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Fundamentals Of Physics
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Short Answer

Question: Consider the fission of U238 by fast neutrons. In one fission event, no neutrons are emitted and the final stable end products, after the beta decay of the primary fission fragments, are C140e and Ru99 . (a) What is the total of the beta-decay events in the two beta-decay chains? (b) Calculate for this fission process. The relevant atomic and particle masses are

U238 238.05079 Ce140 139.90543u n 1.00866u Ru99 9890594u

(a) The number of the beta decay is 10.

(b) The energy release in fission process is 225.98Me V.

See the step by step solution

Step by Step Solution

Step 1: Given data

The mass of U238,mu=238.05079u

The mass of C140e,mCe=139.90543u

The mass of n,mn=1.00866u

The mass of R99u,mRu=98.90594u

Step 2: Determine the formulas to calculate the number of the beta decay and energy for the fission process.

The expression to calculate released energy is given as follows.

Q=-mc2Q=(mu+mn-mCe-mRu-Nme)c2 ...(i)

Here,N is the number of the beta decay.

Step 3: (a) Calculate the number of the beta decay.

Consider the reaction given below.

U238+nC140e+R99u+Ne

Here, is the number of the beta decay.

To calculate the number of the beta decay, equals the atomic number of both the sides of the equation.

Atomic number of uranium, Zu=92

Atomic number of cerium, ZCe=58

Atomic number of Ruthenium, ZRu=44

Calculate the number of beta decay.

Ne+ZRu+ZCe=Zu

Substitute for 92 for Zu, 58 for ZCe, 44 for ZRu and 1 for e into above equation.

N1+44+58=92 N+102=92 N=92-102 N=-10

Here, negative sign indicates that beta decay reduces the atomic number.

Hence the number of the beta decay is 10.

Step 4: (b) Calculate the energy for the fission process.

Recall equation (i).

Q=(mu+mn-mCe-mRu-Nme)×c2Q=(mu+mn-mCe-mRu)c2-mec2

Substitute f 238.05079u for mu, 139.90543u for mCe, 1.00866u for mn, 98.90594u for mRu, 931.5MeV for c2, 0.511MeV for mec2and 10 for N into equation (i).

role="math" localid="1661924965359" Q=(238.05078+1.00866-139.90543-98.90594)931.5MeV-10×0.511MeVQ=0.24809×931.5MeV-10×0.511MeVQ=231.095835MeV-5.11MeVQ=225.99MeV

Hence the energy release in fission process is 225.99MeV.

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