General Science

PHYSICS: NUCLEAR PHYSICS

Nuclear Fission

• Nuclear fission is a reaction in which the nucleus of an atom splits into smaller parts
• Nuclear fission can either release energy or absorb energy: for nuclei lighter than iron fission absorbs energy, while for nuclei heavier than iron it releases energy
• Energy released can be in the form of electromagnetic radiation or kinetic energy
• The amount of free energy contained in nuclear fuel is about a million times that contained in a similar mass of chemical fuel (like petrol)
• The atom bomb or fission bomb is based on nuclear fission
• Example: fission of Uranium-235 to give Barium, Krypton and neutrons

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Nuclear Fusion

• Nuclear fusion is the process by which multiple nuclei join together to form a heavier nucleus
• Nuclear fusion can result in either the release or absorption of energy: for nuclei lighter than iron fusion releases energy, while for nuclei heavier than iron it absorbs energy
• Nuclear fusion is the source of energy of stars.
• Nuclear fusion is responsible for the production of all but the lightest elements in the universe. This process is called nucleosynthesis
• Controlled nuclear fusion can result in a thermonuclear explosion – the concept behind the hydrogen bomb
  
• The energy density of nuclear fusion is much greater than that of nuclear fission
  
• Only direct conversion of mass into energy (collision of matter and anti matter) is more energetic than nuclear fusion
• Example: fusion of hydrogen nuclei to form helium
  

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PIONEERS OF NUCLEAR PHYSICS RESEARCH

Scientist	Nationality	Discovery	Recognition
J J Thomson	Britain	Electron (1897)	Nobel in Physics (1906)
Henri Becquerel	Belgium	Radioactivity (1896)	Nobel in Physics (1903)
Ernest Rutherford	New Zealand	Structure of atom (1907)	Nobel in Chemistry (1908) He is regarded as the father of nuclear physics
Franco Rasetti	Italy/USA	Nuclear spin (1929)
James Chadwick	Britain	Neutron (1932)	Nobel in Physics (1935)
Enrico Fermi	Italy/USA	Nuclear chain reaction (1942) Neutron irradiation	Nobel in Physics (1938)
Hideki Yukawa	Japan	Strong nuclear force (1935)	Nobel in Physics (1949)
Hans Bethe	Germany/USA	Nuclear fusion (1939)	Nobel in Physics (1967)

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APPLICATIONS OF NUCLEAR PHYSICS

Application	Developed by	Working principle	Use
Nuclear power	Enrico Fermi (Italy, 1934)	Nuclear fission	Power generation
Nuclear weapons	Enrico Fermi (Italy, 1934) Edward Teller (USA, 1952)	Nuclear fission Nuclear fusion	Weapons
Radioactive pharmaceuticals	Sam Seidlin (USA, 1946)	Radioactive decay	Cancer, endocrine tumours, bone treatment
Medical imaging	David Kuhl, Roy Edwards (USA, 1950s)	Nuclear magnetic resonance (for MRI) Positron emission (for PET)	MRI: Musculosketal, cardiovascular, brain, cancer imaging PET: cancer, brain diseases imaging
Radiocarbon dating	Willard Libby (USA, 1949)	Radioactive decay of carbon-14	Archaeology

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IMPORTANT NUCLEAR RESEARCH FACILITIES

