Heat butter in a large soup pot and cook onion, celery and carrots until tender over low heat, stirring occasionally. Add flour, cook 5 minutes, stirring constantly. Do not brown. Gradually stir in broth until blended. Bring to a boil, cover and cook over low heat 5 minutes. Add bell pepper, rice and chicken and heat another five minutes. Sti rin warm half and half, heat but do not boil. Season to taste and serve.