线程池中的C#并行线程

I介绍了以下将线程分配到多核处理器以执行任务的方法，然而，在Windows任务管理器中，它显示仅使用一个特定的核心。如何使这5个线程平行？

private void ActivateProcess
{
   ...
   ThreadPool.QueueUserWorkItem(new WaitCallback(Worker1));
   ThreadPool.QueueUserWorkItem(new WaitCallback(Worker2)); 
   ThreadPool.QueueUserWorkItem(new WaitCallback(Worker3));
   ThreadPool.QueueUserWorkItem(new WaitCallback(Worker4));
   ThreadPool.QueueUserWorkItem(new WaitCallback(Worker5));
}
...
private void Worker1(Object stateInfo)
{
    try
    {
        //for (int i = 0; i < _NumberOfLoop; i++)
        Parallel.For(0,(long)_NumberOfLoop, i =>
        {
            if (_ForceToStop)
                throw new System.ArgumentException(
                    "Force stop at WorkerThread 1", "Aborted");
            // Process: Process a tasks
            ...
        });
    }
    catch (Exception ex)
    {
        ...
    }
}