Nuclear research facilities in the world

Facility	Location	Established	Famous for
Brookhaven National Lab	New York	1947	Until 2008 world’s largest heavy-ion collider
European Organization for Nuclear Research (CERN)	Geneva	1954	World’s largest particle physics lab Birthplace of the World Wide Web Large Hadron Collider (LHC)
Fermilab	Chicago	1967	Tevatron – world’s second largest particle accelerator
ISIS	Oxfordshire (England)	1985	Neutron research
Joint Institute for Nuclear Research	Dubna, Russia	1956	Collaboration of 18 nations including former Soviet states, China, Cuba
Lawrence Berkeley National Lab	California	1931	Discovery of multiple elements including astatine, and plutonium
Lawrence Livermore National Lab	California	1952
Los Alamos National Lab	New Mexico, USA	1943	The Manhattan Project
National Superconducting Cyclotron lab	Michigan	1963	Rare isotope research
Oak Ridge National Lab	Tennessee	1943	World’s fastest supercomputer – Jaguar
Sudbury Neutrino Lab	Ontario	1999	Located 2 km underground Studies solar neutrinos
TRIUMF (Tri University Meson Facility)	Vancouver	1974	World’s largest cyclotron
Yongbyon Nuclear Scientific Research Centre	Yongbyon, North Korea	1980	North Korea’s main nuclear facility
Sandia National Lab	New Mexico, USA	1948	Z Machine (largest X-ray generator in the world)
Institute of Nuclear Medicine, Oncology and Radiotherapy (INOR)	Abbottabad, NWFP (Pakistan)
Pakistan Institute of Nuclear Science and Technology (PINSTECH)	Islamabad	1965

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Nuclear research facilities in India 

Facility	Location	Established	Famous for
Bhabha Atomic Research Centre	Bombay	1954	India’s primary nuclear research centre India’s first reactor Apsara
Variable Energy Cyclotron Centre (VECC)	Calcutta	1977	First cyclotron in India
Institute for Plasma Research (IPR)	Gandhinagar	1982	Plasma physics
Indira Gandhi Centre for Atomic Research (IGCAR)	Kalpakkam	1971	Fast breeder test reactor (FBTR) KAMINI (Kalapakkam Mini) light water reactor Built the reactor for Advanced Technology Vessel (ATV)
Saha Institute for Nuclear Physics	Calcutta	1949
Tata Institute for Fundamental Research (TIFR)	Bombay	1945

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CHEMISTRY: POLYMERS

Overview

• A polymer is a large molecule consisting of repeating structural units
• The repeating units are usually connected by covalent chemical bonds
• Polymers can be of two types
  • Natural polymers: shellac, amber, rubber, proteins etc
  • Synthetic polymers: nylon, polyethylene, neoprene, synthetic rubber etc
• Synthetic polymers are commonly referred to as plastics
• The first plastic based on a synthetic polymer to be created was Bakelite, by Leo Baekeland(Belgium/USA) in 1906
• Vulcanization of rubber was invented by Charles Goodyear (USA) in 1839. Vulcanization is the process of making rubber more durable by addition of sulphur
  
• The first plastic to be created was Parkesine (aka celluloid) invented by Alexander Parkes (England) in 1855

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Synthesis of polymers

• The synthesis of polymers – both natural and synthetic – involves the step called polymerization
• Polymerization is the process of combining many small molecules (monomers) into a covalently bonded chain (polymer)
• Synthetic polymers are created using of two techniques
  • Step growth polymerization: chains of monomers are combined directly
  • Chain growth polymerization: monomers are added to the chain one at a time
• Natural polymers are usually created by enzyme-mediated processes, such as the synthesis of proteins from amino acids using DNA and RNA

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Categories of polymers

• Organic polymers are polymers that are based on the element carbon. Eg: polyethylene, cellulose etc
• Inorganic polymers are polymers that are not based on carbon. Eg: silicone, which uses silicon and oxygen
• Copolymer is one that is derived from two or more monomeric units. Eg: ABS plastic
• Fluoropolymers are polymers based on fluorocarbons. They have high resistance to solvents, acids and bases. Eg: teflon

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TYPES OF BIOPOLYMERS

DNA as a biopolymer

1. Structural proteins
   1. Structural proteins are proteins that provide structural support to tissues
   2. They are usually used to construct connective tissues, tendons, bone matrix, muscle fibre
   3. Examples include collagen, keratin, elastin
2. Functional proteins
   1. Proteins that perform a chemical function in organisms
   2. Usually used for initiate or sustain chemical reactions
   3. Examples include hormones, enzymes
3. Structural polysaccharides
   1. They are carbohydrates that provide structural support to cells and tissues
   2. Examples include cellulose, chitin
4. Storage polysaccharides
   1. Carbohydrates that are used for storing energy
   2. Eg: starch, glycogen
5. Nucleic acids
   1. Nucleic acids are macromolecules composed of chains of nucleotides
   2. Nucleic acids are universal in living beings, as they are found in all plant and animal cells
   3. Eg: DNA, RNA

