Nuclear related questions

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(1) What is electric quadrupole moment?The nuclear electric quadrupole moment is a parameter which describes the effective shape of theellipsoid of nuclear charge distribution. A non-zero quadrupole moment Q indicates that the charge

distribution is not spherically symmetric. By convention, the value of Q is taken to be positive if theellipsoid is prolate and negative if it is oblate.

(2) What are thermal neutrons? Why are they so named?Slow neutrons that are approximately in thermal equilibrium with a moderator. They have a distributionof speeds similar to that of the molecules of a gas at the temperature of the moderator. Data concerningnuclear interactions are often given for standard thermal neutrons of speed 2200 metres per second,which is approximately the most probable speed at normal laboratory temperatures. They are namedso, because, they come in equilibrium with the temperature of the system.

(3) Explain the following terms:

(i) Nuclear SpinThe Nuclear Spin is different from the electron spin. The nuclear spin represents the total angularmomentum of the nucleus. The nucleus is, although, composed of neutrons and protons but it acts as if it is a single entity which has intrinsic angular momentum.

The nuclear spin depends on the mass number, if the mass number is odd then the nucleus has half-integer spin like the electron while if the nucleus has even mass number then its spin will be integerspin.

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(ii) Nuclear Magnetic Dipole Moment

(iii) Nuclear Electric Quadrupole Moment

(4) Write down the main features of nuclear force.

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(5) Discuss briefly the following:

(i) Nuclear Electric Quadrupole Moment

(ii) Nuclear DensityNuclear density is the density of the nucleus of an atom, averaging about 41017 kg/m3. The descriptiveterm nuclear density is also applied to situations where similarly high densities occur, such as withinneutron stars. Nuclear density is same for all the nuclei.

(iii) Uncertainty Principle forbids electrons in nucleusUncertainty principal is:

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x(mv)=h/2

The mass of an electron is 9.1 10 -31 kg, and it can't move any faster than the speed of light, so thesmallest space an electron can be restricted to without violating the uncertainty principle is 4 10 -13 m;about 270 times farther than a messenger meson can reach. This shows that the uncertainty principle

forbids it from being restricted to a space as small as an atomic nucleus.

(6) Give any two evidences of neutron-proton model of nucleus.

(7) Does the nucleus has sharp boundries? How is the mass distributedin the nucleus?The nucleus does not have a sharp outer boundary. Experiments have shown that the nucleus is shapedlike a sphere with a radius that depends on the atomic mass number of the atom as R=R oA

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The total mass of an atom is pretty much entirely concentrated within the nucleus, and since thenucleus is composed of protons and neutrons, which are roughly the same mass, one could safely saythat the mass of the nucleus is uniformly distributed.

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(8) Show the nuclear density is same for all the nuclei.

Ans. If V be the volume, then:

Using the equation for nuclear radius

Where

R = nuclear radius in metres (m)r 0 = is the radius of a nucleon approx 1.3 fmA = nucleon number

The mass (M) of the whole nucleus is the mass of a nucleon (m) multiplied by the number of nucleons (A)

Mass M = Am

Density can be found using the equation below;

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This relation shows that the nuclear density is constant and does not change with changingnuclei.The nuclear density of a nucleus is approx 1.8 x 10 17 kgm -3.

(9) Why the number of neutrons tends to exceed the number of proton

in stable nuclei?Ans. We can understand why the N/Z ratio must increase with atomic number in order to have nuclearstability when we consider that the protons in the nucleus must experience a repulsive Coulomb force.The fact that stable nuclei exist means that there must be an attractive force tending to hold the eutronsand protons together. This attractive nuclear force must be sufficient in stable nuclei to overcome thedisruptive Coulomb force. Conversely, in unstable nuclei there is a net imbalance between the attractivenuclear force and the disruptive Coulomb force. As the number of protons increases, the total repulsiveCoulomb force must increase. Therefore, to provide sufficient attractive force for stability the number of neutrons increases more rapidly than that of the protons.

