Fission
✬Fission is the process by which a heavy nucleus splits into medium-sized nuclei. It is induced by bombarding a heavy nucleus with neutrons.
✬To compute the energy involved in the reaction, compare the mass of the reactants and products.
❃ Mass of the reactants:
235U= 235.0439µ
1n= + 1.0087µ
Total mass= 236.0526µ
❃ Mass of the products:
138Ba= 137.905µ
95Kr= 94.900µ
31n=+ 3.026µ
Total mass= 235.831µ
✬Note that the total mass of the reactants is greater than the total mass of the products.
(…to be continued…)
Sunday, September 23, 2007
Thursday, September 20, 2007
Reactors and Nuclear Energy
Mass Defect and Binding Energy
✬Nuclear reactions can be analyzed in terms of the masses and energies of the nuclei and particles before and after the reaction. Here, we shall use Einstein's equation E=mc2 in analyzing nuclear reactions.
✬The mass of the nucleus is equal to the combined masses of its protons and neutrons.
✬Nuclear masses are measured using an instrument called mass spectrometer.
✬1µ=1.6600 x 10-27 kg
✬mass of proton=1.0073µ
mass of neutron=1.0087µ
mass of electron=0.0005µ
✬The difference in mass is known as mass defect, ∆ m.
✬Mass seems to disappear when protons and neutrons combine to form a nucleus. Einstein's principle of mass-energy equivalence says that the missing mass (mass defect) is converted into energy.
✬The energy equivalent of the mass defect is known as the binding energy BE.
✬Nuclear binding energy is not energy stored in the nucleus; rather, it represents the difference in mass-energy of the nucleus due to conversion.
(...to be continued…)
✬Nuclear reactions can be analyzed in terms of the masses and energies of the nuclei and particles before and after the reaction. Here, we shall use Einstein's equation E=mc2 in analyzing nuclear reactions.
✬The mass of the nucleus is equal to the combined masses of its protons and neutrons.
✬Nuclear masses are measured using an instrument called mass spectrometer.
✬1µ=1.6600 x 10-27 kg
✬mass of proton=1.0073µ
mass of neutron=1.0087µ
mass of electron=0.0005µ
✬The difference in mass is known as mass defect, ∆ m.
✬Mass seems to disappear when protons and neutrons combine to form a nucleus. Einstein's principle of mass-energy equivalence says that the missing mass (mass defect) is converted into energy.
✬The energy equivalent of the mass defect is known as the binding energy BE.
✬Nuclear binding energy is not energy stored in the nucleus; rather, it represents the difference in mass-energy of the nucleus due to conversion.
(...to be continued…)
Thursday, September 13, 2007
Radiation and radioactivity
Scientists distinguish radiation from radioactivity, which is a property of some types of matter. Radioactivity causes matter to release certain forms of radiation as the result of changes in the nuclei of the atoms that make up the matter.
To understand radiation and radioactivity, it is necessary to understand how an atom is constructed and how it can change. An atom consists of tiny particles of negative electric charge called electrons surrounding a heavy, positively charged nucleus. Opposite electric charges attract each other, and like charges repel (push away) each other. The positively charged nucleus therefore attracts the negatively charged electrons and so keeps them within the atom.
The nucleus of every element except the most common form of hydrogen consists of particles called protons and neutrons. (A normal hydrogen nucleus is made up of a single proton and no neutrons.) Protons carry a positive charge, and neutrons have no charge. The most common form of helium, for example, has two protons and two neutrons in the nucleus and two electrons outside the nucleus. Protons and neutrons consist of even smaller particles called quarks.
Within the nucleus, the positively charged protons repel one another because they have like charges. The protons and neutrons remain together in the nucleus only because an extremely powerful force holds them together. This force is called the strong nuclear force or the strong interaction.
An atom can change the number of protons and neutrons in its nucleus by giving off or taking in atomic particles or bursts of energy--that is, by giving off or taking in radiation. But any change in the number of protons in the nucleus produces an atom of a different element. Radioactive atoms spontaneously release radiation to take on a more stable form. The process of giving off atomic particles is called radioactive decay. As radioactive elements decay, they change into different forms of the same element or into other elements until they finally become stable and nonradioactive.
Radioactive decay takes place at different rates in different elements or different forms of the same element. The rate of decay is measured by the half-life, the length of time needed for half the atoms in a sample to decay. For example, the half-life of cesium 137, a radioactive form of the metal cesium, is about 30 years. After about 60 years, approximately a fourth of the original cesium 137 remains. After another 30 years, only an eighth remains, and so on. The half-life of radon 222 is about 3.8 days. Half-lives vary from fractions of a second to billions of years.
To understand radiation and radioactivity, it is necessary to understand how an atom is constructed and how it can change. An atom consists of tiny particles of negative electric charge called electrons surrounding a heavy, positively charged nucleus. Opposite electric charges attract each other, and like charges repel (push away) each other. The positively charged nucleus therefore attracts the negatively charged electrons and so keeps them within the atom.
