be substantial [@andy] but appears to be hard to distinguish phenomenologically from . The gradient operators within $T_{\rm P}$ make calculations harder, and the present inversion method does not apply to it.

### The  operator

In this work we assume that the inter-nucleus potential $V$ contains a tensor force component of  form [@satchlerbook]: $${\mbox{$T_{\rm R}$}}V_R(r) \equiv ({\bf (s\cdot \hat{r})^2} -2/3) V_R(r).
\label{eq:tensor}$$

We quote the matrix elements of the interaction  for future reference. The diagonal matrix elements of  are:

                                                $l=J-1$                   $l=J$                    $l=J+1$
  -------------------------------- --------------------------------- ---------------- ---------------------------------
   $<Jl|{\mbox{$T_{\rm R}$}}|Jl>$   $-\frac{1}{3} \frac{J-1}{2J+1}$   $ \frac{1}{3}$   $ -\frac{1}{3}\frac{J+2}{2J+1}$

and the non-diagonal matrix elements are: $$<J\, J-1|{\mbox{$T_{\rm R}$}}|J\, J+1> = <J\, J+1|{\mbox{$T_{\rm R}$}}|J\, J-1> = 
\frac{[J(J+1)]^{1/2}}{2J+1} \label{eq:diagTR}.$$

### The radial form of the  interaction

The derivation of $ V_R(r)$ from the folding model has been discussed at length long ago by Keaton and his colleagues [@kaprc8; @kav; @keaton] and also by Raynal [@raynalpl]. Within the folding model, the deuteron  interaction arises directly from the D-state component. The overall general success of folding models for central and spin-orbit interactions suggests that folding model calculations of $ V_R(r)$ should give at least approximately the correct radial form and overall magnitude, but this has not been borne out 