Neutrons and protons in nuclei are assumed to exist in separate nucleon orbitals just as electrons are inelectron orbitals in atoms. If the number of neutrons is much larger than the number of protons, theneutron orbitals occupied extend to higher energies than the highest occupied proton orbital. As N/Zincreases, a considerable energy difference can develop between the last (highest energy) neutronorbital filled and the last proton orbital filled. The stability of the nucleus can be enhanced when an oddneutron in the highest neutron orbital is transformed into a proton fitting into a vacant lower energyproton orbital.

(11) What is nuclear magneton? How it differs from Bohar magneton?The nuclear magneton (symbol

N), is a physical constant of magnetic moment, defined by:

where:

e is the elementary charge,

is the reduced Planck constant,

mp is the proton rest mass

In SI units, its value is approximately: N = 5.05078324(13)1027 J/T.

The nuclear magneton is the natural unit for expressing magnetic dipole moments of heavy particlessuch as nucleons and atomic nuclei. On the contrary, the dipole moment of the electron, which is muchhigher as a consequence of much higher charge-to-mass ratio, is usually expressed in correspondingunits of the Bohr magneton which is given as:

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In SI units, its value is approximately: B = 9.27400968(20)1024 J/T.

(12) What is parity?

(13) Why even-even nuclei are most stable?

There are no concrete theories to explain the stability of nucleus, but there are only generalobservations based on the available stable isotopes. It appears that neutron to proton (n/p) ratio is thedominant factor in nuclear stability. This ratio is close to 1 for atoms of elements with low atomicnumber and increases as the atomic number increases. One of the simplest ways of predicting thenuclear stability is based on whether nucleus contains odd/even number of protons and neutrons:

Protons Neutrons Number of Stable Nuclides StabilityOdd Odd 4 least stableOdd Even 50Even Odd 57Even Even 168 most stable

Nuclides containing odd numbers of both protons and neutrons are the least stable means moreradioactive.

Nuclides containing even numbers of both protons and neutrons are most stable means lessradioactive.

Nuclides contain odd numbers of protons and even numbers of neutrons are less stable thannuclides containing even numbers of protons and odd numbers of neutrons.

In general, nuclear stability is greater for nuclides containing even numbers of protons and neutronsor both.

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(14) Why does nuclear radius depend on mass number?As mass number changes, the nuclear radius changes. Each time we add a nucleon in the nucleus, thenuclear radius is increased. The relation is given as:

(15) List different types of magnetic moments that can be associatedwith nucleons.Tow types of magnetic moments can be associated with nucleons.

A charged particle rotating about an axis can be taken as a small ring carrying current, To this current isassociated a magnetic dipole moment that is related to the particle angular momentum L through=eL/2mc, where e is the charge and m the mass of the particle. It is common to write

L= eg L/ 2mcL

where where the factor g L is called orbital g factor, equal to 1for protons and 0 for neutrons.

A particle can have an intrinsic angular momentums. Thus it is fair to admit that an intrinsic magneticmoment can also be associated to a particle, given by

S= eg S/2mcs

where the constant g , the sping-factor.

(17) Calculate nuclear density.

If V be the volume, then:

Using the equation for nuclear radius

Where

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R = nuclear radius in metres (m)r 0 = is the radius of a nucleon approx 1.3 fmA = nucleon number

The mass (M) of the whole nucleus is the mass of a nucleon (m) multiplied by the number of nucleons (A)

Mass M = Am

Density can be found using the equation below;

This relation shows that the nuclear density is constant and does not change with changingnuclei.The nuclear density of a nucleus is approx 1.8 x 10 17 kgm -3.

(18) Explain the non existence of electrons in the nucleus on the basis of magnetic moments.

(19) Explain the concept of nuclear magnetic dipole moment.The spin angular momentum is given as

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{I (I + 1)}1/2 h / 2

Where I is the nuclear spin quantum number. Also, magnetic dipole moment is given as

= IA

where I is current in amperes, or coulomb per second and

A is the enclosed area of loop.

