To play, download this ATR file: https://github.com/jeffpiep/reactorX/raw/master/reactorX.atr
Load the REACTORX.ATR file with the Altirra Emulator. It will boot to the DOS menu. 
If it boots to BASIC, enter "DOS" to get the menu.
* Select "L"
Enter "REACTORX.COM"

Press FIRE to start.

Use your joystick to move the white "+"-shaped ship. Bump the particles into the
outer wall. Don't hit the outer wall with your ship or will lose a life. Push all 
three particles into the wall to win.

Press RESET to return to the DOS menu (or built-in BASIC).
Go back to * to play again.

To see the BASIC program code, from the DOS menu ...
Select "C"
enter: REACTORX.BAS, S:

To see the BASIC program code in FastBasic, download this ATR file: 
https://github.com/jeffpiep/reactorX/raw/master/dev/reactorX.atr

Enter "FBI" to load integrer-only FastBasic.
Press CTRL-L to load and enter "REACTORX.BAS"
You will now see the BASIC code.
Press CTRL-R to run or CTRL-Q to quit.
You can play by entering "REACTORX.COM" at the DOS prompt.