var articleStoreLanguageModels = session
.CreateFullTextQuery(luceneQuery, typeof(StoreArticleLanguage))
.SetProjection(ProjectionConstants.THIS, ProjectionConstants.SCORE)
.SetSort(Lucene.Net.Search.Sort.RELEVANCE);

foreach (object[] row in articleStoreLanguageModels.List())
{
     StoreArticleLanguage storeArticleLanguage = (StoreArticleLanguage)row[0];
     float score = (float)row[1]; //NaN
}