Question 381:
easyAn element A decays into element C by a two step process $A \rightarrow B + _{2}He^{4}; B \rightarrow C + 2e^{-}$. Then
(1989)
In alpha decay ($A \rightarrow B$), the atomic number Z decreases by 2. In two beta decays ($B \rightarrow C$), the atomic number increases by $2 \times 1 = 2$. Thus, the final atomic number of C equals the initial atomic number of A. Elements with the same Z are isotopes.
Question 382:
easyCurie is a unit of
(1989)
Curie (Ci) is a non-SI unit of radioactivity, originally defined as the activity of 1 gram of radium-226 ($3.7 \times 10^{10}$ decays per second).
Question 383:
easyA radioactive element has half life period 800 years. After 6400 years what amount will remain?
(1989)
The number of half-lives $n = \frac{6400}{800} = 8$. The fraction remaining is $(1/2)^n = (1/2)^8 = 1/256$.
Question 384:
easyThe binding energy of deuteron is 2.2 MeV and that of $^4_2He$ is 28 MeV. If two deuteron are fused to form one $^4_2He$ then the energy released is:
(2006)
Energy released $Q = \text{Binding Energy of Product} - \text{Total Binding Energy of Reactants}$. $Q = 28 - (2.2 + 2.2) = 28 - 4.4 = 23.6$ MeV.
Question 385:
easyIn the reaction $^2_1H + ^3_1H \rightarrow ^4_2He + ^1_0n$, if the binding energies of $^2_1H$, $^3_1H$, and $^4_2He$ are respectively a, b and c (in MeV), then the energy (in MeV) released in this reaction is:
(2005)
The energy released $Q$ is the difference between the total binding energy of the products and the total binding energy of the reactants. $Q = BE(^4_2He) - [BE(^2_1H) + BE(^3_1H)] = c - (a + b) = c - a - b$.
Question 386:
easyFor the given reaction, the particle X is:n$^{11}_{6}C \rightarrow ^{11}_{5}B + \beta^+ + X$
(2000)
In $\beta^+$ (positron) decay, a proton is converted into a neutron, releasing a positron ($e^+$ or $\beta^+$) and an electron neutrino ($\nu$) to conserve lepton number. Hence, particle X is a neutrino.
Question 387:
easyA radioactive elements emits one $\alpha$ and $\beta$ particle then mass number of daughter element is:
(1999)
The emission of one $\alpha$ particle reduces the mass number by 4. The emission of a $\beta$ particle does not change the mass number. Therefore, the net effect is that the mass number is decreased by 4.
Question 388:
easyFor nuclear reaction $_{92}U^{235} + _{0}n^{1} \rightarrow _{56}Ba^{144} + …… + 3 _{0}n^{1}$:
(1998)
Let the unknown product be $^{A}_{Z}X$. Balancing the atomic numbers: $92 + 0 = 56 + Z + 0 \Rightarrow Z = 36$. Balancing the mass numbers: $235 + 1 = 144 + A + 3 \Rightarrow A = 236 - 147 = 89$. The element with $Z=36$ is Krypton (Kr), so the product is $_{36}Kr^{89}$.
Question 389:
easyWhich of the following is used as a moderator in nuclear reaction?
(1997)
Moderators are used in nuclear reactors to slow down fast neutrons to thermal energies. Heavy water ($D_2O$) and graphite are commonly used as moderators. Cadmium is typically used for control rods.
Question 390:
easyIn a radioactive decay process, the negatively charged emitted $\beta$-particles are:
(2007)
In $\beta^-$ decay, a neutron inside the nucleus transforms into a proton, emitting an electron (the $\beta$-particle) and an antineutrino. Thus, they are electrons produced as a result of the decay of neutrons.