To submit a GIS application please visit the BNL Guest, User & Visitor (GUV) Center at https://www.bnl.gov/guv/gis.php and submit your registration (or renew/extend a previous guest appointment). The additional information below may help fill the form.
Host name: Gustavo Nobre
BNL Department: Nuclear Science and Technology (NE)
Research Facility: None
Type of research: Open research / Nuclear Data / Nuclear Physics (whichever of these options that is available)
Experimental area: None
As for justification you can write something along the lines:
I would like to attend the Nuclear Data Week (CSEWG-USNDP-NDAG) organized by BNL's National Nuclear Data Center.