For a circular path, we write area as

A = r2

And the current i.e. a charge per unit time interval, we can write for a charge of +e and time

interval of 2 r / therefore we can write current I as

I = e / (2 r / )

= e / 2 r

Thus, the magnitude of magnetic dipole moment is given as

= I A

= (e / 2 r ) ( r2)

= e r / 2

Let us introduce mp the mass of proton in above equation. Therefore, We have

= mp e r / 2 mp

Rewriting the above equation as

= ( e / 2 mp ) mp r

= Magnetic moment Angular momentum

Thus, the magnetic dipole moment is given as ( e / 2 mp ) (i.e. the magnetic moment) times itsangular momentum (mp r). This is known as a reference nuclear magnetic moment, called thenuclear magneton, N by

N = ( e / 2 mp ) (h / 2 )

= 5.051 10-27 J/T

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where the unit relation 1 T = 1 N /C m S is used.

The nuclear magnetic moments are expressed in terms of the nuclear magneton N byintroducing a factor called nuclear g factor, symbol gN. Thus, for any nucleus, we write

= gN I (I + 1) N

Values of g N are different for different nuclei.

(20) Explain the concept of nuclear quadrupole moment.

(21) What is average binding energy? How it varies with A.The total energy required to break up a nucleus into its constituent protons and neutrons can becalculated from, called nuclear binding energy. It we divide the binding energy of a nucleus by thenumber of protons and neutrons (number of nucleons), we get the binding energy per nucleon. This isthe common term used to describe nuclear reactions because atomic numbers vary and total bindingenergy would be a relative term dependent upon that. The following figure (adapted from Beiser), calledthe binding energy curve, shows a plot of nuclear binding energy as a function of mass number.

(22) What do you mean by Even-Even Nuclei?A nucleus which has an even number of neutrons and an even number of protons.

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(23) Obtain the ratio of desities of 79 197 Au and 47 107 Ag.Since

This implies that the densities of both elements will be equal and their ratio will be equal to 1.

(24) What do you mean by charge independence of nuclear force?The nuclear force is nearly independent of whether the nucleons are neutrons or protons. This propertyis called charge independence. It depends on whether the spins of the nucleons are parallel orantiparallel, and has a noncentral or tensor component. This part of the force does not conserve orbitalangular momentum, which is a constant of motion under central forces.

(25) Nuclear forces are short range. Explain.Production and destruction of the messenger mesons violates the law of conservation of mass & energy!However, if the messenger particle has a very short lifetime, and so exists only within a very small space,the particle can exist within the limitations set by the uncertainty principle. Particles like this are calledvirtual particles.

If you believe the uncertainty principle, and you believe that nothing can move faster than the speed of light, you can estimate the range of the strong nuclear force as follows. The uncertainty principle says

that you can't exactly determine the position and momentum of a very small particle simultaneously. If x is the uncertainty in the particle's position, and (mv) is the uncertainty in the particle's momentum,the uncertainty principle says that

x(mv)=h/2

where m is the particle's mass, v is its velocity, and h is Planck's constant (6.626 10 -34 Js). The virtualparticle must exist within x = h/2(mc) of the nucleon that generated it. Now, given that the mass of messenger mesons is about 2.5 10 -28 kg, and the uncertainty in the velocity can't be any larger than thespeed of light (2.9979 108 m/s), the virtual particle can't move any more than

x = h/(2(mc)) = 1.4 10-15

m

from the nucleon that generated it without violating the uncertainty principle or the universal speedlimit. That's the range of the strong nuclear force.

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(26) What is amu?a unit of mass used to express atomic and molecular weights that is equal to one twelfth of the mass of an atom of carbon-12. It is equivalent to 1.66x10 -27 kg.

(27) E xpalin binding energy and mass defect. Binding Energy: The nuclear binding energy is an energy required to break up a nucleus into itscomponents protons and neutrons. In essence, it is a quantitative measure of the nuclear stability.The concept of nuclear binding energy is based on Einsteins famous equatio n, E = mc 2, where E isthe energy, m is the mass and c is the velocity of light, and according to which the energy and massare inter-convertible.

Mass Defect: The difference between experimental mass of the atom and the sum of the massesof its protons, neutrons, and electrons is known as mass defect (m). As in the following Fig.

m = mass of products mass of reactants= experimental mass of an atom calculated mass of an atom

This mass defect can be further transformed into energy using Einstein s equation in the followingform:E = m x c 2 In this equation, E is the change in energy in joule, m is the mass defect in amu, and c is thevelocity of light that is equal to 3.0 x 10 8 m/s. Substituting these values into above equation andconverting all the units to joules gives the energy in proper units (J), which is of course little bittedious. To make things simpler, one can directly convert the mass defect into energy using thefollowing conversation factor (if you are interested, see the following box for derivation of thisrelationship).

