Unity: AddExplosionForce only works sometimes

So I have a sphere for the player, and whenever the player is damaged by an object it should knock the ball into the opposite direction, so I am using AddExplosionForce to do the effect, but sometimes it knocks the player back and sometimes it doesn't do anything. Is there something I can do to fix my code (below) or an alternative to doing this effect? Thank you!

    private void OnTriggerEnter(Collider other){
    if(other.tag == "Pickup")
    {
        if(other.GetComponent<pickupScript>().ReturnSize() >= score)
        {
            score--;
            //explodeforce in oposite direction
            GetComponent<Rigidbody>().AddExplosionForce(500.0f, other.transform.position, .501f, .5f, ForceMode.Impulse);
            //add effects
        }
     }