Alpha particles are 

1. 2 free protons

2. helium atoms

3. singly ionized helium atoms

4. doubly ionised helium atoms

Subtopic:  Radioactivity (OLD NCERT) |
 61%
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A radioactive sample with a half-life of 1 month has the label: 'Activity = 2 microcurie on 1-8-1991'. What would be its activity two months earlier? 

1. 1.0 microcurie       

2. 0.5 microcurie           

3. 4 microcurie             

4. 8 microcurie

Subtopic:  Radioactivity (OLD NCERT) |
 53%
From NCERT
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If the nuclear force between two protons, two neutrons and between a proton and a neutron is denoted by \(F_{pp} ,F_{nn}\) and \(F_{pn}\) respectively, then:
1. \(F_{p p} \approx F_{n n} \approx F_{p n}\)
2. \(F_{p p} \neq F_{n n}\) and \(F_{p n} = F_{n n}\)
3. \(F_{p p} = F_{n n} = F_{p n}\)
4. \(F_{p p} \neq F_{n n} \neq F_{p n}\)
Subtopic:  Nuclear Energy |
From NCERT
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A radioactive element has half-life period 800 yr. After 6400 yr, what fraction will remain? 

1. 12

2. 116 

3. 18 

4.1256

Subtopic:  Radioactivity (OLD NCERT) |
 76%
From NCERT
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In a given reaction,

XAZYAZ+1KA-4Z-1KA-4Z-1

Radioactive radiations are emitted in the sequence of  

1.  α, β, γ 

2. γ, α, β 

3. β, α, γ 

4. γ, β, α

Subtopic:  Radioactivity (OLD NCERT) | Types of Decay |
 90%
From NCERT
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An observer A sees an asteroid with a radioactive element moving by at a speed = 0.3 c and measures the radioactivity decay time to be TA. Another observer B is moving with the asteroid and measures its decay time as TB. Then TA and TB are related as below [VITEEE 2008]

1. TB < TA

2. TB = TA

3. TB > TA

4. Either 1 or 3 depending on whether the asteroid is approaching or moving away from A.

 

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If a proton and anti-proton come close to each other and annihilate, how much energy will be released:

1. 1.5×10-10 J           

2. 3×10-10 J         

3. 4.5×10-10 J         

4. None of these

Subtopic:  Mass-Energy Equivalent |
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The stable nucleus that has a radius half of the radius of \(\mathrm{Fe}^{56}\) is:
1. \(\mathrm{Li}^7\)
2. \(\mathrm{Na}^{21}\)
3. \(\mathrm{S}^{16}\)
4. \(\mathrm{Ca}^{40}\)

Subtopic:  Nucleus |
 67%
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A sample of radioactive element has a mass of 10 g at an instant t = 0. The approximate mass of this element in the sample after two mean lives is [2003]

1. 3.70 g

2. 6.30 g

3. 1.35 g

4. 2.50 g

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The mass density of a nucleus varies with mass number A as 

1. A2

2. A 

3. Constant 

4. 1A

Subtopic:  Nuclear Binding Energy |
 78%
From NCERT
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