1amu = 1.4945 x 10 -10 J

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(33) What is the unit to measure the size of nucleus?We use the unit Fermi (10 -15 m) to measure the size of nucleus.

(34) What is packing fraction? Why it is so named?Packing fraction is defined as a way of expressing the variation of isotopic mass from whole massnumber (atomic mass).

This fraction can have positive or can have negative sign. A positive packing fraction describes atendency towards instability. A negative packing fraction means isotopic mass is less than actual massnumber. This difference is due to the transformation of mass into energy in the formation of nucleus. Aplot of packing fraction against corresponding mass nos of various elements is as shown.

(36) How does the binding energy curve explain fission and fusion?The key to energy production in stars lies in what nuclear physicists call the curve of binding energy,which is illustrated in the following figure.

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This plot shows the amount of binding energy per nucleon (A nucleon is either a neutron or a proton.The nucleon number is the sum of the number of neutrons plus protons in a nucleus; thus, it is equal tothe atomic mass number) as a function of the atomic mass number A. The energy units are MeV, whichstands for "million electron-volts", a standard unit of energy in nuclear physics.

This curve indicates how stable atomic nuclei are; the higher the curve the more stable the nucleus.Notice the characteristic shape, with a peak near A=60. These nuclei (which are near iron in the periodictable and are called the iron peak nuclei) are the most stable in the Universe. The shape of this curvesuggests two possibilites for converting significant amounts of mass into energy.

Fission Reactions: From the curve of binding energy, the heaviest nuclei are less stable than the

nuclei near A=60. This suggests that energy can be released if heavy nuclei split apart into smaller nucleihaving masses nearer A=60. This process is called fission. It is the process that powers atomic bombs andnuclear power reactors.

Fusion Reactions: The curve of binding energy suggests a second way in which energy could bereleased in nuclear reactions. The lightest elements (like hydrogen and helium) have nuclei that are lessstable than heavier elements up to A~60. Thus, sticking two light nuclei together to form a heaviernucleus can release energy. This process is called fusion, and is the process that powers hydrogen(thermonuclear) bombs and (perhaps eventually) fusion energy reactors.

In both fission and fusion reactions the total masses after the reaction are less than those before. The"missing mass" appears as energy, with the amount given by the famous Einstein equation.

(37) What are amu and eV?"amu is a unit to measure the mass of atom. The atomic mass unit, 1 gram divided by Avogadro'snumber, is almost the mass of a hydrogen atom, which is mostly the mass of the proton. To convert tomegaelectronvolts, use the formula:

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1 amu = 931.46 MeV/c 2 = 0.93146 GeV/c 2

1 MeV/c 2 = 1.07410 -3 amu

The eV is a unit of energy. It is the amount of energy gained (or lost) by the charge of a single electronmoved across an electric potential difference of one volt.

1 electron volt = 1.60217646 10 -19 joules

(38) What is nuclear magnetic moment?

(39) What do you mean by odd-odd, odd-even and even-even nuclei?Draw the stability curve.Odd-odd nuclei means a nucleus having odd number of protons and odd number of neutrons.

Odd-even nuclei means a nucleus having odd number of protons and even number of neutrons.

Even-even nuclei means a nucleus having even number of protons and even number of neutrons.

Protons Neutrons Number of Stable Nuclides StabilityOdd Odd 4 least stableOdd Even 50 less stableEven Odd 57 less stableEven Even 168 most stable

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(40) Why the number of neutrons tends to exceed the number of protons in stable nuclei?If there is an excess of protons, Coulomb repultion will take place making the nucleus unstable.

Also, in nuclei, proton shells are higher than neutron shells. When neutrons are larger in number thanprotons in a nucleus, the neutron shells go to a higher level than proton level and play a remark ablerole in the stability of nucleus.

