"on walking" does not work

[BALTICA]

I had been doing this script for a while and "on walking" didn't work.

I would like to know if there is any alternative to achieve the same task
and sorry for my bad english, i speak spanish

on walking:
    set {_distance} to distance between player and location 0, 0, 0
    set {_radiation} to 400 - {_distance}
    if {_radiation} < 0:
        stop
    else if {_radiation} < 150:
        stop
    else if {_radiation} < 300:
        set {_chance} to a random integer between 1 and 100
        if {_chance} is between 1 and 20:
            apply potion of nausea of tier 1 without particles to player for 10 seconds
    else if {_radiation} > 301:
        set {_chance} to a random integer between 1 and 100
        if {_chance} is between 1 and 20:
            apply potion of nausea of tier 1 without particles to player for 10 seconds
        if {_chance} is between 1 and 9:
            apply potion of wither of tier 1 without particles to player for 15 seconds
        if {_chance} is between 1 and 12:
            apply potion of blindness of tier 1 without particles to player for 15 seconds

 

[Minecoll_YT]

This script is not recommended because it uses many resources, but I can't think of another solution rn, maybe loop all players and check if there are in a specific area

on any movement:
  set {_distance} to distance between player and location(0, 0, 0, world "WORLDNAME")
  set {_radiation} to 400 - {_distance}
  if {_radiation} is more than 300:
    set {_chance} to a random integer between 1 and 100
    if {_chance} is between 1 and 20:
      apply potion of nausea of tier 1 without particles to player for 10 seconds
  else if {_radiation} is less than 300:
    set {_chance} to a random integer between 1 and 100
    if {_chance} is between 1 and 20:
      apply potion of nausea of tier 1 without particles to player for 10 seconds
    if {_chance} is between 1 and 9:
      apply potion of wither of tier 1 without particles to player for 15 seconds
    if {_chance} is between 1 and 12:
      apply potion of blindness of tier 1 without particles to player for 15 seconds