A certain radioactive element has a half-life of 20 years. If we have a block with 10 g of the element in it, after how many years will there be just 2.5 g of the element in the block?
80 years
40 years
100 years
60 years
The activity of a radioactive sample decreases to
(1/3)rd of its original value in 3 days. Then, in 9 days its activity will become
(1/27) of the original value
(1/9) of the original value
(1/18) of the original value
(1/3) of the original value
If r1 and r2 are the radii of the atomic nuclei of mass numbers 64 and 125 respectively, then the ratio (r1/r2) is
64/125
5/4
4/5
A radioactive element forms its own isotope after 3 consecutive disintegrations. The particles emitted are
3 β-particles
2 β-particles and 1α-particle
2 -βparticles and 1 γ-particle
2 α-particles and 1 β-particle
A radioactive substance contains 10000 nuclei and its half-life period is 20 days. The number of nuclei present at the end of 10 days is
7070
9000
8000
7500
A radioisotope has a half-life of 5 yr. The fraction of the atoms of this material that would decay in 15 yr will be
1
2/3
7/8
5/8
A particle of mass m at rest decays into two particles of masses m1 and m2 having non zero velocities. The ratio of de-Broglie wavelengths of the particles is
m1/m2
m2/m1
1.0
Which of the following nuclei is fissionable but not possible?
C.
does not undergo fission reaction directly, but it is fissionable because it may be converted into fissionable
In nuclear reaction
the atomic mass and number of P are, respectively:
170,69
172,69
172,70
170,70
A radioactive substance has activity 64 times higher than the required normal level. If T1/2 = 2h, then the time, after which it should be possible to work with it, is:
16 h
6 h
10 h
12 h