Is it possible for a hydrogen ( H 1 1 ) nucleus to emit an alpha particle? Give a reason for your answer.

No, as alpha radiation is nothing but the nucleus of helium ( H 2 4 e ). With the emission of an alpha particle ( H 2 4 e ), the atomic number of the radioactive nucleus decreases by two and mass number by four. The nucleus of hydrogen does not contain two protons and two neutrons, and it has less number of electrons than the alpha particle. So it can not emit an alpha particle.

EASY

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Which type of nuclear radiation has the lowest ionizing power?

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Important Questions on Thermionic Emission and Radioactivity

MEDIUM

Science>Physics>Thermionic Emission and Radioactivity>Radioactivity

Two radioactive materials

A

and

B

have decay constants

10 λ

and

λ

, respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of

A

to that of

B

will be

\frac{1}{e}

after a time:

MEDIUM

Science>Physics>Thermionic Emission and Radioactivity>Radioactivity

A piece of wood from a recently cut tree shows

20

decays per minute. A wooden piece of the same size placed in a museum (obtained from a tree cut many years back) shows

2

decays per minute. If the half-life of

C^{14}

5730 years

, then the age of the wooden piece placed in the museum is approximately
[This question was awarded a bonus and proper correction was made to avoid that]

MEDIUM

Science>Physics>Thermionic Emission and Radioactivity>Radioactivity

Two radioactive substances

A

and

B

have decay constants

5 λ

and

λ

respectively. At

t = 0

, a sample has the same number of the two nuclei. The time taken for the ratio of the number of nuclei to become

{(\frac{1}{e})}^{2}

will be

EASY

Science>Physics>Thermionic Emission and Radioactivity>Radioactivity

Is it possible for a hydrogen (

{}_{1}^{1}H

) nucleus to emit an alpha particle? Give a reason for your answer.

EASY

Science>Physics>Thermionic Emission and Radioactivity>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

HARD

Science>Physics>Thermionic Emission and Radioactivity>Radioactivity

In a radioactive sample,

_{19}^{40} K

nuclei either decay into stable

_{20}^{40} C a

nuclei with decay constant

4.5 \times 10^{- 10}

per year or into stable

_{18}^{40} A r

nuclei with decay constant

0.5 \times 10^{- 10}

per year. Given that in this sample all the stable

_{20}^{40} C a

and

_{18}^{40} A r

nuclei are produced by the

_{19}^{40} K

nuclei only. In time

t \times 10^{9}

years, if the ratio of the sum of stable

_{20}^{40} C a

and

_{18}^{40} A r

nuclei to the radioactive

_{19}^{40} K

nuclei is

99,

the value of t will be : [Given

l n 10 = 2.3

]

MEDIUM

Science>Physics>Thermionic Emission and Radioactivity>Radioactivity

Half-lives of two radioactive elements

A

and

B

are

20 minutes

and

40 minutes

, respectively. Initially, the samples have an equal number of nuclei. After

80 minutes

, the ratio of decayed numbers of

A

and

B

nuclei will be:

EASY

Science>Physics>Thermionic Emission and Radioactivity>Radioactivity

The variation of decay rate with number of active nuclei is correctly shown in graph

A Question Image

B Question Image

C Question Image

D Question Image

EASY

Science>Physics>Thermionic Emission and Radioactivity>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

MEDIUM

Science>Physics>Thermionic Emission and Radioactivity>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,

MEDIUM

Science>Physics>Thermionic Emission and Radioactivity>Radioactivity

A radioactive nucleus decays by two different processes. The half-life for the first process is

10 s

and that for the second is

100 s

. The effective half-life of the nucleus is close to:

MEDIUM

Science>Physics>Thermionic Emission and Radioactivity>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

Science>Physics>Thermionic Emission and Radioactivity>Radioactivity

Some amount of a radioactive substance (half-life

= 10

days ) is spread inside a room and consequently, the level of radiation becomes

50

times the permissible level for normal occupancy of the room. After how many days will the room be safe for occupation?

MEDIUM

Science>Physics>Thermionic Emission and Radioactivity>Radioactivity

A radio isotope ‘

X

’ with a half life

1.4 \times 10^{9}

years decays to ‘

Y

’ which is stable. A sample of the rock from a cave was found to contain ‘

X

’ and ‘

Y

’ in the ratio

1 : 7

. The age of the rock is

MEDIUM

Science>Physics>Thermionic Emission and Radioactivity>Radioactivity

A radioactive sample of half life

23.1 days

is disintegrating continuously. The percentage decay of the sample between the

15^{th}

and

16^{th}

day will be [Take,

e^{0.03} = 1.03

]

EASY

Science>Physics>Thermionic Emission and Radioactivity>Radioactivity

In one average lifetime of a radioactive nucleus,

EASY

Science>Physics>Thermionic Emission and Radioactivity>Radioactivity

A hypothetical radioactive element has a half-life of

20

years. The time it takes for

80 %

of the substance to decay is

(\ln 5 = 1.6, \ln 2 = 0.7)

EASY

Science>Physics>Thermionic Emission and Radioactivity>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} ?

HARD

Science>Physics>Thermionic Emission and Radioactivity>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}]

MEDIUM

Science>Physics>Thermionic Emission and Radioactivity>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:

Which type of nuclear radiation has the lowest ionizing power?

Important Questions on Thermionic Emission and Radioactivity

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