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TYPES OF SYNTHETIC POLYMERS

1. Thermoplastics
   1. Thermoplastics are plastics that turn into liquids upon heating
   2. Also known as thermosoftening plastic
   3. Thermoplastics can be remelted and remoulded
   4. Eg: polyethylene, Teflon, nylon
   5. Recyclable bottles (such as Coke/Pepsi) are made from thermoplastics
2. Thermosetting plastics
   1. Thermosettings plastics are plastics that do not turn into liquid upon heating
   2. Thermosetting plastics, once cured, cannot be remoulded
   3. They are stronger, more suitable for high-temperature applications, but cannot be easily recycled
   4. Eg: vulcanized rubber, bakelite, Kevlar
3. Elastomers
   1. Elastomers are polymers that are elastic
   2. Elastomers are relatively soft and deformable
   3. Eg: natural rubber, synthetic polyisoprene

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IMPORTANT NATURAL POLYMERS AND THEIR APPLICATIONS

Polymer		Application	Notes
Collagen		Connective tissue Gelatine (food)	Most abundant protein in mammals
Keratin		Hair, nails, claw etc
Enzymes		Catalysis
Hormones		Cell signalling
Cellulose		Cell wall of plants Cardboard, paper	Most common organic compound on Earth
Chitin		Cell wall of fungi, insects
Starch		Energy storage in plants	Most important carbohydrate in human diet
Glycogen		Energy storage in animals
DNA		Genetic information
RNA		Protein synthesis

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IMPORTANT SYNTHETIC POLYMERS AND THEIR APPLICATIONS

Polymer	Developed by	Constituent elements	Application	Notes
Parkesine	Alexander Parkes (Britain, 1855)	Cellulose	Plastic moulding	First man-made polymer
Bakelite	Leo Baekeland (USA, 1906)	Phenol and formaldehyde	Radios, telephones, clocks	First polymer made completely synthetically
Polyvinylchloride (PVC)	Henri Regnault (France, 1835)	Vinyl groups and chlorine	Construction material	Third most widely used plastic
Styrofoam	Ray McIntre (USA, 1941)	Phenyl group	Thermal insulation	Brand name for polystyrene
Nylon	Wallace Carothers (USA, 1935)	Amides	Fabric, toothbrush, rope etc	Family of polyamides First commercially successful synthetic polymer
Synthetic rubber	Fritz Hoffman (Germany, 1909)	Isoprene	Tyres, textile printing, rocket fuel
Vulcanized rubber	Charles Goodyear (USA, 1839)	Rubber, sulphur	Tyres	Vulcanized rubber is much stronger than natural rubber
Polypropylene	Karl Rehn and Guilio Natta (Italy, 1954)	Propene	Textiles, stationary, automotive components	Second most widely used synthetic polymer
Polyethylene	Hans von Pechmann (Germany, 1898)	Ethylene	Packaging (shopping bags)	Most widely used synthetic polymer
Teflon	Roy Plunkett (USA, 1938)	Ethylene	Cookware, construction, lubricant	Brand name for polytetrafluoroehtylene (PTFE) Very low friction, non-reactive

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DEGRADATION OF POLYMERS

Ozone cracking in natural rubber tubing

• Degradation of polymers can be desirable as well undesirable: desirable when looking for biological degradation, undesirable when faced with loss of strength, colour etc
• Polymer degradation usually occurs due to hydrolysis of covalent bonds connecting the polymer chain
• Polymer degradation can happen because of heat, light, chemicals and galvanic action
• Ozone cracking is the cracking effect of ozone on rubber products such as tyres, seals, fuel lines etc. Usually prevented by adding antiozonants to the rubber before vulcanization
• Chlorine can cause degradation of plastic as well, especially plumbing
• Resin Identification Code is the system of labelling plastic bottles on the basis of their constituent polymers. This Code helps in the sorting and recycling of plastic bottles
• Degradation of plastics can take hundreds to thousands of years

