How Can I check "is player below a radius from the block"?

So best results i got with this code. But you should propably change the tickrate to bigger.
 

static{

block = (BlockTestBlockish)(new BlockTestBlockish().setHardness(2.0F)
.setResistance(10.0F)
.setUnlocalizedName("TestBlockish")
.setLightOpacity(0)
.setStepSound(Block.soundTypeStone)
.setCreativeTab(CreativeTabs.tabBlock)
);block.setBlockBounds(0.0F,0.0F,0.0F,1.0F,1.0F,1.0F);
block.setHarvestLevel("pickaxe", 0);
}

public void generateSurface(World world, Random random, int chunkX, int chunkZ){}
public void generateNether(World world, Random random, int chunkX, int chunkZ){}
static class BlockTestBlockish extends Block
{

int a1 = 0,a2 = 0,a3 = 0,a4 = 0,a5 = 0,a6 = 0;

boolean red = false;

private World worldion = null;
private BlockPos position = null;

protected BlockTestBlockish()
{
        super(Material.ground);

GameRegistry.registerBlock(this, "TestBlockish");

}

public void onBlockAdded(World world, BlockPos pos, IBlockState state){
int i = pos.getX();int j = pos.getY();int k = pos.getZ();world.scheduleUpdate(new BlockPos(i, j, k), this, this.tickRate(world));

}

@Override
public int tickRate(World world)
{
    return 40;
}

public void updateTick(World world, BlockPos pos, IBlockState state, Random random){
 this.worldion = world;
 this.position = pos;
 if(!world.isRemote){
getLightValue();}
world.scheduleUpdate(pos, this, this.tickRate(world));
}

@Override
public int getLightValue() {
    int value = 0;
World world = this.worldion;
BlockPos pos = this.position;
if(world != null) {

if(!world.isDaytime()){
AxisAlignedBB box = new AxisAlignedBB(pos.getX() - 3, pos.getY() -3, pos.getZ() -3, pos.getX() + 3, pos.getY() + 3, pos.getZ() + 3);
     
     
        List list = world.getEntitiesWithinAABB(EntityPlayer.class,box);
         if(!list.isEmpty()){
             
             value = 15;
         }
         else{
            value = 8;
         }
}

if(world.isDaytime()){
value = 0;
}

}

else{
value = 8;
}

        return value;
}
}

Do you have defined the varible worldion of type World?

Hey, I'm trying to create a creature that explodes, if there are 3 blocks from the player, can you help me?