(41) Differentiate between X- rays and -rays.1. Gamma rays cause more harm to human body than the X- rays.2. Gamma rays have shorter wavelengths than the X-rays.3. X rays are emitted by the electrons outside the nucleus, and gamma rays are emitted by the

excited nucleus itself.4. X rays are used in hospitals for taking X-rays but gamma rays are not.

(42) In case of successive radioactive disintegration, what is themeaning of permanent equilibrium?In case of successive radioactive decay, unstable radio

(43) Differentiate between a nuclear decay process and a nuclearreaction.Nuclear decay process is the process by which an atomic nucleus of an unstable atom loses

energy by emitting ionizing particles (ionizing radiation). There are many different types of radioactivedecay (see table below). A decay, or loss of energy, results when an atom with one type of nucleus,called the parent radionuclide, transforms to an atom with a nucleus in a different state, or to adifferent nucleus containing different numbers of protons and neutrons. Either of these products isnamed the daughter nuclide. In some decays the parent and daughter are different chemical elements,and thus the decay process results in nuclear transmutation (creation of an atom of a new element).

Nuclear reaction is semantically considered to be the process in which two nuclei, or else a nucleusof an atom and a subatomic particle (such as a proton, neutron, or high energy electron) from outsidethe atom, collide to produce one or more nuclides that are different from the nuclide(s) that began the

process. Thus, a nuclear reaction must cause a transformation of at least one nuclide to another. If anucleus interacts with another nucleus or particle and they then separate without changing the natureof any nuclide, the process is simply referred to as a type of nuclear scattering, rather than a nuclearreaction.

In principle, a reaction can involve more than two particles colliding, but because the probability of three or more nuclei to meet at the same time at the same place is much less than for two nuclei, suchan event is exceptionally rare (see triple alpha process for an example very close to a three-body nuclear

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reaction). "Nuclear reaction" is a term implying an induced change in a nuclide, and thus it does notapply to any type of radioactive decay (which by definition is a spontaneous process).

Natural nuclear reactions occur in the interaction between cosmic rays and matter, and nuclearreactions can be employed artificially to obtain nuclear energy, at an adjustable rate, on demand.

Perhaps the most notable nuclear reactions are the nuclear chain reactions in fissionable materials thatproduces induced nuclear fission, and the various nuclear fusion reactions of light elements that powerthe energy production of the Sun and stars. Both of these types of reactions are employed in nuclearweapons.

(44) A certain radioactive element disintegrates for an interval of timeequal to its mean life. Is it true or not?According to the relation:

an element can not disintegrated completely in a time equal to its mean life.

(45) Discuss the factor which support the neutrino hypothesis of -decay.the study of beta decay provided the first physical evidence of the neutrino. In 1911 Lise Meitner andOtto Hahn performed an experiment that showed that the energies of electrons emitted by beta decayhad a continuous rather than discrete spectrum. This was in apparent contradiction to the law of conservation of energy, as it appeared that energy was lost in the beta decay process. A second problemwas that the spin of the nitrogen-14 atom was 1, in contradiction to the Rutherford prediction of .

In 1920-1927, Charles Drummond Ellis (along with James Chadwick and colleagues) established clearlythat the beta decay spectrum is really continuous, ending all controversies. It also had an effective upperbound in energy, which was a severe blow to Bohr's suggestion that conservation of energy might betrue only in a statistical sense, and might be violated in any given decay. Now the problem of how toaccount for the variability of energy in known beta decay products, as well as for conservation of momentum and angular momentum in the process, became acute.

In a famous letter written in 1930 Wolfgang Pauli suggested that in addition to electrons and protonsatoms also contained an extremely light neutral particle which he called the neutron. He suggested thatthis "neutron" was also emitted during beta decay (thus accounting for the known missing energy,momentum, and angular momentum) and had simply not yet been observed. In 1931 Enrico Fermirenamed Pauli's "neutron" to neutrino, and in 1934 Fermi published a very successful model of betadecay in which neutrinos were produced. The neutrino interaction with matter was so weak that

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detecting it proved a severe experimental challenge, and was not accomplished until 1956. However,the properties of neutrinos were (with a few minor modifications) as predicated by Pauli and Fermi.

