Is it possible to create Lookup or Master-Detail Relationship from Activity Object (Task/Event)

Is it possible to create Lookup or Master-Detail Relationship from Activity Object (Task/Event)?

No, it is not possible to create Lookup or Master-Detail Relationship from Activity Object (Task/Event).
Event we can’t create Text Area (Rich) field also.

Event Custom Fields Creation

We can create the following fields
Auto Number
Formula
Roll-Up Summary
Checkbox
Currency
Date
Date/Time
Email
Geolocation
Number
Percent
Phone
Picklist
Picklist (Multi-Select)
Text
Text Area
Text (Encrypted)
URL