The nucleus of every element except the most common form of hydrogen consists of particles called protons and neutrons. (A normal hydrogen nucleus is made up of a single proton and no neutrons.) Protons carry a positive charge, and neutrons have no charge. The most common form of helium, for example, has two protons and two neutrons in the nucleus and two electrons outside the nucleus. Protons and neutrons consist of even smaller particles called quarks.
Within the nucleus, the positively charged protons repel one another because they have like charges. The protons and neutrons remain together in the nucleus only because an extremely powerful force holds them together. This force is called the strong nuclear force or the strong interaction.
An atom can change the number of protons and neutrons in its nucleus by giving off or taking in atomic particles or bursts of energy--that is, by giving off or taking in radiation. But any change in the number of protons in the nucleus produces an atom of a different element. Radioactive atoms spontaneously release radiation to take on a more stable form. The process of giving off atomic particles is called radioactive decay. As radioactive elements decay, they change into different forms of the same element or into other elements until they finally become stable and nonradioactive.
Radioactive decay takes place at different rates in different elements or different forms of the same element. The rate of decay is measured by the half-life, the length of time needed for half the atoms in a sample to decay. For example, the half-life of cesium 137, a radioactive form of the metal cesium, is about 30 years. After about 60 years, approximately a fourth of the original cesium 137 remains. After another 30 years, only an eighth remains, and so on. The half-life of radon 222 is about 3.8 days. Half-lives vary from fractions of a second to billions of years.
Thursday, August 23, 2007
Radiation
*Radiation-energy travelling through space
*Sunshine is one of the most familiar forms of radiation.
*Ultraviolet- short wavelength
*Stable atom-remains the same
*Unstable atom-changes to be more stable
-have excess energy
*Isotopes-two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei.
*Radioisotopes-radioactive isotopes
*Nucleons-make the nucleus
*Becquerel-one atomic decay per second
*Curie-former unit of radioactivity
*Half-life–time taken for half of the atoms to decay
*Ionizing radiation-produces ions in the materials it strikes
*Several types of ionizing radiation
>>X-rays & Gamma rays-virtually identical
-x-rays are produced artificially
-great penetrating power
-barriers of concrete, lead or water are used for protection from them
>>Alpha particles-two protons & two neurons
-have a positive electrical charge
-have little penetrating power
-they give up their energy over a short distance
-can inflict more severe biological damage
>>Beta particles-smaller than alpha particles
-penetrate 1-2 cm of water
>>Cosmic radiation-more intense at higher altitudes
>>Neutrons-very penetrating
-mostly come from the splitting of atoms inside a nuclear reactor
*Sieverts-absorbed by the body
*Grays- not absorbed by the body
Health risks from ionizing radiation
*Can cause measurable increase in cancer and leukemia
*Can cause genetic mutations
*Can cause sickness and death within weeks of exposure
*Embryos including human fetus are sensitive to radiation damage
*Also used in radiation therapy to kill cancerous cells and can often save lives
*Large doses are used to kill bacteria in food or sterilize bandages and medical equipment
*Background radiation-main source of exposure for most people
Four Ways of protection from radiation
*Limiting time- the dose is reduced and the risk of illness is eliminated by limiting by the exposure time
*Distance- the intensity of radiation decreases with distance from its source
*Shielding- barriers give good protection from penetrating radiation
*Containment- radioactive materials are confined and kept in closed handling facilities
*Sunshine is one of the most familiar forms of radiation.
*Ultraviolet- short wavelength
*Stable atom-remains the same
*Unstable atom-changes to be more stable
-have excess energy
*Isotopes-two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei.
*Radioisotopes-radioactive isotopes
*Nucleons-make the nucleus
*Becquerel-one atomic decay per second
*Curie-former unit of radioactivity
*Half-life–time taken for half of the atoms to decay
*Ionizing radiation-produces ions in the materials it strikes
*Several types of ionizing radiation
>>X-rays & Gamma rays-virtually identical
-x-rays are produced artificially
-great penetrating power
-barriers of concrete, lead or water are used for protection from them
>>Alpha particles-two protons & two neurons
-have a positive electrical charge
-have little penetrating power
-they give up their energy over a short distance
-can inflict more severe biological damage
>>Beta particles-smaller than alpha particles
-penetrate 1-2 cm of water
>>Cosmic radiation-more intense at higher altitudes
>>Neutrons-very penetrating
-mostly come from the splitting of atoms inside a nuclear reactor
*Sieverts-absorbed by the body
*Grays- not absorbed by the body
Health risks from ionizing radiation
*Can cause measurable increase in cancer and leukemia
*Can cause genetic mutations
*Can cause sickness and death within weeks of exposure
*Embryos including human fetus are sensitive to radiation damage
*Also used in radiation therapy to kill cancerous cells and can often save lives
*Large doses are used to kill bacteria in food or sterilize bandages and medical equipment
*Background radiation-main source of exposure for most people
Four Ways of protection from radiation
*Limiting time- the dose is reduced and the risk of illness is eliminated by limiting by the exposure time
*Distance- the intensity of radiation decreases with distance from its source
*Shielding- barriers give good protection from penetrating radiation
*Containment- radioactive materials are confined and kept in closed handling facilities
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