(46) What are radio isotopes? Discuss their three uses.

Radioisotopes are atoms that contain an unstable combination of neutrons and protons.Thecombination can occur naturally, as in radium-226, or by artificially altering the atoms. In some cases, anuclear reactor is used, in others, a cyclotron. Atoms containing this unstable combination regainstability by shedding radioactive energy, hence the term radioisotope. The process of shedding theexcess radioactive energy is called decay. The radioactive decay process of each type of radioisotope isunique and is measured with a time period called a half-life.

Uses: In nuclear medicine, radioisotopes are used for diagnosis, treatment, and research. Radioactive

chemical tracers emitting gamma rays or positrons can provide diagnostic information about aperson's internal anatomy and the functioning of specific organs. This is used in some forms of tomography: single-photon emission computed tomography and positron emission tomographyscanning and Cerenkov luminescence imaging.

Radioisotopes are also a method of treatment in hemopoietic forms of tumors; the success fortreatment of solid tumors has been limited. More powerful gamma sources sterilise syringesand other medical equipment.

In biochemistry and genetics, radionuclides label molecules and allow tracing chemical andphysiological processes occurring in living organisms, such as DNA replication or amino acidtransport.

In food preservation, radiation is used to stop the sprouting of root crops after harvesting, to killparasites and pests, and to control the ripening of stored fruit and vegetables.

In industry, and in mining, radionuclides examine welds, to detect leaks, to study the rate of wear, erosion and corrosion of metals, and for on-stream analysis of a wide range of mineralsand fuels.

(47) Describe the law of absorption of rays in matter.

(48) Explain Geiger-Nuttal law.The Geiger Nuttall law or Geiger Nuttall rule relates the decay constant of a radioactive isotope withthe energy of the alpha particles emitted. Roughly speaking, it states that short-lived isotopes emit moreenergetic alpha particles than long-lived ones.

The relationship also shows that half-lives are exponentially dependent on decay energy, so that verylarge changes in half-life make comparatively small differences in decay energy, and thus alpha particle

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energy. In practice, this means that alpha particles from all alpha-emitting isotopes across many ordersof magnitude of difference in half-life, all nevertheless have about the same decay energy.

Formulated in 1911 by Hans Geiger and John Mitchell Nuttall, in its modern form the Geiger Nuttall lawis

where is the decay constant ( = ln2/half -life), Z the atomic number, E the total kinetic energy (of thealpha particle and the daughter nucleus), and a1 and a2 are constants. The law works best for Nucleiwith Even atomic number and Even atomic mass . The trend is still there for Even-Odd, Odd-Even, andOdd-odd nuclei but not as pronounced.

(49) Alpha rays and gama rays can have same energy. What is thedifference between them?

(50) Differentiate internal conversion and electron capture.Internal Conversion: The excited nucleus transfers its excess energy to one of orbital electronsand this electron is ejected from the atom. As there is vacancy in K or L shell, an electron from highershell will make a transition to K or L shell and thereby emitting a characteristic X-ray. The nucleus in thisprocess remains same.

Electron Capture: In this, the nucleus captures an orbital electron. Inside the nucleus, thecaptured electron combines with a proton to form a neutron. Therefore, atomic number of the nucleusdecreses by one.

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(51) What is neutrino? How does its emission explain beta spectrum?Neutrino is an electrically neutral, weakly interacting elementary subatomic particle with half-integerspin. The neutrino (meaning "small neutral one" in Italian) is de noted by the Greek letter (nu). Allevidence suggests that neutrinos have mass but that their mass is tiny even by the standards of subatomic particles. Their mass has never been measured accurately.

Neutrinos do not carry electric charge, which means that they are not affected by the electromagneticforces that act on charged particles such as electrons and protons. Neutrinos are affected only by theweak sub-atomic force, of much shorter range than electromagnetism, and gravity, which is relativelyweak on the subatomic scale. Therefore a typical neutrino passes through normal matter unimpeded.

(52) What is radioactive dating?Because the radioactive half-life of a given radioisotope is not affected by temperature, physical orchemical state, or any other influence of the environment outside the nucleus save direct particle

interactions with the nucleus, then radioactive samples continue to decay at a predictable rate. That is,any radioactive nucleus acts as a clock. If determinations or reasonable estimates of the originalcomposition of a radioactive sample can be made, then the amounts of the radioisotopes present canprovide a measurement of the time elapsed.

