Your questions are listed below, followed by answers.

1. What will be the skin dose in case of pure gamma field? Can we multiply the whole body dose (Hp10) by weighting factor (0.01) and add to the whole body dose?

No to both.

The energy of the gamma radiation determines both the whole body dose and the skin dose. The skin dose is not always 0.01 of the whole body dose.

When using Hp10 for the whole body dose for the appropriate gamma energy, there is no need to make a skin dose determination and add it to the whole body dose. The skin dose is part of the whole body dose.

If you are approaching a limit for skin dose based on beta radiation, then it is necessary to add the gamma dose to the beta dose.

2. For example, If the whole body dose to worker is 2 mSv (no beta dose), what will be the skin dose?

The skin dose will depend on the gamma energy. See ICRU 57 for the skin dose by gamma energy.

3. In case of NPP where beta is also there, can we add the dose to skin due to gamma to the dose to skin due to beta ? Also what is the procedure to find the skin dose due to beta alone?

Yes. Add the gamma dose to the beta dose. Beta dose can be estimated using VARSKIN or other beta dosimetry codes. It is necessary to know the beta energy at the skin for a correct dose. The beta energy distribution may be reduced from the unshielded beta distribution because of distance or protective clothing. Distance and protective clothing will reduce the dose.

4. What is the percentage of skin dose due to photons? How it varies in case of isotropic source and collimated beam source. Also how it varies with field size and source to surface distance (SSD) ?

The skin dose from photons is energy dependent, see ICRU 57. The skin dose is independent of field size, but the dose is delivered to the field area.

5. How can we experimentally find the percentage of skin dose in case of pure gamma field using ionization chamber/TLD?

The skin dose can be determined using an ionization chamber or TLD. The ionization chamber air dose measurement is assumed equal to KERMA. Use KERMA to determine the skin dose for the isotopic energy. A TLD is more complicated as the usual calibration is for the calibration energy. If the isotopic energy is much different from the calibration energy, an adjustment may be necessary to estimate KERMA.

6. Is there some IAEA document dealing with reporting of doses for occupational workers ?

See

Assessment of Occupational Exposure Due to External Sources of Radiation. SAFETY GUIDE No. RS-G-1.3

I have two downloadable publications that may be of interest:

Measurement of Effective Dose

Beta Dosimetry

Thanx for your detailed reply. I have two specific queries which I am listing below:

1. What will be the skin dose if the effective dose is 2 mSv. (for Cs-137 (660 KeV) the conversion coefficients for Hp(10) and Hp(0.07) are same). Does it mean that skin dose is also 2 mSv for 660KeV photons in this case) ?

2. If a person has received only a skin dose of 50 mSv, what will be his effective dose due to this ?

To your second question. It´s very easy, if the skin dose is 50 mSv, you have to multply with the wt-factor for the skin 0.01. The result for the effective dose from the exposition of the skin is 0.5 mSv.

Dear Hanno

Thanks for yor reply. I would be eagerly waiting for your respose to query no 1.

regards

Anuj

@Anuj,

please read my mail.

@Anuj, to your first question:

As far as I know, there is no simple way to calculate skin dose from effective dose. The reason ist the energy dependence, the field size dependence of the effective dose contribution and the unknown dose distribution in the body, which caused the effective dose.

The skin dose first has to be calculated as average dose. If you only expose 10% of the skin, you have to "distribute" this dose to the total skin. As example if you expose with 1 mSv at 10% of the skin, the nominal skin dose will be 0.1 mSv because of averaging.

If you read Josephs public answer you will find the same thoughts.

Thanx a lot Sir for your detailed reply...

@Anuj

Your second question 1 is

1. What will be the skin dose if the effective dose is 2 mSv. (for Cs-137 (660 KeV) the conversion coefficients for Hp(10) and Hp(0.07) are same). Does it mean that skin dose is also 2 mSv for 660KeV photons in this case) ?

The answer to this is not very satisfying because it is a major source of confusion. Hp(10) is 2 mSv and Hp(0.07) is 2 mSv. Hp(10) as modeled on a slab ICRU phantom is a conservative estimate of 660 keV whole body dose AP incidence. The measured absorbed dose using an extrapolation chamber then converting to effective dose is lower. Nevertheless, Hp(10) Sv is acceptable for the effective dose in Sv. Hp(0.07) Sv as modeled on a slab is close to the measured absorbed dose on a slab before converting to effective dose in Sv. The Hp(0.07) Sv must be multiplied by 0.01.

