1.

Find the binding energy of a nucleus consisting of equal numbers of protons and neutrons and having the radius one and a half time smaller than of `Al^(27)` nucleus.

Answer» Correct Answer - `Be^(8),E_(b)=56.5MeV`
The mass of defect is given by `E_(b)=Deltamc^(2)`
where `Delta m =` mass defect
If `m_(n)=` mass of neutron, `m_(p)=` mass of proton, `m_(N)=` mass of formed nucleus
For binding energy of `._(z)X^(A)`,
Here the number of proton `=Z`, The number of neutron `=A-Z`
`:. Deltam =Zm_(p)+(A-Z)m_(n)-m_(N)`
If atomic masses of the neucleus is given, then
`:. Delta m=Zm_(p)+Zm_(e )+(A-Z)m_(n)-(m_(N)+Zm_(e ))`
`=Z(m_(p)+m_(e ))+(A-Z)m_(n)-M_(N)`
`=ZM_(H)+(A-Z)m_(n)-M_(N)`
Here `M_(H)=` atomic mass of hydrogen
`M_(N)=` atomic mass of formed atom.
`:." "R=R_(0)A^(1//3)`
`R_(Al)=R_(0)(27)^(1//3)`
`R=R_(0)A^(1//3)`
But `R=(R_(Al))/((3)/(2))=(2)/(3)R_(Al)`
or `R_(0)A^(1//3)=(2)/(3)R_(0)(27)^(1//3)`
`:. " " A=((2)/(3))^(3)=27=(8)/(27)xx27=8`
From periodic table, the element is `Be^(8)`
Atomic masses are `1.007825` for hydrogen, `1.008665` for nuetron, `8.00531` for `Be`
`Deltam=(4m_(H)+4m_(n)-M_(N))"amu"`
`=(4xx1.007825+4xx1.008665-8.00531)"amu"`
`=(4.0313+4.034660-8.00531)"amu"`
`E_(b)=Delta mc^(2)=0.06065xx931 MeV`
`=56.4651 MeV=56.5 MeV`


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