Nuclear Physics chapter number 18 class 10 notes pdf high-quality download #18. Matric Notes Class 10th Physics chapter 10 to chapter 19 the best notes 2021.
Conceptual Questions Chapter 18 Physics Notes
Table of Contents
Q.1) The atomic number of one particular isotope is equal to its mass number. Which isotope it?
Answer:
Protium, 1H1
Q.2) Which is more likely to expose, a film kept in a cardboard box, α-particles or β-particles? Explain.
Answer:
β-particles are more likely to be exposed as they can penetrate through paper and can also penetrate a few millimetres of aluminium, thus having a range of 1m in air.
As for α-particles, they can barely penetrate a sheet of paper and has a range of no more than a few centimetres in air.
Q.3) Is it possible for a form of heavy hydrogen to decay by emitting an alpha particle? Explain.
Answer:
Heavy hydrogen is one of the stable isotopes of Hydrogen. It can not decay by an alpha decay.
Q.4) Different isotopes of a given element have different masses but they have the same chemical properties. Explain why chemical properties are unaffected by a change of isotope.
Answer:
Different isotopes of an element have the same number of protons in the nucleus, giving them the same atomic number which is responsible for the chemical properties of an isotope. As the atomic number gives the number of electrons in the outermost shell which determines the chemical behavior for an element, hence having similar atomic number implies similar chemical properties.
Q.5) What fraction of a radioactive sample has decayed after two half-lives have elapsed?
Answer:
After 1 half-life, clearly half of the original isotope remains i.e, 1/2.
And after 2 half-lives, 1/2+ (1/2 of 1/2), i.e.
1/2+ 1/4= 3/4 of the original mass has decayed.]
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Q.6) Can carbon-14 dating give the age of fossil dinosaur skeletons? Explain.
Answer:
Carbon-14 has a half-life of 5730 years. As long as the creature is alive, it will continue to absorb and collect carbon-14. Once the creature dies, no further carbon-14 will be ingested, and the proportion of carbon 14 will start to decline.
Carbon-14 can be used for biological tissues as old as 50 or 60 thousand years but is more accurate for younger samples as an abundance of C-14 nuclei in them is greater.
Dinosaur bones, on the other hand, are millions of years old so carbon-14 dating is only effective on samples that are less than 50,000 years old.
Q.7) Some food is treated with gamma radiation to kill bacteria. Why is there not a concern that people who eat such food might be consuming containing gamma radiation?
Answer:
The intensity of the gamma radiation used in food sterilization, to ensure that it stays well below the level where radioactivity can be induced in the food being sterilized. The energy of sterilizing gamma radiation is limited to (I believe) 4 million electron volts, which is well below the threshold required to induce radioactivity.
Q.8) Radioactive α-emitters are relatively harmless outside the body, but can be dangerous if ingested or inhaled. Explain.
Answer:
 α-emitters emit  α-rays which is highly ionizing but has  the smallest range of about a few centimeters in air. This makes it dangerous when inhaled or digested.
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Q.9) If nuclear radiation is harmful. How it can be used for treatment of diseases?
Answer:
Medical Uses:
Radio-pharmaceuticals- drugs that contain radioactive material- are important in the diagnosis and treatment of many diseases. They can be injected into the body, inhaled or taken orally as medicines or to enable imaging of internal organs and bodily processes. Ionizing radiation has two very different uses in medicine-for diagnosis and therapy.
a. Medical diagnostics:Â
Every organ in our bodies acts differently from a chemical point of view. Doctors and chemists have identified a number of chemicals which are absorbed by specific organs. The thyroid, for example, takes up iodine, the brain consumes quantities of glucose, and so on. With this knowledge, radio pharmacists are able to attach various radioisotopes to biologically active substances. Images are then obtained via gamma camera or a PET scan in nuclear diagnostics which enables to accurately detect disease progression and staging in vital organs.
A radioisotope used for diagnostic must emit gamma rays of sufficient energy to escape from the body and it must have a half-life short enough for it to decay away soon after imaging is completed.
b. Radiation therapy:Â
High energy radiations can be used to destroy selected tissues, such as a cancerous tumor. Cobalt 60 which emit a beta particle and high energy gamma-ray can be used to treat various cancers. Some radioisotopes are made to absorb by selected organ and radiation is concentrated on the infected tissue. For example,cancerous thyroid can be treated with iodine-131.
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Comprehensive Questions Physics Notes for class 10th pdf 2021
Q.1) What is nucleus? How a nuclide is represented symbolically?
Answer:
All matter is composed of atoms that are in turn composed of a heavier, central, positively charged core called ‘nucleus’ surrounded by a less massive negatively charged crowd of electrons. The nucleus lies at the center of the atom, occupying only 10-15 of its volume since the electrical force comes from both the electron and the nucleus.
