Physics - Nuclear Physics and Radioactivity
Exam Duration: 45 Mins Total Questions : 30
Find the density of \(^{12}_6C\) nucleus.
- (a)
2.7X10-17 kg/m3
- (b)
2.4X1017 kg/m3
- (c)
2.7X1015 kg/m3
- (d)
2.4X10-15 kg/m3
Assuming that all laws of thermodynamics can be applied to a nucleus, the \(\alpha\)-decay of a nucleus may be regarded as an
- (a)
isothermal process
- (b)
isobaric process
- (c)
adiabatic process
- (d)
isochoric process
Which one of the following processes represents a \(\gamma \ decay\)?
- (a)
\(^A_ZX+\gamma\rightarrow ^A_{Z-1}X+a+b\)
- (b)
\(^A_ZX+^1_0n\rightarrow ^{A-3}_{Z-2}X+c\)
- (c)
\(^A_ZX+^o_{-1}e\rightarrow ^A_{Z-1}X+g\)
- (d)
\(^A_ZX^*\rightarrow ^A_{Z}X+f\)
The half-life of 131I is 8 day. Given a sample of 131I at time t=0, we can assert that
- (a)
no nucleus will decay before t=4 days
- (b)
no nucleus will decay beore t=8 days
- (c)
all nuclei will decay before t=16 days
- (d)
given nucleus may decay at any time after t=0
If one starts with one curie of radioactive substance (T1/2=12h), then the activity left after a period of 1 week will be about
- (a)
1 curie
- (b)
120 micro curie
- (c)
60 micro curie
- (d)
8 mili curie
A and B are two radioactive substances whose half-lives are 1 and 2 yr respectively. Initially, 10g of A and 1g of B is taken. The time (approximate) after which they will have same quantity remaining is
- (a)
6.62 yr
- (b)
5 yr
- (c)
3.2yr
- (d)
7 yr
The ratio of half-life and mean life of a radioactive sample is
- (a)
ln 2
- (b)
1
- (c)
\(1\over ln \ 2\)
- (d)
\(1\over 2\ ln \ 2\)
From a newly formed radioactive substance (Half-life 2 h), the intensity of radiation is 64 times the permissible safe level. The minimum time after which work can be done safely from this source is
- (a)
6h
- (b)
12h
- (c)
24h
- (d)
128h
Let mp be the mass of a proton mn the mass of a neutron, M1 the mass of a \(^{20}_{10}Ne\) nucleus and M2 the mass of a \(^{40}_{20}Ca\)
- (a)
M2=2M1
- (b)
M2>2M1
- (c)
M2<2M1
- (d)
M1<10(mn+mp)
Which of the following is a wrong description of binding energy of a nucleus?
- (a)
It is the energy required to break a nucleus into its constituent nucleons.
- (b)
It is the energy made available when free nucleons combined to form a nucleus
- (c)
It is the sum of the rest mass energies of its nucleons minus the rest mass energy of the nucleus
- (d)
It is the sum of the kinetic energy of all the nucleons in the nucleus.
The binding energy per nucleon of O16 is 7.97MeV and that of O17 is 7.75MeV. The energy required to remove a neutron from O17 in MeV is
- (a)
3.52
- (b)
3.64
- (c)
4.23
- (d)
7.86
For a substance, the average life for \(\alpha-\)emission is 1620yr and for \(\beta-\)emission is 405yr. After how much time, the \(1\over 4\) of the material remains after \(\alpha \ and \ \beta\) emission?
- (a)
1500yr
- (b)
300yr
- (c)
449yr
- (d)
810yr
A radioactive sample has a disintegration rate of 36X105 disintegrations per minute. The sample itself consisting of 10-5\(\mu\) mole of the active nuclei. The disintegration constant, \(\lambda\) is given by
- (a)
6 x 10-7s-1
- (b)
6 x 1015s-1
- (c)
6 x 109 s-1
- (d)
10-8 s-1
The half-life of radioactive polonium(Po) is 138.6day. For ten lakh polonium atoms, the number of disintegrations in 24 h is
- (a)
2000
- (b)
3000
- (c)
4000
- (d)
5000
The radioactivity of a sample is R1 at a time T1 and R2 at a time T2. If the half-life of the specimen is T, then the number of nuclei that have disintegrated in the time (T2-T1) is proportional to
- (a)
(R1T1-R2T2)
- (b)
R1+R2
- (c)
(R1XR2)/T
- (d)
(R1-R2)R
Half-life of a radioactive substance is 20min. Difference between points of time when it is 33% disintegrated and 67% disintegrated is approximately
- (a)
10min
- (b)
20min
- (c)
30min
- (d)
40min
Suppose we consider a larger number of containers each containing initially 10000 atoms of a radioactive material with a half-life of 1yr. After 1 yr,
- (a)
all the containers will have 5000 atoms of the material
- (b)
all the containers will contain the same number of atoms of the material but that number will only be approximately 5000
- (c)
the containers will in general have different number of the atoms of the material but their average will be close to 5000
- (d)
None of the containers can have more than 5000 atoms.
