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suchintan mondal Grade: 12

1)a radioactive material has mean life 1620 yrs and 540 yrs for alpha-emission and beta- emission respectively.The time in which half of the material remains undecayed emitting both these radiations is________

2)mass of 2 curie uranium(234)is_______

3)Half life of radium is 1620yrs &its atomic weight =226kg/kilomole.No. of atoms that will decay from 1 gm. of sample per second will be _________

4)Ratio of momenta of an electron of mass me and an alpha particle of mass ma which are accelerated from rest by a potential difference of 250V is_______

8 years ago

Answers : (2)

Askiitians expert Anirudh iitk
8 Points

Answer to qsn no 4:

the kinetic energy = qV. In either case the q has same numerical value.( since an alpha particle is a hydrogen nucleus = +1 unit charge wheras an electron  has -1 unit charge)

so, the kinetic energy has same value

hence p^2/2m is the same. therefore,  (p1/p2)^2 = (m1/m2). the required ratio is therefore sqrt of (me/ma)

8 years ago
Askiitians expert Anirudh iitk
8 Points

nswer to qsn no 3:

226g/mol => 226 g of the material will have avagadros number of atoms. hence, 1 g will have A/226 atoms. Now in this case, this is the starting amterial ie N0 . And it is a first order eaction.

hence, N = N0e-kt

-dN/dt = kN0e-kt. U know K from half life and if u adjust the units in terms of seconds ie. 1620x365x24x60x60 sec,then put t=0 in the above eqn. You will get the rate of decomposition in terms of atoms/sec for initial conc. this is the answer u seek

8 years ago
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