Nuclides are represented symbolically by:
Q.2) What is radioactivity? Give the nature, ionizing and penetration abilities of the three types of radioactive emission.
Answer:
The spontaneous release of subatomic particles or gamma rays by unstable
atoms as their nuclei tend to break apart into other particles to attain stability
is called radioactivity · An element which possesses such property is called
radioactive element.
Some nuclides are unstable, in order to attain stability, elements emit three types
of radiation alpha ( α ), in which the emitted particles are 4He nuclei; beta (β), in
which the emitted particles are either electrons or positrons (positive electrons)
and gamma (γ), in which the emitted”rays” are high-energy electromagnetic
radiations. Nuclei which do not emit radiations are termed as ‘stable nuclei’.
Nature of emissions:
It is found that all the three kinds of radiation have different nature.
i. Alpha (α) emissions :
Alpha particles are infact helium nuclei (i.e two protons and two neutrons bound together) emitted from the nucleus. When the ratio of neutrons to protons in the nucleus is too low, certain atoms restore the balance by emitting alpha particles. Alpha emissions occur in very large atoms (that is, they have high atomic numbers).
ii. Beta ( β) emissions :
Beta particles consist of electrons emitted from the nucleus. Beta particle emission occurs when the ratio of neutrons to protons in the nucleus is too high. In this case, an excess neutron transforms into a proton and an electron. The proton stays in the nucleus and the electron is ejected energetically. A neutron by itself is unstable ; the lone neutron on average of about 12 minutes will decay into a proton and an electron.
The spontaneous decay of free protons has never been observed and the proton is therefore, considered a stable particle. A neutron with a proton is stable. Neutron
iii. Gamma emissions :
Gamma rays are electromagnetic radiation emitted from the nucleus. Gamma ray emission occurs when the nucleus of a radioactive atom has too much energy.
Relative Ionizing abilities:
The phenomena by which radiation can split matter into positive and negative ions is called ionization. All the three types of radiation (alpha ‘α’, beta ‘β’ and gamma’γ’) have quite different ionizing abilities in air. Alpha (α) particles ionize air much strongly due to its large mass and charge than beta (β) and gamma (γ) radiations. Gamma radiation has the least ionizing ability as compared to alpha’α’ and beta ‘β’ radiations.
Relative Penetration abilities :
Penetrating ability is how deeply a radiation can go into a material. All the three types of radiation (alpha ‘α’, beta ‘β’ and gamma ‘γ’) have quite different penetrating abilities as well. Alpha particles barely penetrate a sheet of paper and has a range of no more than a few centimeters in air; beta particles can penetrate a few millimeters of aluminum has range in air of about 1 m, and gamma rays can penetrate several centimeters of lead and has an infinite range in air.
α-particles can be easily absorbed by our hand, whereas beta and gamma will pass through. Beta radiations, on the other hand, will be easily stopped by a concrete block. Whereas gamma will travel a few centimeters before being absorbed fn concrete.
Q.3) What are nuclear transmutations? What changes in the composition of the nucleus is observed when alpha or beta particles are emitted? Explain by symbolic equations.
Answer:
In radioactivity, an unstable nucleus emits radiations to become more stable. Among 3000 known nuclides, only 257 are stable. The process through which an unstable nucleus (parent nucleus) transforms (or changes) in to a more stable nuclide (daughter nucleus) is called nuclear transmutation (or nuclear decay).In these nuclear transmutations, the original element is called parent and newly formed element is termed as daughter.
Alpha decay :
In alpha decay, the original ‘parent’ nuclide is converted to a ‘daughter’ by the emission of an α particle. Balancing the reaction shows that the daughter nuclide has a nucleon number reduced by four and a charge reduced by two. Mathematically,
Where ‘Q’ is the energy released in the process. Nuclide ‘X’ changes into nuclide
‘Y’ with the emission of alpha ‘α’ particle and the release of energy ‘Q’.
Beta decay :
Unlike α-decay, β (or electron) decay of a nuclei does not change the number of nucleons. In essence, β-decay changes a neutron into a proton.
Where ‘Q’ is the energy released in the process. Nuclide ‘X’ changes into nuclide
‘Y’ with the emission of alpha ‘α’ particle and the release of energy ‘Q’.
Q.4) Radioactive sources are said to have half life. What is the meaning of half life?
Answer:
Half-life :
“The time it takes for half of the radioactive nuclei in a sample to decay is called the half-life.”
Individual disintegrations of nuclei are random, but the probability that any given nucleus wilt decay in a given interval of time is constant and is a characteristic of that particular nuclide.
