EASY

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After three 'average life times' of a radioactive sample, the amount of substance remains $x %$ of the original amount. Then, approximate value of $x$ is

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Important Questions on Nuclei

HARD

Physics>Modern Physics>Nuclei>Radioactivity

At some instant, a radioactive sample

S_{1}

having an activity

5 μ Ci

has twice the number of nuclei as another sample

S_{2}

which has an activity of

10 μ Ci

. The ratio of half lives of

S_{1} a n d S_{2}

MEDIUM

Physics>Modern Physics>Nuclei>Radioactivity

For a radioactive material, the half-life is

10 minutes

. If initially there are

600

number of nuclei, the time taken (in

minutes

) for the disintegration of

450

nuclei is

HARD

Physics>Modern Physics>Nuclei>Radioactivity

Let

N_{β}

be the number of

β

particle emitted by

1 gram

{Na}^{24}

radioactive nuclei having a half life of

15 h

. In

7.5 h

, the number

N_{β}

is close to

[N_{A} = 6 .023 \times 10^{23} {mole}^{- 1}]

EASY

Physics>Modern Physics>Nuclei>Radioactivity

A radioactive element has a rate of disintegration

10, 000

disintegrations per minute at a particular instant. After four minutes it becomes

2500

disintegrations per minute. The decay constant per minute is

HARD

Physics>Modern Physics>Nuclei>Radioactivity

An accident in a nuclear laboratory resulted in deposition of a certain amount of radioactive material of half-life

18

days inside the laboratory. Tests revealed that the radiation was

64

times more than the permissible level required for safe operation of the laboratory. What is the minimum number of days after which the laboratory can be considered safe for use?

EASY

Physics>Modern Physics>Nuclei>Radioactivity

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

0.3

. Then,

t

is given by:

(Consider \log_{e} (x) = \log (x))

EASY

Physics>Modern Physics>Nuclei>Radioactivity

A nucleus of uranium decays at rest into nuclei of thorium and helium. Then:

MEDIUM

Physics>Modern Physics>Nuclei>Radioactivity

Two species of radioactive atoms are mixed in equal number. The disintegration of the first species is

λ

and of the second is

\frac{λ}{3}

. After a long time the mixture will behave as a species with mean life of approximately

MEDIUM

Physics>Modern Physics>Nuclei>Radioactivity

Using a nuclear counter the count rate of emitted particles from a radioactive source is measured. At

t = 0

it was

1600

counts per second and

t = 8

seconds it was

100

counts per second. The count rate observed, as counts per second, at

t = 6

seconds is close to:

MEDIUM

Physics>Modern Physics>Nuclei>Radioactivity

At a given instant, say

t = 0,

two radioactive substance

A

and

B

have equal activities. The ratio

\frac{R_{B}}{R_{A}}

of their activities after time

t

itself decays with time

t

e^{- 3 t} .

If the half-life of

A

l n 2,

the half-life of

B

is:

EASY

Physics>Modern Physics>Nuclei>Radioactivity

A decay chain of the nucleus

{}_{92}^{238}U

involves eight

α

-decays and six

β

-decays. The final nucleus at the end of the process will be

HARD

Physics>Modern Physics>Nuclei>Radioactivity

A solution containing active cobalt

{}_{27}^{60}{Co}

having an activity of

0 .8 μCi

and decay constant

λ

is injected in an animal's body. When

1 c m^{3}

blood is drawn from the animal's body after

10 h

of injection, the activity was found to be

300 dpm

(decays per minute), then the total volume of blood in the animal's body is close to

[1 Ci = 3 .7 \times 10^{10} dps

(decays per second) and at

t = 10 h

the value of

e^{- λ t} = 0.84]

MEDIUM

Physics>Modern Physics>Nuclei>Radioactivity

The beta particles of a radioactive metal originate from-

EASY

Physics>Modern Physics>Nuclei>Radioactivity

The half-life of a radioactive substance is

30 \min

. The time (in minutes) taken between

40 %

decay and

85 %

decay of the same radioactive substance is

EASY

Physics>Modern Physics>Nuclei>Radioactivity

A nuclear decay is possible if the mass of the parent nucleus exceeds the total mass of the decay particles. If

M (A, Z)

denotes the mass of a single neutral atom of an element with mass number A and atomic number Z, then the minimal condition that the

β

decay,

X_{Z}^{A} \to Y_{Z + 1}^{A} + β^{-} + \bar{v_{e}}

, will occur is (

m_{e}

denotes the mass of the

β

particle and the neutrino mass

m_{v}

can be neglected):

MEDIUM

Physics>Modern Physics>Nuclei>Radioactivity

The half-life of a particle of mass

1.6 \times 10^{- 26} kg

6.9 s

and a stream of such particles is travelling with the

K . E .

of a particle being

0.05 eV

. The fraction of particles which will decay when they travel a distance of

1 m

is,

EASY

Physics>Modern Physics>Nuclei>Radioactivity

Radioactive material

A

has decay constant

8 λ

and material

B

has decay constant

λ

. Initially they have the same number of nuclei. After what time, the ratio of number of nuclei of material

A

to that

B

will be

\frac{1}{e} ?

MEDIUM

Physics>Modern Physics>Nuclei>Radioactivity

In a radioactive decay chain, the initial nucleus is

_{90}^{232} Th

. At the end, there are

6

α

-particles and

4 β

-particles which are emitted. If the end nucleus is

_{Z}^{A} X, A

and

Z

are given by:

EASY

Physics>Modern Physics>Nuclei>Radioactivity

A sample of radioactive material

A

, that has an activity of

10 mCi (1 Ci = 3.7 \times 10^{10} d e c a y s^{- 1})

has twice the number of nuclei as another sample of a different radioactive material

B

which has an activity of

20 mCi

. The correct choices for half-lives of

A

and

B

would then be, respectively:

MEDIUM

Physics>Modern Physics>Nuclei>Radioactivity

The activity of a radioactive sample is measured as

9750

counts per minute at

t = 0

and as

975

counts per minute at

t = 5

minutes. The decay constant is approximately,

After three 'average life times' of a radioactive sample, the amount of substance remains x% of the original amount. Then, approximate value of x is

Important Questions on Nuclei

Learn and Prepare for any exam you want !

After three 'average life times' of a radioactive sample, the amount of substance remains $x %$ of the original amount. Then, approximate value of $x$ is