Place shrimp in a bowl (You may either coarsely chop the shrimp, or leave them whole, depending on your preference.) Add lemon, covering shrimp completely. Cover, and refrigerate for 30 minutes, or until opaque and slightly firm.
Add tomatoes, onions, cucumber, radishes, and garlic; toss to combine. Gradually add cilantro and jalapenos to desired taste (jalapeno will grow stronger while marinating). Stir in tomato and clam juices to desired consistency. Cover, and refrigerate for 1 hour. Serve chilled with tortilla chips.