A nucleus of uranium decays at rest into nuclei of thorium and h

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131.

A radio isotope X with a half life 1.4 x 109 yr decays of Y which is stable. A sample of the rock from a cave was found to contain X and Y in the ratio 1:7. The age of the rock is,

  • 1.96 x 109 yr

  • 3.92 x 109 yr

  • 4.20 x 109 yr

  • 4.20 x 109 yr

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132.

The half-life of radioactive isotope X is 20 yr. It decays to another element Y which is stable.The two elements X and Y were found to be in the ratio 1:& in a sample of given rock is estimated to be

  • 40 yr

  • 60 yr

  • 80 yr

  • 80 yr

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133.

A radioactive nucleus of mass M emits a photon of frequency v and the nucleus recoils.The recoil energy will be

  • h2v2 / 2Mc2

  • zero

  • hv

  • hv

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134.

The power obtained in a reactor using U235 disintegration is  1000kW. The mass decay of U235 per hour is

  • 20 μg

  • 40 μg

  • μg

  • μg

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135.

The half - life of a radioactive isotope X is 50 yr. It decays to another element Y which is stable. The two elements X and Y were found to be in the ratio of 1: 15 in a sample of a given rock. The age of the rock was estimated to be

  • 200 yr

  • 250 yr

  • 100 yr

  • 100 yr

347 Views

136.

Fusion reaction takes place at high temperature because

  • atoms get ionised at high temperature

  • kinetic energy is high enough to overcome the coulomb repulsion between nuclei

  • molecules break up at high temperature

  • molecules break up at high temperature

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137.

A nucleus X presubscript straight n presuperscript straight m emits one α - particle and two β- particles. The resulting nucleus is 

  • straight Z presubscript straight n presuperscript straight m minus 6 end presuperscript
  • straight X presubscript straight n presuperscript straight m minus 4 end presuperscript space space
  • straight Y presubscript straight n minus 2 end presubscript presuperscript straight m minus 4 end presuperscript
  • straight Y presubscript straight n minus 2 end presubscript presuperscript straight m minus 4 end presuperscript
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138.

A nucleus of uranium decays at rest into nuclei of thorium and helium. Then, 

  • the helium nucleus has more kinetic energy than the thorium nucleus

  • the helium nucleus has less momentum than the thorium nucleus

  • the helium nucleus has more momentum than the thorium nucleus

  • the helium nucleus has more momentum than the thorium nucleus


A.

the helium nucleus has more kinetic energy than the thorium nucleus

straight U presubscript 92 superscript 238 space rightwards arrow Th presubscript 90 superscript 238 space plus space He presubscript 2 superscript 4

According space to space law space of space consevation space of space linear space momentum comma space we space have
vertical line straight P subscript Th vertical line space equals space vertical line straight P subscript He vertical line
rightwards double arrow space As comma space kinetic space energy space of space an space element
KE space equals fraction numerator straight P squared over denominator 2 straight m end fraction
where space straight m comma space is space mass space of space an space element space
Thus comma space
KE space proportional to space 1 over straight M
So comma space straight M subscript He space less than space straight M subscript Th space rightwards double arrow space straight K subscript He space greater than space straight K subscript Th
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139.

Two radioactive nuclei P and Q, in a given sample decay into a stable nucleous R. At time t =0, number of P species are 4No and that of Q are No.Half -life of P (for conversion to R) is 1 min where asthat of Q is 12 min. Initially there are no nuclei of R present in the sample. When number of nuclei of R presnent in the sample would be


  • 3No

  • 9No / 2

  • 5No/2

  • 5No/2

1298 Views

140.

The mass of a Li presubscript 3 presuperscript 7 nucleus is 0.042u less than the sum of the masses of all its nucleons. The binding energy per nucleon is Li presubscript 3 presuperscript 7 nucleus is nearly

  • 46 MeV

  • 5.6 MeV

  • 3.9 MeV

  • 3.9 MeV

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