delayed neutron
C2Technical/Scientific
Definition
Meaning
A neutron emitted by a fission product nucleus some time after nuclear fission occurs, as opposed to a prompt neutron emitted immediately.
In nuclear physics and engineering, a neutron released from a radioactive fission product after a measurable delay (typically milliseconds to minutes), crucial for the control and time-dependent behavior of nuclear reactors.
Linguistics
Semantic Notes
This is a highly specialized compound noun used almost exclusively in nuclear physics, reactor engineering, and related technical fields. It refers to a specific physical phenomenon, not a general concept of delay.
Dialectal Variation
British vs American Usage
Differences
No significant lexical or grammatical differences. The term is identical in both varieties due to its technical, international scientific nature.
Connotations
Purely technical and neutral in both varieties.
Frequency
Extremely low frequency in general language, but standard and identical in frequency within the specialized nuclear field in both the UK and US.
Vocabulary
Collocations
Grammar
Valency Patterns
The [fission product] emits a delayed neutron.The reactor's behavior depends on the [property] of delayed neutrons.Scientists measured the [parameter] for delayed neutrons.Vocabulary
Synonyms
Neutral
Vocabulary
Antonyms
Usage
Context Usage
Business
Not used.
Academic
Used in advanced physics and nuclear engineering papers, theses, and textbooks.
Everyday
Virtually never used.
Technical
Core term in nuclear reactor physics, safety analysis, and reactor kinetics modelling.
Examples
By Part of Speech
adjective
British English
- The delayed-neutron fraction is a key reactor parameter.
American English
- The delayed-neutron data was critical for the simulation.
Examples
By CEFR Level
- Delayed neutrons are important for controlling nuclear reactors.
- The reactor's stability is heavily influenced by the delayed neutron fraction, which determines the response time to control rod movements.
- Precise measurements of delayed neutron yields from various fissionable isotopes are essential for advanced reactor design.
Learning
Memory Aids
Mnemonic
Think of a firework with a second, smaller explosion after the main bang. The main bang is the prompt neutron; the later, smaller pop is the 'delayed' neutron.
Conceptual Metaphor
N/A (Highly technical term with little metaphorical extension.)
Watch out
Common Pitfalls
Translation Traps (for Russian speakers)
- Avoid translating 'delayed' as 'замедленный', which means 'slowed down' (like a slow neutron). The correct translation is 'запаздывающий нейтрон', emphasizing a time delay in emission.
Common Mistakes
- Confusing it with 'thermal neutron' or 'slow neutron', which refer to neutron speed, not time of emission.
- Using it as a general adjective-noun phrase (e.g., 'the neutron was delayed') instead of the fixed technical compound noun.
- Misspelling as 'delayed nutron'.
Practice
Quiz
What is the primary role of delayed neutrons in a nuclear reactor?
FAQ
Frequently Asked Questions
No, 'delayed' refers to the time of its emission after fission, not its speed. Both delayed and prompt neutrons can have a range of speeds (energies).
They are emitted by unstable fission product nuclei (precursors) as they undergo radioactive decay, which happens some time after the initial fission event.
They increase the average generation time between neutron cycles, making the chain reaction slow enough to be controlled by mechanical systems like control rods.
No. The vast majority of neutrons in a sustained chain reaction are prompt neutrons. Delayed neutrons constitute only a small fraction (less than 1% for uranium-235) but are vital for controllability.