The answer to your second question 2 is answered above and agrees with the answer by Hanno.

@Hanno

Did you answer Anuj by email? Please share.

Dear Joseph, the first mail had the following content:

##

I try to give some hints.

1. IAEA Report 1145 is appended

2. I understand, that you want to use the wt-factor for skin 0,01. to get the contribution to effective dose.

3. The relative dose part of a gamma ray exposition depends strongly from the photon energy. For high energy photons (MeV) the skin dose is about 10-50 % of the maximum dose. So your question cannot be answered without precise knowledge of photon energy and fieldsize.

3. If you know the organ dose for the skin you can add the known betadose linearly without correction, because the weighting factors are both 1.

4. Skin dose depends from field size (s.point 2) and from distance to ssource, but not so much. The main additional effect is the scattered photon contribution and a growing distribution from electrons by interaction with air molecules. .

5. You have to measure the depth dose distribution. Normally you use a waterphantom or PMMA slides. The surface dose can well be estimated by TLD measurements.

Regards

'##

The second mail content is identical with the answer above:

##

As far as I know, there is no simple way to calculate skin dose from effective dose. The reason ist the energy dependence, the field size dependence of the effective dose contribution and the unknown dose distribution in the body, which caused the effective dose.

The skin dose first has to be calculated as average dose. If you only expose 10% of the skin, you have to "distribute" this dose to the total skin. As example if you expose with 1 mSv at 10% of the skin, the nominal skin dose will be 0.1 mSv because of averaging.

If you read Josephs public answer you will find the same thoughts.

##

Regards Hanno

Dear Joseph

I think the answer given by you for Query 1 seems to be making things clearer to me to some extent. Can you please eloborate the folowing text further :

"Hp(10) as modeled on a slab ICRU phantom is a conservative estimate of 660 keV whole body dose AP incidence. The measured absorbed dose using an extrapolation chamber then converting to effective dose is lower. Nevertheless, Hp(10) Sv is acceptable for the effective dose in Sv. Hp(0.07) Sv as modeled on a slab is close to the measured absorbed dose on a slab before converting to effective dose in Sv. The Hp(0.07) Sv must be multiplied by 0.01."

@Anuj

Hanno stated that a major problem in skin dose to a restricted field is how to convert to effective dose. Effective skin dose is for the skin dose of the whole body. How the conversion is made from a restricted field to the whole body depends on the which regulation pertains to assigning the dose. Dose assignment and reporting is a regulatory matter and must be followed. The regulation may not have a scientific bases, but a practical one. This is not a criticism. It is to say that any answer I make to your question is an explanation of international recommendations and practical measurements.

I have measured the absorbed dose in an ICRU slab at a depth of 10 mm and 0.07 mm using an extrapolation chamber constructed of the same material as the slab (except for necessary air gaps and conducting materials). The measured absorbed dose in Gy followed the shape of Hp(10) and Hp(0.07) in Sv, but was slightly less.

The absorbed dose in Gy at 10 mm is converted to Sv by multiplying by 1. The measurement at 10 mm is a calibrated, direct measurement in Sv.

The absorbed dose in Gy at 0.07 mm is converted to Sv by multiplying by 0.01. The measurement at 0.07 mm is not a calibrated, direct measurement in Sv.

The ICRU Hp(0,07) should be considered Gy, not Sv. An Hp(0.07) measurement on an ICRU slab must be multiplied by 0.01 to convert to Sv. This is not clear in ICRU 57.

Sv is an expression of risk as effective dose. An instrument can calibrated to read directly in Hp(10) or Hp(0.07), but not to both.

Note: The referenced measurements were made in the late 1980s. I did not publish the results. I believe I have the data and analysis in a box, somewhere.

I know of others who have done the same measurements in greater detail. As far as I know, these are also not in the open literature.

Dear Joseph,

I´m a little bit confused by your factor 0.01 for the skin. Do I understand, that you cite the wT-factor for the skin, then I´ve no problem. Do you mean the organ dose for the skin, you are not allowed to use a factor of 0.01, you must use the weighting factor for photons or electron wR=1.0.

The next problem I read is the declaration of the unit for Hp to be Gy.

Please give me some hints.

PS1: I do critics since a long time, that all radition protection doses have the same unit Sv, that means:

- equivalent does (soft tissue , Q-factors),

- the personal dose (personal dosemeter like films etc., beeing interpreted for simplicity as effective dose)

- Hp(010), Hp(0.07) as doses in elnlarged field or in basal layer of the skin

- effective dose containing wt-factors for stochastic risk.

