A radioactive sample at any instant has its disintegration rate 5000 disintegration per minute. After 5 minutes, the rate is 1250 disintegrations per minute. Then, the decay constant (per minute) is 

(1) 0.8 In 2               

(2) 0.4 In 2

(3) 0.2 In 2               

(4) 0.1 In 2

Radioactive nuclei that are injected into a patient collect at certain sites within its body, undergoing radioactive decay and emitting electromagnetic radiation. These radiations can then be recorded by a detector. This procedure provides an important diagnostic tool called 

(1) Gamma camera

(2) CAT scan

(3) Radiotracer technique

(4) Gamma ray spectroscopy

A radioactive decay chain starts from ${}_{93}{}^{237}\mathrm{Np}$ and produces ${}_{90}{}^{229}\mathrm{Th}$ by successive emissions. The emitted particles can be 

(1) Two $\mathrm{\alpha }$-particles and one $\mathrm{\beta }$-particle

(2) Three ${\mathrm{\beta }}^{+}$ particles

(3) One $\mathrm{\alpha }$ particle and two ${\mathrm{\beta }}^{+}$ particles

(4) One $\mathrm{\alpha }$ particle and two ${\mathrm{\beta }}^{-}$ particles

The half-life of a sample of a radioactive substance is 1 hour. If $8\times {10}^{10}$ atoms are present at t = 0, then the number of atoms decayed in the duration t = 2 hour to t = 4 hour will be

(1) $2\times {10}^{10}$         

(2) $1.5\times {10}^{10}$

(3) Zero               

(4) Infinity

Carbon dating is best suited for determining the age of fossils if their age in years is of the order of 
(1) ${10}^3$            

(2) ${10}^4$

(3) ${10}^5$             

(4) ${10}^6$

A count rate meter shows a count of 240 per minute from a given radioactive source. One hour later the meter shows a count rate of 30 per minute. The half-life of the source is

(1) 120 min                   

(2) 80 min

(3) 30 min                     

(4) 20 min

The half-life of a radioactive substance is 40 years. How long will it take to reduce to one fourth of its original amount and what is the value of decay constant 

(1) 40 year, 0.9173/year           

(2) 90 year, 9.017/year

(3) 80 year, 0.0173 year           

(4) None of these

A radioactive material has a half life of 10 days. What fraction of the material would remain after 30 days

(1) 0.5               

(2) 0.25

(3) 0.125           

(4) 0.33

Starting with a sample of pure ${}_{66}\mathrm{Cu}$, $\frac{7}{8}$ of it decays into Zn in 15 min. The corresponding half-life is 

(1) 5 min               

(2) $7\frac{1}{2}$ min
(3) 10 min             

(4) 15 min

A radioactive material has a half-life of 8 years. The activity of the material will decrease to about 1/8 of its original value in 

(1) 256 year           

(2) 128 year

(3) 64 year             

(4) 24 year