kill the Session of User while Loggedin n out in ASP.NET

Question

I have a asp.net web application login page which has buil-in Authentication of asp.net and login.aspx page created by Login control of asp.net. Now i have a problem in login and logout.

When user pressed "Login" the link is redirected to "userProfile.aspx" page. But, when the user press "Back" button from the browser the user goes to "SignUp" the page .

         When user pressed "Logout" the link is redirected to "LoginPage.aspx" page. But, when the user press "Back" button from the browser the user goes to "userProfile"to the page to the application which i want to avoid and it must ask to enter Login Credentials.