444 8 Nuclear Physics – II
The reaction above will take place for low energy incident deuterons in a
s-wave state leaving the^12 C nucleus in the ground state.
Given that the deuteron has spin 1 and positive parity while the alpha par-
ticle has zero spin and positive parity, estimate the spin of^14 N in the ground
state.
Can the alpha particle come off with orbital angular momentuml=1?
If the incident kinetic energy of the deuteron is 20 MeV in the laboratory
frame, calculate the laboratory kinetic energy at whichα’s should scatter from(^12) C to test the principle of detailed balance. What is the expected ratio between
the cross-sections for the direct and inverse reactions? Atomic masses of
(^14) N, (^2) H and (^4) He are 14.003074, 2.014102, 4.002603 amu respectively. 1 amu
=931.44 MeV.
[University of Bristol 1969]
8.74 A beam of 460 MeV deuterons impinges on a target of bismuth. Given the
binding energy of the deuteron is 2.2 MeV, compute the mean energy, spread
in energy and the angle of the cone in which the neutrons are emitted.
[Osmania University 1975]
8.2.14 Fission and Nuclear Reactors........................
8.75 1.0 g of^23 Na of density 0.97 is placed in a reactor at a region where the ther-
mal flux is 10^11 /cm^2 /s. Set up the equation for the production of^24 Na and
determine the saturation activity that can be produced. The half-life of^24 Na is
15 h, and the activation cross-section of^23 Na is 536 millibarns.
[Osmania University 1964]
8.76 Suppose 100 mg of gold (^19779 Au) foil are exposed to a thermal neutron flux
of 10^12 neutrons/cm^2 /s in a reactor. Calculate the activity and the number
of atoms of^198 Au in the sample at equilibrium [Thermal neutron activation
cross-section for^197 Au is 98 barns and half-life for^197 Au is 2.7 h]
[Osmania University]
8.77 Estimate the energy released in fission of^23892 U nucleus, givenac= 0 .59 MeV
andas= 14 .0MeV.
[Osmania University 1962]
8.78 A small container of Ra–Be is embedded in the middle of a sphere of paraffin
wax of a few cm radius so as to form a source of (predominantly) thermal
neutrons. This source is placed at the centre of a very large block of graphite.
Derive an expression for the density of thermal neutrons at a large distancer
from the source in terms of the source strengthQ, the diffusion coefficientD
and diffusion lengthL.
AsmallBF 3 counter is placed in the graphite at a distance of 3 m from
the above source contains 10^20 atoms of^10 B. The cross-section of^10 Bfor
the thermal neutron capture follows a 1/vlaw and has a magnitude of 3,000