HESSI SHUTTER PARAMETERS

The purpose of this document is to summarize the as-built parameters of
the HESSI shutters.

There are 'thin' and 'thick' shutters associated with each
subcollimator. Each shutter was fabricated from an aluminum disk, which
was machined by Tecomet to form 3 concentric circular subareas of
different thicknesses. The shutter parameters are slightly different for
each subcollimator due both to fabrication tolerances and due to
different design parameters. (The differences were required in order to
minimize any spatial coherence between the shutter geometry and the
grids.) Nevertheless the overall goal was to have roughly similar
transmissions for all subcollimators.

The primary objective of the shutter calibration was to determine the
surface density of each subarea of each shutter. The calibration was
based on 5 types of data.

1.  The OGCF was used to confirm that the diameters of the subareas on
    each shutter matched their nominal values.

2.  The XGCF was used to measure the transmission of the shutters for
    Fe55 and Cd109 sources (6 and 23 keV respectively). In each case the
    sources were collimated to a beam of about 10 mm diameter which was
    directed at the center of the shutter. Cd109 data was also taken
    with the beam restricted to the outer area.

3.  The thicknesses of the outer and middle areas were measured
    mechanically.

4.  Radiographs were taken of the inner area to confirm that thickness
    variations were sufficiently small that they could be neglected.

5.  Each shutter was accurately weighed so that the average surface
    density could be determined directly.

Analysis of the calibration data yielded the individual shutter
parameters (diameters and surface densities) shown in the table below.
Also tabulated is the diameter of the graded-Z guard ring which defines
the effective diameter of the front segment of each detector.

For each individual shutter, the diameters were converted to the
fraction of available area corresponding to each subarea (3 per
shutter). When both shutters are IN, there are effectively 5 subareas,
whose fractional area and combined surface density was also calculated.
The fractional area and surface density for each subarea, attenuator
setting and subcollimator are tabulated in the boxed area in the
'Attenuator Parameter Table'. The boxed area was copied to a text file (
APT_yyyymmdd.txt where yyyymmdd is the version date) and is included in
\\ssw\\hessi\\dbase\\spec_resp.

During data analysis, the latest version of the attenuator parameter
table is used by the function, hsi_shutter_transmission, to calculate
the attenuator transmission as a function of energy, subcollimator and
attenuator state. This calculation uses log-log interpolation of the
NIST tables for aluminum which are read by the function, read_mat_xcom.

Plots of shutter transmission as a function of energy are shown in
Figures 1 and 2 for a typical subcollimator. (These plots are normalized
so that both attenuators OUT would give 1 and so do not include the
effect of blankets, etc. The dotted, dashed and dot-dashed lines
correspond to THIN, THICK and THIN+THICK cases respectively.)

Corresponding plots of the effective radius (relative to the graded-Z
ring) of the transmitting area is shown in Figure 3, which illustrates
that at low energies, all the transmission is through the innermost
area.

There are two approaches by which in-flight data can be used to confirm
the shutter transmission. First, the continuity of semi-calibrated light
curves when a shutter inserted or removed can be checked as a function
of energy. Second, ratios of semi-calibrated spectra among detectors can
be compared with and without attenuators, again as a function of energy.
If significant anomalies are found, the in-flight data can be combined
with prelaunch calibration data to improve the attenuator parameter
table so that the updated calibration can be applied retroactively to
the existing flare database.

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  **HESSI                                                                                                                                                           
  ATTENUATOR                                                                                                                                                        
  PARAMETER                                                                                                                                                         
  TABLE**                                                                                                                                                           

                                                                                                                                                                    

                                                              **1**         **2**      **3**      **4**      **5**      **6**      **7**      **8**      **9**      

  Graded-Z ring   mm                                          58.5          58.5       57.5       58.5       58.5       58.5       57.5       58.5       58.5       
  diameter                                                                                                                                                          

                                                                                                                                                                    

  Shutter ID                                                  A1-1          A2         A3         A4         A5-1       A6         A7-1       A8         A9-1       

  Inner diameter  mm                                          1.716         1.716      1.716      1.716      1.940      1.716      2.050      1.940      3.360      

  Middle diameter mm                                          24.300        24.300     24.300     24.300     24.300     24.300     24.300     24.300     24.300     

  Inner surface   g/cm2                                       0.0133        0.0135     0.0134     0.0127     0.0153     0.0133     0.0162     0.0156     0.0262     
  density                                                                                                                                                           

  Middle surface  g/cm2                                       0.177         0.179      0.178      0.178      0.154      0.179      0.153      0.151      0.166      
  density                                                                                                                                                           

  Outer surface   g/cm2                                       0.414         0.412      0.415      0.415      0.389      0.414      0.391      0.391      0.397      
  density                                                                                                                                                           

                                                                                                                                                                    

  Shutter ID                                                  B1-1          B2         B3         B1-3       B5         B6         B7         B8         B9-1       

  Inner diameter  mm                                          6.743         6.743      6.743      6.743      6.743      6.743      6.743      6.743      6.15       

  Middle diameter mm                                          17.1          17.1       17.1       17.1       17.1       17.1       17.1       17.1       17.1       

  Inner surface   g/cm2                                       0.0192        0.0191     0.0189     0.0188     0.0188     0.0187     0.0187     0.0185     0.0208     
  density                                                                                                                                                           

  Middle surface  g/cm2                                       0.261         0.260      0.257      0.262      0.262      0.257      0.262      0.256      0.260      
  density                                                                                                                                                           

  Outer surface   g/cm2                                       0.112         0.112      0.110      0.114      0.114      0.107      0.115      0.109      0.114      
  density                                                                                                                                                           

                                                                                                                                                                    

