4 - Nuclear Physics Questions Answers

the half life of radium is 1620 year & its atomic weight is 226gm/mole. the number of atoms that will decay from its 1g sample per second is

1) 3.16 x 1010

2)3.6 x 1012

3) 3.1 x 1015

4) 31.1 x 1015

Joshi sir comment

for radioactivity we know that it is a first order process

so dN/dt = -λN

so dN/1 = -[0.6932/(1620*3.1*107)]*(1/226)*6.023*1023

solve now

A RADIOACTIVE SUBSTANCE EMITS n BETA PARTICLES IN THE FIRST 2 SECONDS & 0.5 n BETA PARTICLES IN THE NEXT 2 SECONDS . THE MEAN LIFE OF THE SAMPLE IS

ANS 2/(ln2) s

Joshi sir comment

A RADIOACTIVE SUBSTANCE EMITS n BETA PARTICLES IN THE FIRST 2 SECONDS & 0.5 n BETA PARTICLES IN THE NEXT 2 SECONDS. Definitely by definition its half life will be 2 sec.

so mean life = half life / ln2                  This is the relation between mean life and half life.

A NUCLEUS OF MASS NO. 220, INITIALLY AT REST , EMITS AN  .α PARTICLE . IF THE Q  VALUE OF THE Rxn  IS 5.5MeV THE ENERGY OF THE EMITTED α PARTICLE WILL BE ??

ANS 5.4 MeV

Joshi sir comment

5.5*216/220 = 216/40 = 5.4 MeV                                  here 216 is the mass of nucleus after ejecting α particle.

The activity of a freshly prepared  radioactive sample is 10^10 disintegrations per second, whose mean life is 10^9 sec.

The mass of an atom of this radioisotope is 10 ^ -25 kg.  The mass (in mg) of the radioactive sample is