Neutron source
Alpha rays source for radiotherapy
When they are necessary
Has is used when you're referring to "it", "she" or "he". Have is used when you're referring to "I", "You", "They" and "We"
yes it does
I/you/we/they suppose. He/she/it supposes. The present participle is supposing.
Past tense - calculated. Present tense - I/you/we/they calculate. He/she/it calculates. Future tense - will calculate.