The half life of a radioactive substance is 20 minutes. The approximate time interval (t_{2} - t_{1}) between the time t_{2} when 2/3 of it has decayed and time t_{1} when 1/3 of it had decayed is
14 min
20 min
28 min
7 min
B.
20 min
Half-lives of two radioactive elements A and B are 20 minutes and 40 minutes, respectively. Initially, the samples have equal number of nuclei. After 80 minutes, the ratio of decayed numbers of A and B nuclei will be:
1: 16
4 : 1
1: 4
5: 4
D.
5: 4
Given 80 min = 4 half-lives of A = 2 half-lives of B.
Let the initial number of nuclei in each sample be N.
For radioactive element A,
N_{A} after 80 min = N/2^{4}
⇒ Number of A nuclides decayed =
Assume that a neutron breaks into a proton and an electron. The energy released during this process is(Mass of neutron = 1.6725 x 10^{–27}kg; mass of proton = 1.6725 x 10^{–27}kg; mass of electron = 9 x 10^{–31}kg)
0.73 MeV
7.10 MeV
6.30 MeV
5.4 MeV
A.
0.73 MeV
Proton, Deuteron and alpha particle of the same kinetic energy is moving in circular trajectories in a constant magnetic field. The radii of the proton, deuteron and alpha particle are respectively r_{p}, r_{d} and r_{α}. Which one of the following relations is correct?
r_{α} = r_{p}= r_{d}
r_{α} = r_{p}< r_{d}
r_{α} > r_{d}> r_{p}
r_{α} = r_{d}> r_{p}
B.
r_{α} = r_{p}< r_{d}
For charged particle moving with a speed v, in magnetic field B, on a circular track of radius
A radioactive nucleus (initial mass number A and atomic number Z) emits 3 α–particles and 2 positions. The ratio of number of neutrons to that of protons in the final nucleus will be
B.
In positive beta decay a, proton is transformed into a neutron and a positron is emitted
p^{+} → n^{0} + e^{+}
Number of neutrons initially was A-Z
Number of neutrons after decay (A-Z) -3 x 2 (due to alpha particles) + 2 x 1 (due to positive beta decay)
The number of protons will reduce by 8. so, the ratio number of neutrons to that of protons =
A radioactive nucleus A with a half-life T, decays into a nucleus B. At t = 0, there is no nucleus B. At some time t, the ratio of the number of B to that of A is 0.3. Then, t is given by
t = T log (1.3)
D.
At time t
also let initially there are total N_{0} number of nuclei
N_{A} + N_{B} = N_{0}
550 Views