One such method is called carbon dating, which is limited to the dating of organic (once living) materials.The longer-lived radioisotopes in minerals provide evidence of long time scales in geological processes.While original compositions cannot be determined with certainty, various combination measurementsprovide self-consistent values for the the times of formations of certain geologic deposits. These clocks-in-the-rocks methods provide data for modeling the formation of the Earth and solar system.

(53) Why is -spectrum continuous?

(78) Define the range of alpha particle.Range is defined as the distance moved by an alpha particle in a given material before it comes to rest.

(79) What is internal conversion process?In the internal conversion process, the wavefunction of an inner shell electron penetrates the nucleus(i.e. there is a finite probability of the electron in an s atomic orbital being found in the nucleus) andwhen this occurs, the electron may couple to the excited state of the nucleus and take the energy of thenuclear transition directly, without an intermediate gamma ray being first produced.

The process of imparting energy from the nucleus to an orbital electron is a quantum process and maybe seen as taking place by means of a virtual photon. In that sense the photon involved can be

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considered as a "virtual gamma ray", which appears as a feature in an equation that describes theprocess, rather than as a directly measurable emission. The kinetic energy of the emitted electron isequal to the transition energy in the nucleus, minus the binding energy of the electron.

Most internal conversion electrons come from the K shell (the 1s state, see electron shell), as these two

electrons have the highest probability of being found inside the nucleus. However, the s state in the L,M, and N shells (i.e., the 2s, 3s, and 4s states) are also able to couple to nuclear fields and cause ICelectrons from these shells (called LMN internal conversion). Ratios of K-shell to other L, M, or N shellinternal conversion probabilities for various nuclides have been prepared.[2]

Since the atomic binding energy of the s electron must be supplied in order to eject it from the atom inthe internal conversion process, K shell internal conversion cannot happen if the decay energy of theatom is insufficient to do overcome K-shell binding energy. There are a few radionuclides in which thedecay energy is not sufficient to convert (eject) a 1s (K) electron, and these nuclides, when they decay byinternal conversion, must decay exclusively from the L, M, or N shells (i.e., by ejecting 2s, 3s, or 4selectrons).

After the IC electron has been emitted, the atom is left with a vacancy in one of its electron shells,usually (as noted) an inner one. This hole will be filled with an electron from one of the higher shells andconsequently one or more characteristic x-rays or Auger electrons will be emitted, as the remainingelectrons in the atom cascade down to fill the vacancy.

(79) What is internal conversion coefficient?In nuclear physics, the internal conversion coefficient describes the rate of internal conversion.

The internal conversion coefficient may be empirically determined by the following formula:

There is no valid formulation for an equivalent concept for E0 (electric monopole) nuclear transitions.

There are theoretical calculations that can be used to derive internal conversion coefficients. Theiraccuracy is not generally under dispute, but it should be understood that since they depend on quantummechanical models involving purely electromagnetic interactions between nuclei and electrons, theremay be unforeseen effects which result in a conversion coefficient differing from one that is empiricallydetermined.

(81) What is induced radioactivity? Give one example.The process of indicating radioactivity in a givenstable isotope by bombarding it with some suitableparticles of proper kinetic energy is known as induced activity or artificial activity.

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Such artificial radioisotopes once produced decay like natural radioisotopes.

(82) Distinguish between atomic and nuclear physics. Atomic physics is the field of physics that studies atoms as an isolated system of electrons and anatomic nucleus. It is primarily concerned with the arrangement of electrons around the nucleus and theprocesses by which these arrangements change. This includes ions as well as neutral atoms and, unlessotherwise stated, for the purposes of this discussion it should be assumed that the term atom includesions.

Nuclear physics is the field of physics that studies the constituents and interactions of atomicnuclei. The most commonly known applications of nuclear physics are nuclear power generation andnuclear weapons technology, but the research has provided application in many fields, including thosein nuclear medicine and magnetic resonance imaging, ion implantation in materials engineering, andradiocarbon dating in geology and archaeology.

