I am playing with Ngram viewer and I plugged in several subatomic particles and saw this graph (see attached). The term "proton" was used starting the 1920 and neutron was discovered in 1932, which is consistent with the starting points in the graph. But neutron has a peak around the 1960s. Did anything significant happened that year about neutron?
Google Ngrams are based on searching mentions in book hits from the corresponding time period. By looking at the titles and contexts where the word is mentioned one can usually figure out what the dominant reason for its occurence is. Here is the Ngram for neutron and here are the book hits for the 6 year range around the spikes in 1957 and 1961. Radiochemistry, chemistry of radioactive materials, and other nuclear reactor related contexts seem to dominate:
"fissionable nuclides and for fast neutron fission", "Reactors for University Research", "Radiochemistry of Iron", "A Glossary of Terms in Nuclear Science and Technology", "Radiochemistry of the Transcurium Elements", "Radiochemistry of Silicon", "Radiochemistry of Osmium", "condensate from the dissolution of neutron-activated uranium metal", etc.
So it seems the spikes are due to the rise of nuclear power in late 1950-s, which created the need for technological literature on how different materials behave in radioactive conditions, measurement standards, etc. All of that mentioned fission chain reactions and their neutron multiplication factors, among other things.
In 1955 the "First Geneva Conference" of the UN met to discuss nuclear power, in 1957 EURATOM and the International Atomic Energy Agency (IAEA) were launched. Calder Hall, the first commercial nuclear power plant, opened in UK in 1956, the Shippingport in Pennsylvania, the first commercial one in the US, opened in 1957. The U.S. Army had a nuclear power program since 1954, its nuclear power plant at Fort Belvoir, Virginia, opened in 1957 even before Shippingport. Army's experimental nuclear reactor at the National Reactor Testing Station in Idaho had a steam explosion and meltdown, which killed its three operators, in January 1961, see History of Nuclear Power.