Apex domains cannot have CNAME records.
Question and response
Question
dig atomic.ac. NS
Answer
atomic.ac. 5 NS ns3.atomic.ac.
atomic.ac. 5 NS ns1.atomic.ac.
atomic.ac. 5 NS ns2.atomic.ac.
Authority
The response has no authority records.
Additional
ns1.atomic.ac. 5 A 102.135.240.4
ns2.atomic.ac. 5 A 102.135.244.4
ns3.atomic.ac. 5 A 172.236.20.38
ns1.atomic.ac. 5 AAAA 2c0f:ef18:0:0:0:0:0:4
ns2.atomic.ac. 5 AAAA 2c0f:ef18:1:0:0:0:0:4
ns3.atomic.ac. 5 AAAA 2600:3c13:e001:34:0:0:0:cafe
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0