particle collision with objects not working.

I have been trying to get particle collision with objects working for ages now. Here is how I have the object im shooting at setup

my particle effect which I want to act as bullets bouncing off the object is as follows:

Here is how I am moving the object my 'second enemy' script shown in the screenshot.

 #pragma strict
 var positionY : float; 
 var positionX : float;
 var endTime : float;
 var speed : float;
 
 function Start () {
 positionY = Random.Range(5, 8);
 // minimum of -2.618306 and maximum x position of 1.24835
 positionX = Random.Range(-2.618306, 1.24835);
 speed = Random.Range(1, 2);
 transform.position.x = positionX;
 }
 
 function Update () {
 speed += 0.001;
 positionY -= 0.01*speed;
 if(positionY < -3.38){
 positionY = Random.Range(5, 8);
 // minimum of -2.618306 and maximum x position of 1.24835
 positionX = Random.Range(-2.618306, 1.24835);
 speed = Random.Range(1, 2);
 transform.position.x = positionX;
 randomPositionX();
 }
 
 transform.position.y = positionY;
 
 
 
 }
 
 function randomPositionX () {
 positionX = Random.Range(-2.618306, 1.24835);
 transform.position.x = positionX;
 }

Please help me figure out how to get the particles to collide with all objects in the game. At the moment they are just going straight through objects :(. everything.