PS2: Would you be able and show your old 1980 results

Thanks and Regards

Hanno

Yes. The wT-factor for skin to obtain effective dose.

I use the definitions

Mean Absorbed Dose. The mean absorbed dose, DT, in a specified tissue or

organ of the human body, T, given by

DT = (1/mT)∫mTDdm or εT/mT

where mT is the mass of tissue or organ, D is the absorbed dose in the mass

element dm, and εT is the total energy imparted in the tissue or organ. The unit of

absorbed dose is joule per kilogram (J kg-1) and its special name is gray (Gy).

Effective Dose. The summation of the equivalent doses in tissue or organs, each

multiplied by the appropriate tissue-weighting factor. It is given by the

expression

E = ΣTwT•HT

where HT is the equivalent dose in tissue or organ, T, and wT is the tissue weighting

factor for tissue, T. The unit of effective dose is joule per kilogram (J

kg-1) and its special name is sievert (Sv).

Sv should be used for effective dose, only. Sv is a term of risk not of dose. It is an unfortunate definition. It was not made explicit in any ICRU or ICRP document that Sv was restricted to risk, hence the confusion with organ dose.

I agree that the organ dose for the skin must have wR = 1.0. The organ dose is in Gy.

It is particularly confusing that Hp(10) in Gy equals Hp(10) is Sv, but Hp(0.07) in Gy (the skin organ dose) does not equal Hp(0.07) in Sv (the skin effective dose).

I do not agree that organ doses and effective doses have units of Sv. What I prefer is that the definitions and procedures be more explicit. It is not helpful that each new ICRP must alter the definitions and/or names.

I am looking for the data from my 1980s results. It is not promising.

Joe

Thanks dear Joseph,

I presumed your statement about the units and appreciate now the small differences in understanding of units and correlation to the different doses. I´m not sure, that you can use your definitions in the international dispute and especially Anujs discussions.

In the mean time I´ve had a look into ICRP 60. There mSv is used for all dose units in radiation protection. Possibly we should start a discussion?

Regards

Hanno

I agree that ICRP 60 uses Sv indiscriminately. I use the definitions in ICRU 57. ICRU 57 is the standard as issued in 1998 based on ICRP 60 issued in 1991. There is now ICRP 103, which changed the weighting factors, but not the definitions as agreed in ICRU 57.

I believe the ICRU 57 definitions do apply to international discussion and Anuj's questions.

Are us suggesting a discussion as a separate RG question or privately by email?

Joe

Dear Joseph,

if you like, please start a public discussion under your name. I think it´s worthwhile.

Regards

Dear Hanno and Joseph

I think the basic problem lies in the calculation of Hp(d) values as follows :

The Hp(d) data of ICRP and ICRU were calculated for a phantom in a vacuum, which means that secondary electron transport had not been used. But instead the kerma approximation was used, so Hp(0.07) is never lower than Hp(10) for normal incidence.

Is it not unrealistic to generate the Hp(d) data of ICRP and ICRU using a phantom in a vacuum, as all irradiation of human body would take place while working in ambient atmosphere. Are these values not questionable in real sense of the problem ?

@Anuj concerning secondary electrons.

Secondary electrons are of minor importance for Hp(10), but can be important for Hp(0.07) and high energy gammas.

More important are the codes used to calculate the phantom doses. I have anecdotal evidence questioning the codes. I have no direct knowledge of the codes or any real problems, but I know improvements have been made in other codes. I think comparisons are needed to other codes and the codes compared to data.

I agree, the ICRU 57 tables should be questioned.

Most important is that ICRP and ICRU are committees and generate committee reports. Committees are known to have internal and external influences that may limit the scientific value of the reports. There is a great deal of work, science, and integrity in these reports, but as scientists we must be wary and inquisitive. The reports are based on the best available evidence. It is our job to fix the areas where best-available is not enough.

I have uploaded a spreadsheet to Measurement of Effective Dose (MED). The spreadsheet is titled ICRU 57. The spreadsheet includes the relevant ICRU 57 tables that support MED and several of the figures in MED.

In my opinion, you can multiply Hp(0.07) by 0.01 only if its value corresponds to the avaerage skin equivalent dose taking into account the surface of the entire body. By the way, what is the organ dose relevant to the skin? Here we should know what is the mass of the skin. But this has never been defined. Thank you. Jozef S

For the mass of the skin, you may be interested in the following Q&A:

https://www.researchgate.net/post/How_to_estimate_the_area_of_human_body_using_theoretical_models