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Biodegradable plastics

• Biodegradable plastics are plastics than can break down upon exposure to sunlight (especially UV), water, bacteria etc
• Biopol is a biodegradable polymer synthesized by genetically engineered bacteria
• Ecoflex is a fully biodegradable synthetic polymer for food packaging

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Bioplastics

• They are organic plastics derived from renewable biomass sources such as vegetable oil, corn, starch etc

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Oxy-biodegradable plastics

• Plastics to which a small amount of metals salts have been added
• As long as the plastic has access to oxygen the metal salts speed up process of degradation
• Degradation process is shortened from hundreds of years to months

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BIOLOGY: GENETIC DISORDERS

About genetic disorders

Huntington's disease is inherited in the autosomal dominant fashion

• Genetic disorders are disorders that are passed on from generation to generation
• They are caused by abnormalities in genes or chromosomes
• Some genetic disorders may also be influenced by non-genetic environmental factors. Eg: cancer
• Most genetic disorders are relatively rare and only affect one person in thousands or millions
• To recollect, males have XY chromosome pairs while females have XX pairs

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Single Gene Disorders

• Single gene disorders result from the mutation of a single gene
• They can be passed onto subsequent generations in multiple ways
• Single gene disorders include sickle cell disease, cystic fibrosis Huntington disease

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Multiple gene disorders

• Multiple gene disorders result from mutation on multiple genes in combination with environmental factors
• They do not have a clear pattern of inheritance, which makes it difficult to assess risk of inheriting a particular disease
• Examples include heart disease, diabetes, hypertension, obesity, autism

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TYPES OF SINGLE GENE GENETIC DISORDERS

1. Autosomal dominant

   

   Sickle cell disease is inherited in the autosomal recessive pattern
   1. Only one mutated copy of the gene is necessary for inheritance of the mutation
   2. Each affected person usually has one affected parent
   3. There is a 50% chance that the child will inherit the mutated gene
   4. Autosomal dominant disorders usually have low penetrance i.e. although only one mutated copy is needed, only a small portion of those who inherit that mutation will develop the disorder
   5. Eg: Huntington’s disease, Marfan syndrome
2. Autosomal recessive
   1. Two copies of the gene must be mutated for a person to be affected
   2. An affected person usually has unaffected parents who each have one mutated gene
   3. There is a 25% chance that the child will inherit the mutated gene
   4. Eg: Cystic fibrosis, sickle cell disease, Tay-Sachs disease, dry earwax, Niemann-Pick disease
3. X-linked dominant
   1. X-linked dominant disorders are caused by mutations on the X chromosome
   2. Males and females are both affected by such disorders. However, males are affected more severely
   3. For a man with a X-linked dominant disorder, his sons will all be unaffected (since they receive their father’s Y chromosome)while his daughters will all be affected (since they receive his X chromosome)
   4. A woman with a X-linked dominant disorder has a 50% chance of passing it on to progeny
   5. Eg: Hypophosphatemic rickets, Rett syndrome, Aicardi syndrome
4. X-linked recessive

   

   X-linked recessive with a carrier mother
   1. Caused by mutations on the X-chromosome
   2. Males are affected more frequently than females
   3. The sons of a man affected by a X-linked recessive disorder will not be affected, while his daughters will carry one copy of the mutated gene
   4. The sons of a woman affected by a X-linked recessive disorder will have have a 50% chance of being affected by the disorder, while the daughters of the woman have a 50% chance of becoming carriers of the disorder
   5. Eg: colour blindness, muscular dystrophy, hemophilia A
5. Y-linked disorders
   1. Caused by mutations on the Y chromosome
   2. Y chromosomes are present only in males
   3. The sons of a man with Y-linked disorders will inherit his Y chromosome and will always be affected while the daughters will inherit his X chromosome and will never be affected
   4. Eg: male infertility
6. Mitochondrial disorders
   1. These disorders are caused by mutations in the mitochondrial DNA
   2. Only mothers can pass on mitochondrial disorders to children, since only egg cells (from the mother) contribute mitochondria to the developing embryo
      
   3. Eg: Leber’s Heriditary Optic Neuropathy