakan imbas lain dari kejamnya radiasi Chernobyl. Mutasi gen 11q23 ini merupakan salah satu contoh nyata yang berhubungan dengan leukimia pada bayi. "Temuan ini merupakan bukti langsung pertama, bahwa radiasi ternyata menimbulkan mutasi pada anak manusia," ulas Sir Alec Jeffreys, ahli genetika dari Universitas Leicester.

Sir Alec melakukan penelitian pada 79 keluarga yang tinggal di Mogilev, Belarus, kawasan yang terkena radiasi tinggi, kurang lebih 300 kilometer dari Chernobyl. Ia meneliti anak-anak di keluarga tersebut yang lahir antara Februari-September 1994. Sebagai perbandingan, ia juga meneliti 105 anak-anak yang tidak terkena radiasi dari Inggris.

Hasilnya, anak-anak Mogilev terbukti mengalami mutasi gen dua kali lebih tinggi dibandingkan anak-anak di Inggris. Mutasi tersebut jelas diturunkan oleh orang tua mereka, dan secara permanen terkode pada gen anak-anak mereka. Artinya, mutasi tersebut juga akan diturunkan pada generasi-generasi selanjutnya.

Menurut Sir Alec, mutasi pada keluarga di Mogilev berhubungan dengan tingkatan kontaminasi permukaan oleh caesium 137, sebuah isotop radioaktif. Bahkan ahli genetika dari Akademi Sains Rusia Yuri Dubrova menyatakan, kelompoknya melihat lokasi genetik tertentu yang dikenal dengan nama minisatellites yang mengalami laju mutasi 1000 kali lipat lebih tinggi dibandingkan gen lainnya.

Sementara itu, Robert Baker dari Universitas Teknologi Texas meneliti dua kelompok tikus, yaitu kelompok yang tinggal satu kilometer dari reaktor, dan yang hidup 32 kilometer dari reaktor. Yang diteliti adalah mitokondria DNA (bagian sel yang diturunkan induk betina) pada anak tikus-tikus.

Hasilnya, walau tikus yang hidup dekat reaktor terlihat sehat dan subur, tapi mereka mengalami laju mutasi ratusan kali lebih tinggi dari kondisi normal. "Artinya, lingkungan yang tercemar akibat ledakan Chernobyl memberikan dampak nyata perubahan gen pada mahluk hidup sekitarnya," ulas Robert Baker.

Nada miris terdengar dari mulut peneliti Universitas Texas Austin David Hillis. "Kita sekarang tahu, dampak mutasi akibat kecelakaan nuklir mungkin lebih besar daripada yang diharapkan," komentar Hillis.

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