In a nuclear reactor, moderators slow down the neutrons which come out in a fission process. The moderator used light nuclei. Heavy nuclei will not serve the purpose, because
- (a)
They will break up
- (b)
elastic collision of neutrons with heavy nuclei will not slow them down
- (c)
the net weight of the reactor would be unbearably high
- (d)
substances with heavy nuclei do not occur in liquid or gaseous state at room temperature
Match the categories of nuclei given in column I with their examples given in column II and select the correct option from the choices given below.
column I | column II |
---|---|
A. Isotopes | 1. 6C14, 7N14 |
B. Isobars | 2. 3Li7, 4Be8 |
C. Isotones | 3. 1H1,1H2,1H3 |
- (a)
A B C 3 2 1 - (b)
A B C 2 1 3 - (c)
A B C 3 1 2 - (d)
A B C 1 2 3
Assume that a neutron breaks into a proton and an electron. The energy released during this process in (mass of neutron = 1.6725X10-27kg, mass of proton=1.6725X10-27 kg, mass of electron =9X10-31kg)
- (a)
0.73 MeV
- (b)
7.10 MeV
- (c)
6.30 MeV
- (d)
5.4 MeV
The half-life of a radioactive substance is 20min.The approximate time interval (t2 - t1) between the time t2 when \(2\over 3\) of it has decayed and time t1 when \(1\over 3\) of it had decayed is
- (a)
14 min
- (b)
20 min
- (c)
28min
- (d)
7 min
A nucleus of mass M+\(\Delta m\) is at rest and decays into two daughter nuclei of equal mass \(M\over 2\) each. Speed of light is c. The binding energy per nucleon for the parent nucleus is E1 and that for the daughter nuclei is E2. Then
- (a)
E2=2E1
- (b)
E1>E2
- (c)
E2>E1
- (d)
E1=2E2
A nucleus of mass M+\(\Delta m\) is at rest and decays into two daughter nuclei of equal mass \(M\over 2\) each . The speed of daughter nuclei is
- (a)
\(c{\Delta m\over M+\Delta m}\)
- (b)
\(c\sqrt{2\Delta m\over M}\)
- (c)
\(c\sqrt{\Delta m\over M}\)
- (d)
\(c\sqrt{\Delta m\over M+\Delta m}\)
A radioactive nucleus (initial mass number A and atomic number Z) emits 3\(\alpha\)-particles and 2 positrons. the ratio of number of neutrons to that of protons in the final nucleus will be
- (a)
\(A-Z-8\over {Z-4}\)
- (b)
\(A-Z-4\over Z-8\)
- (c)
\(A-Z-12\over {Z-4}\)
- (d)
\(A-Z-4\over {Z-4}\)
The half-life period of a radioactive element X is same as the mean life time of another radioactive element Y. Initially, they have the same number o atoms. Then
- (a)
X will decay faster than X
- (b)
Y will decay faster than X
- (c)
Y and X have same decay rate initially
- (d)
X and Y decay at same rate always
Starting with a sample of pure 66Cu, 7/8 of it decays into Zn in 15min. The corresponding half-life is
- (a)
10min
- (b)
15min
- (c)
5min
- (d)
\(7{1\over 2}\) min
A nuclear transformation is denoted by X(n,\(\alpha\))\(\rightarrow ^7_3Li\). Which of the following is the nucleus of element X?
- (a)
\(^{12}_6 C\)
- (b)
\(^{10}_5 B\)
- (c)
\(^9_5B\)
- (d)
\(^{11}_4Be\)
A nucleus disintegrates into two nuclear parts which have their velocities in the ratio 2:1. The ratio of their nuclear sizes will be
- (a)
21/3 : 1
- (b)
1:31/2
- (c)
31/2 : 1
- (d)
1:21/3