Neutrons

Question 1

Delayed neutrons are fission neutrons that…

Answer 1

are expelled at a lower average kinetic energy than most other fission neutrons.

Question 2

Delayed neutrons are neutrons that…

Answer 2

are produced from the radioactive decay of certain fission fragments.

Question 3

Which one of the following is a characteristic of a prompt neutron?

Answer 3

Accounts for more than 99 percent of fission neutrons.

Question 4

A neutron that is expelled 1.0 x 10-2 seconds after the associated fission event is a __________
neutron

Answer 4

delayed

Question 5

A neutron that is expelled 1.0 x 10-6 seconds after the associated fission event is a __________
neutron.

Answer 5

delayed

Question 6

Which one of the following types of neutrons has an average neutron generation lifetime of 12.5
seconds?

Answer 6

Delayed

Question 7

In a comparison between a delayed neutron and a prompt neutron produced from the same fission
event, the prompt neutron is more likely to… (Assume that both neutrons remain in the core.)

Answer 7

require a greater number of collisions to become a thermal neutron.

Question 8

In a comparison between a delayed neutron and a prompt neutron produced from the same fission
event, the prompt neutron is more likely to… (Assume that both neutrons remain in the core.)

Answer 8

cause fast fission of a U-238 nucleus.

Question 9

A neutron that is released 1.0 x 10-10 seconds after the associated fission event is classified as a
__________ fission neutron.

Answer 9

delayed

Question 10

In a comparison between a prompt neutron and a delayed neutron produced from the same fission
event, the delayed neutron requires __________ collisions in the moderator to become thermal; and is
__________ likely to cause fission of a U-238 nucleus. (Assume that both neutrons remain in the
core.)

Answer 10

fewer; less

Question 11

In a comparison between a delayed neutron and a prompt neutron produced from the same fission
event, the prompt neutron is more likely to…

Answer 11

leak out of the core while slowing down.

Question 12

In a comparison between a delayed neutron and a prompt neutron produced from the same fission
event, the delayed neutron is more likely to…

Answer 12

become a thermal neutron.

Question 13

During a brief time interval in a typical reactor operating steady-state near the beginning of a fuel
cycle, 1.0 x 10^3 delayed neutrons were emitted.
Approximately how many prompt neutrons were emitted during this same time interval?

Answer 13

1.5 x 10^5

Question 14

Which one of the following types of neutrons in a reactor is more likely to cause fission of a U-238
nucleus in the reactor fuel? (Assume that each type of neutron remains in the reactor until it interacts
with a U-238 nucleus.)

Answer 14

A prompt fission neutron beginning to slow down.

Question 15

During a brief time interval in a typical reactor operating steady-state at the beginning of a fuel cycle,
1.0 x 10^5 delayed neutrons were emitted.
Approximately how many prompt neutrons were emitted in the reactor during this same time interval?

Answer 15

1.5 x 10^7

Question 16

A neutron that appears 1.0 x 10^-16 seconds after the associated fission event is classified as a
__________ fission neutron.

Answer 16

Prompt

Question 17

During a brief time interval in a typical reactor operating steady-state near the beginning of a fuel
cycle, 4.25 x 105 delayed neutrons were produced.
Approximately how many prompt neutrons were produced in the reactor during this same time
interval?

Answer 17

6.5 x 10^7

Question 18

In a comparison between a delayed neutron and a prompt neutron produced from the same fission
event, the delayed neutron is more likely to… (Assume that each neutron remains in the core unless
otherwise stated.)

Answer 18

be absorbed in a B-10 nucleus.

Question 19

Which one of the following is the process that produces the majority of delayed neutrons in an
operating nuclear power plant reactor?

Answer 19

A thermal neutron is absorbed by a fuel nucleus. The fuel nucleus fissions. During the decay
process of the fission products, a delayed neutron is emitted.

Question 20

During a brief time interval in a typical reactor operating steady-state near the beginning of a fuel
cycle, 4.25 x 10^10 prompt neutrons were produced.
Approximately how many delayed neutrons were produced in the reactor during this same time
interval?

Answer 20

2.8 x 10^8

Question 21

Which one of the following is the process that produces the majority of prompt neutrons in an
operating nuclear power plant reactor?

Answer 21

A thermal neutron is absorbed by a fuel nucleus. Almost immediately, the nucleus fissions and
emits one or more prompt neutrons.

Question 22

Delayed neutrons are fission neutrons that…

Answer 22

are responsible for less than one percent of all fissions.

Question 23

Which one of the following nuclei will cause the greater loss of kinetic energy from a 2.1 MeV fission
neutron during a head-on collision? (Assume that each nucleus is stationary just prior to the collision
and the neutron is elastically scattered in all cases.)

Answer 23

A helium-4 nucleus in the fuel rod fill gas.