The most common and most likely answer to this crossword clue is the 7 letter word NEUTRON
I've seen this crossword clue in The Times
N
E
U
T
R
O
N
More clues leading to the result NEUTRON
- Rupture regularly found in noble gas particle
- Convict at last in cell, one not charged
- Tiny particle could make one turn queasy
- Convict finally put in cell that’s very small
- Particle new to Planck, and not recalled after brief time
- A bit of a nerve, pinching Juliet’s rear? One’s not charged
- Particle produces trigger initially in nerve cell
- Uncharged particle centrally sited within nerve cell
- Unreactive material producing temperature in brain cell
- News about diversion of route — no charge for it
Buddy explains!

The straight part
We know that "Tiny particle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tiny particle = neutron.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does NEUTRON mean?
NEUTRON noun- A subatomic particle forming part of the nucleus of an atom and having no charge; it is a combination of an up quark and two down quarks.