The amount of radioactive isotope in the sample decreases with time as shown in the Half-life curve below. The number of nuclei present at time t = O is N = No, and the number present at t = T1/2 is N = N0/2. The number present at  t = 2T1/2 is N = No/4, and so on. The value of the half-Life depends on the nature of the radioactive nucleus. For example, radium has a half-life of 1600 years,  because it takes this amount of time for one-half of a given quantity of this isotope to disintegrate.
Q.5) What are radioisotopes? Explain their uses for various applications?
Answer:
Radioisotopes:
One of two or more forms of a chemical element having the same number of protons, or the same atomic number, but having different numbers of neutrons, or different atomic weights is calIed an isotope.
“The isotope that are unstable and emit radiations are called radioactive isotopes or simply radioisotopes.”Isotopes of elements that occur naturally are somewhat stable. But the isotopes, manufactured in nuclear laboratories by bombarding of subatomic particles, usually have a short life span, mostly due to their unstable nature and radioactivity. Among about 3000 known nuclides, only 257 are stable. The time scale of these decay processes ranges from a small fraction of a microsecond to billions of years.
Uses of radioisotopes:
A radioactive isotope behaves in just the same way as the normal isotope chemically, which make it useful in wide variety of applications. Over 2, 000 radioisotopes-radioactive isotopes-either exist in nature or have been made artificially by bombarding stable isotopes in particle accelerators. They are useful in so many applications that the word isotope is commonly used to mean radioisotope, as if stable isotopes did not exist. Few of the uses of radioisotopes are discussed below.
i) Food preservation:
Food irradiation is a method of treating food in order to make it safer to eat and have a Longer shelf Life. Even after it has been packaged, gamma rays can penetrate the packing and be used to kill bacteria, mould and insects in food. This process prolongs the shelf-life of the food, but sometimes changes the taste.
ii) Sterilising:
Gamma rays are also used to sterilise hospital equipment by irradiation, especially plastic syringes that would be damaged if heated.
iii) Agriculture:
If a plant is given fertilizer tagged with radioactive carbon-14 then the plant releases “beta radiation” and thus by measuring radioactivity in different parts of the plant, the uptake of fertilizer by the plant can be determined.
This technique has helped in elaborating the complex process of photosynthesis as well. Higher yield varieties of seeds have also been developed after mutation through radiation.
iv) Medical Uses:
Radiopharmaceuticals-drugs that contain radioactive material are important in the diagnosis and treatment of many diseases. They can be injected into the body, inhaled, or taken orally as medicines or to enable imaging of internal organs and bodily processes. Ionizing radiation has two very different uses in medicine-for diagnosis and therapy.
a. Medical diagnostics:
Every organ in our bodies acts differently from a chemical point of view. Doctors and chemists have identified a number of chemicals which are absorbed by specific organs. The thyroid, for example, takes up iodine, the brain consumes quantities of glucose, and so on. With this knowledge, radio pharmacists are able to attach various radioisotopes to biologically active substances. Images are then obtained via gamma camera or a PET scan in nuclear diagnostics which enables to accurately detect disease progression and staging in a vital organ.
A radioisotope used for diagnosis must emit gamma rays of sufficient energy to escape from the body and it must have a half-life short enough for it to decay away soon after imaging is completed.
b. Radiation therapy :
High energy radiations can be used to destroy selected tissues, such as a cancerous tumor.
Cobalt 60 which emit beta particle and high energy gamma-ray can be used to treat various cancers. Some radioisotopes are made to absorb by selected organ and radiation is concentrated on the infected tissue. For example, cancerous thyroid can be treated with iodine-131.
Q.6) How is carbon-14 used to determine the ages of wood, bones and Other artifacts?
Answer:
Radioactive Dating :
Archaeologists and geologists use radioactive dating to estimate the age of ancient objects. One common procedure uses carbon-14 which has a half-life of 5730 years. As long as the creature is alive, it will continue to absorb and collect carbon-14. Once the creature dies, no further carbon-14 will be ingested, and the proportion of carbon-14 will start to decline.
The proportion of the total amount of carbon that is carbon-14 is very small. Nevertheless, the amount is measurable. A measurement of the activity present can, therefore, be used to estimate the age of the specimen. Carbon-14 dating can
be used for biological tissues as old as 50 or 60 thousand years, but is most accurate
for younger samples, since the abundance of 14C nuclei in them is greater. Very old
biological materials contain no 14C at all.
Materials with relatively longer half-lives can be used to determine the age of geologic formations. Uranium-238, for example, with a half-life of 4. 53×109 years, can be used to date even the oldest deposits on Earth.
Q.7) What are fission and fusion?
Answer:
NUCLEAR FISSION
“The process of splitting of nuclei into intermediate size nuclei is called nuclear
fission.”
