| 1 | SUBROUTINE PAIR
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| 2 | C VERSION 4.00 -- 26 JAN 1986/1900
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| 3 | C******************************************************************
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| 4 | C FOR A PHOTON ENERGY LESS THAN 2.1 MEV, THE APPROXIMATION IS
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| 5 | C MADE THAT ONE PAIR ELECTRON (OR POSITRON) HAS ONLY ITS REST
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| 6 | C MASS ENERGY. FOR PHOTON ENERGY BETWEEN 2.1 MEV AND 50 MEV THE
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| 7 | C BETHE-HEITLER CROSS SECTION IS EMPLOYED. ABOVE 50 MEV THE
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| 8 | C COULOMB CORRECTED BETHE-HEITLER CROSS SECTION IS USED.
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| 9 | C (BUTCHER AND MESSEL, OP. CIT., P. 17-19, 22).
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| 10 | C******************************************************************
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| 11 | DOUBLE PRECISION PEIG,PESE1,PESE2
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| 12 | COMMON/BREMPR/DL1(6),DL2(6),DL3(6),DL4(6),DL5(6),DL6(6),DELCM, ALP
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| 13 | *HI(2),BPAR(2),DELPOS(2),PWR2I(50)
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| 14 | *KEEP,RANDPA.
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| 15 | COMMON /RANDPA/ FAC,U1,U2,RD,NSEQ,ISEED,KNOR
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| 16 | DOUBLE PRECISION FAC,U1,U2
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| 17 | REAL RD(3000)
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| 18 | INTEGER ISEED(103,10),NSEQ
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| 19 | LOGICAL KNOR
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| 20 | *KEEP,RUNPAR.
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| 21 | COMMON /RUNPAR/ FIXHEI,THICK0,HILOECM,HILOELB,
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| 22 | * STEPFC,NRRUN,NSHOW,PATAPE,MONIIN,
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| 23 | * MONIOU,MDEBUG,NUCNUC,
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| 24 | * CETAPE,
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| 25 | * SHOWNO,ISHW,NOPART,NRECS,NBLKS,MAXPRT,NDEBDL,
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| 26 | * N1STTR,MDBASE,
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| 27 | * DEBDEL,DEBUG,FDECAY,FEGS,FIRSTI,FIXINC,FIXTAR,
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| 28 | * FIX1I,FMUADD,FNKG,FPRINT,FDBASE
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| 29 | * ,GHEISH,GHESIG
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| 30 | COMMON /RUNPAC/ DSN,HOST,USER
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| 31 | DOUBLE PRECISION FIXHEI,THICK0,HILOECM,HILOELB
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| 32 | REAL STEPFC
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| 33 | INTEGER NRRUN,NSHOW,PATAPE,MONIIN,MONIOU,MDEBUG,NUCNUC,
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| 34 | * SHOWNO,ISHW,NOPART,NRECS,NBLKS,MAXPRT,NDEBDL,
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| 35 | * N1STTR,MDBASE
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| 36 | INTEGER CETAPE
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| 37 | CHARACTER*79 DSN
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| 38 | CHARACTER*20 HOST,USER
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| 39 |
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| 40 | LOGICAL DEBDEL,DEBUG,FDECAY,FEGS,FIRSTI,FIXINC,FIXTAR,
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| 41 | * FIX1I,FMUADD,FNKG,FPRINT,FDBASE
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| 42 | * ,GHEISH,GHESIG
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| 43 | *KEEP,STACKE.
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| 44 | COMMON/STACKE/ E,TIME,X,Y,Z,U,V,W,DNEAR,IQ,IGEN,IR,IOBS,LPCTE,NP
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| 45 | DOUBLE PRECISION E(60),TIME(60)
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| 46 | REAL X(60),Y(60),Z(60),U(60),V(60),W(60),DNEAR(60)
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| 47 | INTEGER IQ(60),IGEN(60),IR(60),IOBS(60),LPCTE(60),NP
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| 48 | *KEND.