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(83) Why do most alpha particles fired through a piece of gold foilemerge almost undeflected?Most alpha particles fired through a piece of gold foil emerge almost undeflected, because atom haslarge empty spaces.

(84) Why do a few alpha particles fired at a piece of gold foil bouncebackward?

1. They encountered a strong positive charge, aka the nucleus.2. Mass of atom is concentrated at the center of the atom, called nucleus. When incident particles

interact with nucleus at an angle of 90, it reflects back.

(85) What did Benjamin Franklin postulated about electricity?

(86) What is a cathode ray?Cathode rays (also called an electron beam or e-beam) are streams of electrons observed in vacuumtubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, the glassopposite of the negative electrode is observed to glow, due to electrons emitted from and travellingperpendicular to the cathode (the electrode connected to the negative terminal of the voltage supply).They were first observed in 1869 by German physicist Johann Hittorf, and were named in 1876 by EugenGoldstein kathodenstrahlen, or cathode rays.

(87) What property of a cathode ray is indicated when a magnet isbrought near the tube?** When a magnetic field is applied, the cathode ray is deflected from its normal straight path into acurved path. This shows that

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(88) What did J.J. Thomson discovered about cathode ray?He measured charge to mass ratio of cathode ray by making the cathode ray travel in straight line bybalancing the effect of electric and magnetic field. He found that its e/m ratio was much higher thanthat of proton, suggesting either the particle were very light or very lightly charged.

(89) What did Robert Millikan discovered about the electron?Millikan measured the fundamental charge of matter - the charge on an electron. And the mass of electron. Using oil drop method.

The mass of an electron is 9.11x 10 -18 g. On the carbon-12 relative scale, the electron would have aweight of 0.000549 atomic weight units. The negative charge on an electron of -1.60 x 10 -19 coulomb isset as the standard charge of -1.

(90) What did Johann Jakob Balmer discover about the spectrum of hydrogen?After chemists and physicists began using the spectroscope to catalog the wavelengths of the lighteither emitted or absorbed by a variety of compounds, these data were then used to detect thepresence of certain elements in everything from mineral water to sunlight. No obvious patterns werediscovered in these data, however, until 1885 when Johann Jacob Balmer analyzed the spectrum of hydrogen.

When an electric current is passed through a glass tube that contains hydrogen gas at low pressure thetube gives off blue light. When this light is passed through a prism as shown below, four narrow bands

of bright light are observed against a black background. These narrow bands have the characteristicwavelengths and colors shown in the table below. Balmer noticed that these data fit the followingequation to within 0.02%.

In this equation, RH is a constant known as the Rydberg constant, which is equal to 1.09678 x 10-2 nm-1,and n is an integer between 3 and 6.

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(91) What did Johannes Rydberg and Waiter Ritz discover about atomicspectra?Rydberg's great intuition was that the periodicity was a result of the structure of the atom. His firstresearch was into the relationship between the spectral lines of elements. In 1890 he found a generalformula giving the frequency of the lines in the spectral series as a simple difference between twoterms. His formula for a series of lines is:

= R(1/m2

1/n2

)

where n and m are integers. The constant R is now known as the Rydberg constant.

In the early 1900s Rydberg continued to work on the periodic table, reorganizing it, finding newmathematical patterns, and even casting it into spiral form. In the main his theoretical work wasconfirmed by Henry Moseley's discovery that the positive charge on the nucleus gave a better periodicordering than the atomic weight.

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The Rydberg-Ritz Combination Principle is the theory proposed by Walter Ritz in 1908 to explain therelationship of the spectral lines for all atoms. The principle states that the spectral lines of any elementinclude frequencies that are either the sum or the difference of the frequencies of two other lines.

An atom can be excited to a higher energy state via absorption of a photon with sufficient energy, or

decay to a lower energy state through spontaneous emission of a photon. However, according to theprinciples of Quantum mechanics, these excitations can only occur at certain energy intervals. TheRydberg Ritz combination principle helps explain this process.

Radioactivity

Radioactivity is the spontaneous emission of energy from the nucleus of certain atoms. The most

familiar radioactive material is uranium.