The fission process often produces free neutrons and gamma rays, and
releases a Large amount of energy-
Discovery: Nuclear fission was discovered in December 1 7, 1 938 by Otto Hahn and his assistant Fritz Strassmann, and explained theoretically in January 1939 by Lise Meitner and her nephew Otto Robert Frisch.
They found that a uranium nucleus, after absorbing a low energy neutron (thermal neutron), splits into two fragments of intermediate size. The splitting of a massive nucleus into two Less massive fragments was termed as nuclear fission. It can be represented by the following nuclear reaction:
When 236U* is an intermediate excited state that lasts for only about 10-12 s before
splitting into X and Y. The resulting nuclei X and Y are called fission fragments. Many
combinations of X and Y are possible as fission fragments in the above nuclear
reaction.
The figure below shows the actual mass distribution of fragments in the fission of
235U. The process results in the production of several neutrons typically two or three. On
the average, about 2. 5 neutrons are released per event. A typical reaction of this type is:
When 236U* is an intermediate excited state that lasts for only about 10-12 s before
splitting into X and Y. The resulting nuclei X and Y are called fission fragments. Many
combinations of X and Y are possible as fission fragments in the above nuclear
reaction.
The figure below shows the actual mass distribution of fragments in the fission of
235U. The process results in the production of several neutrons typically two or three. On
the average, about 2. 5 neutrons are released per event. A typical reaction of this type is:
Measurement show that large amount of energy is released in this process relative to the amount of energy released in chemical processes. Thus, energy released is very high. It is found that 1 kg of uranium delivers as much energy as 3000 tons of coal.
NUCLEAR FUSION:
“When two light nuclei combine to form a heavy nucleus, the process is called nuclear fusion.”
When two nuclei form a large nucleus, the mass of larger nucleus is less then the mass of nuclei that formed it. This toss in mass appears in the form of energy. A self sustaining fusion reaction is also possible but the energy required is possible only in the environments of stars including sun. One such cycle is
A. Proton-proton: In this process the direct collision of protons result in the formation of heavier nuclei whose collision in turn produces helium nuclei as shown below. The initial reaction in proton-proton cycle is:
A deutron produced in the above reaction may combine with other proton as
Finally, two such reactions can combine to form helium-4 with the release of two protons as:
Q.8) What are background radiations? What are its major sources?
Answer:
All living creatures, from the beginning of time, have been and are still being exposed to radiation. When a radiation detector is used it will record these radiations called natural background radiation, it comes from three sources:
a. Cosmic Radiation:
The earth, and all living things on it, are constantly bombarded by radiations from space. The dose from cosmic radiation varies in different parts of the world due to differences in elevation and to the effects of the earths magnetic field.
b. Terrestial Radiation:
Radioactive material is also found throughout nature. It is in the soil, water and vegetation. Low levels of uranium, thorium, and their decay products are found everywhere. The dose from terrestrial sources also varies in different parts of the world.
c. Internal Radiation:
All people also have radioactive potassium-40, carbon-14, lead-210, and other isotopes inside their bodies from birth.
Q.9) What are radiation hazards? How can we safeguard ourselves from radiation?
Answer:
Radiation Hazards:
Nuclear radiation is potentially harmful to humans because the ionization it produces can significantly alter the structure of molecules within living cell. The alterations can lead to the death of the cell and even of the organism itself. The amount of biological damage produced by ionizing radiation is different for different kind of radiation.
The effects of radiation on humans can be grouped into two categories, according to the time span between initial exposure and the appearance of physiological symptoms:
1. Short-term or acute effects that appear within a matter of minutes, days, or weeks.
2. Long-term or latent effects that appear years, decades or even generations later.
Radiation from the material can damage cells of the person directly. This is damage by irradiation. Some of the radioactive material can be swallowed or breathed in. While inside the body, the radiation it emits can produce damage by contamination.
Radiation sickness is the general term applied to the acute effects of radiation. Depending on the severity of the dose, a person with radiation sickness can exhibit nausea, vomiting, fever, diarrhea and loss of hair. Ultimately, death can occur.
Long term effects of radiation may appear as a result of high-level, brief exposure or low level exposure over a long period of time. Some long-term effects are hair loss, eye cataracts, and various kinds of cancer. In addition, genetic defects caused by mutated genes may be passed on from one generation to the next.
Safety Measures:
There are three general guidelines for controlling exposure to ionizing radiation:
a. minimizing exposure time
b. Maximizing distance from the radiation source
c. Shielding yourself from the radiation source
While working with radiation Lab coats, shoes and safety glasses must be worn in the laboratory. Materials/equipment which are not required must not be brought into the laboratory or stored inside. An inventory of radioactive sources used in the laboratory must be maintained and updated.