  **Conversion to                                                                                                                                                   
  ssw Attenuator                                                                                                                                                    
  parameter table                                                                                                                                                   
  format**                                                                                                                                                          

  LABEL                                                       APT1-1                                                                                                

  VERSION-DATE                                                6-Jun-01                                                                                              

  DESCRIPTION                                                 GH: Preflight                                                                                         
                                                              CBE of                                                                                                
                                                              shutter                                                                                               
                                                              parameters,                                                                                           
                                                              from XGCF                                                                                             
                                                              data, nominal                                                                                         
                                                              diameters,                                                                                            
                                                              25-apr-01                                                                                             
                                                              calib                                                                                                 
                                                              analysis,                                                                                             
                                                              updated ring                                                                                          
                                                              diam                                                                                                  

  fraction1       detector-middleB               THIN         0.9146        0.9146     0.9116     0.9146     0.9146     0.9146     0.9116     0.9146     0.9146     

  fraction2       middleB-innerB                 THIN         0.0722        0.0722     0.0747     0.0722     0.0722     0.0722     0.0747     0.0722     0.0744     

  fraction3       innerB                         THIN         0.01329       0.01329    0.01375    0.01329    0.01329    0.01329    0.01375    0.01329    0.01105    

  fraction4       0                              THIN         0             0          0          0          0          0          0          0          0          

  fraction5       0                              THIN         0             0          0          0          0          0          0          0          0          

  Surf.Density1   outerB                         THIN         0.1120        0.1119     0.1105     0.1140     0.1138     0.1068     0.1153     0.1088     0.1142     

  Surf.Density2   middleB                        THIN         0.2611        0.2596     0.2571     0.2621     0.2617     0.2567     0.2618     0.2564     0.2605     

  Surf.Density3   innerB                         THIN         0.0192        0.0191     0.0189     0.0188     0.0188     0.0187     0.0187     0.0185     0.0208     

  Surf.Density4   0                              THIN         0             0          0          0          0          0          0          0          0          

  Surf.Density5   0                              THIN         0             0          0          0          0          0          0          0          0          

  fraction1       detector-middleA               THICK        0.8275        0.8275     0.8214     0.8275     0.8275     0.8275     0.8214     0.8275     0.8275     

  fraction2       middleA-innerA                 THICK        0.1717        0.1717     0.1777     0.1717     0.1714     0.1717     0.1773     0.1714     0.1692     

  fraction3       innerA                         THICK        0.000860      0.000860   0.000891   0.000860   0.001100   0.000860   0.001271   0.001100   0.003299   

  fraction4       0                              THICK        0             0          0          0          0          0          0          0          0          

  fraction5       0                              THICK        0             0          0          0          0          0          0          0          0          

  Surf.Density1   outerA                         THICK        0.4143        0.4125     0.4150     0.4150     0.3894     0.4137     0.3907     0.3908     0.3972     

  Surf.Density2   middle A                       THICK        0.1770        0.1792     0.1775     0.1778     0.1542     0.1794     0.1534     0.1513     0.1656     

  Surf.Density3   innerA                         THICK        0.0133        0.0135     0.0134     0.0127     0.0153     0.0133     0.0162     0.0156     0.0262     

  Surf.Density4   0                              THICK        0             0          0          0          0          0          0          0          0          

  Surf.Density5   0                              THICK        0             0          0          0          0          0          0          0          0          

  fraction1       detector-middleA               THICK+THIN   0.8275        0.8275     0.8214     0.8275     0.8275     0.8275     0.8214     0.8275     0.8275     

  fraction2       middleA-middleB                THICK+THIN   0.0871        0.0871     0.0902     0.0871     0.0871     0.0871     0.0902     0.0871     0.0871     

  fraction3       middleB-innerB                 THICK+THIN   0.0722        0.0722     0.0747     0.0722     0.0722     0.0722     0.0747     0.0722     0.0744     

  fraction4       innerB-innerA                  THICK+THIN   0.01243       0.01243    0.01286    0.01243    0.01219    0.01243    0.01248    0.01219    0.00775    

  fraction5       innerA                         THICK+THIN   0.000860      0.000860   0.000891   0.000860   0.001100   0.000860   0.001271   0.001100   0.003299   

  Surf.Density1   outerA+outerB                  THICK+THIN   0.5263        0.5244     0.5254     0.5289     0.5032     0.5206     0.5060     0.4995     0.5114     

  Surf.Density2   middleA+outerB                 THICK+THIN   0.2890        0.2911     0.2880     0.2918     0.2680     0.2862     0.2687     0.2600     0.2798     

  Surf.Density3   middleA+middleB                THICK+THIN   0.4381        0.4388     0.4346     0.4400     0.4159     0.4361     0.4151     0.4076     0.4261     

  Surf.Density4   MiddleA+innerB                 THICK+THIN   0.1963        0.1983     0.1964     0.1966     0.1730     0.1981     0.1721     0.1698     0.1863     

  Surf.Density5   innerA+innerB                  THICK+THIN   0.0326        0.0326     0.0323     0.0315     0.0340     0.0320     0.0350     0.0341     0.0470     

                                                                                                                                                                    

  Comments:       6-Jun-01                                    Graded-Z ring                                                                                         
                                                              diameters                                                                                             
                                                              corrected per                                                                                         
                                                              DS memo.                                                                                              

                  APT1-1 is the current best                                                                                                                        
                  estimate preflight version of                                                                                                                     
                  the attenuator parameter                                                                                                                          
                  table.                                                                                                                                            

                  **Boxed area should be pasted                                                                                                                     
                  into a text file named                                                                                                                            
                  \'label.txt\' which is read by                                                                                                                    
                  hsi_rd_shutter_parameters.**                                                                                                                      
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