you are still linking to the URL that contains /_?
... yes but whenever user tries to go to link onclick event ,in new tab he see the _/ in it
Regardless of whether we implement a redirect in .htaccess to "fix" this, you do still need to physically remove the /_ part from the URLs in the HTML source that the users click on. Otherwise, they are not "hidden"...
If you want to use htaccess, you can use the http header X-Robots-Tag: noindex to accomplish what you need for the specific files you need, or with a pattern.
You can also provide other instructions, such as noarchive, nofollow, or even be specific for a particular crawler, for example Googlebot:
X-Robots-Tag: googlebot: nofollow
X-Robots-Tag: otherbot: ...