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| 49 | COMMON/THRESH/RMT2,RMSQ,ESCD2,AP,API,AE,UP,UE,TE,THMOLL
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| 50 | COMMON/UPHIOT/THETA,SINTHE,COSTHE,SINPHI, COSPHI,PI,TWOPI,PI5D2
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| 51 | DOUBLE PRECISION PZERO,PRM,PRMT2,RMI,VC
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| 52 | COMMON/USEFUL/PZERO,PRM,PRMT2,RMI,VC,RM,MEDIUM,MEDOLD,IBLOBE,ICALL
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| 53 | COMMON/ACLOCK/NCLOCK,JCLOCK
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| 54 | C_____IF (NCLOCK.GT.JCLOCK) THEN
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| 55 | C______WRITE(MDEBUG,* )' PAIR: NP=',NP,' IR=',IR(NP),' IOBS=',IOBS(NP)
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| 56 | C______CALL AUSGB2
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| 57 | C_____END IF
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| 58 | PEIG=E(NP)
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| 59 | EIG=PEIG
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| 60 | IF (EIG.LE.2.1) THEN
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| 61 | ESE2=PRM
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| 62 | ELSE
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| 63 | IF (EIG.LT.50.) THEN
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| 64 | LVX=1
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| 65 | LVL0=0
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| 66 | ELSE
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| 67 | LVX=2
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| 68 | LVL0=3
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| 69 | END IF
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| 70 | 961 CONTINUE
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| 71 | CALL RMMAR(RD,2,2)
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| 72 | RNNO30=RD(1)
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| 73 | RNNO31=RD(2)
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| 74 | IF (RNNO31.GE.BPAR(LVX)) THEN
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| 75 | LVL=LVL0+1
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| 76 | CALL RMMAR(RD,2,2)
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| 77 | RNNO32=RD(1)
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| 78 | RNNO33=RD(2)
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| 79 | BR=0.5*(1.0-MAX(RNNO32,RNNO33,RNNO30))
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| 80 | ELSE
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| 81 | LVL=LVL0+3
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| 82 | BR=RNNO30*0.5
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| 83 | END IF
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| 84 | IF((BR.EQ.0.0))GO TO961
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| 85 | DEL=1.0/(EIG*BR*(1.0-BR))
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| 86 | IF((DEL.GE.DELPOS(LVX)))GO TO961
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| 87 | DELTA=DELCM*DEL
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| 88 | IF (DELTA.LT.1.0) THEN
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| 89 | REJF=DL1(LVL)+DELTA*(DL2(LVL)+DELTA*DL3(LVL))
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| 90 | ELSE
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| 91 | REJF=DL4(LVL)+DL5(LVL)*LOG(DELTA+DL6(LVL))
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| 92 | END IF
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| 93 | CALL RMMAR(RNSCRN,1,2)
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| 94 | IF((RNSCRN.LE.REJF))GO TO962
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| 95 | GO TO 961
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| 96 | 962 CONTINUE
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| 97 | ESE2=BR*EIG
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| 98 | END IF
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| 99 | PESE2=ESE2
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| 100 | PESE1=PEIG-PESE2
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| 101 | E(NP)=PESE1
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| 102 | E(NP+1)=PESE2
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| 103 | THETA=RM/EIG
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| 104 | CALL UPHI(1,1)
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| 105 | NP=NP+1
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| 106 | SINTHE=-SINTHE
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| 107 | CALL UPHI(3,2)
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| 108 | CALL RMMAR(RNNO34,1,2)
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| 109 | IF (RNNO34.LE.0.5) THEN
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| 110 | IQ(NP)=2
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| 111 | IQ(NP-1)=3
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| 112 | ELSE
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| 113 | IQ(NP)=3
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| 114 | IQ(NP-1)=2
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| 115 | END IF
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| 116 | RETURN
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| 117 | END
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