detect sqrt in expression?

I need a way to detect the op sqrt in an expression.

So far, neither ?isinop or listofops seems to work:
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Maxima 5.25.1 http://maxima.sourceforge.net
using Lisp GNU Common Lisp (GCL) GCL 2.6.8 (a.k.a. GCL)

(%i1) display2d:false$

(%i2) ?isinop(a*bessel_j(0,x),bessel_j);

(%o2) bessel_j(0,x)

(%i3) ?isinop(a*sqrt(x),sqrt);

(%o3) false

(%i4) ?isinop(sqrt(x^2),sqrt);

(%o4) false

(%i5) load(nint);

(%o5) "c:/work2/nint.mac"

(%i6) listofops(a*sqrt(x^2+y^2)/b);

(%o6) {"*","+","^"}

(%i7) listofops(a*bessel_j(0,x)/c);

(%o7) {"*","^",bessel_j}
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Ted Woollett