set diskName to "BOOTCAMP"

tell current application
    set deviceLine to (do shell script "diskutil list | grep \"" & diskName & "\" | awk '{ print substr($0,69,9) }'")
    if deviceLine = "" then
        display dialog "The disk \"" & diskName & "\" cannot be found." buttons {"OK"} default button 1 with title "Error" with icon caution
    end if
    set foundDisks to paragraphs of deviceLine
end tell

tell application "Finder"
    if disk diskName exists then
        tell current application
            repeat with i from 1 to number of items in foundDisks
                set this_item to item i of foundDisks
                if this_item contains "disk" then
                    do shell script "diskutil unmount /dev/" & this_item
                end if
            end repeat
        end tell
    end if
end tell