Consider a radioactive material of half-life 1.0 minute. If one of the nuclei decays now, the next one will decay

after 1 minute
after \(\frac{1}{log_{e}2}\) minute
after ¹⁄_N minute, where N is the number of nuclei present at that moment
after any time

Solution

Because radioactivity is a spontaneous phenomenon.

Which of the following statements is true?

\(_{78}pt^{192}\, has\, 78\, neutrons\)
\(_{84}po^{214}\, \rightarrow \,_{82}pb^{210}+\beta ^{-}\)
\(_{92}U^{238}\, \rightarrow \,_{90}Th^{234}+_{2}He^{4}\)
\(_{90}Th^{234}\, \rightarrow \,_{91}pa^{234}+_{2}He^{4}\)

From the following equations,pick out hte possible nuclear reactions.

A. \(_{6}C^{13}+_{1}H^{1}\rightarrow _{6}C^{14}+4.3\, Mev\)

B. \(_{6}C^{12}+_{1}H^{1}\rightarrow _{7}C^{13}+2\, Mev\)

C. \(_{7}C^{14}+_{1}H^{1}\rightarrow _{8}C^{15}+7.3\, Mev\)

D. \(_{}C^{14}+_{1}H^{1}\rightarrow _{8}knC^{15}+7.3\, Mev\)

Solution

B,C

The mass and energy equivalent to 1 amu are respectively

1.67 × 10^–27gm, 9.30 MeV
1.67 × 10^–27kg, 930 MeV
1.67× 10^–27kg, 1 MeV
1.67 × 10^–34kg, 1 MeV

The rest energy of an electron is

510 KeV
931 KeV
510 MeV
931 MeV

Solution

The average binding energy per nucleon is maximum for the nucleus

\(_{2}He^{4}\)
\(_{8}O^{16}\)
\(_{26}Fe^{56}\)
\(_{92}U^{238}\)

Solution

Binding energy per nucleon increases with atomic number. The greater the binding energy per nucleon the more stable is the nucleus.

For \(_{26}Fe^{56}\) number of nucleons is 56.

This is most stable nucleus, since maximum energy is needed to pull a nucleon away from it.

Which one is correct about fission?

Approx. 0.1% mass converts into energy
Most of energy of fission is in the form of heat
In a fission of U²³⁵ about 200 eV energy is released
On an average, one neutron is released per fission of U²³⁵

The binding energy per nucleon for \(_{1}^{2}\)H and \(_{2}^{4}\)H erespectively are 1.1 MeV and 7.1 MeV. The energy released in MeV when two \(_{1}^{2}\)H nuclei fuse to form \(_{2}^{4}\)He is