Oracle Database Express Edition (XE)

Hi Friends,

I want to use RMAN backup for my 10gXE database so I need to start archivelog.
I do the following:

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
 
Total System Global Area  805306368 bytes
Fixed Size                  1261444 bytes
Variable Size             234881148 bytes
Database Buffers          566231040 bytes
Redo Buffers                2932736 bytes
Database mounted.
SQL> archive log start;
Statement processed.
SQL> archive log list
Database log mode              No Archive Mode
Automatic archival             Disabled
Archive destination            /mnt/EVA-DISK/RMAN/arch_xe
Oldest online log sequence     63
Current log sequence           64

Why is that I can not start the archive log?

Thanks a lot