#1 Balance the following nuclear equation 65 Cr -------- 0 B+ -1 #2 Which of the

Question

#1 Balance the following nuclear equation

65 Cr -------- 0 B+

                      -1

#2 Which of the following isotopes is more likely to decay via electron emission rather than positron emission?

47 Fe

55 Cu

60 Ti

79 Zr

91 Rd

#3 A given isotopes has a half-life of 5.0 years. How long will it take a sample of this isotopes to decay to 1/4 its original?

#4 How many neutrons are in an atom of 95 Mo?

#5 The half-life for the decay of U-235 is 7e8 years. How many years does it take for 0.16 g U-235 to decay to 0.010 g U-235?

Explanation / Answer

2) 60Ti would be most likely to decay with an electron emission. The reason being that very generally stable isotopes occur at a neutron to proton ratio of 1:1, this is a very general however useful trend. 60Ti has 22 protons by definition being titanium, therefore having 38 neutrons to be the isotope that it is. Note the gross difference in the ratio. In order for it to approach stability there needs to be an increase in protons relative to neutrons, and a reduction in neutrons relative to protons. In order to achieve this a neutron emits a ?- particle or electron and in the process becomes a proton, this results in a reduction of 1 neutron and the addition of a proton. This is closer to a roughly stable 1:1 ratio. Also note the atomic mass number does not change however the atomic number does. Ie the new isotope still has 60 nucleons (protons and neutrons) but has a different number of protons. In this example the new isotope is 60 V, that is vanadium with 23 protons and 37 neutrons.

3) 2 half-lives = 10 years.

4) 95 - 42 = 53

5) It takes 4 half-lives for 0.16 grams to become 0.10 grams..

SO time taken = 4*7*10^8 = 28*10^8 years.

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